Citation
Paleolimnology of the Maya region

Material Information

Title:
Paleolimnology of the Maya region
Creator:
Brenner, Mark, 1952- ( Dissertant )
Deevey, Edward S. ( Thesis advisor )
Nordlie, Frank G ( Reviewer )
Gilbert, Carter R. ( Reviewer )
Crisman, Thomas L. ( Reviewer )
Jones, Douglas S. ( Reviewer )
Place of Publication:
Gainesville, Fla.
Publisher:
University of Florida
Publication Date:
Copyright Date:
1983
Language:
English
Physical Description:
viii, 249 leaves : ill., maps ; 28 cm.

Subjects

Subjects / Keywords:
Chemicals ( jstor )
Lakes ( jstor )
Mayan culture ( jstor )
Microfossils ( jstor )
Nutrients ( jstor )
Phosphorus ( jstor )
Pollen ( jstor )
Sediments ( jstor )
Soils ( jstor )
Watersheds ( jstor )
Dissertations, Academic -- Zoology -- UF
Paleolimnology -- Guatemala ( lcsh )
Zoology thesis Ph. D
Genre:
bibliography ( marcgt )
non-fiction ( marcgt )
Spatial Coverage:
Guatemala -- Peten

Notes

Abstract:
Archaeologically supported estimates of riparian Maya populations were combined with paleolimnological information to quantify the impact of prolonged, prehistoric Maya settlement on the watersheds and lakes of the karsted lowlands in Peten, Guatemala. The pollen record indicates that regional, human-induced deforestation beg^n prior to the Middle Preclassic period (1000 B.C.). Forest recovery commenced with depopulation at the end of the Postclassic period (1600 A.D.). Vegetation removal caused profound changes in sediment and nutrient loading of the Peten lakes, and the impact was sustained for nearly 3 millennia. Pre-Maya organic sedimentation was replaced by rapidly accumulating inorganic deposits, but was restored some 400 years ago when forest regrowth began. Maya exploitation in the catchments accelerated the rate of total phosphorus delivery to the lakes. In the absence of soil-anchoring vegetation, phosphorus reached the lake shores as colluvium, i.e. as redeposited soil. As was shown in 1979 at Lakes Yaxha and sacnab, phosphorus loading was Maya-density-dependent (0.5 kg P*capita^-l-yr^-1). Settlement and core chemistry data from 3 other basins are consistent with the quantitative conceptual model based on this constant. Computed microfossil accumulation rates, though confounded by diagenesis, indicate that productivity in the Peten lakes was not enhanced by the anthropogenic phosphorus. Severe siltation may have inhibited lacustrine production; moreover, most of the haya-period phosphorus load was probably delivered to the lakes in biologically unavailable form. Shallow-water and deep-water cores from 2 lakes demonstrate the differential distribution ("focusing") of sediment and imply that single cores in conical basins are inadequate to describe accurately the accumulation of chemical and fossil constituents. Soil and sediment chemistry data (46 soil profiles, 40.5 m of analyzed Holocene lake sediments cored from 4 basins) indicate that Peten soils lost perhaps a third of their phosphorus stock as Maya-generated colluvium. Agricultural yields may therefore have declined due to soil nutrient depletion, concomitant lacustrine siltation could have reduced the availability of aquatic protein. Together, nutrient sequestering and siltation may have tunctioneu as a servomechanism, restricting haya population growth and contributing to the 9th century Classic population collapse.
Thesis:
Thesis (Ph. D.)--University of Florida, 1983.
Bibliography:
Bibliography: leaves 237-248.
General Note:
Typescript.
General Note:
Vita.
Statement of Responsibility:
by Mark Brenner.

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University of Florida
Holding Location:
University of Florida
Rights Management:
Copyright [name of dissertation author]. Permission granted to the University of Florida to digitize, archive and distribute this item for non-profit research and educational purposes. Any reuse of this item in excess of fair use or other copyright exemptions requires permission of the copyright holder.
Resource Identifier:
029087185 ( AlephBibNum )
09789239 ( OCLC )
ABZ0546 ( NOTIS )

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PALEOLIMNOLOGY OF THE MAYA REGION


By


\MARK BRENNER





















A DISSERTATION PRESENTED TO THE GRADUATE SCHOOL
OF THE UNIVERSITY OF FLORIDA IN
PARTIAL FULFILLMENT OF THE REQUIREMENTS
FOR THE DEGREE OF DOCTOR OF PHILOSOPHY







UNIVERSITY OF FLORIDA


1983



















ACKNOhLEDGEMENTS


I would like to thank the many people who have helped me complete

this project. First and foremost; .I thank my committee chairman, Dr.

E.S. Deevey, for guidance and encouragement. Dr. Deevey.introauced me

to paleolimnology, and I am indebted to him for nurturing my

fascination with the lacustrine sediment record. I appreciate the

input of Dr. Frank Nordlie, who taught me the fundamentals of

limnological research. I am grateful to Drs. Tom Crisman, Carter

Gilbert, and Doug Jones for reviewing the thesis and for teaching

courses that inspired some of the ideas in this work.

The multidisciplinary nature of this paleoecological study

demanded the collaboration of a large number of researchers. I was

reliant on assistance from many individuals, and I want to acknowledge

their aid. The success of the 1978 coring operation was largely aue to

Sid Flannery's help. He also helped produce some of the core chemistry

data. Dr. Sam Garrett-Jones also collaborated on the 1978 drilling

campaign and generated pollen data. Dr. Hague Vaughan provided me with

instruction in paleolimnological techniques and was responsible tor

producing several pollen profiles.

I have fond memories of the many months spent in Peten with Drs.

Don and Prudence Rice. I am grateful.to them for allowing me to use












both their published and unpublished archaeological data. Special

thanks are due Pru for delivering me to the hospital in Guatemala city

during my 1979 bout with hepatitis.

Dr. Mike Binford's presence in Peten in 1980 made that a most

productive field season. Mike provided granulometric data from Peten

cores and listened patiently to many of my ideas, answering nurneious

questions along the way. I am also grateful for the feedback obtained

from other members of the Paleoecology Lab: bob Snodgrass, Tom

Whitmore, and Antonia Higuera-Diaz.

Carl Miles and Andy Ogram instructed me in the use of the atomic

absorption spectrophotometer and the Leco induction furnace. Liz

Fisher provided encouragement every step of the way. her aid is

gratefully acknowledged. Rhoda Bryant typed the final manuscript, and

her aid is certainly appreciated.

The successes of the "Historical Ecology of the Maya" project have

been largely attributable to the cooperation of many Guatemalans.

Special thanks are due the following friends tor assistance far beyond

the call of duty: Rafael and Clemencia Sagastume, Jaime and Mari

Sobalvarro, Antonio and Aura Ortiz, and Robert Dorion. I thank the

many residents of northern Guatemala who have made me feel at home in

Peten.

Finally, I would like to thank the Peten. This study sheas some

light on Peten's prehistory. Many questions remain unanswered, and the

region, with its spectacular Maya ruins, tropical forests, and lakes,

continues to captivate my imagination. I look forward to visiting and

working in the area again.









This project was supported by grants to Dr. E.S. Deevey (NSF DEB

77 06629, NSF EAR 79 26330, and EAR 82 14308). A graduate research

assistantship from the University of Florida Division of Sponsored

Research is also gratefully acknowledged.




















TABLE OF CONTENTS


ACKNOWLEDGEMENTS . . . . . . . . .. . .... ii

ABSTRACT . . . . . . . . ... . . . . . vii

INTRODUCTION . . . . . . . . ... . . ..... 1

Prehistoric Maya and Contemporary human Populatiuci
Densities of Peten, Guatemala . . . . . . . 1
Maya Cultural Development in the Tropical Forest Ecosystem .
The Origins of Maya Civilization . . . . . . ... 6
Maya Agricultural Practices . . . . . . . . .. .10
The Classic Maya Collapse . . . . . . . . ... 14
The Historical Ecology of the Maya . . . . . ... .17
Measuring Maya Environmental Impact Paleolimnologically . 17
Lake-Watershea Interactions . . . . . . ... .18
The Paleolimnological Perspective . . . . . . 22
The Contemporary Peten Environment . . . . . . . 26
Geology ................ ....... .. 26
Climate and Rainfall .................. 28
Soils . . . . . . . . . . . . . 29
Vegetation . .. . .. . .. .. . .. ... 32
Regional Limnology . . . . . . . ... .. .36
Maya Settlement in the Yaxha ano Sacnab Catchments . .. .. 45
Maya Demography . . . . . . . . .. . . 45
The Twin Basin Seoiment Record . . . . . . . 49
Phosphorus Loading of Lakes Yaxha and Sacnab . . .. .52

THE HISTORICAL ECOLOGY OF THE MAYA AT LAKES QUEXIL, SALPEiEN,
AND MACANCHE . . . . . . . .. . . . 55

The Archaeological Record . . . . . . . . ... 55
Soil Chemistry . . . . . . . ... ..... .65

PALEOLIMNOLOGY OF LAKE QUEXIL . . . . . . . . .. 83

Comparing Shallow-water and Deep-water Sedimentation ... .83
Proximate Chemical Composition of the Lake Quexil
Sediments ................... .... 97
Chemical Accumulation Rates in Lake Quexil Sediments . 1U2












Paleoproductivity in Lake Quexil . ... ........ .... . .. 11
The Significance of Microfossils . . .. . . . .... 11b
The Microfossils of the Quexil Cores . . . . .. 120
Microfossil Accumulation Rates and Phosphorus Loading . 141
carbon-Nitrogen Ratios in Quexil Core H . . . ... 152
Comparing Microfossil Accumulation Rates at the Two
Quexil coring Sites.. .. . . . .. ... . 154

TESTING THE PHOSPHORUS LOADING MODEL DEVELOPED AT YAXHA-SACNAB .160

Coring in Lakes Salpeten, Macanche, and Quexil, 1980 ... ... .160
Sediment Chemistry of the Macanche and Salpeten Cores . 175
Assessing the Maya Annual Per Capita Phosphorus Output ...... 176
Zoning the Cores Chemically . . . . . . ... 178
The Impact of Sediment Focusing . . . . . . .. 191
Zoning the Cores Palynologically . . . . . . . 201
Assessing the Impact of Soil Nutrient Loss . . . . .. 205
Erosion Rates for the Peten Watersheds ....... . . .. 210

SUMMARY ............................. . .224

BIBLIOGRAPHY ......... . . . . . . . .237.

BIOGRAPHICAL SKETCH .... . . . . . . .. ...... . 249














Abstract of Dissertation Presented to the Graduate School
of the University of Florida in Partial Fulfillment of the.
Requirements for the Degree of Doctor of Philosophy


PALEOLIMNOLOGY OF THE MAYA REGION

Mark Brenner

April .1b3

Chairman: Edward S. Deevey, Jr.
Major Department:: Zoology

Archaeologically supported estimates of riparian Maya populations

were combined with paleolimnological information to quantify the impact

of prolonged, prehistoric Maya settlement on the watersheds ano lakes

of the karsted lowlands in Peten, Guatemala. The pollen record

indicates that regional, human-induced deforestation began prior to the

Middle Preclassic period (1000 B.C.). Forest recovery commenced with

depopulation at the end of the Postclassic period (1600 A.D.).

Vegetation removal caused profound changes in sediment and

nutrient loading of the Peten lakes, ano the impact was sustained for

nearly 3 millennia. Pre-Maya organic sedimentation was replaced by

rapidly accumulating inorganic deposits, but was restored some 400

years ago when forest regrowth began. Maya exploitation in the

catchments accelerated the rate of total phosphorus delivery to the

lakes. In the absence of soil-anchoring vegetation, phosphorus reached

the lake shores as colluvium, i.e. as redepositea soil. As was shown

in 1979 at Lakes Yaxha and sacnab, phosphorus loading was

Maya-density-dependent (0.5 kg P*capita-l1yr-1). Settlement


vii









and core chemistry data from 3 other basins are consistent with the

quantitative conceptual model based on this constant.

Computed microfossil accumulation rates, though confounded by

diagenesis, indicate that productivity in the Peten lakes was not

enhanced by the anthropogenic phosphorus. Severe siltation may have

inhibited lacustrine production; moreover, most of the haya-perion

phosphorus load was probably delivered to the lakes in biologically

unavailable form.

Shallow-water and deep-water cores from 2 lakes demonstrate the

differential distribution ("focusing") of sediment and imply that

single cores in conical basins are inadequate to describe accurately

the accumulation of chemical and fossil constituents.

Soil and sediment chemistry data (46 soil profiles, 40.5 m of

analyzed Holocene lake sediments cored from 4 basins) indicate that

Peten soils lost perhaps a third of their phosphorus stock as

Maya-generated colluvium. Agricultural yields may therefore have.

declined due to soil nutrient depletion. Concomitant lacustrine

siltation could have reduced the availability of aquatic protein.

Together, nutrient sequestering and siltation may have tunctioneu as a

servomechanism, restricting haya population growth and contributing to

the 9th century Classic population collapse.



















INTRODUCTION

Prehistoric Maya and Contemporary Human Popqlation Densities of
Peten, Guatemala


Guatemala's northern Peten region encompasses 35,854 km2 and

constitutes a large portion of the core area in which southern lowland

Maya civilization arose and developed (Fig. 1). Tropical, lowland, cry

forest (Holdridge 1947) covers most of the Peten (Lundell 1937), as

well as portions of Belize, Nexico's Yucatan peninsula, Tabasco, ano

Chiapas. It was in this environmental context that lowland Maya

culture originated and persisted for several millennia before

collapsing mysteriously in the 9th Century A.D. (Culbert 1973).

Perhaps as a testimony to the inhospitable nature ot the tropical

forest, the Peten remains largely depopulated today. Cowgill and

Hutchinson (1963a) reported a Peten population of 20,362 in 1957,

although very recent development has raised the figure nearly 10-fold

(Castellanos 1980). The sparse nature of contemporary human settlement

is placed in perspective by comparison with assessments of Late Classic

(550-850 A.D.) Maya population levels. Delimiting Tikal's areal extent

to just under 163 km2, Haviland's (1969, 1972) Late Classic estimates

for this site alone fall between 40,000 and 49,000. Thompson (196b)

indicates that proposed figures for pre-Columbian population levels are

highly variable. They range from a low of just over a million for the
































Fig. 1. Regional map. The Maya Lohlanos incluue arLa. ot belize,
Guatemala's Peten region, and portions of Mexico's Yucatan
Peninsula, labasco, and Chiapas.





























Campeche


Peten


100 km


16N


Yucatan













entire Maya region to 13,000,000 for the Yucatan peninsula alone.

Admitting that his own whole-area estimate of 3,000,UUU might be a bit

low, Thompson (1966) was prepared to revise his figure upward, but

conceded that the data base was so small as to make all assessments of

Late Classic levels mere "guesstimates." In a more recent study, Adams

et al. (1981) accept the notion that soae 14,000,000 inhabitants

occupied the Maya lowlands by A.D. 800.

Accurate appraisals of modern Peten population levels are also

difficult to obtain, partly due to the seasonal immigration into the

area associated with industries such as the harvest of "chicle"

(Simmons et al. 1959, Cowgill and Hutchinson 1963a). From the turn of

the century until the late 1960's, "chicle" was Peten's most important

commodity, and the flourishing business attracted large numbers of men

from Mexico, highland Guatemala, and other Central American countries

(Schwartz 1974). The last two decades have witnessed a profound change

in the region, as new settlers, pressured by land shortages in the

highlands to the south, have streamed into Peten in response to the

promise of abundant agricultural terrain. Formed in 1956, the

governmental agency, Empresa Nacional de Fomento y Desarrollo Economico

del Peten (FYDEP) began a land distribution program in the rlio-1960's,

finally granting titles to the assigned parcels in 1974. Under the

auspices of FYDEP, road building and maintenance were priority

projects, and by 1970 the overland route from Flores to Guatemala City

was completed, making the Peten interior more accessible than ever

before. In addition, communication systems were established, air

service was improved, and as a consequence of the subsequent human














influx, the region is beginning to lose its distinctive cultural

identity.

The attraction of available lana has converted highlanders into

"Peteneros" at an alarming rate. Schwartz (1977) reported an increase

from 25,910 Peten inhabitants in 1964 to about 100,000 only 13 years

later. Castellanos (1980) indicates that the rapid immigration that

continue through the late 1970's left the Peten with soiie 20b0,(i

people by the close of the decade. While government efforts to

relocate land-hungry highlanders appear laudable, the program is not

without its drawbacks. Native "Peteneros," while enjoying the new

prosperity, feel their patrimonies are threatened (Schwartz 1977) ana

concern exists thatthere will be insufficient employment opportunities

to accommodate the newcomers.

Another issue that must be addressed is how the immigrants are

faring with subsistence farming practices in the Peten lowlanas. They

are unaccustomed to the high temperatures ot the region and unfamiliar

with the soils, vegetation, and shifting agricultural techniques that

characterize the area. Whether the recent settlers will be able to

cope in the new environment remains to be seen, but the Peten will

continue to undergo drastic social and environmental change in the

future as a result of increasing population density.

While the modern "experiment" in the use of the tropical, lowlana

forest is in its incipient stage, and it would clearly be premature to

pass judgment on its success now, it can be said that the prolonged

persistence of prehistoric Maya culture in the same context constituted

a success that is without parallel. Bronson (1978) has likened the














Maya.to three Asian civilizations that developed in apparently similar

settings, but this hardly detracts from the achievements of the haya,

and the latter are, with the possible exception of the Olmec, the only

New World high civilization to arise and flourish within a tropical,

lowland forest ecosystem.



Maya Cultural Development in the Tropical Forest Ecosystem



While some anthropologists are perplexed by the apparent

incompatibility of high civilization ano the tropical forest setting,

adherents of "environmental determinism" have gone so far as to deny

that lowlano Maya culture could have developed in situ. Meggers (1954)

argued strenuously that Classic Maya culture (250-850 A.D.), with its

monumental architecture, art, hieroglyphics, concept of zero, corbeed

arches, calendrical system, and stela cult, could not have arisen

autochthonously. Believing that the degree of cultural complexity

achieved is dependent upon the agricultural potential of a region,

Meggers classified the Peten as an area of limited agricultural

potential (Type 2), and thus believed the area was not conducive to the

florescence so evident in the archaeological record. The logical

conclusion, based on the assumptions of this agriculturally

deterministic law, was that Classic Maya culture was imported into the

lowlands fully formed and was destined to decline following its

arrival. This simple theory accounted for both the mysterious origin

and inexplicable downfall of the civilization.














In the years following Meggers' (1954) paper, a number of

refutations were published, perhaps laying to rest the broco claims of

environmental determinists, but keeping alive the controversy

surrounding the enigma of the prehistoric high.civilization in the

tropical forest environment. Coe (1957) took exception to Meggers'

claims for a number of reasons. He contested her view that there is a

lack of Preclassic-classic transition in the lowland record and felt

there was no archaeological basis for the argument that classic culture

was imported from the highlands. Additionally, he pointed out that

several lowland Maya achievements, such.as the corbeled arch, the Long

Count, and the stela cult, seem to have no non-lowland origin. Coe's

disagreement with Meggers extended to the perception of the Classic

Maya collapse. While Meggers referred to a "gradual decline,"

initiate following the arrival ot Classic culture in the lowlanas, Coe

pointed out that the evidence indicated a rather widespread, rapid

termination following some 600 years of incremental growth.

In the year following Coe's reply to Meggers, Altschuler (1958)

presented Formative phase ceramic evidence that supported the claim for

autochthonous origin of lowland Classic Maya civilization. His

conviction was that political problems generate the 9th century

collapse. Specifically, he proposed that the ruling class attempted a

political structuring that was doomed to failure because it lacked the

developed techniques of exploitation.

Ferdon (1959) disagreed with Meggers' assessment of the Peten's

agricultural potential, and using his criteria of temperature, soils,














precipitation, and land form, reclassified the lowlands as a favorable

(Type 3 = improvable) site for agriculture. This analysis aid not

constitute a refutation of deterministic law as applied to the haya by

Meggers. It simply freed the civilization from having to conform to

the expectations dictated by a Type 2 (limited potential) environment.

However, Ferdon did take issue with environmental aeterminism ano

presented data supporting his contention that there is no correlation

between natural agricultural potential ana cultural develop.ernt.

Having disproved the role of determinism in the eventual Classic

collapse, he proposed the notion that grass invasion of cleared plots

and the subsequent inability to plow the tracts contributed to the

downfall of the civilization.



The Origins of Haya Civilization



Recent archaeological excavations in the Orange Walk district of

Belize have established that occupation of that area coinenced as early

as the third millennium B.C. At the site of Cuello, fragments of

partially burned wood associated with ceramic material assigned to the

Early Formative Swasey complex (Hammond et al. 1979) have produced

several radiocarbon dates indicating an age ot between 4000 and 5000

calendar years (Hammond et al. 1976, Hammond et al. 1977, Hammono 1960,

1982). These data confirm the claim that lowlana classic Maya cultural

ontogeny had its roots in the lowlands.

Within the Peten region per se, the earliest ceramic material

discovered to date comes from the sites of Seibal ano Altar de















Sacrificios (Adams and Culbert 1977). Assigned respectively to the

Real and Xe complexes, the material is date to the Middle Preclassic

(1000-250 B.C.). Middle Preclassic settlement is known at Tikal and

has also been documented in the Yaxha-Sacnab watersheds of eastern

Peten (Rice 1976). Following an extensive settlement survey and

test-pitting program during the 1979-80 field season, occupation of

this age is now recorded in four more central PeEen drainages (Rice and

Rice 1980a).

While the numerous discoveries of Preclassic settlement in the

lowlands contradict the argument that Classic culture was brought to

the region intrusively, debate continues as to what factors were the

driving forces contributing to the formation of lowland Classic Maya

civilization (Adams 1977). .Although influences from beyond the

lowlands are considered, several intrinsic processes are invoked to

explain the cultural growth and change that produced the social ranking

and stratification that ultimately characterized the Classic period.

Willey (1977) provides a multi-causal model for Classic Maya

development based on a synthesis of processual interpretations proposed

by others. In formulating his 'overarching model," he incorporates

these models and processes that are broadly assigned to three major

categories: (1) ecology-subsistence-demography, (2) warfare, (3)

trade. Be notes that none of these models advocates a monocausal

explanation for the Classic Maya rise ano cautions that the role of

ideology should not be discounted.














Invoking environmental factors, though not as a determinist,

Sheets (1979, 1981) sees the rise of Classic Maya civilization in the

lowlands as reflecting a natural disaster in the highlands of El

Salvador. Acknowledging that Classic haya culture woulo have developed

in any case, he argues that the eruption of El Salvador's Ilopango

volcano in A.D. 260 might have accelerated the process by forcing

increased political and agricultural organization to cope with the

influx of immigrants who descended to the lowlands when highland

agricultural land was rendered useless by the deposition of a thick ash

blanket. Additionally, he points out that Tikal's Early Classic

(250-550 A.D.) florescence may have been stimulated by the diversion of

trade routes with Mexico that previously had passed along the Pacific

coast. With the coastal road destroyed, Tikal became the major eastern

site on the traoe route that extended into the basin of Mexico.



Maya Agricultural Practices



During the last two decades, Maya archaeology has become

preoccupied with questions about pre-Hispanic agricultural practices.

Until that time, the prevailing dogma was that Maya subsistence was

dependent on maize-based, swidden (slash-and-burn, shifting)

agriculture. How this belief became entrenched in the literature

remains unclear, but it was not necessarily supported by the

archaeological record. Though corn is depicted in Maya art, the

contemporary reliance on the "milpa" and the ubiquity of cornfields in

the Guatemalan lowlands at the time of colonial contact ana toaay must














certainly have contributed to the acceptance of the doctrine. While

this agricultural technique may be appropriate for the sparsely

populated modern Peten, there is doubt as to whether it was a feasible

alternative during Classic haya times. Because slash-and-burn requires

land to be fallowed for long periods, much larger areas than the plots

actually under cultivation are required. In the swicaen cycle, forest

is felled during the dry season (January-May), and prior to the onset

of the rains, the dried vegetation is burned, delivering nutrients to

the soil. Following the burn, seeds are sown in holes bored with a

dibble stick, and growth commences after the first showers of the rainy

season with no additional working of the soil required.

Confronted with differing assessments of Peten's agricultural

potential (Meggers vs. Ferdon), Cowgill (1962) sought to resolve the

disparity and interviewed 40 farmers in the region of Lake Peten-ltza

in an effort to ascertain actual corn production. Summarizing the data

from the interviews, she noted that first year plot yields were

1425 lb*acre-1, second year plots averaged 1010 lb*acte-1, and

the five farmers who tried three years of successive planting averaged

417 lb'acre-1, with the decline likely due to nutrient depletion.

Stable swidden of this nature would demand a four-year fallow following

a single crop and six to eight years' rest on a plot worked two years

in succession. Cowgill concluded that swidden farming could support

about 38-77 people*km-2, and tentatively noted that classic period

population densities may have exceeded the restrictions imposed by

stable swidden strategy.














Recent surveys of ancient Maya settlement in the Peten make it

easier to evaluate the feasibility of slash-ano-burn to have supported

prehistoric populations. Rice (1978) useu demographic data gleaned

from the archaeological record together with agricultural output

information to formulate a model that demonstrates the insufficiency ot

maize-baseo agriculture to have met the subsistence neeus ot

populations in the Yaxha-Sacnab subbasins. At this locality, where

slow, steady exponential population growth occurLre from. the iioCale

Preclassic (1000-250 B.C.) until the Late Classic (550-b5U A.D.) (Rice

1978, Deevey et al. 1975), oepenuence on maize-basea swiocen

agriculture would have resulted in tooo shortages by Lat 'Preclassic

(250 B.C.-250 A.D.) times, necessitating shorter tall(w perious or the

farming of less.preferrea sites solely in order to meet subsistence

needs. The incorporation into the subsistence strategy oi root crops,

as originally hypothesized by Bronson (196b) or breadnut, "ramon"

(Brosimum alicastrum) ((Puleston 976, 1b92), is sr-o1w by tt.e nmoue to

have greatly enhanced the probability of supporting large Liassic

populations.

With the demise ot the myth that .,aya subsistence was tota

reliant on maize-based swidden came suggestions for other food sources

ano tood-prooucing systems. Lange (1971) proposed that narinie

resources might have.been an important constituent in the haya diet.

An inventory of Peten's potential iloral ana taunal traoe ittins

(Voorhies 1962) contains a varied assortment of foou types, but the

list of comestibles is by no means compete, as perishaLie goous,














incapable of being transported long distances, were excluoea from this

tabulation. According to hilkin i19/1), t.aoya tuou procurenmet was

likely dependent on an array of systems that incluaeo gardening,

arboriculture, gathering ana intensive practices such as terracing,

irrigation, and drainage.

There is now abunuant archaeological evidence that the loularno

Maya did employ intensive agricultural techniques. In Campeche,

Mexico, riogeG tielos ale known in the Rio LanoelaLiai LeioC iSlr.eien

and Puleston 1972), and hatheny (1976) reports that extensive measures

for water control were taken at Luzna. In the Rio Bec Legioin ot the

southern Yucatan peninsula, terraces ana raise fielos are reporter by

Turner (1974), ana Turner ana HiBrrisozn (1961) Laive aiscoveiea rai&.s

fields at Pulltrouser Swamp, Belize, that may have been conistructea as

early as Late Preclassic (250 b.C.-450 A.L.) times, thereby in oictlig

the great antiquity of the intensive agricultural systems.

The widespread presence of relict canals assuciateu with intensive

cultivation has been documented using raoar imagery (Aoams 1980, AGams

et al. 1981). The canals, locate near swamps, lakes, pounds, ahn

rivers, were apparently constructed for drainage purposes ano have been

veritieo on the ground in areas at hexico altu Belize. Archaeological

ground truth within the Peten is less secure, but should the grio

patterns from the raoar mapping prove to be drainage canals, it winl

indicate the tremendous scale on which intensive agriculture was

practice in the haya lowlands.














The classic Maya Collapse



The recent revelation that classic haya subsistence was at least

in part dependent on intensive agricultural practices helps explain how

the populations of the densely settled region were supported. Unless

it can be claimed that these subsistence strategies caused

environmental detriment, their discovery contributes little to the

search for a cause of the Classic Maya collapse. What makes the Maya

downfall such a perplexing event in New World Prehistory is that the

disintegration of the framework that characterized the socially

stratified Classic culture was accompanied by an extreme demographic

change involving the relatively rapid depopulation of ceremonial

centers as well as the countryside. With a shift in archaeological

focus, beginning around 1950, from an exclusive preoccupation with

ceremonial architecture to an interest in settlement surveys, the

magnitude of the population decline was more fully appreciated (Willey

1982). Willey (1956) expressed the need for more settlement work, but

the lack of evidence for Postclassic (1000-1600 A.D.) occupation of

housemounds excavated during his Belize valley surveys led him to the

conclusion that commoners disappeared with the demise of elite

society. Stated simply,

If collapse occurred--and, indeed, something did
occur--Maya priest and peasant collapsed and
vanished together. Willey (1956: 781)

Adams (1973) has summarized the "collapse" problem and provides a

concise recapitulation of the hypotheses that have been proposed to















account for the Maya downfall. Adams details the archaeological

evidence for the disappearance of the elite class, and his summary view

of the collapse encompasses not only the cessation of elite activity,

but the attendant population decline, both of which occurred throughout

the southern Maya lowlands within a period of 50-100 years.

Noting that there has been a recent tendency to reject single-

factor reasons for the collapse in favor of multiple-factor models,

Adams nevertheless classifies the explanations into broao categories.

Ecological models invoke various environmental disasters, such as soil

exhaustion, water loss and erosion, and savanna grass competition.

Under this heading, Sabloff (1973) might ado insect infestation and

climatic change. Catastrophic events such as earthquakes (Mackie 1561)

and hurricanes are proposed, but serious earthquakes are not

characteristic of the lowlands, and events stemming from disasters such

as these are hard to document using the archaeological record.

Meggers' (1954) 'environmental determinism" is considered an

evolutionary model, but is now discredited because it is known that

lowland culture arose autochthonously, ana the agricultural potential

of the region has been reevaluated. A demographic model for the

population decline was set forth by Cowgill ana hutchinson (1963a), but

receives little attention today. Studying the Indian populations

around Lake Peten-Itza, they discovered that by the fifteenth year of

life, the sex ratio in the population was 1.8cT:1.02. Ihis they

attributed to the poor care given female children between one and four

years of age, by which time the skewed ratio is established. Neglect














and consequent high mortality of female children (1-5 years) is

documented for many non-industrial countries (Cowyill and Hutchinson

1963b), but is likely compensated for by slightly higher male death

rates in the ensuing years. It is pointed out that the extreme case

discovered in the Indian populations of the Peten could have disastrous

consequences. An explanation for Classic haya depopulation was sought

using this scenario, with the realization that it would have to be

applied in a long-term situation.

The destruction of the social structure as a consequence ot

internal revolution has been posited as a factor influencing the

collapse, but while it may account for the disintegration of the social

hierarchy, this alone would not necessarily have led to depopulation.

Invasion from outside the area has also been proposed, and in view of

the post-collapse Toltec takeover in the northern Yucatan, such a

scenario is not out of the question. There is some archaeological

basis for the claim that intrusive elements were present at Seibal and

Altar de Sacrificios prior to the decline.

Finally, disease has been repeatedly implicated as a causal factor

in the collapse, though debate surrounds claims about the pre-Columbian

presence in the New World of illnesses like malaria, yellow fever, and

syphilis. Recent paleopathology work with skeletal material from Altar

de Sacrificios has revealed the occurrence of health problems in the

Maya population that occupied the site. Evidence for physical injury

in the bone sample is minimal, but vitamin C deficiency and anemia,

either diet-related or parasite-inouced, are amply documented (Saul














1973). Additionally, the presence of bone lesions indicative of

syphilis or yaws is noted.

It is clear that the various explanations for the collapse are not

mutually exclusive, and several of the proposed causal factors may have

worked in concert to produce the resultant downfall. Unfortunately,

some of the proposed hypotheses are difficult to reject using the

archaeological record alone, but a systematic program ot testing the

different single-factor theories may one day lead to a synthetic mocel

that reasonably explains the classic Maya disappearance. Such an

approach will doubtless be dependent on evidence provided by

ecologists, ethno-historians, soil scientists, and others outbioe the

realm of archaeology per se.



The Historical Ecology of the Maya

Measuring Maya Environmental Impact Paleolimnologically



This.study does not directly address the question of the

mysterious Maya collapse, though the data collected do in fact suggest

that ecological factors played a role in the event. Instead, the

design of the experiment was chosen with the objective of shedding

light on the impact that long-term Maya agro-engineering practices haa

on the watersheds and lakes of the Peten. In a sense, the question has

been approached conversely in the anthropological literature, as social

scientists have sought to determine the influence the natural

environment had on settlement patterns, foou-producing systems,













socio-political organization, etc. Cognizant of the fact that the

interaction between humans'ana the ecosystem constitutes a feedback

loop, this study takes a decidedly "ecocentric" viewpoint, exploring

the effects of prolonged, dense human occupation on terrestrial ana

aquatic systems of the tropical lowlands. The Peten lake district

(Fig. 2) provides a unique opportunity to examine human-environment

interaction, for, in fact, the "experiment," exploitation of the

lowland tropical forests and lakes, has already been conducted by a

civilization now long.gone. The results of that experiment need.only

be elucidated, and with this in minor, the "Historical Ecology ot the

Maya" project was conceived in 1971. Employing a multidisciplinary

approach, the program involved the use of archaeological and

paleolimnological techniques to examine changes in.the aquatic and

terrestrial systems that resulted from extended human interference.



Lake-Watershed Interactions



Proper study of lacustrine systems in general ana the

paleolimnological record in particular demands a view of lake basins as

integral parts of a larger landscape. Though often considered as.

distinct entities, aquatic and terrestrial ecosystems are .inextricably

linked by meteorologic, geologic, ana biologic processes that transfer

nutrients and energy from one system to the other (Likens and Bormann

1974a). Lakes can be considered "downhill" with respect to their

terrestrial surroundings and the meteorologic, geologic, and biologic




























Figure 2. The Peten Lake District.















TIkal


Nokum
x


* C -- --
L. p.e. t ..

FLOtS


/-;i '"


MI- *.-


ha






- *


S0 5 10 20 km








L. Oq uvi


L. P.rdida



1J7<


L. Sacpuy















vectors that join the systems ultimately carry nutrients from upland

sites of accumulation to the waters below. The kincrs of nutrients and

their rates of supply have a profound effect on the lake, exerting a

controlling force on the physical, chemical and biological processes

that occur in the aquatic realm. Mature, intact, terrestrial

ecosystems tend to maintain tight nutrient cycles, with loss to the

lacustrine sector minimized by the presence of the soil-anchoring,

standing vegetation. When the biological component of the land system

is disturbed, through forest clearance, nutrient cycles are disrupted,

accelerating the delivery of'dissolveo and particulate matter to the

lake.

Inadvertent enrichment of lake waters can occur as a result of

forest clearance, but often, lacustrine pollution occurs as if by

design. The "downhill" nature of lakes makes them convenient disposal

systems for unwanted, accumulated wastes like domestic sewage and

industrial by-products. These practices are not without their

consequences and our contemporary cultural eutrophication problems stem

from the casual manner in which many lakes have been used as recipients

of sewage and agricultural run-off rich in plant nutrients (aEmondson

1968, 1970, 1972; Vallentyne 1974). The realization that the source

area for some of these unwanted.nutrient inputs lies some distance from

the water's edge demands that investigators look beyond the lake itself

in the study of lacustrine processes. Furthermore, awareness of acid

rain problems (Likens and Bormann 1974b) demonstrates the neeo for

consideration of the regional airshed in assessing lake dynamics.















Bormann and Likens (1967) suggested that small watersheds make

ideal sites for examining nutrient cycle problems ano proposed that the

entire watershed be considered the basic unit for ecosystem-level lake

study. Modern studies at Hubbard Brook, New Hampshire, have

accumulated biogeochemical output data from undisturbed, natural

ecosystems (drainage basins) (Likens et al. 1977), ano these baseline

values can be compared to nutrient losses from clear-cut forests

(Bormann et al. 1968). Contemporary investigations of this type

measure altered nutrient outputs as they occur. That is, data on the

rate of nutrient transfer between the terrestrial-aquatip interface can

be collected immediately following a "treatment" like deforestation.

In attempting to assess the effect of past events on lakes, it is

necessary to rely on the paleolimnological record.



The Paleolimnological Perspective



Paleolimnological study can document past changes in a lake ana

its drainage, because shifting conditions in the watershed had an

impact on the lake; and a record of the alterations, though perhaps

somewhat distorted, is preserved within the sediments on the lake

bottom. Frey (1974) has said,

The task of the paleolimnologist is to "read" the
history of the lake-watershed-atmosphere systems
from the record "written" in the sediments.
(1974:95)

In dealing with the origin and developmental history of basins,

paleolimnology can address questions about the ontogeny of lakes that














were free from human disturbance. Climatic change can be inferred from

the palynological record and theoretical questions about ecosystem

development can be approached using sedimented microfossil assemblages

(Deevey 1969). With the greater awareness that human activity can

radically alter watershed nutrient cycles, paleolimnological techniques

are being used increasingly as a tool to assess the iagnituoe ot

human-induced changes. Sometimes historic data on demographics and

waste dumping are known for a lake-watershed system, but the

limnological record is restricted to the postdisturbance period. In

Lake Washington, east of Seattle, the sediments yielded information

concerning baseline lacustrine conditions, prior to the eutrophication

that resulted from excessive sewage input to the lake (Eamondson 1974).

The paleolimnological record, in conjunction with early historical

records or archaeological data, has been used to establish the impact

of human activity on a number of basins, sedimentary changes having

been correlated with density of occupation or shifts in lana use

(Cowgill and Hutchinson 1964). Like the vast majority of contemporary

limnological investigations, most paleolimnological projects have been

undertaken in the temperate area lakes of now-industrialized countries

(Mikulski 1976, Penninyton 1978, Vuorinen 1978, Warwick 19bU). lnere

is a paucity of literature concerning tropical paleolimnology,

especially with regard to the impact of human disturbance on tropical

ecosystems. Though regrettable, there are several factors that likely

account for the restricted development of tropical paleoliinology.

First, well-established limnological research centers are generally














confined to temperate regions, often in close proximity to lake

districts. Therefore, mounting drilling campaigns in tropical areas

can be quite costly, necessitating a large initial outlay for travel.

Once in the tropics, one may encounter additional ditticulties. Poor

road conditions or a complete lack thereof can render potential coring

sites inaccessible. Also, such projects often require the permission

of foreign government officials, and even when permits are forthcoming,

the local political or scientific community may lack the infrastructure

to be of assistance. Political instability is a hazard to be

considered and makes many potentially exciting study sites

'off-limits." Finally, little is known of the regional limnology in

most tropical areas, making interpretation of the paleolimnological

record somewhat less secure.

Despite the many drawbacks and logistical difficulties associated

with paleolimnological work in the tropics, there are significant

arguments that convincingly speak to the need for more study in these

regions. As the human populations in tropical countries continue to

increase, deforestation and resource exploitation will accompany the

demographic change. What impact the forest felling and farming

practices will have on freshwater sources is not known. Limnological

monitoring of newly settled drainages must begin, and sediment studies

can be used to gather baseline information from basins with a long

history of occupation. With continued demophoric growth in the

tropics, management schemes for freshwater resources will have to be

instituted and cannot be formulated using the temperate data base.














Despite the differences between temperate and tropical systems,

paleolimnological techniques should be applicable in both settings for

documenting human intrusion in watersheds. Nutrient cycles in

undisturbed, tropical watersheds are very tight and maintained by the

standing vegetation. Any disruption in the drainage basin should have

a noticeable, if not profound, effect on the lake and consequently the

sediments (Oldfield 1977).

Several characteristics of the Peten lakes recommend them as study

sites. First, the basins are closed, and because the lakes lack

outlets, the sediments are the ultimate sink for much of the dissolved

and particulate matter washing into the lake as well as biogenic

material formed autochthonously. Secondly, a long history of haya

settlement in the Peten watersheds should be expected because of the

scarcity of surface water in the lowlands. Initial settlement in the

region might be supposed to have clustered around readily available

sources of water. That access to water was a problem for the haya is

evident in the archaeological record at some sites in the interior.

The long dry season necessitated the construction of reservoirs at

Tikal, and evidently some "chultuns," hollowed-out, underground

caverns, were employed for water storage (Matheny 1982). To the north,

in the drier Yucatan, the situation was even more critical, and it has

been pointed out that the Maya of that region developed a civilization,

in a sense based on groundwater, with population centers located near

water supplies in the form of natural cenotess," caves, ano "aguadas,"

or man-made wells (Back 1981).














One scenario for the initial Maya invasion of the Peten interior

envisions the pioneers entering on the river systems ano later

expanding into the drier regions of the central core area (Puleston ana

Puleston 1971). It has been suggested that the lack ot available water

and necessity to cope with the problem may have been the driving force

that led to substantial social organization, ihe oldest Peten sites of

Seibal and Altar de Sacrificios are situated on rivers, and it is

conceivable that the earliest emigrants from these communities, or

other, as yet undiscovered river villages, traded the benefits of

riverine settlement for the advantages of riparian occupation on the

lake shores. Both localities would have been favorable settlement

areas, providing water as well as sources of aquatic protein.



The Contemporary Peten Environment

Geology



With the exception of the mountainous Lacanoon area in the

northwest and the extension of the Belizean Maya Mountains in the

extreme southeast, the Peten is characterized by low-lying karstea

terrain varying in elevation from about 100 to 300 m above sea level.

As is typical of limestone regions, the countryside is irregularly

pocked with caverns and sinkholes. The haystack hill topography

developed on limestones of Cretaceous and Tertiary age (West 19b4).

The Peten lake district (Fig. 2), with its center at 170N,

8940'W, lies within the Santa Amelia Formation, a deposit of early














Eocene age (Vinson 1962). North of the lake region, the Santa Amelia

is overlain by the slightly younger limestones of the Buena Vista

Formation, the basal portion of which contains a 200-m thick zone of

gypsum. Both formations are locally interbedaed with dolomite and

gypsum. During middle Tertiary times, compressional folding and

concomitant emergence resulted in a mid-Eocene to Oligocene

depositional hiatus, though locally there are deposits in the Peten of

Oligocene to Pliocene age. By late Pliocene, uplitt, folding, ano

faulting put an end to Tertiary sedimentation in the region.

The lake chain at 17N (Fig. 2) is aligned along a series oi

east-west trending en echelon faults, the basins occupying depressions

below steep north shore scarps (Tamayo and West 1964). The principal

lakes in the fault zone chain extend some 80 km from westernmost Sacpuy

eastward to the twin basins of Yaxha and sacnab, only 30 km tron the

Belize border. Farther to the west, but outside the main graben, lies

the relatively large and limnologically unexplored Lake Perdica. In

addition to the localized standing bodies of water are seasonally

inundated depressions interspersed between the limestone hills,

features that are not uncommon over a large portion of the Peten

landscape. These "bajos" or "akalches" are characterize by thick clay

soils that give rise to swamp-thicket vegetation. It has been

suggested that the "bajos" were once shallow lakes, providing water,

lacustrine resources and a mode of transportation for the Maya who

inhabited the shores. The silting-in of these shallow basins has been

invoked as a contributing factor for the Classic collapse (Cooke 1931,













Harrison 1977). A 5-m pit dug in the Bajo ae Santa Fe, near Tikal,

revealed that indeed the clays that lined the floor to the.aepression

resulted from the solution of:upland limestone, but there was no

evidence for lacustrine deposition having occurred during Holocene

times (Cowgill and Hutchinson 1973).

The calcareous bedrock of the Peten provided the resource base for

Maya architectural endeavors, as building stone was easily quarried.

In addition, limestone was burned and mixed with calcareous sano

("sascab") to make construction mortar or plaster. The Maya also

exploited the localized flint and chert beas, using the siliceous rock

for making points and cutting tools (hest 1964).



Climate and Rainfall



Lying at low altitude, within the tropic, the Peten is

characterized by year-round high temperatures, the mean annual value in

excess of 25C (Vivo Escoto 1964). Mean monthly temperatures for the

region range between 22*C and 26C, but as expected in tropical areas,

daily fluctuations in temperature often exceed the limits of the

monthly extremes.

Within the Peten, precipitation is highly variable from station to

station and varies on an annual basis at any given site. Rainfall

records indicate annual precipitation values ranging from ca 90b to ca

2500 mm. A regional, yearly mean of 1601 mm is reported based on 54

station-years of data collected at 10 sites (Deevey 197b). Within the

tropics, as a rule, the distribution of rainfall throughout the year is














highly seasonal (Richards 1979), and Peten is no exception. There is a

long dry season from January to May with a secondary period of reduced

rainfall, "canicula," interrupting the wet season in July or August.

The most pronounced aridity occurs from January to March during which

time the rainfall amounts to less than 10% of the total annual income

(Deevey 1978).



Soils



The soils of the Peten catchments represent a large potential

source for lacustrine nutrients. Under conditions of deforestation,

enhanced delivery of dissolved and particulate matter to the lakes is

expected, and the tremendous erosive potential of intense tropical

rains is a major contributing factor in the transfer of nutrients from.

the land to water.. The extreme seasonality and heavy downpours

characteristic of the tropics make rainfall at those latitudes more

erosive than equivalent annual precipitation in temperate areas where

the rains are distributed more evenly throughout the year (Stevens

1964).

Roughly 0.4% of the Peten landscape is covered by the major lakes,

and the balance of the region is overlain by soils assigned to 26

series by Simmons et al. (1959). They relegated the department soils

to two major groups: savanna soils that cover some 9.8% of Peten ano

forest soils that blanket 89.8% of the.region. These major categories

were further divided, savanna soils characterized as deep well-drained,














deep poorly or deficiently-drained, and shallow deficiently-drained.

Within these subdivisions, the soils were assigned to a particular

series based on a number of characteristics, including parent material,

relief, color, texture and consistency, ano profile thickness. With

the exception of some localized soils that overlie clay-rich schists

and some alluvial deposits, Peten soils are derived from the underlying

limestones.

Zonal soils develop under the primary influences of regional

climate and vegetation, their distribution being highly correlated with

patterns reflected in the climatic regime and plant associations.

Within the central portion of the Peten, soil genesis is influenced

tremendously by the calcareous bedrock as well as drainage factors, to

the extent that zonal soil development is precluded. In the lake

district, the local geology ana hydrology have generated primarily

intrazonal soils assigned to the Renazina and Bydromorphic great soil

groups (Stevens 1964). Azonal Lithosols, black calcareous soils

resembling Rendzina are abundant, and Stevens (1964) speculates that

these youthful soils are now regenerating following a long period of

erosion and depletion induced by Maya farming practices.

Though 26 soil series are described for the Peten, only three

surround the lakes examined in this study. The Yaxa series covers some

15.57% of the Peten and consists of shallow well-drained forest soils

that often cap flat expanses as well as hilly slopes. These black

calcareous Lithosols are highly fertile, and cultivation of these soils

is only restricted by their high erosivity and presence on steep














slopes. Yaxa soils surround Lake Macanche and nearly encompass Lake

Salpeten, the southwest shore of which is contacted by soils or the

Macanche series. Macanche series soils blanket 5.11% of the department

landscape and are shallow soils with deficient drainage. Confined to

primarily level topography, these Rendzinas are highly fertile and not

particularly subject to erosion. Poor drainage and the adhesive nature

of the soils are the only drawbacks for agriculture. Indeed, the black

calcareous Lithosols and Rendzinas were certainly exploited by the haya

and.numerous Classic Maya ceremonial centers are found in association

with soil series of these groups (Stevens 1964).

According to Simmons et al. (1959), the western edge of Lake

Quexil is contacted by Yaxa soils, but the balance of the drainage is

occupied by soils of the Exkixil series. A deep poorly drained savanna

soil, the Exkixil series is restricted to only 0.23% of the Peten and

is found in flat areas. These soils can be assigned to the

Hydromorphic great soils group ana are typified by high clay and silt

content and poor fertility. They are not easily eroded and tooay

support grasses and open oak woodland.

It is noteworthy that the soils map developed by Simmons et al.

(1959) is rather crude with respect to accurately delimiting the areas

covered by the various soil types. Within the Peten, great variation

in topography and perhaps bedrock geology can be encountered over short

distances. This in turn leads to great heterogeneity and patchiness of

soil types within limited areas. ihe incongruity of mappeo soil zones

(Simmons et al. 1959, and personal observations) is most clearly














demonstrated at Lake Quexil. While the map shows the Quexil watershed

to be dominated by Exkixil series soils, the true drainage is primarily

covered by forest soils, probably of the Yaxa series.



Vegetation



Though commonly referred to as "tropical rain toiest," the

vegetation of Peten grows in a region that is too dry for the

development of true rain forest. Employing the climatic data criteria

established by Holdridge (1947), the Peten falls within the tropical,

lowland, dry forest life zone. Lundell (1937) applied the tenm "quasi-

rain-forest" and though the vegetation is principally evergreen, some

species lose their leaves periodically, the degree ot deciduousness

dependent on the annual distribution and amount of rainfall.

Simple description of the Peten vegetation is impossible due to

the variability of vegetation types that reflect topographic and

edaphic differences. Wagner (1964) reports that some 75% of the uplana

forest is covered by the "zapotal" association, named for the

prevalence of "chico zapote" (Manilkara) in the miaole tier of the

forest. Characterizing this dominant association, he notes that the

major floristic components in the top story are Calophyllum, Swietenia,

Rheedia, Lucuma, Sideroxylon, as well as several species of Ficus.

Below the uppermost tier lies a middle story of Manilkara, Vitex,

Ficus, Cecropia, Bursera, Spondias, Aspidosperma, Brosimum,

Pseudolmedia, and members of the Leguminosae ano Lauraceae. Averaging













10 m, the lower story is typified by Trichilia, Siderokylon, Sapium,

Sebastiania, Misanteca, Parmentiera, Myriocarpa, Lucuma, Louteridium,

Laetia, Deherainia, Annona, Sabal, Pimenta, Protium, Ocotea,

Zanthoxylon, ana species of Pithecolobium, aalisia, Cordia, and

Croton. The underwood plants are piper, Psychotria, Ruellia, Justicia,

and various palms. Lianas are common, as are orchids, bromeliads, ano

ferns.

Wagner's (1964) enumeration of the genera that typify tie.Peten

forest provides an impression of the floristic composition of at least

one major association. The forest can also be described base on its

physiognomy.. During a 1974, week-long reconnaissance and vegetation

sampling trip near Lake Yaxha, Ewel ana Myers (1974) identities four

vegetation types, the physiognomy of which reflected the underlying

topography. Three of the four distinct vegetation classes were

sampled, including (1) the forests of steep slopes and ridges, located

on well-orained soils and possessing an irregular canopy, the tourlaea

crowns of the tallest individuals often separated by large openings;

(2) Gentle slope forests occupying deeper soils, with standing water in

localized depressions, and typified by a smooth canopy with only

occasional emergents; and (3) Seasonally dry "bajo" vegetation of

short stature (< 20 m), with a smooth canopy and a high incidence of.

windfall. The unexamined wet "ba]o" vegetation appears on aerial

photos and evidently consists of stunted vegetation with closely packed

trees. As part of their sampling procedure, Ewel and hyers established

six 0.1 ha plots, two in each of the three investigated vegetation














types. Identifying all trees with a stem diameter of more than 10 cm

at breast height, the investigators tallied 57 taxa. Strangely, many

of the upland site species were shared by the "bajo" localities, though

trees .on the latter sites were much smaller.

In a similar study, I established five 10 m x 100 m plots in three

vegetation types in.the central Peten. One plot was placed in high

forest near Lake Macanche. The remaining 0.1 ha units were located in

forested areas of the primarily savanna region lying south and

southwest of .Lake Peten-Itza and in the area close to the

archaeological sites of Chakantun and Fango (Rice and Rice 1979). At

each of these sites, a sampling transect was designated in a

substantial, forested area bordered by savanna and a second plot was

established in a "sukche," an island of forest surrounded by savanna.

All trees with a diameter ot more than 5 cm at breast height were

recorded, revealing a diverse flora of 77 taxa on the five transects.

While high forest of great complexity is a most striking feature

of the Peten landscape, nearly 10% of the region is covered by

savanna. ihe most expansive grasslands lie to the south of Lake

Peten-Itza and in many areas interdigitate with stands of forest.

While the savanna is relatively devoid of woody growth in some places,

other localities like the area south of Lake Quexil support numerous

oaks (Quercus). At other sites, "nanze," Byrsonima is the.predominant

tree and is distributed rather evenly over the grassland.

It has been suggested by Lundell (1937) that the savannas are in

fact vegetational artifacts of human disturbance, created by Maya land













clearance and repeated burning. Reinvasion of the deforested areas by

trees may be prevented by human-induced edaphic changes, but tire

frequency is certainly a factor maintaining the grassland (Vaughan

1979). Palynological investigations of the sediments from savanna

Lakes Oquevix and Ija as well as studies of grassland soils will be

necessary to resolve questions about the genesis ana maintenance of

this unique vegetation.

Lundell (1937) believed that the high forest of mooern Peten was

absent during the Maya florescence, the land having been cleared for

agricultural purposes. This contention is now amply supported by

palynological evidence from a number of Peten lake sediment cores

(Tsukada 1966, Vaughan 1979, Deevey et al. 198bc). Lundell (1937) also

felt that the modern standing vegetation represents a climatic climax

forest, there having been sufficient time for its development following

the Maya decline. This view is somewhat contradicted by his belief

that the prevalence of many useful tree species on Maya ruins

constitutes evidence for the claim that the ancient Maya practiced

arboriculture. Fruit-bearing trees, such as Brosimum, Talisia, and

Manilkara, are common on sites as are other economically useful

species, such as incense producers like Protium. While it has been

suggested that these trees were selectively spared during Maya forest

clearance or cultivated to some extent, Puleston (197b, 1982) argues

strenuously that at least one species, "ramon" (Brosimum alicastrum)

was actively planted and that its starch-rich seeds comprise a major

portion of the Maya diet. Another possibility that may account for the

presence of economically useful trees on previously occupied sites is














that the topographic and agronomic factors that may have been

attractive to Maya settlers, like upland, level, well-drained fertile

areas (Rice and Rice 1960b), may simply coincide with the ecological

requirements of the tree species. Additionally, it is possible that

the Maya modified the edaphic conditions, inadvertently creating

optimal chemical or drainage microenvironments for the growth of the

trees, thereby permitting them to flourish after the Classic collapse

(Lambert ana Arnason 1982).



Regional Limnology



The principal basins of the Peten lake district were former when

water filled the troughs of the east-west graben that lies at 17*N.

Most of the lakes are small (< 5 km2) with the exception of the two

largest, Peten-Itza (99.6 km2) and Yaxha (7.4 km2). today Lake

Peten-Itza supports a substantial human population on its shores, the

major riparian settlement occupying areas in contact with the southern

arm of the lake. The bulk of the lakeside residents inhabit three

towns, including the mainland "pueblos," San Benito, ano Santa Elena,

as well as Peten's political hub, Flores, formerly an island community

but now connected to the southern shore by a causeway. San Andres and

San Jose are the principal towns on the north shore of the lake and

overlook the deep, main basin. Lakes Macanche ana Sacpuy also support

small, but rapidly growing "aldeas," while the remainder of the lakes

are largely undisturbed, though isolated houses ana farn.ing activity in

the watersheds have been noted.














While relatively small in surface area, the lakes are rather deep,

many in excess of 30 m. The maximum depth is often associated with

sinks or trenches that are responsible for the conical morphometry of

some basins (Deevey et al. 1980a). Typically, the basins possess deep

trenches in proximity to the north shore, where steep scarps descend to

the lake edge. Southern shores are generally flatter, ana water depth

increases gradually with distance from land.

Despite the fact that exchange with groundwater in the lakes was

shown to be one-way downward and slow, based on studies at Yaxha ano

Sacnab (Deevey et al. 1980a), the lakes are prone to rapid fluctuations

in level that are probably not solely dependent on direct precipitation

and drainage income. A rise of about 3 m was detected in all the lakes

between 1979 and 1980 and was likely associated with groundwater

intrusion. The notion that changes in the regional water table did

occur is supported by the formation of a new lake in the savannas, a

basin that local residents claim filled when groundwater broke through

the country rock. The lakes continued to rise above the 1980 level (P.

Rice, pers. comm.), but this is not the first time they have aovancea.

Older residents of the Peten report that Lake Peten-Itza rises every

40 years, maintaining a high stand for five years before retreating

S(Anonymous 1980a). The last high water was recorded in 1938, when the

level was several meters above the 1980 mark, and much of Flores was

inundated. Other lakes in the district have also experienced high

stands in the past. Supporting evidence comes from the presence of

aquatic snail shells in soils (old lake muds?) well above modern lake














surfaces. H.K. Brooks (pers. comm.) reports snail shells some 13 m

above the 1973 Yaxha surface. Fred Thompson (pers. conu.) ioentifieo

three species of aquatic gastropods, Pyrgophorus exiguus, cochliopina

infundibulum, and Aroapyrgus cf. petenensis, founo in Salpeten south

shore soil samples collected from pits dug several meters higher than

the 1980 peak water mark.

Limnological reconnaissance of the Peten lakes was first

undertaken by Brezonik and Fox in the summer of 1969. They reported

the clinograde oxygen profiles and thermal stratification that

characterize the basins (Brezonik and Fox 1974). Surface waters in the

Peten often exceed 30C, and while thermal stratification aoes seem to

be persistent, hypolimnetic water temperatures sometimes differ from

epilimnetic values by only 3-4C. Encountering anoxic hypolinnia in

most Peten lakes as well as benthic fauna indicative of oxygen stress,

Brezonik and Fox (1974) concluded that thermal stratification of the

lakes was stable. Additionally, they found evidence of meromixis in

Lake Quexil and two small, but deep sinkhole basins, Paxcaman ano

Juleque. The maintenance of the thermocline was attributed to three

factors: the lakes are well protected from strong winds by the

forested limestone bluffs that surround them; the basins are typically

small, but very deep, with contours that inhibit mixing; ana finally,

they note that the density difference per degree change in temperature

is much greater in warm waters than in cold waters.

Over the past decade, the Peten lakes have been sampled

extensively and intensively, supplementing and contradicting some oi














the original findings. Lake Quexil has been studied during several

field seasons, and neither chemical data nor conductivity readings

point to modern meromixis, though an episode of early Holocene

meromixis was detected in the sediment record (Deevey et al., in

press). If contemporary meromixis is to be documented in Peten waters,

it will probably be encountered in the small deep sinks like Juleque

and Paxcaman or in sulfate-rich Monifata I (Leevey-et al. 1980a).

Numerous oxygen profiles from several of the basins show complete

oxygen depletion in hypolimnetic waters to be rare and indicate that

Peten lakes are perhaps polymictic, their frequent circulation

associated with nocturnal cooling. However, predawn data from Lakes

Quexil and Macanche taken in May 1977 demonstrate the persistence ot

the thermal gradient through the night, surface temperatures exceeding

bottom values in the two basins by 5.9C ano 4.00C respectively.

Repeated night sampling, between May and July 1980 of a deep sink

(43 m) located near the northern shore and within Peten-Itza's southern

basin, failed to reveal a breakdown of the thermal gradient.

Oligomixis, or irregular ano uncommon turnover, may better define the

mixing regime of the Peten.lakes, the frequency nevertheless sufficient

to prevent prolonged hypolimnetic anoxia. If episodes of mixis are to

be detected, the most probable period for their occurrence is between

August and December when cooler air temperatures, strong winos, ana

heavy rains might induce turnover. Unfortunately, these are the months

for which limnological data are scanty.














Calcium and bicarbonate are the major cation and anion of Peten

waters, but exceptions are tound in magnesium and sulfate-rich lakes

that may overlie dolomite or gypsum beds. That geological variation

occurs over short distances is quite evident when nearby lake waters

are compared chemically. Lakes Macanche and Salpeten are only

2 km apart but differ appreciably. hacanche is a magnesium sulfate

lake and contains about twice as many magnesium as calcium ions, while

the sulfate:bicarbonate ionic ratio is 1.3:1. Salpeten is a calcium

sulfate lake in which magnesium ions are half as prevalent as calcium

ions, and there are nearly 60 sulfate ions for each bicarbonate ion.

The aptly named Salpeten, also seen in the literature as Peten-suc and

Sucpeten, is highly saline, and the water contains 4.76 g1l-1 total

dissolved solids. Peten waters are alkaline, their ph ranging from

neutrality to 6.6, with surface waters generally producing daytime

readings around 8.0.

Nutrient concentrations of Peten lakes are surprisingly low for

basins in limestone terrain. In a survey of eight lakes, Brezonik ana

Fox (1974) reported total phosphorus concentrations from < 10-33 ug

Pl1-1, relegating these water bodies to the oligo-mesotrophic

(5-10 ug P*1-1) or meso-eutrophic (10-30 ug P-1-1) categories,

as defined by Wetzel's (1975) modification of Vollenweider's (1968)

phosphorus-dependent trophic classification scheme. In another series

of total phosphorus determinations, nine examined lakes displayed a

range from Ib to 54 ug P'1-1, the low value being from savanna Lake

Oquevix (Deevey et al. 1980a). The generally higher phosphorus levels














discovered in the latter study are perhaps attributable to more

complete digestions or.higher sestonic content in the samples, but

demand placement of the lakes in the meso-eutrophic (10-30 ug

P'1-1) or eutrophic (30-100 ug P-1-i) categories. Assignment

to the trophic classes is tentative as a large fraction (40-80%) of the

seston, measured in fresh sediment from traps or cores, is inorganic

(Deevey et al. 1977, Deevey et al. 1980b). Much of this resuspended

silt may contain mineralogic phosphorus that is biologically

unavailable. In any case, high N:P ratios (>25) in Peten waters and

surficial sediments suggest that productivity is phosphorus limited.

Secchi disc transparency, an indirect measure of productivity,

measures turbidity in Peten lakes, as organic color is low (brezonik

and Fox 1974). However, measured transparencies may not be a very good

indication of algal standing crops if much suspended material is

inorganic seston. Secchi disc readings range from 1 to 5 m, the

clearest water generally found in the sulfate-rich lakes. Lake Quexil,

dominated by calcium and bicarbonate ions, displays low transparency,

less than 2 m at times, ano because seston of the lake shows relatively

high loss on ignition (50-60%), the rapid disappearance of the disc

with depth may indicate a.substantial algal biomass. It is noteworthy

that Lake Quexil (also seen in the literature and on maps as Lckixil,

Ekichil, or Exiquil) derives its name from the Maya word Ekexiil

(another variant) that means "agua oscura con hierbas," or water

darkened by weeds (Anonymous 1980b).














Direct measurement of productivity was accomplished by light-aark

bottle experiments, conducted by H.H. vaughan at twin Lakes Yaxha ana

Sacnab in 1973 and 1974. Five sets of experiments at Yaxha and three

at Sacnab yielded nearly identical mean values, 251.6 + 121.6 mg

C-m-2*day-I (Yaxha) and 251.7 + 11U0. mg Ccm-2*day-1

(Sacnab). A single experiment was undertaken at Lake Quexil in

mid-March 1978 and gave a gross production figure of 196 mg

C.m-2.day-1 (Deevey et al. 1960a). The values obtained suggest

that the lakes are at the low end of the mesotrophic (250-1000 mg

C.m-2.day-1) or upper end of the oligotrophic (50-300 mg

C*m-2-day-1) scale (Wetzel 1975), but this assignment is

tentative as production undoubtedly fluctuates throughout the year, and

the data set is small. Nevertheless, the range of production values

encountered in the twin lakes, 157.6-449.3 mg C'm-2.day-1

(Yaxha) and 135.3-354.5 mg Cmm-2-day-1 (Sacnab) is indicative

of oligotrophy or mesotrophy using temperate standards.

The Peten lakes that are free from human impact generally support

a small algal biomass, at times apparently dominated by the cyanophyte,

Lyngbya (Brezonik and Fox 1974). Peten waters are noticeably deficient

in diatoms, though Melosira ambigua and M. granulata are common in

Lakes Yaxha and Sacnab. Members of the Bacillariophyceae are rare in

the lake sediments, probably due to dissolution at high pH. While

Yezdani's checklist of Peten phytoplankton (Leevey et al. 198Ua) is

long, the implied diversity is misleading, as several dominants

probably constitute a large fraction of the standing crop year-rouna.

The chlorophyte Botryococcus braunii and the blue-green Microcystis















aeruginosa are nearly ubiquitous ano are encountered in large numbers.

B. braunii constantly oominates net tows anu its conspicuous absence

from centrifuged water samples collected by Brezonik ano Fox probably

resulted from resuspension following centritugation. As a Qonmlhiat, b.

braunii is indicative of oligotrophic conditions in temperate regions,

but its value as an indicator species in the Ieten likec is

questionable, as it is founa unoer a variety of conditions in tropical

ana subtropical basins (hutchlnson 19Sb7.

The open water zooplankton is numerically aominateo by copepoas,

the four most abunoant species being Liaptomu acr sails, hesocyciop

inversus, M. eaax, and Iropocyclops prasinus mexicanus. Another

important member of the zooplankton is the enuemic, peiagic ostracoo,

Cypria petenensis that distinguishes itself by being rare or absent in

sulfate waters. Juveniles are present in the water column at all

times, while adults are migratory, leaving the benthic habitat anc

entering the pelagic environment only at night, a strategy that Likely

helps them avoid predation by fish. Eubosmina tubicen (Leevey ana

Leevey 1971) is the only common pianktornic cl.oocerara, with

representatives of the Sididae, Daphniidae, hacrothricidae, ano

Chyaoriaae notably rarer in open water net tows.

Thirty-two species of entomostracans are reported from plankton

tows in 10 Peten lakes, the most diverse tauna (23 spp.) truno in the

largest lake, Peten-Itza (Deevey et al. 1980b). The lakes average 11.4

species each, the least diverse tauna encountered in sultate-rich Lakes

Salpeten (4 spp.) and Monifata I (5 spp.). hhile the planktonic














component of the entomostracan fauna is notably universe, systematic

sampling of a littoral zone study site in Lake Peten-Itza has expar.aea

the list of entomostracan taxa, with 31 species of chydorids (29

identified, 2 unknown) alone, having been enumerated (M.h. Bintord,

pers. comm.). Only six chydorid species were taken in the Lake

Petenxil plankton (Deevey et al. 1980b), but some four tires as many

species were identified from remains in the Petenxil sediments (Goulden

1966). Chydorid remains are integrated into the sedimentaLy matrix

over space and time so that more taxa are frequently encountered in mud

samples than can be collected in a systematic lake sampling program

(Frey 1960).

Twenty-two species of fish have been identified fror. collections

made in five lakes (R.M. Bailey, pers. comm.), and three of these, the

clupeid Dorosoma petenense, the characin Astyanax fasciatus, and an

atherinid Melaniris sp., may be responsible for the low diversity and

small body size that characterize the Peten zooplankton. Other

potential consumers are the second characin Hyphessobrycon compressus,

as well as several poeciliids and juvenile cichlids. Some members of

the latter family attain significant size (1-2 kg), and some Cichlasoma

species and the "blanco," Petenia splendid, are exploited by modern

"Peteneros," as they undoubtedly were during Maya times.














Maya Settlement in the Yaxha and Sacnab catchments

Maya Demography



Twin Lakes Yaxha and Sacnab were originally selected as stuoy

sites because early archaeological reports indicated differential

degrees of Maya settlement in the two watersheds (Bullaro 1960). It

was surmised that the dissimilar levels of environmental impact woulo

be reflected in the paleolimnological record. laxha supported an urban

center on its north shore, and the island site of Topoxte, lying within

Lake Yaxha, was densely inhabited during Postclassic times (1000-1600

A.D.). Urbanization never developed in the Sacnab watershed, and the

drainage remained devoid of habitation following the classic collapse.

In order to assess changing ancient Maya riparian population

densities, Don S. and Prudence M. Rice established transects radiating

from the lake shores that were searched for housemounds. The

transects, 2 km long and 0.5 km wide, were located on the lake edges at

randomly selected points and ran in a north-south direction,

perpendicular to the fault line, thereby permitting the sampling of all

microtopographic zones. Six sampling units were staked out at Yaxha,

and four were established at Sacnab (Fig. 3), the total area of the

transects in each case equivalent to about 25% of the subbasin

drainages. At Yaxha, the island of lopoxte was also designated as a

sampling area. The plots were systematically searched for mounds, ano

a randomly selected 25% of the mounds were test-pitted so that periods

of occupation could be established using the ceramic sherds extracted.




























Figure 3. Twin Lakes Yaxha and Sacnab, showing the position of the archaeological sampling transects
and soil pits. Op = operation.




































































SCALE


2Cnnou,. in n.)













These data were then employed to calculate population densities for the

ceramically defined periods using the assumptions previously applied at

Tikal,.that 84% of the mounds discovered were residences and that the

average household consisted of 5.6 persons (Havilano 1970). by

convention, the calculated densities represented levels of occupation

at the end of the ceramically defined periods.

Middle Preclassic (1000-250 B.C.) population densities were

slightly higher at Sacnab (34 persons*km-t) than at Yaxha (22

persons*km-2), but by the close of the Late Preclassic (25U

B.C.-250 A.D.), Yaxha, having grown more quickly, had 70

persons*km-2 to Sacnab's 51 persons*km-2. A lag in growth at

Yaxha permitted Sacnab to catch up by the end of the Early Classic

(250-550 A.D.), the two subbasins hosting 101 persons*km-2 ano 102

persons'km-2 respectively. The centripetal draw of the Yaxha urLan

center ultimately left that subbasin with a dense (256

persons*km-2) human population by the ena of the Late Classic

(550-850 A.D.), at which time Sacnab supported 168 persons-km-.'

Considered as a single population, the prehistoric Maya of the combined

twin basins increased their numbers slowly, doubling about every four

centuries, the logarithmic phase of population growth lasting about

1700 years (Deevey et al. 1979).














The Twin Basin Sediment Recora



Using a Livingstone piston corer (Deevey 1965), H.K. Brooks

obtained a sediment core from Lake Yaxha in 1973, and a year later H.H.

Vaughan and D.S. Rice collaborated to raise a shallow-water long core

from Lake Sacnab (Fig. 4). Palynological study of the 7.4-m Yaxha core

revealed a stratigraphy identical to that discovered by isukana (9tt)

in the sediments of Lake Petenxil, 50 km to the west. Seaiments rich

in pollen of grassland and grassland arboreal species were overlain by

postdisturbance mud dominated by high forest pollen indicators.

Evidently, cores from both the lakes had failed to penetrate Maya-

period muds, dense urban settlement at Yaxha resulting in the

deposition of more than 6 m of clay-rich sediment. However, the 6.3-m

Sacnab core demonstrated that the savanna pollen zone was underlain by

organic-rich sediments with a high proportion or horaceae pollen. The

basal, high forest pollen section showed some indications of human

disturbance and was assigned an Early Preclassic age, a time period for

which archaeological evidence is lacking in Peten, but that is coeval

with the Early Formative at Cuello, in Belize. With supplementary

evidence for a predisturbance high forest zone coming from Lake Quexil

(Vaughan 1979, Deevey et al. 1979), Tsukada's (1966) conclusion that

the Maya had transformed savanna into high forest was reevaluated. In

fact, the Maya had converted high forest into grassland, the forests

later recovering after the abandonment of the region.




























Figure 4. Bathymetric maps of Lakes Yaxha and Sacnab, showing the locations where long cores were
retrieved for paleolimnological study.


































0 LONG CORE SITES
------. *3 METER SHORE, 1962
- SHORE LINE. 1973
6 DEPTH IN METERS
A TRAP
CORE


0 1 2
km














Phosphorus Loading of Lakes Yaxha and Sacnab



Efforts to assess past changes in trophic state ot the lakes were

attempted through an evaluation of ancient phosphorus budgets.

Phosphorus has been shown to be the limiting nutrient in many aquatic

systems (Schindler 1974, Vallentyne 1974) with productivity highly

dependent on total phosphorus loading rates (Vollenheiaer 19tb, Lillon

and Rigler 1974, Oglesby and Schaffner 1978). Phosphorus, unlike

carbon and nitrogen, lacks an atmospheric compartment in its

biogeochemical cycle. Thus, nearly all phosphorus transported from the

watershed to the lake is ultimately sequestered in the basin

sediments. Phosphorus movement in the watershed is essentially

unidirectional, removal from a lake by.mechanisms such as insect

emergence representing a small proportion of the phosphorus originally

delivered to the lake (Vallentyne 1952).

Past rates of nutrient delivery to the basin can be calculated

when phosphorus concentrations in the seaiment are known ana several

levels in a core are accurately dated. Unfortunately, radiocarbon

dates run on bulk sediments from the Peten lakes, even those pretreated

for carbonate removal, proved to be unreliable due to the hard-water

lake effect. Ancient carbonates, lacking the radioisotope, are

solubilized, and their carbon is incorporated into autochthonous

organic material, making dates appear too old (Deevey ana Stuiver

1964). Ultimately, all bulk sediment radiocarbon dates were

disregarded and archaeologically correlated dates were assiSnea to

levels in the cores based on the identification of discrete pollen














assemblages (Vaughan and Deevey, 1961). The assumption used for zoning

the cores was that the degree of deforestation expressed in the pollen

profiles reflected changing population densities as derived from the

archaeological program.

When phosphorus loading rates to the twin basins weLe calculated,

they tracked the slow, steady exponential rise in population aensity

that occurred between the Middle Preclassic and Late Classic. Roughly

delimiting the area circumscribed by the two drainages, export of

phosphorus from the watersheds, already seen to be haya density

dependent, was shown to occur at a rate of about 0.5 kg*person-1

yrt-1. The calculated per capital rate of delivery is, perhaps

coincidentally, almost equal to the physiological output of phosphorus

(0.55 kg) from human bodies that are in equiliLrium with respect to

their intake and output of the nutrient (Vollenweider 1968). Watershed

soils were the principal source of disturbance-zone phosphorus,

nutrient-rich surface soils moving rapidly downhill by colluviation

following Maya-induced deforestation (Brenner 1976, Leevey et al.

1979). Because bulk soil transport was the primary mechanism carrying

phosphorus from the land to the lake, it was impossible to determine

what proportion of the sedimented nutrient actually cycled through

human bodies.

Disturbance-zone sediments of the twin lakes are highly inorganic

and do not indicate that the episode of deforestation was accompanied

by high lacustrine productivity. Large amounts of silica and detrital

carbonate were transported with the phosphorus as soil was eroded into

the lakes. The siliceous, Maya-zone sediments are aominateo by














montmorillonite clay, the residue of the down-wasted country rock.

High phosphorus delivery rates might be expected to correlate with high

autochthonous organic production. That high rates of nutrient input

were associated with inorganic mud suggested that much seaimented

phosphorus was biologically unavailable and bypassed the biota before

deposition on the lake bottom. Corroborating evidence for this

inference came from microfossil analyses that failed to demonstrate

that high primary or secondary production was associated with the

enhanced phosphorus delivery (Brenner 1978). Unfortunately, enumerated

microfossil remains from Peten sediments provide unreliable estimates

of past productivity. Though amounts and accumulation rates of

microfossils decreased with increasing phosphorus input to the twin

basins, strong diagenesis (postdepositional destruction) makes the

thanatocoenosis a poor estimator of the biocoenosis trom which it was

derived.




















IhE HISTORICAL ECCLOGY OF THE MAYA AT LAKES QUEXiL,

SALPETEN, AND MACANCHE

The Archaeological Recora



The goal of this stuoy is to expand the geographic scope of the

"Historical Ecology of the Maya" project westwaLo to exazaite tthet

unexplored lake basins. With soil, archaeological, ano

paleolimnological oata trom the new watersheds, seolnmentatioi, processes

in the Peten lakes can be evaluate better, and the phosphorus loading

model developed at Yaxha ano Sacnab can be testee. Ihe new lakes

considered, Quexil, Macanche, ana Salpeten, hitter trom the twin basins

in failing to display the slow, steaay exponential human population

growth from the Middle Preclassic until the Late Classic peak.

Instead, the archaeological record shows that haya population it, the

western watersheds experience a decline curing the Terminal Freclassic

(100 B.C.-250 A.D.) ano Early Classic (25b-550 A.D.) before risitr. once

again in the Late Classic (550-850 A.D.) and finally collapsing about

650 A.D.

Archaeological study of the three watersheds was oirecteo Lu

Don S. and Prudence M. Rice during the 1979 and 1980 field seasons. to

sample about k5% of the watershed area, three transects raOiating itcm

the lake edge were established in each basin, ano some 25% of the















mounds surveyed were test-pitted to determine time of occupation. At

Quexil (Fig. 5), a single north shore transect was lasi out ana two

south shore sampling plots were staked. Transects were run in a north-

south direction, and as at Yaxha were U.b km wloe. In keeping with

procedures used at the twin basins, the north shore transect was 2 km

long, but the south shore surveys were run about .2i km, to the Lase

of the karst uplift that encloses the basin. This permitted the

sampling of a large savanna south of the lake. Aaoitionaill, Quexil's

two islands were searched, revealing b structures on the western island

and 20 on the eastern island.

At Salpeten, standard size (2 km x U.5 km) transects uere

established with north-south orientation, two on the north shore ano a

single plot on the south shore (Fig. 6). A large, oensely settler site

on salpeten's peninsula was also investigated. The site, called

Zacpeten, is primarily of Postclassic age. At hacanche (Fig. 7), the

single north shore transect and two south shore plots were oriented

northwest-southeast. Mounds discovered within a walled site (Op 2),

Muralla de Leon, were also surveyed, as were some structures between

transects. In this basin, time period of occupation was determined by

test-pitting about 25% of the mounds both on and off transects. Using

the proportion of mounas showing occupation outing the various serious,

population levels were figure based on the density of mounds founa on

the aelimitec transects. In all three drainages, changing, haya

population densities were calculated employing the assumptions used at

Tikal (Haviland 1970) and at Yaxha ane SacnaL, that 64% of the icunus

were residences ana each household consisted of 5.6 persons. Figure b



































Figure 5. Lake Quexil, showing the position of the archaeological
sampling transects and soil pits. Op = operation.







LAKE QUEXIL
0 km 1
SArchaeological Transects
Soil Pits


~^/
I
-iu


Op2





































Figure 6. Lake Salpeten, showing the position oi the archaeological
sampling transects ana soil pits. Op = operation.








LAKE SALPETEN


0 km 1
I I

SArchaeological Transects
SSoil Pits


Op 3



































Figure 7. Lake Macanche, showing the position ot the archaeological
sampling transects and soil pits. Op = operation.













LAKE MACANCHE

0 km 1

[ | Archaeological Transects
SSoil Pits
l'Op 2





7
Op 1


1N-


Op 3































Figure 8. Cruce population densities, calculated trom housemoura
densities, in the tive lake basins for which both
archaeological and paleolimnological histories have teen
studied. Population reconstructions are based on
radiocarbon dated ceramic chronologies.














300-

200-
YAXHA
100-



0 1000


200
SACNAB
100



0 1000


200
SQOUEXIL
S100-



0 1000


300-

200o MACANCHE

100-


0 1000


300-

200- SALPETEN

100-


0 1000


I I
1000 0 1000 2000
B.C. A.D.

Date















shows the changing population patterns for five Peten watersheds base

on mainland transect mouno densities.



Soil Chemistry



Translocatec soils were shown to have been the principai source or

phosphorus for Lakes Yaxha and Sacnab curing the period of haya forest

disturbance (Deevey et al. 1975). In extening the stuuy to three new

watersheds, soil samples were collected from several localities in each

basin to assess total phosphorus ana other chemical concentrations and

distributions in riparian soil profiles. Because bulk movement of

soils is the mechanism by which phosphorus reaches the lakes, totat

phosphorus was analyzed rather than the plant-available fraction.

During the 19b0 fiela season, 21 soil pits were aug in the ,uexil

drainage (Fig. 5), while 11 trenches were dug in both the Nacanche and

Salpeten basins (Figs. 6 anc 7). In each case, soil pit locations were

determined subjectively in order to sample several microtopographic

zones as well as areas associated with haya construction. IIn most

instances, samples were collected along archaeological transects so

that distances from shore coulQ Le determined by rereience to

established, staked positions in the archaeological sampling plot.

Soil pits were dug to bedrock, sterile "sascab," or as oeep as ha%

feasible. Maximum depth from site to site was variable, but none of

the sample depths exceeded 100 cm. Samples were remove rrom the

exposed profile wall at 10 cm intervals, each sample representing a















composite of soil collected over the full 10 cm. About 100-200 g of

soil were taken at each level ano stored in inoivioual plastic bags.

In the lab, four levels from each soil pit (0-10 cm, 10-20 cm, an

intermediate level between 20 cm and bottom, ana bottom) were removed

and air-cried, though only top ano bottom samples were considered in

Quexil's shallow pit #4. A subsample of each air-orieu level was

extracted and ground with a mortar ana pestle. A portion of the

powered soil (1-6 g) was removed, weighed, ano place in a 'ihermoiylte

Type 1500 furnace for two hours at 5500C to assess organic matter

content by loss on ignition. Following combustion ana reweighing, a

0.3-1.5 g sample of ash was remove, weighed, ano digested in lb ml of

a heated 2:1 nitric-perchloric acio mixture. hhen aense, white hbloU

fumes appeared, the 250 ml beakers containing the mixture were covered

with watchglasses and the oxidation process was continued toL an

additional hour, with distilled water added periodically to prevent

total drying. After digestion, samples were tilterer atnc the nitrate

was brought to a known volume. The filtrate was delivered to the

University of Florida Institute of Food ano Agricultural sciences Soils

Laboratory, where cation concentrations were determined by atomic

absorption ano phosphorus analyses were run on a lechnicc.n Auto

Analyzer. I measured sulfur content in filtrate samples from surface

ana bottom profile levels using the turbioimetric procedure in StanoaLo

Methods (APHA 1971). Sulfate turbidity was read on a Coleman Mooel 14

Universal Spectrophotometer. Prior to running sultate analyses on the

digested, ashed soils, a series of paired ash-whole soil determinations















were made to assess sulfur loss due to ignition. Measured sulfur

content, as concentration per grani whole soil was shown not to aitfte

statistically when the two methods were compared. All soil chemical

concentrations are expressed as amount per gram of air-orieo wiole

soil.

Total phosphorus analyses run on soil profiles from Quexil,

Macanche, and Salpeten reveal that in all three watersheos a strong

gradient is maintained with respect to the nutrient, surface soils

clearly enriched as compared to levels deeper in the profiles (Figs.

5-12). Though exceptions oo occur, increasing depth in the profile is

generally accompanied by decreasing phosphorus concentration. This

trend is evident when the mean surface soil (0-10 cm) phosphorus

concentration in a basin is compared to the mean value obtained for the

basal (variable depth) levels of the pits. At Quexil, where the 21

soil pits were dug to an average of 74.3 cm, mean phosphorus

concentration in surface soils was 178 ug P'g-1, or 2.46 times the

average concentration (112 ug Pg9-1) calculated tor the deepest

strata in the pits. The average depth attained at Macanche was 73.6

cm, ano an even stronger phosphorus graoient was revealed by analyses

of the 11 profiles from the watershed. The mean surface soil

phosphorus level (594 ug P*g-1) exceeds the bottom concentration

(181 ug P*g-1) by 3.28 times. At Salpeten, where 11 pits

bottomed-out at a mean depth of 62.7 cm, the average surficial soil

nutrient concentration (598 ug P*g-1) was 2.21 times the mean founa

in the basal profile levels (271 ug P.g-i).



































Figure 9. Total phosphorus concentrations at selected levels in soil
pits 1-12 at Quexil.













QUEXIL



0
20

40
60"
Bo PIT 1 PIT2 PIT3

100








E 40
60
S80 PIT4 PIT 5 PIT 6
C 100



0


.. 20.
0
4 40
60
so PIT 7 PIT a PIT 9
100 i .




0
20
40
60

80 PIT 10 PIT 11 PIT 12

100, 1 I

0 200 400 600 800 1000 0 200 400 600 800 1000 0 200 400 600 800 1000


,g P-g-i



































Figure 10. Total phosphorus concentrations at selected levels in soil
pits 13-21 at Quexil.

















QUEXIL


0
1/
20
40
60
so PIT 13 PIT 14
100


PIT 15


0
20
40
60
so PIT 16 PIT 17 PIT 18
100 I I I


0
20-
40-
60.
80 PIT 19
100 ,
I0 I0 I 8I 1
0 200 400 600 800 1000


( PIT 20 PIT 21


200 600 800 1000 0 200 600 1000
0 200 400 600 800 1000 0 200 400 600 800 1000


pg P-g9-



































Figure 11. Total phosphorus concentrations at selected levels in 11
soil pits at Salpeten.












SALPETEN


PIT 3


0
20
40
60.
0o PIT 4 PIT 5 PIT 6
too


PIT 8


PIT9


0
20
40
60
so PIT 10
100

0 200 400 600 800 1000


PIT 11



0 200 400 600 800 1000 0 200 400 600 800 1000


pug P-g-'


































Figure 12. Total phosphorus concentrations at selected levels in ii
soil pits at Macanche.












MACANCHE



0

20


60


100



0


20
E 40
U 60
. so PIT4 PIT5 PIT6





0.

20
40

60

'o PIT7 PIT8 PIT 9
100 .
os









20


60"


8o PIT 10 PIT 1
100
I II i I I I I I I I I I I
0 200 400 600 800 1000 1200 0 200 400 600 800 1000 1200 0 200 400 600 800 1000


ug P-g-'













To assess how organic matter and various soil chemical

concentrations change with oepth in the profile, mean conLcentrations

for all of the combined top two levels (0-1U cm and i0-20 cm) in the

profiles of a basin are compare to the average concentrations

calculated for the summed bottom two levels (intermediate between 20 cm

ana bottom, plus bottom) of the basin pits liable i). Quexil's shallow

pit #4 was excluded from this tabulation because only two levels were

analyzed, ano assessments ot changing sultur concentrations witi aepth

are reliant on surface and bottom analyses only. Aaoitionally, whole

profile mean concentrations tor the various soil paraneteir are given,

thereby permitting a rough interbasin comparison of soil

characteristics.

Organic matter distribution in the soil profiles displays a trent

similar to that seen for phosphorus, % loss on ignition generally

decreasing with greater depth. Surface soils are also enriched in

sulfur, deeper profile levels noticeably deficient with respect to the

nutrient. Similar trends in organic matter 'anu sulfur concentrations

suggest that much soil sulfur is present in organic form. However,

ignition of the.samples at b50C caused no apparent loss ot sultur,

perhaps indicating that the bulk of sulfur is present in mineral form,

or that the organic sulfur fraction is not volatilized on1 turning.

High inorganic sulfur content would not be unexpected, particularly at

Salpeten where a gypsum outcrop overlooks the northwest shore ot the

lake. Were this the case, sulfur distribution woula be expected to

track magnesium and calcium in the profiles, but it aoes not.














Table 1. Summarized chemical concentrations from soil pits ouy in the
Quexil, Macanche, and Salpeten watersheds. Concentrations in
the two uppermost levels of the profile were aveiageu as were
the two bottommost samples, thus giving a rough idea of
chemical graaients in the soil profiles. Whole profile mean


concentrations
concentrations
only.


are also given for each chemical type. Sulfur
were determined on surface ana bottom levels


Profile Profile Loss on Ca Mg Fe
Levels Depth n Ignition % ag*gm-1 mygm-i1 si .gs-I


QUEX1L


Top 2 1-10 cm
Levels 10-20 cm


Bottom 2
Levels


Variable


Whole All
Profile Samples


Top 2
Levels

Bottom 2
Levels


14.1


0-10 cm
10-20 cm


Variable


3.4 2b.3


MALANCHE


Whole All
Profile Samples


SALPETEN


Top 2 0-10 cm
Levels 10-20 cm


44 14.3 2b4


31.2 5.7


Bottom 2
Levels

Whole
Profile


Variable

All
Samples














Table 1--extended.


Al Na K P S
mggm-g1 ug*gm-1 uggm-1 ug gm-1 9 -gi1


41.6


47.2


44.4





8.6


8.0


8.3







13.1


16.0


14.6


848


673


761





609


453


531







1240


1226


1233













Cation distributions throughout the soil profiles are more even,

without the pronounced top-to-Lottom gradieit seen tot suitut,

phosphorus and organic matter. Potassium concentrations are slightly

higher in upper soils of the profiles, while sodium content is a bit

richer in the deeper levels. In all three watersheds, calcium is a bit

more concentrated in deeper soils, a trena that is anticipated in

limestone terrain. Magnesium displays rather uniform concentration

throughout the soil profiles, and though at Quexil upper level strata

contain slightly higher amounts of the cation than deep soils, the

trend is reversed at Macanche and Salpeten.

Intra-basin variation in the chemical profiles is most apparent at

Quexil, where forest soils, presumably of the Yaxa series, were sampled

along with Exkixil, savanna soils. Low fertility, Exkixil soils are

depleted in phosphorus as compared to forest soils. Surface soils from

the six savanna profiles (#1, #5, #8, #9, #10, #11) have a mean

concentration of 164 ug P*g-1, while the 15 forest pits display an

average upper level concentration about twice as high (324 ug

P.g-1). Disregarding shallow pit #4, mean whole profile

concentrations for various chemical constituents in the six savanna

pits can be compared to values obtained on the 14 forest trenches.

Aluminum is highly concentrated in the clay-rich savanna soils (105.4

mg Al'g-1), whereas the forest profiles contain only 18.4 mg

Al-g-1 High iron content in the savanna soils evidently is

responsible for the rich red color of the earth south of Quexil, and

savanna iron levels (b7.15 mg Fe.g-1) exceed forest soil levels













(7.0 mg Feg9-1) by nearly an order of magnitude. The lack ot

calcium in grassland soils is striking, as they possess only 2.4 mg

Ca*g-1. Forest soils, differing by more than two orders or

magnitude, contain 256.1 mg Ca*g-1. Purest soils are also richer

in magnesium than savanna soils, the two series containing 4.1 nmg

Mg*g-l and 1.7 mg hg'g-1 respectively.

When mean, whole profile chemical concentrations are compared on

an inter-orainage basis, several differences are apparent. Average

iron and aluminum concentrations are higher at Quexil than at Macanche

and Salpeten because of the high metal content of the grassianb soils

at Quexil. Likewise, calcium deficiency in the Quexil savannas is

largely responsible for giving that basin an overall mean whole protlie

calcium value that is relatively low. Magnesium content of the

Macanche and Salpeten soils exceeds that in Quexil by.7.1 anoa 9. times

respectively. The difference is not accounted for solely by the low

magnesium content of Quexil's savanna profiles, because even forest

soils at Quexil possess considerably less magnesium than encountered in

samples from Salpeten anr hacanche. Lolomiitizatior. in the hacanche-

Salpeten-district, also reflected in.the water chemistry of the two

lakes, is the probable cause of high magnesium levels in the basin

soils.

Though it is not certain, high sulfur concentrations eetermir.ed

for the hacanche and Salpeten watershed soils probably point to the

presence of gypsum in the underlying bedrock of these uasins.

Evaporites are evidently less common at Quexil, ana soil sulfur values














from the three basins generally reflect chemical levels in the lake

waters (Deevey et al. 1980a).

Phosphorus is highly concentrated in the upper levels of Peten

soil profiles, and under conditions of deforestation, erosional

processes would be expected to carry large amounts of the nutrient to

the lakes. Rapid mobilization of the available phosphorus traction is

possible, but not likely, as the homogeneous distribution in the

profiles of highly soluble sodium and potassium argues against

leaching.

Maya agro-engineering activities enhance delivery rates ot

phosphorus to the lakes not only by accelerating downhill bulk

transport of soils, but perhaps by first concentrating the nutrient in

surface soils through physiological cycling, interment, ano refuse

disposal. Though the oata are meager, three soil profiles Qug in

housemounds as well as several other pits located near construction

contain extremely high levels of phosphorus suggesting an anthropogenic

source for the nutrient in enriched surface soils. At Saipeten, south

shore soil pits #6 ano #7 were piaceo in housemounos sibb ano jitj,

last occupied during Late Classic times. Surface soils from these pits

contain 821 ug P*g-1 ano 9i2 ug P*g-1 respectively, much more

than the overall mean value for surficial soils in the basin (558 ug

P.g-1). On the north shore of the lake, soil pit tl was locate at

the crest of a steep slope, in close proximity to rubble from collapse

construction. Ceramic sheros were encountered in the excavated soil

pits, and its surface soils contained 995 ug P*g-1. Dowunlope tron














this site, topsoil from pit #2 yielded 895 ug P-g-l. The four

Salpeten soil pits within or near Maya structures had an average

surface soil nutrient concentration of 906 ug pg-l1, while top

level soils of the remaining seven pits had a mean of only 42C ug

p.g-l.

At Quexil, soil pit #21 was located in south shore housemouno

#823, a structure that was occupied during middle and Late Preclassic

times ana again in the Late classic period. Surficial soils from the

pit contain 467 ug P-g-1, significantly more than the overall

surface soil mean of 278 ug P-g-1 for the waterbhea. At hacanche,

pits #1 and #2 lie on the north shore slope just below construction ano

their highly enriched surface soils contain 1074 ug Pg9-l ano 1275

ug p9g-1 respectively, exceeding the mean surface concentration

(465 ug P*g-1) found in the remaining 5 pits.



















PALEOLIMNOLOGY OF LAKE QUEXIL

Comparing Shallow-hater ana Deep-hater Sedimentation



The primary goal of the paleolimnological research undertaken in

the three new watersheos was to assess how the proximate composition ot

the sediments and accumulation rates of various chemical constituents

of the muo varied as a function of shifting Maya population levels.

The first basin considered was Lake Quexil, lying some b km east of

Flores and only 1 km from Lake Petenxil (Fig. 2), the basin where Maya

impact on the Peten sedimentary record was first revealed (Cowgill et

al. 1966).

In 1972, H.h. Vaughan ano G.H. Yezoani useu a Livingstone piston

corer (Deevey 1965) to get a 6.5-m section in 7 m of water. Ihe core

was taken south of the lake's western island (Fig. 13). The sfali lake

(area = 2.101 km2, 2max = 32 m, = 7.2 rt: Deevey et al. 18ba)

was cored again in 1978. In March of that year, M.S. Flannery, 5.L.

Garrett-Jones, ano 1 raised a 9.2-m core from 2b ru ot watel usin a

modified, gravity-driven, Kullenberg apparatus (Fig. 13). This core,

designated Quexil H, was one of several long cores coiiecteu in the

lake's deep, central basin in our effort to secure sediments of

Pleistocene age.





























Figure 13. Bathymetric map of Lake Quexil, showing the locations of several coring sites in the
basin.













LAKE QUEXIL S


Site Core
S Shallow-
C C
H H
F F
X 80-1
X 80-2


Year
1972
1978
1978
1978
1980
1980


Water death
7m
29.8 m
27.7 m
19.8 m
29.0 m
29.0 m


CONTOUR INTERVAL 2m
0 500 IW m

SCALE


Depth below M.W. Interface
0-6.5 m
0-7.9 m
0-9.2 m
0-9.8 m
7.49-19.88 m
4.57-9.65 m


Lake
Quexil
Quexil
Quexil
Quexll
Quexll
Quexil













The shallow-water core was returned to Florida in the aluminum.

coring tubes, ano the ,uexil H core was transported to the Florioa

State Museum in the plastic tubing that lined the iron Kullenberg

coring pipe. Cores were refrigerated at 4C prior to ano following

extrusion. Sediment chemistry ana palynology of the shallow-water

section were reported elsewhere (Brenner 1978, Deevey et ai. 1975,

Vaughan 1979), but without accompanying aata on Maya population

densities in the basin. This consideration not only correlates

sedimentary changes with shifting population levels, but by comparing

two sediment columns, demonstrates the profound influence that core

location and basin morphometry haa on sediment chemistry ana measure

sediment accumulation rates.

Samples were removed from the extruaeo cores at 5-20 cm intervals,

and water content was evaluated on weighed volumetric samples by drying

at 1100c. A second set of samples was dried for total carbon ano

nitrogen analyses that were run on a Perkin-Elmer Model 240 Elemental

Analyzer. A third series of volumetric samples was weighle anr

digested in 15 ml of 2:1 nitric-perchloric acid. After oxidation, the

samples were filtered, ana the filtrate was brought to a known volume.

Cation analyses were run on the filtrate by atomic absorption at the

University of Florida Institute of Food ana Agricultural Sciences Soils

Laboratory. Filtered digestate from the deep core samples was analyze

for phosphorus content on a lechnicon Auto Analyzer at the Soils

Laboratory. Aliquots of digestate from the shallow-water core were

retained for phosphorus analyses, which were run colcrimetrically on a













Coleman Model 14 Universal Spectrophotometer following blue color

development by the ascorbic acid-ammonium molyboate method in Standaro

Methods (APHA 1971). Sulfur content in Quexil core H was measured by

assessing the quantity in the filtered digestate using the

turbidimetric technique in Standard Methods (APHA 1971).

When all chemical analyses were complete, chemical concentrations

in dry sediment were calculated (Figs. 14 and 15), and level by level

proximate composition of the sediment was figured (Figs. 16 ano 17). To

compute the chemical make-up of the mud at each level, the carbonate

equivalents of magnesium and calcium were first calculated, thereby

permitting the assessment of inorganic (carbonate) carbon content.

Next, the inorganic carbon quantity was subtracted from the total

carbon value to yield an organic carbon figure. Then, as at Yaxha ana

Sacnab (Deevey and Rice 1980), the organic carbon value was multiplied

by 2.5 to produce a figure for organic matter content. Iron is

reported as the oxide, Fe203, and Si02, likely an

alumino-silicate, is the residue following subtraction of organic

matter, CaCO3, MgCO3, and Fe203.

Dating the cores was once again dependent on changes in the

relative pollen diagrams. An exception was provided by numerous wood

fragments that were encountered at 623-624 cm in the shallow-water

core. Age determination on these allochthonous plant remains is free

from the confounding effects of haro-water-lake error, ano a dated

sample (DAL 198) gave a 14C age of 8410 + 160 years (Ogaen and Hart

1977). Corrected to about 9400 siaereal years (Deevey et al. 1979),




































Figure 14. The chemical stratigraphy of the Quexil shallow-water core.













QUEXIL
Shallow-Water Core

Ctot NIot Ptot Ca Mg Fe *SiO"
mg-g-' mg-g-' pg.g-' mgg-i' mg"g-' mg-gg1' mBgg'


Corg
mgg-'



























Figure 15. The chemical stratigraphy of Quexil core H.









QUEXIL
Core H


CaCO3&
Corg MgCO3 Ctot Ntot C/N Ptot Ca Mg Fe Mn K S SiO
mg*g-I mg.g-' mg.g-' mg.g-' Ai1g-1 mg.g-' mg-g-' mg.g-' gg-' i pg.g' mgg'-1 mg.-g-
100 200 300 40 0 100 300 5 15 10 20 400 00 I 5 15 20 40 200 600 00 00 10 20 400 800


DRY
WEIGHT
%




Full Text

PAGE 1

PALEOLIMNOLOGY OF THE MAYA REGIODi By MARK BRENNER A DISSERTATION PRESENTED TO THE GRADUATE SCHOOL OF THE UNIVERSITY OF FLORIDA IN PARTIAL FULFILLMENT OF THE REQUIREMENTS FOR THE DEGREE OF DOCTOR OF PHILOSOPHY UNIVERSITY OF FLORIDA 1983

PAGE 2

UNIVERSITY OF aORlOA 3 1262 08666 474 4

PAGE 3

ACKNOVJLEDGEMENTS I would like to thank the many people who have helped me complete this project. First and foremost, I thank my committee, chairman, Dr. E.S. Leevey, for guidance and encouragement. Dr. Deevey.introQUced me to paleolimnology, and I am indebted to him for nurturing my fascination with, the lacustrine sediment record. I appreciate the input of Dr. Frank Nordlie, who taught me the fundamentals of limnological research. I am grateful to Drs. Tom crisman, carter Gilbert, and Doug Jones for reviewing the thesis and for teaching courses that inspired some of the ideas in this work. The multidisciplinary nature of this paleoecological study demanded the collaboration of a large number of researchers. I was reliant on assistance from many individuals, and I want to acknowledge their aid. The success of the 1978 coring operation was largely due to Sid Flannery's help. He also helped produce some of the core chemistry data. Dr. Sam carrett-Jones also collaborated on the 1978 drilling campaign and generated pollen data. Dr. Hague vaughan provided me with instruction in paleolimnological techniques and was responsible tor producing several pollen profiles. I have fond memories of the many months spent in Peten with Drs. Don and Prudence Rice. I am grateful to them for allowing me to use

PAGE 4

both their published and unpublished archaeological data. Special thanks are due Pru for delivering me to the hospital in Guatemala City during my 1979 bout with hepatitis. Dr. Mike Binford's presence in Peten in 198G made that a most productive field season. Mike provided granulometric data from Peten cores and listened patiently to many of my ideas, ansvwering nuruerous questions along the way. I am also grateful for the feedback obtained from other members of the Paleoecology Lab: bob Snodgrass, Tom Whitmore, and Antonia Higuera-Diaz. carl Miles and Andy Ogram instructed me in the use of the atomic absorption spectrophotometer and the Leco induction furnace. Liz Fisher provided encouragement every step of the way. her aid is gratefully acknowledged. Rhoda Bryant typed the final manuscript, and her aid is certainly appreciated. The successes of the "Historical Ecology of the Maya" project have been largely attributable to the cooperation of many Guatemalans. Special thanks are due the following friends for assistance far beyond the call of duty: Rafael and clemencia Sagastume, Jaime and Mari Spbalvarro, Antonio and Aura Ortiz, and Robert Dorion. I thank the many residents of northern Guatemala who have made me feel at home in Peten. Finally, l would like to thank the Peten. This study sheas some light on Peten's prehistory. Many questions remain unanswered, and the region, with its spectacular Maya ruins, tropical forests, and lakes, continues to captivate my imagination. I look forward to visiting and working in the area again.

PAGE 5

This project was supported by grants to Dr. e.S. Deevey (NSF DEB 77 06629, NSF EAR 79 26330, and EAR 82 14308). A graduate research assistantship from the University of Florida Division of Sponsored Research is also gratefully acknowledged.

PAGE 6

TABLE OF CONTENTS ACKNOWLEDGEMENTS ii ABSTRACT vii INTRODUCTION 1 Prehistoric haj^a and Contemporary Hunian Population Densities of Peten, Guatemala 1 Maya Cultural Development in the Tropical Forest Ecosystem . . b The Origins of Maya Civilization & Maya Agricultural Practices IG The Classic Maya Collapse 14 The Historical Ecology of the Maya 17 Measuring Maya Environmental impact Paleolimnologically . . 17 Lake-Watershed Interactions 18 The Paleolimnological Perspective 22 The Contemporary Peten Environment . 26 Geology 26 Climate and Rainfall 28 Soils 29 Vegetation 32 Regional Limnology 36 Maya Settlement in the Yaxha and Sacnab catchments ....;. 45 Maya Demography 45 The Twin Basin Seaiment Record 49 Phosphorus Loading of Lakes Yaxha and Sacnab 52 THE HISTORICAL ECOLOGY OF THE MAYA AT LAKES QUEXIL, SALPETEN, AND MACANCHE , 55 The Archaeological Record 55 Soil Chemistry 65 PALEOLIMNOLOGY OF LAKE QUEXIL 83 Comparing Shallow-water and Deep-water Sedimentation 83 Proximate Chemical Composition of the Lake Uuexil Sediments 97 Chemical Accumulation Rates in Lake Quexil Sediments . . . 1U2

PAGE 7

Paleoproductivity; in Lake ^uexil . . . . . . . .'. . . . . . . . lib The Significance of Microfossils . . .... . .118 The Microfossils of the Quexil cores ......... . . . 120 Microfossil Accumulation Rates and Phosphorus Loading . . . 141 carbon-Nitrogen Ratios in Quexil Core H .......... 152 Comparing Microfossil Accumulation Rates at the Two Quexil coring Sites . . . . . ..;..... 154 TESTING. THE PHOSPHORUS LOADING MODEL DEVELOPED AT YAXHA^SACNAB . .160 Coring in Lakes Salpeten, Macanche, and Quexil, 1980 ...... 160 Sediment Chemistry of the Macanche and Salpeten Cores . . . 175 Assessing the Maya Annual Per Capita Phosphorus Output .. . . . . 178 Zoning the Cores Chemically . . . . .... . . . . . . . . 178 The Impact of Sediment Focusing 191 Zoning the Cores Palynologically .201 Assessing the Impact , of Soil Nutrient Loss . 205 Erosion Rates for the Peten Watersheds ........ 210 SUMMARY . . ..... . . . . . . . . . ... .... 224 BIBLIOGRAPHY 237 . BIOGRAPHICAL SKETCH . 249

PAGE 8

Abstract of Dissertation Presented to the Graduate School of the University of Florida in Partial Fulfillment of the Requirements for the Degree of Doctor of Philosophy PALEOLIMNOLOGY, OF THE MAYA REGION, Mark Brenner ,, April 1963 Chairman: Edward S.Deevey, Jr. Major Department:. Zoology , ' Archaeologically supported estimates of riparian Maya populations were combined with paleolimnological information to quantify the impact of prolonged, prehistoric Maya settlement on the watersheds ana lakes of the karsted lowlands in Peten, Guatemala. The pollen record indicates that regional, human-induced deforestation beg^n prior to the Middle Preclassic period (1000 B.C.). Forest recovery commenced with depopulation at the end of the Postclassic period (1600 A.D.). Vegetation removal caused profound changes in sediment and nutrient loading of the Peten lakes, and the impact was sustained for nearly 3 millennia. Pre-Maya organic sedimentation was replaced by rapidly accumulating inorganic deposits, but was restored some 400 years ago when forest regrowth began. Maya exploitation in the catchments accelerated the rate of total phosphorus delivery to the lakes. In the absence of soil-anchoring vegetation, phosphorus reached the lake shores as colluvium, i.e. as redeposited soil. As was shown in 1979 at Lakes Yaxha and sacnab, phosphorus loading was Maya-density-dependent (0.5 kg P*capita~l*yr~^). Settlement

PAGE 9

and core chemistry data from 3 other basins are consistent with the quantitative conceptual model based on this constant. Computed microfossil accumulation rates, though confounded by diagenesis, indicate that productivity in the Peten lakes was not enhanced by the anthropogenic phosphorus. Severe siltation may have inhibited lacustrine production; moreover, most of the haya-period phosphorus load was probably delivered to the lakes in biologically unavailable form. Shallow-water and deep-water cores from 2 lakes demonstrate the differential distribution ("focusing") of sediment and imply that single cores in conical basins are inadequate to describe accurately the accumulation of chemical and fossil constituents. Soil and sediment chemistry data (46 soil profiles, 40.5 m ot analyzed Holocene lake sediments cored from 4 basins) indicate that Peten soils lost perhaps a third of their phosphorus stock as Maya-generated colluvium. Agricultural yields may therefore have declined due to soil nutrient depletion, concomitant lacustrine siltation could have reduced the availability of aquatic protein. Together, nutrient sequestering and siltation may have tunctioneu as a servomechanism, restricting haya population growth and contributing to the 9th century Classic population collapse.

PAGE 10

INTRODUCTION Prehistoric Maya and Contemporary Human Population Densities ot Peten,. Guatemala Guatemala's northern Peten region encompasses 35,854 km'^ and constitutes a large portion of the core area in which southern lowland Maya civilization arose and developed (Fig. 1). Tropical, lowland, dry forest (Holdridge 1947) covers most of the Peten (Lundell 1937), as well as portions of Belize, Mexico's Yucatan peninsula. Tabasco, and Chiapas, it was in this environmental context that lowland Maya culture originated and persisted for several millennia before collapsing mysteriously in the 9th Century A.D. (Culbert 1973). Perhaps as a testimony to the inhospitable nature ot the tropical forest, the Peten remains largely depopulated today. Cowgill and Hutchinson (1963a) reported a Peten population of 20,362 in 1957, although very recent development has raised the figure nearly 10-fold (Castellanos 198C). The sparse nature of contemporary human settlement is placed in perspective by comparison with assessments of Late Classic (550-850 A.D.) Maya population levels. Delimiting Tikal 's areal extent to just under 163 km^, Haviland's (1969, 1972) Late classic estimates for this site alone fall between 40,000 and 49,000. Thompson (1966) indicates that proposed figures for pre-Columbian population levels are highly variable. They range from a low of just over a million for the

PAGE 11

F Fig. 1. Regional map. The Maya Lovvlanas incluue aitas otBeliiie, Guatemala's Peten region, and portions of Mexico's Yucatan Peninsula, Tabasco, and Chiapas.

PAGE 13

entire Maya region to 13,000,000 for the Yucatan peninsula alone. Admitting that his own whole-area estimate of J, 000,000 might be a bit low, Thompson (1966) was prepared to revise his figure upward, but conceded that the data base was so small as to make all assessments of Late Classic levels mere "guesstimates." In a more recent study, Adams et al. (1981) accept the notion that some 14,000,000 inhabitants occupied the Maya lowlands by A.D. 800. Accurate appraisals of modern Peten population levels are also difficult to obtain, partly due to the seasonal immigration into the area associated with industries such as the harvest of "chicle" (Simmons et al. 1959, Cowgill and Hutchinson 1963a). From the turn of the century until the late 1960's, "chicle" was Peten 's most important commodity, and the flourishing business attracted large numbers of men from Mexico, highland Guatemala, and other Central American countries (Schwartz 1974). The last two decades have witnessed a profound change in the region, as new settlers, pressured by land shortages in the highlands to the south, have streamed into Peten in response to the promise of abundant agricultural terrain. Formed in 1958, the governmental agency, Empresa Nacional de Fomento y Desarrollo Economico del Peten (FYDEF) began a land distribution program in the niio-1960'&, finally granting titles to the assigned parcels in 1974. Under the auspices of FYDEP, road building and maintenance were priority projects, and by 1970 the overland route from Flores to Guatemala city was completed, making the Peten interior more accessible than ever before, in addition, communication systems were established, air service was improved, and as a consequence of the subsequent human

PAGE 14

influx, the region is beginning to lose its distinctive cultural identity. The attraction of available land has converted highlanders into "Peteneros" at an alarming rate. Schwartz (1977) reported an increase from 25,910 Peten inhabitants in 1964 to about 100,000 only 13 years later. Castellanos (1980) indicates that the rapid immigration that continued through the late 197b's left the Peten with soii.e 200,000 people by the close of the decade. While government efforts to relocate land-hungry;'highlanders appear, laudable, the program is not without its drawbacks. Native "Peteneros," while enjoying the new prosperity, feel th^ir patrimonies are, threatened (Schwartz 1977) ana concern exists, that, ther^ .will be insufficient employment opportunities to accomjiiodate the newcomers. Another issue that must be addressed is how the inmiigrants are faring with subsistence farming practices in the Peten lowlands. They are unaccustomed to the high temperatures of the region and unfamiliar with the soils, vegetation, and shifting agricultural techniques that characterize the area. Whether the recent settlers will be able to cope in the new environment remains to be seen, but the Peten will continue to undergo drastic social and environmental change in the future as a result of increasing population density. While the modern "experiment" in the use of the tropical, lowland forest is in its incipient stage, and it would clearly be premature to pass judgment on its success now, it can be said that the prolonged persistence of prehistoric Maya culture in the same context constituted a success that is without parallel. Bronson (1978) has likened the

PAGE 15

Maya to three Asian civilizations that developed in apparently similar settings, but this hardly detracts from the achieveiiients ot the Maya, and the latter are, with the possible exception of the Olmec, the only New World high civilization to arise and flourish within a tropical, lowland forest ecosystem. Maya cultural Development in the Tropical Forest Ecosystem While some anthropologists are perplexed by the apparent incompatibility of high civilization and the tropical forest setting, adherents of "environmental determinism" have gone so far as to deny that lowland Maya culture could. have developed iji situ . Meggers (1S54) argued strenuously that Classic Maya culture (250-850 A.D.), with its monumental architecture, art, hieroglyphics, concept of zero, corbeled arches, calendrical system, and stela cult, could not have arisen autbchthonously. Believing that the degree of cultural coruplexity achieved is dependent upon the agricultural potential of a region. Meggers classified the Peten as an area of limitec agricultural potential (Type 2), and thus believed the area was not conducive to the florescence so evident in the archaeological record. The logical conclusion, based on the assumptions of this agriculturally deterministic law, was that classic Maya culture was iii.porteo into the lowlands fully formed and was destined to decline following its arrival. This simple theory accounted for both the mysterious origin and inexplicable downfall of the civilization.

PAGE 16

In the years following Meggers' (1954) paper, a number of refutations were published, perhaps laying to rest the broad claims of environmental determinists, but keeping alive the controversy surrounding the enigma of the prehistoric high civilization in the tropical forest environment. Coe (1957) took exception to Meggers' claims for a number, of reasons. He. contested her view that there, is a lack of Preclassic-classic transition in the lowland record and felt there was no archaeological basis for the, argument that classic culture was imported from the highlands. Additionally, he pointed out that several lowland Maya achievements, such as the corbeled arch, the Long Count, and the stela cult, seem to have no non-lowland origin. Coe's disagreement with Meggers extended to the perception of the Classic Maya collapse. While Meggers referred to a "gradual decline," initiated following the arrival of Classic culture in the lowlanas, coe pointed out that the evidence indicated a rather widespread, rapid termination following some 600 years of incremental growth. In the year following Coe's reply to Meggers, Altschuler (1956) presented Formative phase ceramic evidence that supported the claim for autochthonous origin of lowland Classic Maya civilization. His conviction was that political problems generated the 9th century collapse. Specifically, he proposed that the ruling class attempted a political structuring that was doomed to failure because it lacked the developed techniques of exploitation. Ferdon (1959) disagreed with Meggers' assessment of the Peten's agricultural potential, and using his criteria of temperature, soils.

PAGE 17

precipitation, and land form, reclassified the lowlands as a favorable (Type 3 = improvable) site for agriculture. This analysis aid not constitute a refutation of deterministic law as applied to the haya by Meggers. It simply freed the civilization from having to conform to the expectations dictatea by a Type 2 (limited potential) environment. However, Ferdon did take issue with environmental aeterminism ano presented data supporting his contention that there is no correlation between natural agricultural potential and cultural aevelopment. Having disproved the role of determinism in the eventual classic collapse, he proposed the notion that grass invasion of clearea plots and the subsequent inability to plow the tracts contributed to the downfall of the civilization. The Origins of Maya Civilization Recent archaeological excavations in the Orange Walk district of Belize have established that occupation of that area conjiienced as earj.y as the third millennium B.C. At the site of Cuello, fragments of partially burned wood associated with ceramic material assigneo to the Early Formative Swasey complex (Hammond et al. 197 S») have produced several radiocarbon dates indicating an age of between 400(J and 5000 calendar years (Hammond et al. 1976, Hammond et al. 1977, Hammono 1980, 1982). These data confirm the claim that lowlana classic Maya cultural ontogeny had its roots in the lowlands. Within the Peten region per se , the earliest ceramic material discovered to date comes from the sites of Seibal ana Altar de

PAGE 18

Sacrificios (Adams and Culbert 1^77). Assigned respectively to the Real and xe complexes, the material is dateo to the Miodle Preclassic (1000-250 B.C.). Middle Preclassic settlement is known at Tikal and has also been documented in the Yaxha-Sacnab watersheds of eastern Peten (Rice 1976). Following an extensive settlement survey and test-pitting program during the 1979-80 field season, occupation of this age is now recorded in four more central Peten drainages (Rice and Rice 1980a). .While the numerous discoveries of Preclassic settlement in the Ibwlands contradict the argument that Classic culture was brought to the region intrusively, debate continues as to what factors were the driving forces contributing to the formation of lowland Classic Maya civilization^ (Adams 1977). .Althbugh influences from beyona the lowlands are considered, several intrinsic processes are invoked to explain the cultural growth and change that produced the social ranking and stratification that ultimately characterized the classic period. Wiiley (1977) provides a multi-causal model for Classic Maya development based pn a synthesis of processual interpretations proposed by others, in formulating his "overarching model, he incorporates these models and processes that are broadly assigned to three major categories: (l) ecology-subsistence-demography, (2) warfare, (3) trade.. He notes that none of these models advocates a monocausal explanation for the Classic Maya rise ano cautions that the role of ideology should not be discounted.

PAGE 19

10 invoking environmental factors, though not as a determinist, Sheets (197S>, 1981) sees the rise of Classic Maya civilization in the lowlands as reflecting a natural disaster in the highlands of El Salvador. Acknowledging that Classic Maya culture would have developed in any case, he, argues that the eruption of El Salvador's Ilopango volcano in A.D. 260 might have accelerated the process by forcing increased political and agricultural organization to cope with the influx of immigrants who descended to the lowlands when highland agricultural land was rendered useless by the deposition of a thick ash blanket. Additionally, he points out that Tikal's Early Classic (250-550 A.D. ) florescence may have been stimulated by the diversion of trade routes with Mexico that previously had passed along the Pacific coast. With the coastal road destroyed, Tikal became the major eastern site on the trade route that extenaed into the basin of Mexico. Maya Agricultural Practices During the last two decades, Maya archaeology has become preoccupied with questions about pre-Hispanic agricultural practices. Until that time, the prevailing dogma was that Maya subsistence was dependent on maize-based, swidden (slash-and-burn, shifting) agriculture. How this belief became entrenched in the literature remains unclear, but it was not necessarily supported by the archaeological record. Though corn is depictea in Maya art, the contemporary reliance on the "milpa" and the ubiquity of cornfields in the Guatemalan lowlands at the time of colonial contact and today must

PAGE 20

11 certainly have contributed to the acceptance of the doctrine. While this agricultural technique may be appropriate for the sparsely populated modern Peten, there is doubt as to whether it was a feasible alternative during Classic haya times. Because slash-and-burn requires land to be fallowed for long periods, much larger areas than the plots actually under cultivation are required. In the swidden cycle, forest is felled during the dry season (January-May), and prior to the onset of the rains, the dried vegetation is burned, aelivering nutrients to the soil. Following the burn, seeds are sown in holes bored with a dibble stick, and growth commences after the first showers of the rainy season with no additional working of the soil required. Confronted with differing assessments of Peten's agricultural potential (Meggers vs. Ferdon), Cowgill (1962) sought to resolve the disparity and interviewed 40 farmers in the region of Lake Peten-Itza in an effort to ascertain actual corn production. Summarizing the data from the interviews, she noted that first year plot yields were 1425 lb*acre~^, second year plots averaged 1010 lb*acre~^, and the five farmers who tried three years of successive planting averaged 417 Ib'acre"^, with the decline likely due to nutrient depletion. Stable swidden of this nature would demand a four-year fallow following a single crop and six to eight years' rest on a plot worked two years in succession. Cowgill concluded that swidden farming could support about 38-77 people 'km'^, and tentatively noted that classic perioo population densities may have exceeded the restrictions imposed by stable swidden strategy.

PAGE 21

12 Recent surveys of ancient Maya settlement in the Peten make it easier to evaluate the feasibility of slash-ano-Lurn to have supt/orteo prehistoric populations. Rice (1578) usea demographic data gleanea from the archaeological record together with agricultuial output information to formulate a model that demonstrates the insufficiency of maize-based agriculture to have met the subsistence neeos of populations in the Yaxha-Sacnab subbasins. At this locality, where slow, steauy exponential population growth occuiiea from the hiooie Preclassic (1000-250 B.C.) until the Late Classic (550-850 A.D. ) (Rice 1978, Deevey et al. 1975?), depenoence on maize-basea swioaen agriculture would have resulted in food shortages by Late Preclassic (250 B.C. -250 A.D.) times, necessitating shorter tallow peiioGS oi the farming of less, preferred sites solely in order to meet subsistence needs. Ihe incorporation into the subsistence strategy oi, root crops, ., as originally hypothesized by Bronson (196b) or breadnut, "ramon" ( Brosimum alicastrum ) (Puleston ±978, 1982), is shown by the mooei to have greatly enhanced the probability of supporting large classic : populations. With the demise of the myth that Maya subsistence was totaj.xy. reliant on maize-based swidden came suggestions for other food sources ano food-producing systems. Lange (1971) proposed that marine resources might have been an important constituent in the Maya diet. An inventory of Peten's potential floral ano taunax tiaae items (Voorhies 1962) contains a varied assortment of fooa types, but the list of comestibles is by no means complete, as perishaLxe goods.

PAGE 22

1j incapable of being transported long aistances, were excluoea trom thi& tabulation. According to Vvilkin ll^Vi), ha^a toou procurenient v»a& likely dependent on an array of systems that includea garaening, arboriculture, gathering and intensive practices such as terracing, irrigation, and arainage. There is nov» abunuant archaeological eviaence that the iov,iana Maya did employ intensive agricultural techniques. In campeche, Mexico, riogea tielas are Miown in the Rio t,anoelaiia legioi. iSieiiienb and Puleston 1972), and ^atheny (1976) reports that extensive measures tor water control were taken at Luzna. In the Rio Bee region of the southern Yucatan peninsula, terraces ana raiseo fielos are reporteo by Turner (1&74), and Turner ano Harrison (Ibiil) have oiscoverea raittc fields at Pulltrouser Swamp, Belize, that may have been constructed as early as Late Preclassic (2b0 h.C.-
PAGE 23

14 The Classic Maya Collapse The recent revelation that Classic Maya subsistence was at least in part dependent on intensive agricultural practices helps explain how the populations of the densely settled region were supported. Unless it can be claimed that these subsistence strategies caused environmental detriment, their discovery cotitributes little to the search for a cause of the Classic Maya collapse. What makes the Maya downfall such a perplexing event in New World Prehistory is that the disintegration of the framework that characterized the socially stratified Classic culture was accompaniec by an extreme demographic change involving the relatively rapid depopulation of ceremonial centers as well as the countrysiae. With a shift in archaeological focus, beginning around 1950, from an exclusive preoccupation with ceremonial architecture to an interest in settlement surveys, the magnitude of the population decline was more fully appreciated (Willey 1982). Willey (1956) expressed the need for more settlement work, but the lack of evidence for Postclassic (1000-1600 A.D.) occupation of housemounds excavated during his Belize valley surveys led him to the conclusion that commoners disappeared with the demise of elite society. Stated simply. If collapse occurred — and, inoeed, sori.ething did occur — Maya priest and peasant collapsed ana vanished together.. Willey (1956: 7bl) Adams (1973) has summarized the "collapse" problem and provides a concise recapitulation of the hypotheses that have been proposed to

PAGE 24

15 account for the Maya downfall. Adams details the archaeological evidence for the disappearance of the elite class, and his summary view of the collapse encompasses not only the cessation of elite activity, but the attendant population decline, both of which occurred throughout the southern Maya lowlands within a period of 50-100 years. Noting that there has been a recent tenoency to reject singlefactor reasons for the collapse in favor of multiple-factor models, Adams nevertheless classifies the explanations into broad categories. Ecological models invoke various environmental disasters, such as soil exhaustion, water loss and erosion, and savanna grass competition. Under this heading, Sabloff (1973) might add insect infestation and climatic change. Catastrophic events such as earthquakes (Mackie 1S61) and hurricanes are proposed, but serious earthquakes are not characteristic of the lowlands, and events stemming from disasters such as these are hard to document using the archaeological record. Meggers' (1954) "environmental determinism" is considered an evolutionary model, but is now discredited because it is known that lowland culture arose autochthonously, and the agricultural potential of the region has been reevaluated. A demographic model for the population decline was set forth by Cowgill and Hutchinson (1963a), but receives little attention today, studying the Indian populations around Lake Peten-itza, they discovered that by the fifteenth year of life, the sex ratio in the population was 1.8o^:1.0?. This they attributed to the poor care given female children between one and four years of age, by which time the skeweo ratio is established. Neglect

PAGE 25

16 and consequent high mortality of female children (1-5 years) is documented for many non-industrial countries (cowyill and Hutchinson 1963b), but is likely compensated for by slightly higher male death rates in the ensuing years. It is pointed out that the "extreme case discovered in the Indian populations of the Peten could have disastrous consequences. An explanation for classic Maya depopulation was sought using this scenario, with the realization that it would have to be applied in a long-term situation. The destruction of the social structure as a consequence of internal revolution has been posited as a factor influencing the collapse, but while it may account for the disintegration of the social hierarchy, this alone would not necessarily have led to depopulation, invasion from outside the area has also been proposed, and in view of the post-collapse Toltec takeover in the northern Yucatan, such a scenario is not out of the question. There is some archaeological basis for the claim that intrusive elements were present at Seibal and Altar de Sacrificios prior to the decline. Finally, disease has been repeatedly implicated as a causal factor in the collapse, though debate surrounds claims about the pre-Columbian presence in the New World of illnesses like malaria, yellow fever, and syphilis. Recent paleopathology work with skeletal material from Altar de Sacrificios has revealed the occurrence of health problems in the Maya population that occupied the site. Evidence for physical injury in the bone sample is minimal, but vitamin c deficiency and anemia, either diet-related or parasite-induced, are amply documented (Saul

PAGE 26

17 1973). Additionally, the presence of bone lesions indicative of syphilis or yaws is noted. It is clear that the various explanations for the collapse are not mutually exclusive, and several of the proposed causal factors may have worked in concert to produce the resultant downfall. Unfortunately, . some of the proposed hypotheses are difficult to reject using the archaeological record alone, but a systematic program of testing the different single-factor theories may one day lead to a synthetic model that reasonably explains the Classic Maya disappearance. Such an approach will doubtless be dependent on evidence provided by ecologists, ethno-historians, soil scientists, and others outfaiae' the realm of archaeology per se . The Historical Ecology of the Maya Measuring Maya Environmental impact Paleolimnologically Thisstudy does not directly address the question of the mysterious Maya collapse, though the data collected do in fact suggest that ecological factors played a role in the event. Instead, the design of the experiment was chosen with the objective of shedding light on the impact that long-term Maya agro-engineering practices had on the watersheds and lakes of the Peten. In a sense, the question has been approached conversely in the anthropological literature, as social scientists have sought to determine the influence the natural environment had on settlement patterns, fooo-producing systems,

PAGE 27

18 socio-political organization, etc. Cognizant of the fact that the interaction between humans and the ecosystem constitutes a feedback loop, this study takes a decidedly "ecocentric" viewpoint, exploring the effects of prolonged, dense human occupation on terrestrial and aquatic systems of the tropical lowlands. The Peten lake district (Fig. 2) provides a unique opportunity to examine human-environment interaction, for, in fact, the "experiment," exploitation of the lowland tropical forests, and lakes, has already been, conducted by a civilization now long gone. The results of that experiment need only be elucidated, and with this in mind, the "Historical Ecology of the Maya" project was conceived in 1971. Employing a multidisciplinary approach, the program involved the use of archaeological and paleolimnological techniques to examine changes in the aquatic and terrestrial systems that resulted from extended human interference. Lake-Watershed Interactions Proper study of lacustrine systems in general and the paleolimnological record in particular demands a view of lake basins as integral parts of a larger landscape. Though often considered as distinct entities, aquatic and terrestrial ecosystems are inextricably linked by meteorologic, geologic, and biologic processes that transfer nutrients and energy from one system to the other (Likens and Bormann 1974a). Lakes can be considered "downhill" with respect to their terrestrial surroundings and the meteorologic, geologic, and biologic

PAGE 29

20 A vy

PAGE 30

21 vectors that join the systems ultimately carry nutrients from upland sites of accumulation to the waters below. The, kinds of nutrients and their rates of supply have a profound effect on the lake, exerting a controllinci force on the physical, chemical and biological processes that occur in the aquatic realm. Mature, intact, terrestrial ecosystems tend to maintain tight nutrient. cycles, with loss to the : lacustrine sector minimized by the presence of the soil-anchoring, standing vegetation, when the biological component of the land systemis disturbed, through forest clearance, nutrient cycles are disrupted, accelerating the delivery of dissolved and particulate matter to the lake. Inadvertent enrichment of lake waters can occur as a result of forest clearance, but often, lacustrine pollution occurs as if by design. The "downhill" nature of lakes makes them convenient disposal systems for unwanted, accumulated wastes like domestic sewage and industrial by-products. These practices are not without their consequences and our contemporary cultural eutrophication problems stem from the casual manner in which many lakes have been used as recipients of sewage and agricultural run-off rich in plant nutrients (Edmondson 1968, 1970, 1972; Vallentyne 1974). The realization that the source area for some of these unwanted nutrient inputs lies some distance from the water's edge demands that investigators look beyond the lake itself in the study of lacustrine processes. Furthermore, awareness of acid rain problems (Likens and Bormann 1974b) demonstrates the neeo for consideration of the regional airshed in assessing lake dynamics.

PAGE 31

22 Bormann and Likens (1967) suggested that small watersheds make ideal sites for examining nutrient c^cle problems and proposed that the entire watershed be considered the basic unit for ecosystem-level lake study. Modern stud.ies at Hubbard Brook, New Hampshire, have accumulated biogeochemical output data from undisturbed, natural ecosystems (drainage basins) (Likens et al. 1977), and these baseline values can be compared to nutrient losses from clear-cut forests (Bormann et al. 1968). Contemporary investigations of this type measure altered nutrient outputs as they occur. That is, data on the rate of nutrient transfer between the terrestrial-aquatic interface can be collected immediately following a "treatment" like deforestation. In attempting to assess the effect of past events.on lakes, it is necessary to rely on the paleolimnological record. The Paleolimnological Perspective Paleolimnological study can document past changes in a lake and its drainage, because shifting conditions in the watershed had an impact on the lake; and a record of the alterations, though perhaps somewhat distorted, is preserved within the sediments on the lake bottom. Frey (1974) has said. The task of the paleolimnologist is to "read" the history of the lake-watershed-atmosphere systems from the record "written" in the seoiments. (1974:95) In dealing with the origin and developmental history of basins, paleolimnology can address questions about the ontogeny of lakes that

PAGE 32

23 were free from human disturbance. Climatic change can be inferred from the palynological record and theoretical questions about ecosystem development can be approached using sedimented microfossil assemblages (Deevey 1969). With the greater awareness that human activity can radically alter watershed nutrient cycles, paleolimnological techniques are being used increasingly as a tool to assess the niagnitude ot human-induced changes, sometimes historic data on demographics and waste dumping are known for a lake-watershed system, but the limnological record is restricted to the postdisturbance period, in Lake Washington, east of Seattle, the sediments yielded information concerning baseline lacustrine conditions, prior to the eutrophication that resulted from excessive sewage input to the lake (Eamondson 1974). The paleolimnological record, in conjunction with early historical records or archaeological data, has been used to establish the impact of human activity on a number of basins, sedimentalry changes having been correlated with density of occupation ot shifts in land use (Cowgill and Hutchinson 1964). Like the vast majority of contemporary limnological investigations, most paleolimnological projects have been undertaken in the temperate area lakes of now-industrialized countries (Mikulski 1978, Pennington 1978, Vuorinen 1978, Warwick 198U). Inere is a paucity of literature concerning tropical paleolimnology, especially with regard to the impact of human disturbance on tropical ecosystems. Though regrettable, there are several factors that likely account for the restricted development of tropical paleolimnology. First, well-established limnological research centers are generally

PAGE 33

24 confined to temperate regions, often in close proximity to lake districts. Therefore, mounting drilling campaigns in tropical areas can be quite costly, necessitating a large initial outlay for travel. Once in the tropics, one may encounter adaitional difficulties, poor road conditions or a complete lack thereof can render potential coring sites inaccessible. Also, such projects often require the permission of foreign government officials, and even when permits are forthcoming, the local political or scientific conjiiunity may lack the infrastructure to be of assistance. Political instability is a hazard to be considered :and makes many potentially exciting study sites "off-limits." Finally, little is known of the regional limnology in most tropical areas, making interpretation of the paleolimnological record somewhat less secure. Despite the many drawbacks and logistical difficulties associatea with paleolimnological work in the tropics, there are significant arguments that convincingly speak to the need for more study in these regions. As the human populations in tropical countries continue to increase, deforestation and resource exploitation will accompany the demographic change. What impact the forest felling and farming practices will have on freshwater sources is not known. Limnological monitoring of newly settled drainages must begin, and sediment studies can be used to gather baseline information from basins with a long history of occupation. With continued demophoric growth in the tropics, management schemes for freshwater resourceJs will have. to be instituted and cannot be formulated using the temperate data base.

PAGE 34

2b Despite the differences between temperate and tropical systems, paleolimnological techniques should be applicable in both settings for documenting human intrusion in watersheds. Nutrient cycles in undisturbed, tropical watersheds are very tight and maintained by the standing vegetation. Any disruption in the drainage basin should have a noticeable, if not profound, effect on the lake and consequently the sediments (Oldfield 1977). Several characteristics of the Peten lakes reconanend them as study sites. First, the basins are closed, and because the lakes lack outlets, the sediments are the ultimate sink for much of the dissolved and particulate matter washing into the lake as well as biogenic material formed autochthonously. Secondly, a long history of haya settlement in the Peten watersheds should be expected because of the scarcity of surface water in the lowlands. Initial settlement in the region might be supposed to have clustered around readily available sources of water. That access to water was a problem for the haya is evident in the archaeological record at some sites in the interior. The long dry season necessitated the construction of reservoirs at Tikal, and evidently some 'chultuns," hollowed-out, underground caverns, were employed for water storage (Matheny 1982). To the north, in the drier Yucatan, the situation was even more critical, and it has been pointed out that the Maya of that region developed a civilization, in a sense based on groundwater, with population centers located near water supplies in the form of natural "cenotes," caves, and "aguadas," or man-made wells (Back 1981).

PAGE 35

26 One scenario for the initial Maya invasion of the Peten interior envisions the pioneers entering on the river systems and later expanding into the drier regions of the central core area (Puleston and Puleston 1971). It has been suggested that the lack of available water and necessity to cope with the problem may have been the driving force that led to substantial social organization. The oldest Peten sites of Seibal and Altar de Sacrificios are situated on rivers, and it is conceivable that the earliest emigrants from these communities, or other, as yet undiscovered river villages, traded the benefits of riverine settlement for the advantages of riparian occupation on the lake shores. Both localities would have been favorable settlement areas, providing water as well as sources of acjuatic protein. The Contemporary Peten Environment Geology With the exception of the mountainous Lacanoon area in the northwest and the extension of the Bel izean Maya Mountains in the extreme southeast, the Peten is characterized by low-lying karsted terrain varying in elevation from about 100 to 300 m above sea level. As is typical of limestone regions, the countryside is irregularly pocked with caverns and sinkholes. The haystack hill topography developed on limestones of cretaceous and Tertiary age (West 19t>4). The Peten lake district (Fig. 2), with its center at 17°N, 89°40'W, lies within the Santa Amelia Formation, a deposit of early

PAGE 36

27 Eocene age (Vinson 1962). North of the lake region, the Santa Amelia is overlain by the slightly younger limestones of the buena Vista Formation, the basal portion of which contains a 200-m thick zone of gypsum. Both formations are locally inter bedaed with dolomite and gypsum. During middle Tertiary times, compressional folding and concomitant emergence resulted in a mid-Eocene to Oligocene depositional hiatus, though locally there are deposits in the Peten of Oligocene to Pliocene age. By late Pliocene, uplift, folding, ana faulting put an end to Tertiary sedimentation in the region. The lake chain at 17°N (Fig. 2) is aligned along a series ot east-west trending en echelon faults, the basins occupying depressions below steep north shore scarps (Tamayo and West 19fc4). The principal lakes in the fault zone chain extend some 80 km from westernmost Sacpuy eastward to the twin basins of Yaxha and Sacnab, only 30 km from the Belize border. Farther to the west, but outside the main graben, lies the relatively large and limnologically unexplored Lake Perdida. In addition to the localized standing bodies of water are seasonally inundated depressions interspersed between the limestone hills, features that are not uncommon over a large portion of the Peten landscape. These "bajos" or "akalches" are characterizea by thick clay soils that give rise to swamp-thicket vegetation. It has been suggested that the "bajos" were once shallow lakes, providing water, lacustrine resources and a mode of transportation for the Maya who inhabited the shores. The silting-in of these shallow basins has been invoked as a contributing factor for the Classic collapse (Cooke 1931,

PAGE 37

28 Harrison 1977). A 5-m pit dug in the Bajo de Santa Fe, near Tikal, revealed that indeed the clays that lined the floor of the, depression resulted from the solution of upland limestone, but there was no evidence for lacustrine. deposition having occurred ouring Holocene times (Cowgill and Hutchinson 1973). The calcareous bedrock of the Peten provided the resource base for Maya architectural endeavors, as building stone was easily quarried. In addition, limestone was burnea and mixed with calcareous sane ("sascab") to make construction mortar or plaster. The Maya also exploited the localized flint and chert beds, using the siliceous rock for making points and cutting tools (West 1964). Climate and Rainfall Lying at low altituae, within the tropic, the Peten is characterized by year-round high temperatures, the mean annual value in excess of 25°C (Vivo Escoto 1964). Mean monthly temperatures tot the region range between 22*'C and 28''C, but as expected in tropical areas, daily fluctuations in temperature often exceed the limits of the monthly extremes. Within the Peten, precipitation is highly variable from station to station and varies on an annual basis at any given site. Rainfall records indicate annual precipitation values ranging from ca 900 to ca 2500 mm. A regional, yearly mean of 1601 mm is reported based on 54 station-years of data collected at 10 sites (Deevey 1978). Within the tropics, as a rule, the distribution of rainfall throughout the year is

PAGE 38

29 highly seasonal (Richards 1979), and Peten is no exception. There is a long dry season from January to hay with a secondary period of reduced rainfall, "canicula," interrupting the wet season in July or August. The most pronounced aridity occurs from January to March during which time the rainfall amounts to less than 10% of the total annual income (Deevey 1978). Soils The. soils of the Peten catchments represent a large potential source for lacustrine nutrients. Under conditions of deforestation, enhanced delivery of dissolved and particulate matter to the lakes is expected, and the tremendous erosive potential of intense tropical rains is a major contributing factor in the transfer of nutrients from the land to water. The extreme seasonality and heavy downpours characteristic of the tropics make rainfall at those latitudes more erosive than equivalent annual precipitation in temperate areas where the rains are distributed more evenly throughout the year (Stevens 1964). Roughly 0.4% of the Peten landscape is covered by the ma^or lakes, and the balance of the region is overlain by soils assigned to 26 series by Simmons etal. (1959). They relegated the department soils to two major groups: savanna soils that cover some 9.8% of Peten and forest soils that blanket 89.8% of the, region. These major categories were further divided, savanna soils characterized as deep well-drained.

PAGE 39

3U deep poorly or deficiently-drained, and shallow deficiently-drained. Within these subdivisions, the soils were assigned to a particular series based on a number of characteristics, including parent material> relief, color, texture and consistency, and profile thickness. With the exception of some localized soils that overlie clay-rich schists and some alluvial deposits, Peten soils are derived from the undeilying limestones. Zonal soils develop under the primary influences of regional climate and vegetation, their distribution being highly correlated with patterns reflectea in the climatic regime and plant associations. Within the central portion of the Peten, soil genesis is influenced tremendously by the calcareous bedrock as well as drainage factors, to the extent that zonal soil development is precluded. In the lake district, the local geology and hydrology have generated primarily intrazonal soils assigned to the Rendzina and Hydromorphic great soil groups (Stevens 1964). Azonal Lithosols, black calcareous soils resembling Rendzina are abundant, and Stevens (1964) speculates that these youthful soils are now regenerating following a long period of erosion and depletion induced by Maya farming practices. Though 26 soil series are described for the Peten, only three surround the lakes examined in this study. The Yaxa series covers some 15.57% of the Peten and consists of shallow well-drained forest soils that often cap flat expanses as well as hilly slopes. These black calcareous Lithosols are highly fertile, and cultivation of these soils is only restricted by their high erosivity and presence on steep

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31 slopes. Yaxa soils surround Lake Macanche and nearly encompass Lake Salpeten, the southwest shore of which is contacted by soils ot the Macanche series. Macanche series soils blanket 5.11% of the department landscape and are shallow soils with deficient drainage. Confined to primarily level topography, these Rendzinas are highly fertile and not particularly subject to erosion. Poor drainage and the adhesive nature of the soils are the only drawbacks for agriculture. Indeed, the black calcareous Lithosols and Rendzinas were certainly exploited by the haya and. numerous Classic Maya ceremonial centers are found in association with soil series of these groups (Stevens 1964). According to Simmons et al. (1959), the western edge of Lake Quexil is contacted by Yaxa soils, but the balance of the drainage is occupied by soils of the Exkixil series. A deep poorly drained savanna soil, the Exkixil series is restricted to only 0.23% of the Peten and is found in flat areas. These soils can be assigned to the Hydromorphic great soils group and are typified by high clay and silt content and poor fertility. They are not easily eroded and today support grasses and open oak woodland. It is noteworthy that the soils map developed by Simmons et al. (1959) is rather crude with respect to accurately delimiting the areas covered by the various soil types. Within the Peten, great variation in topography and perhaps bedrock geology can be encountered over short distances. This in turn leads to great heterogeneity and patchiness of soil types within limited areas. The incongruity of mapped soil zones (Simmons et al. 1959, and personal observations) is most clearly

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32 demonstrated at Lake Quexii; While the map shows the Quexil watershed to be dominated by Exkixil series soils, the true drainage is primarily covered by forest soils, probably of the Yaxa series. Vegetation Though commonly referred to as "tropical rain forest," the vegetation of Peten grows in a region that is too dry for the development of true rain forest. Employing the climatic data criteria established by Holdridge (1947), the Peten falls within the tropical, lowland, dry forest life zone. Lundell (1937) applied the term "quasirain-forest" and though the vegetation is principally evergreen, some species lose their leaves periodically, the degree ot deciduousness dependent on the annual distribution and amount of rainfall. Simple description of the Peten vegetation is impossible due to the variability of vegetation types that reflect topographic and edaphic differences. Wagner (1964) reports that some 75% of the upland forest is covered by the "zapotal" association, named for the prevalence of "chico zapote" ( Manilkara ) in the midole tier ot the forest. Characterizing this dominant association, he notes that the major floristic components in the top story are Calophyllum , Swietenia , Rheedia , Lucuma , Sideroxylon , as well as several species of Ficus . Below the uppermost tier lies a middle story of Manilkara , Vitex , Ficus , Cecropia , Bursera , Spondias , Aspidosperma , Brosimum , Pseudolmedia , and members of the Leguminosae ana Lauraceae. Averaging

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33 10 m, the lower story is typified by Irichilia , Sideroxylon , Sapium , Sebastiania , Misanteca , Parmentiera , Myriocarpa , Lucuma , Louteridiuiti , Laetia, Deherainia > Annona, Sabal , Pimenta , Protium , Ocotea , Zanthoxylon , and species of Pithecolobium , lalisia , Cordia , and Croton. The underwood plants are Piper , Psychotria , Ruellia , Justicia , and various palms. Lianas are common, as are orchids, bromeliads, ana ferns. Wagner's (1S64) enumeration of the genera that typify tne. Peten forest provides an impression of the floristic composition of at least one major association. The forest can also be aescribed based on its physiognomy. During a 1974, week-long reconnaissance and vegetation sampling trip near Lake Yaxha, Ewel ana Myers (lt»74) iaentitied four vegetation types, the physiognomy of which reflected the underlying topography. Three of the four distinct vegetation classes were sampled, including (1) the forests of steep slopes and ridges, located on well-drained soils and possessing an irregular canopy, the rouiided crowns of the tallest individuals often separated by large openings; (2) Gentle slope forests occupying deeper soils, with standing water in localized depressions, and typified by a smooth canopy with only occasional emergents; and (3) Seasonally dry "bajo" vegetation of short stature (<20 m), with a smooth canopy and a high incidence of windfall. The unexamined wet "bajo" vegetation appears on aerial photos and evidently consists of stunted vegetation with closely packea trees, as part of their sampling procedure, Ewel and hyers establishea six 0.1 ha plots, two in each of the three investigated vegetation

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34 types. Identifying all trees with a stem diameter of more than 10 cm at breast height, the investigators tallied 57 taxa. Strangely, many of the upland site species were shared by the "bajo" localities, though trees on the latter sites were much smaller. In a similar study, I established five 10 m x IQO m plots in three vegetation types in. the central Peten. One plot was placed in high forest near Lake Macanche. The remaining 0.1 ha units were located in forested areas of the primarily savanna region lying south and southwest of Lake Peten-Itza and in the area close to the archaeological sites of Chakantun and Eangb (Rice and Rice 1979). At each of these sites, a sampling transect was designated in a substantial, forested area bordered by savanna and a second plot was established in a "sukche," an island of forest surrounded by savanna. All trees with a diameter of more than 5 cm at breast height were recorded, revealing a diverse flora of 77 taxa on the five transects. While high forest of great complexity is a most striking feature of the Peten landscape, nearly 10% of the region is covered by savanna. The most expansive grasslands lie to the south of Lake Peten-Itza and in many areas interdigitate with stands of forest. • While the savanna is relatively devoid of woody growth in some places, other localities like the area south of Lake Quexil support numerous oaks ( fauercus ). At other sites, "nanze," Byrsonima is the predominant tree and is distributed rather evenly over the grassland. It has been suggested by Lundell (1937) that the savannas are in fact vegetational artifacts of human disturbance, created by Maya land

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35 clearance and repeated burning. Reinvasion of the deforested areas by trees may be prevented by human-induced edaphic changes, but fire frequency is certainly a factor maintaining the grassland (Vaughan 1979). Palynological investigations of the sediments from savanna Lakes Oquevix and Ija as well as studies of grassland soils will be necessary to resolve questions about the genesis ana maintenance of this unique vegetation. Lundell (1937) believed that the high forest of mcaem Peten was absent during the Maya florescence, the land having been cleared for agricultural purposes. This contention is now amply supported by palynological evidence from a number of Peten lake sediment cores (Tsukada 1966, Vaughan 1979, Deevey et al. 1980c). Lundell (1937) also felt that the modern standing vegetation represents a climatic climax forest, there having been sufficient time for its development following the Maya decline. This view is somewhat contradicted by his belief that the prevalence of many useful tree species on Maya ruins constitutes evidence for the claim that the ancient Maya practiced arboriculture. Fruit-bearing trees, such as Brosimum , Talisia , and Manilkara , are common on sites as are other economically useful species, such as incense producers like Protium . While it has been suggested that these trees were selectively spared during Maya forest clearance or cultivated to some extent, Puleston (197fa, 1962) argues strenuously that at least one species, "ramon" ( Brosimum alicastrum ) was actively planted and that its starch-rich seeds comprisea a major portion of the Maya diet. Another possibility that may account for the presence of economically useful trees on previously occupied sites is

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36 that the topographic and agronomic factors that may have been attractive to Maya settlers, like upland, level, well-drained fertile areas (Rice and Rice 1980b), may simply coincide with the ecological requirements of the tree species. Additionally, it is possible that the Maya modified the edaphic conditions, inadvertently creating optimal chemical or drainage microenvironments for the growth of the trees, thereby permitting them to flourish after the Classic collapse (Lambert and Arnason 1982). Regional Limnology The principal basins of the Peten lake district were formed when water filled the troughs of the east-west graben that lies at IT'n. Most of the lakes are small (< 5 km^) with the exception of the two largest, Peten-ltza (99.6 kih^) and Xaxha (7.4 km''), loday. Lake Peten-ltza supports a substantial human population on its shores, the major riparian settlement occupying areas in contact with the southern arm of the lake. The bulk of the lakeside residents inhabit three towns, including the mainland "pueblos," San Benito, and Santa Elena, as well as Peten *s political hub, Flores, formerly an island community but now connected to the southern shore by a causeway. San Andres and San Jose are the principal towns On the north shore of the lake and overlook the deep, main basin. Lakes Macanche and Sacpuy also support small, but rapidly growing "aldeas," while the remainder of the lakes are largely undisturbea, though isolateo houses ana farming activity in the watersheds have been noted.

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37 While relatively small in surface area, the lakes are rather deep, inany in excess of 30 ni. The maximum depth is often associated with sinks or trenches that are responsible for the conical morphometry of some basins (Deevey et al. l&80a). Typically, the basins possess deep trenches in proximity to the north shore, where steep scarps descend to the lake edge. Southern shores are generall;^ flatter, and water depth increases gradually with distance from land. Despite the fact that exchange with groundwater in the lakes was shown to be one-way downward and slow, based on studies at Yaxha ana Sacnab (Deevey et al. 1980a), the lakes are prone to rapid fluctuations in level that are probably not solely dependent on direct precipitation and drainage income. A rise of about 3 m was detected in all the lakes between 1979 and 1980 and was likely associated with groundwater intrusion. The notion that changes in the regional water table did occur. is supported by the formation of a new lake in the savannas, a basin that local residents claim filled when groundwater broke through the country rock. The lakes continued to rise above the 1980 level (P. Rice, pers. comm.), but this is not the first time they have advanced. Older residents of the Peten report that Lake Peten-ltza rises every 40 years, maintaining a high stand for five years before retreating (Anonymous 1980a). The last high water was recorded in 1938, when the level was several meters above the 1980 mark, and much of Flores was inundated. Other lakes in the district have also experienced high stands in the past. Supporting evidence comes from the presence of aquatic snail shells in soils (old lake muds?) well above modern lake

PAGE 47

3b surfaces. H.K. Brooks (pers. coitm. ) reports snail shells some 13 m above the 1973 Idaxha surface. Fred Ihompson (pers. conan. ) iaentifieci three species of aquatic gastropods, Pyrgophorus exiguus , Cochliopina infundibulum , and Aroapyrgus cf . petenensis , found in Salpeten south shore soil samples collected from pits dug several meters higher than the 1S80 peak water mark. Limnological reconnaissance of the Peten lakes was first undertaken by Brezonik and Fox in the summer of 1969. They reported the clinograde oxygen profiles and thermal stratification that characterize the basins (Brezonik and Fox 1974). Surface waters in the Peten often exceed 30°C, and while thermal stratification does seern to be persistent, hypolimnetic water temperatures sometimes differ from epilimnetic values by only 3-4*C. Encountering anoxic hypolimnia in most Peten lakes as well as benthic fauna indicative of oxygen stress, Brezonik and Fox (1974) concluded that thermal stratification of the lakes was stable. Additionally, they found evidence of meromixis in Lake Quexil and two small, but deep sinkhole basins, Paxcaman and Juleque. The maintenance of the thermocline was attributed to three factors: the lakes are well protected from strong winds by the forested limestone bluffs that surround them; the basins are typically small, but very deep, with contours that inhibit mixing; and finally, they note that the density difference per degree change in temperature is much greater in warm waters than in cold waters. over the past decade, the Peten lakes have been sampled extensively and intensively, supplementing and contradicting some ot

PAGE 48

39 the original findings. Lake Quexil has been studied during several field seasons, and neither chemical data nor conauctivity readings point to modern meromixis, though an episode of early Holocene meromixis was detected in the sediment record (Deevey et al., in < press). If contemporary meromixis is to be documented in Peten waters, it will probably be encountered in the small deep sinks like Juleque and Paxcaman or in sulfate-rich Monifata I (Deeveyet al. 19&0a). Numerous oxygen profiles from several of the basins show complete; oxygen depletion in hypolimnetic waters to be rare and indicate that Peten lakes are perhaps polymictic, their frequent circulation associated with nocturnal cooling. However, predawn data from Lakes Quexil and Macanche taken in May 1977 demonstrate the persistence ot the thermal gradient through the night, surface temperatures exceeding bottom values in the two basins by 5. 9 "C and 4.0''C respectively. Repeated night sampling, between May and July 1980 of a deep sink (43 m) located hear the northern shore and within Peten-Itza's southern basin, failed to reveal a breakdown of the thermal gradient. Oligomixis, or irregular and uncommon turnover, may better define the mixing regime of the Peten, lakes, the frequency nevertheless sufficient to prevent prolonged hypolimnetic anoxia, if episodes ot mixis are to be detected, the most probable period for their occurrence is between August and December when cooler air temperatures, strong winds, and heavy rains might induce turnover. Unfortunately, these are the months for which limnological data are scanty.

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40 Calcium and bicarbonate are the major cation and anion of Peten waters, but exceptions are found in magnesium and sulfate-rich lakes that may overlie dolomite or gypsum beds. That geological variation occurs over short distances is quite evident when nearby lake waters are compared chemically. Lakes Macanche and Salpeten are only 2 km apart but differ appreciably, hacanche is a matjnesiuia sulfate lake and contains about twice as many magnesium as calcium ioiis, while the sulfate:bicarbonate ionic ratio is 1.5:1. Salpeten is a calcium sulfate lake in which magnesium ions are half as prevalent as calcium ions, and there are nearly 60 sulfate ions for each bicarbonate ion. The aptly named Salpeten, also seen in the literature as Peten-suc and Sucpeten, is highly saline, and the water contains 4.7b g-l"! total dissolved solids. Peten waters are alkaline, their ph ranging from neutrality to fe.6, with surface waters generally producing daytime readings around 8.0. Nutrient concentrations of Peten lakes are surprisingly low for basins in limestone terrain, in a survey of eight lakes, Brezonik and Fox (1974) reported total phosphorus concentrations from < 10-33 ug P«l~l, relegating these water bodies to the oligo-mesotrophic (5-10 ug P'l"^) or meso-eutrophic (10-30 ug P'l"l) categories, as defined by Wetzel's (1975) modification of Vollenweider 's (1968) phosphorus-dependent trophic classification scheme. In another series of total phosphorus determinations, nine examined lakes displayed a range from 18 to 54 ug P'l"^, the low value being from savanna Lake Oquevix (Deevey et al. 1980a). The generally higher phosphorus levels

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41 discovered in the latter study are perhaps attributable to more complete digestions or higher sestonic content in the samples, but demand placement of the lakes in the meso-eutrophic (10-30 ug P*l~^) or eutrophic (30-lUO ug P'l"-'-) categories. Assignment to the trophic classes is tentative as a large fraction (40-80%) of the seston, measured in fresh sediment from traps or cores, is inorganic (Deevey et al. 1977, Deevey et al. 1980b). Much of this resuspended silt may contain mineralogic phosphorus that is biologically unavailable, in any case, high N:P ratios (>25) in Peten waters and surficial sediments suggest that productivity is phosphorus limited. Secchi disc transparency, an indirect measure of productivity, measures turbidity in peten lakes, as organic color is low (Brezonik and Fox 1974). However, measured transparencies may not be a very good indication of algal standing crops if much suspended material is inorganic seston. Secchi disc readings range from 1 to 5 m, the clearest water generally found in the sulfate-rich lakes. Lake CjUexil, dominated by calcium and. bicarbonate: ions, displays low transparency, less than 2m at times, and because seston of the lake shows relatively high loss on ignition (50-60%), the rapid disappearance of the disc with depth may indicate a substantial algal biomass. It is noteworthy that Lake Quexil (also seen in the literature and on maps as Eckixil, Ekichil, or Exiquil) derives its name from the Maya word Ekexiil (another variant) that mean;^ "agua oscura con hierbas," or water darkened by weeds (Anonymous 1980b). ',/

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42 Direct measurement of productivity was accomplished by light-dark bottle experiihents, conducted by H.H. Vaughan at twin Lakes Yaxha and Sacnab in 1973 and 1974. Five sets of experiments at Yaxha and three at Sacnab yielded nearly identical mean values, 251.6 _+ 121.6 mg C'm-2'day-l (Yaxha) and 251.7 + 110.0 mg C'm-2«day-l (Sacnab). A single experiment was undertaken at Lake Quexil in mid-March 1978 and gave a gross production figure of 198 mg C'm~2'day~^ (Deevey et al. 19&0a). The values obtained suggest that the lakes are at the low end of the mesotrophic (250-1000 mg C*m~2'day~l) or upper end of the oligotrophic (50-300 mg C*m~2«day~l) scale (Wetzel 1975), but this assignment is tentative as production undoubtedly fluctuates throughout the year, and the data set is small. Nevertheless, the range ot production values encountered in the twin lakes, 157.6-449.3 mg C*m"2-day~^ (Yaxha) and 135.3-354.5 mg C'm~2«day"^ (Sacnab) is indicative of oligotrophy or mesotrophy using temperate standards. The Peten lakes that are free frora human impact generally support a small algal biomass, at times apparently dominated by the cyanophyte, Lyngbya (Brezonik and Fox 1974). Peten waters are noticeably deficient in diatoms, though Melosira ambigua and M^. granulata are common in Lakes Yaxha and Sacnab. Members of the Bacillariophyceae are rare in the lake sediments, probably due to dissolution at high pK. While Yezdani's checklist of Peten phytoplankton (Deevey et al. 1980a) is long, the implied diversity is misleading, as several dominants probably constitute a large fraction ot the stanoing crop yeeir-rouna. The chlorophyte Botryococcus braunii and the blue-green Microcystis

PAGE 52

aeruginosa are nearly ubiquitous ano are encountered in large numbers. B. braunii constantly aoiainates net tows ana its conspicuous absence from centrifuged water samples collected by Brezonik ana Fox probably resulted from resuspension tollowing centritugation. As a oominaiit, h. braunii is indicative of oligotrophic conditions in temperate regions, but its value as an inoicator species iii the teteii lakes is questionable, as it is founa unoer a variety of conditions in tropical ana subtropical basins (Hutchinson 1967;. The open water zooplankton is numerically aominateo by copepoas, the four most abunoant species being Diaptomus goisalis , he socy clops inversus , M^. edax , and gropocyclops prasinus mexicanu s. Another important member of the zooplankton is the enaemic, pelagic ostracoo, Cypria petenensis that distinguishes itself by being rare or absent in sulfate waters. Juveniles are present in the water coluir.n at ail times, while adults are migratory, leaving the benthic liabitat and entering the pelagic environment only at night, a strategy that likexi helps them avoid predation by fish. Eubosmin a tubicen (Deevey ana Deevey 1S»71) is the only common planktonic ciaoocerah, with representatives of the Sididae, Daphniidae, Macrothricidae, ana Chydoridae notably rarer in open water net tows. Thirty-two species of entomostracans are reported from plankton tows in 10 Peten lakes, the most diverse fauna (23 spp.) touno in the largest lake, Peten-Itza (Deevey et al. lS>80b). The lakes average 11.4 species each, the least aiverse tauna encountereu in sultate-rich Lakes Salpeten (4 spp.) and Monifata I (b spp.). hhile the planktonic

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44 component of the entomostracan fauna is notably undiverse, systematic sampling of a littoral zone study site in Lake Peten-ltza has expaiidea the list of entomostracan taxa, with 31 species of chydorids (29 identifiea, 2 unknown) alone, having been enumerated (M.Vi. Bintord, pers. comm.). Only six chydorid species were taken in the Lake Petenxil plankton (Deevey et al. 1980b), but some tour times as many species were identified from remains in the Petenxil sediments (Goulden 1966). Chydorid remains are integrated into the sedimentary matrix over space and time so that more taxa are frequently encountered in mud samples than can be collected in a systematic lake sampling program (Frey 1960). Twenty-two species of fish have been identified fror.i collections made in five lakes (R.M. Bailey, pers. comm.), and three of these, the clupeid Dorosoma petenense , the characin Astyanax fasciatus , and an atherinid Melaniris sp., may be responsible for the low diversity and small body size that characterize the Peten zooplankton. Other potential consumers are the second characin Hyphessobrycon compressus , as well as several poeciliids and juvenile cichlids. Some members of the latter family attain significant size (1-2 kg), and some Cichlasoma species and the "bianco," Petenia splendida , are exploited by mouern "Peteneros," as they undoubtedly were during Maya times.

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45 Maya Settlement in the Yaxha and Sacnab catchments Maya Demography Twin Lakes Yaxha and Sacnab were originally selectee as study sites because early archaeological reports indicated differential degrees of Maya settlement in the two watersheds (Bullard i960). It was surmised that the dissimilar levels of environmental impact would be reflected in the paleolimnological record. Yaxha supportea an urban center on its north shore, and the island site of Topoxte, lying within Lake Yaxha, was densely inhabited during pcstclassic times (1000-1600 A.D.). Urbanization never developed in the Sacnab watershed, and the drainage remained devoid of habitation following the classic collapse. In order to assess changing ancient Maya riparian population densities, Don S. and Prudence M. Rice established transects radiating from the lake shores that were searched for housemounds. The transects, 2 km long and 0.5 km wide, were located on the lake edges at randomly selected jpoints and ran in a north-south direction, perpendicular to the fault line, thereby permitting the sampling of all microtopographic zones. Six sampling units were staked out at Yaxha, and four were established at Sacnab (Fig. 3), the total area of the transects in each case equivalent to about 25% of the subbasin drainages. At Yaxha, the island of Topoxte was also designated as a sampling area. The plots were systematically searched for mounds, and a randomly selected 25% of the mounds were test-pitted so that periods of occupation could be established using the ceramic sherds extracted.

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>

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47

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48 These data were then employed to calculate population densities for the ceramically defined periods^ using the assumptions previously applied at Tikal, that 84% of the mounds discovered were residences and that the average household consisted of 5.6 persons (Havilano 1970). by convention, the calculated densities represented levels oiE occupation at the end of the ceramically defined periods. Middle Preclassic (1000-250 B.C.) population densities were slightly higher at Sacnab {34 persons •km"-') than at Vaxha (22 persons • km~2 ) , but by the close of the Late Preclassic (250 B.C. -250 A.D.), Yaxha, having grown more quickly, had 70 persons'km"^ to Sacnab's 51 persons'km"^. A lag in growth at Yaxha permitted Sacnab to catch up by the end of the Early Classic (250-550 A.D.), the two subbasins hosting 101 persons«km~^ and 1(12 persons'km~2 respectively. The centripetal draw of the Yaxha urban center ultimately left that subbasin with a dense (256 persons*km~2) human population by the end of the Late Classic . (550-850 A. D. ) , at which time Sacnab supported 168 persons • km"''. ' Considered as a single population, the prehistoric Maya of the combined twin basins increased their numbers slowly, doubling about every four centuries, the logarithmic phase of population growth lasting about 1700 years (Deevey et al. 1979).

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49 The Twin Basin Sediment Record Using a Livingstone piston coter (Deevey 1965), H.K. Brooks obtained a sediment core from Lake Yaxha in 1973, and a year later H.H. Vaughan and D.S. Rice collaborated to raise a shallow-water long core from Lake Sacnab (Fig. 4). Palynological study of the 7.4-m Yaxha core revealed a stratigraphy identical to that discovered by Tsukada (i9tt) in the sediments of Lake Petenxil, 5Ci km to the west. Sediments rich in pollen of grassland and grassland arboreal species were overlain by postdisturbance mud dominated by high forest pollen indicators. Evidently, cores from both the lakes had failea to penetrate hayaperiod muds, dense urban settlement at Yaxha resulting in the deposition of more than 6 m of clay-rich sediment. However, the 6.3-m Sacnab core demonstrated that the savanna pollen zone was underlain by organic-rich sediments with a high proportion ot Moraceae pollen. The basal, high forest pollen section showed some indications of human disturbance and was assigned an Early Preclassic age, a time period for which archaeological evidence is lacking in Peten, but that is coeval with the Early Formative at Cuello, in Belize. With supplementary evidence for a predisturbance high forest zone coming from Lake Quexil (Vaughan 1979, Deevey et al. 1979), Tsukada's (1966) conclusion that the Maya had transformed savanna into high forest was reevaluated. In fact, the Maya had converted high forest into grassland, the forests later recovering after the abandonment of the region.

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W3

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51

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52 Phosphorus Loading of Lakes Yaxha and Sacnab Efforts to assess past changes in trophic state ot the lakes weie attempted through an evaluation of ancient phosphorus budgets. Phosphorus has been shown to be the limiting nutrient in man^ aquatic systems (Schindler 1974, Vallentyne 1S74) with productivity highly dependent on total phosphorus loading rates (Vollenvveiaer 19tb, Dillon and Rigler 1974, Oglesby and Schaffner 1978). Phosphorus, unlike carbon and nitrogen, lacks an atmospheric compartment in its biogeochemical cycle. Thus, nearly all phosphorus transported from the watershed to the lake is ultimately sequestered in the basin sediments. Phosphorus movement in the watershed is essentially unidirectional, removal from a lake by mechanisms such as insect emergence representing a small proportion of the phosphorus originally delivered to the lake (Vallentyne 1952). Past rates of nutrient delivery to the basin can be calculated when phosphorus concentrations in the sediment are known ana several levels in a core are accurately dated. Unfortunately, radiocarbon dates run on bulk sediments from the Peten lakes, even those pretreated for carbonate removal, proved to be unreliable due to the hard-water lake effect. Ancient carbonates, lacking the radioisotope, are solubillzed, and their carbon is incorporated into autochthonous organic material, making dates appear too old (Deevey and Stuiver 1964). Ultimately, all bulk sediment radiocarbon dates were disregarded and archaeologically correlatea dates were assignee to levels in the cores based on the identification of discrete pollen

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53 assemblages (Vaughan and Deevey, 1981). The assumption used for zoning the cores was that the degree of deforestation expressed in the pollen profiles reflected changing population densities as derived from the archaeological program. When phosphorus loading rates to the twin basins weie calculated, they tracked the slow, steady exponential rise in population density that occurred between the Midole Preclassic and Late Classic. Roughly delimiting the area circumscribed by the two drainages, export of phosphorus from the watersheds^ already seen to be haya density dependent, was shown to occur at a rate of about 0.5 kg-person"-'•yr~i. The calculated per capita rate of delivery is, perhaps coincidentally, almost equal to the physiological output of phosphorus (0.55 kg) from human bodies that are in equilibriuru with respect to their intake and output of the nutrient (Vollenweider 1968). Watershed soils were the principal source of disturbance-zone phosphorus, nutrient-rich surface soils moving rapidly downhill by colluviation following Maya-induced deforestation (Brenner 1976, Deevey et al. 1979). Because bulk soil transport was the primary mechanism carrying phosphorus from the land to the lake, it was impossible to determine what proportion of the sedimented nutrient actually cycled through human bodies. Disturbance-zone sediments of the twin lakes' are highly inorganic and do not indicate that the episode of deforestation was accompanied by high lacustrine productivity. Large amounts of silica and detrital carbonate were transported with the phosphorus as soil was eroded into the lakes. The siliceous, Maya-zone sediments are dominatea by

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54 montmorillonite clay, the residue of the down-wasted country rock. High phosphorus delivery rates might be expected to correlate with high autochthonous organic production. That high rates of nutrient input were associated with inorganic mud suggested that much seaimented phosphorus was biologically unavailable and bypassed the biota before deposition on the lake botton,. Corroborating evioence for this inference came from microfossil analyses that failed to demonstrate that high primary or secondary production was associateo with the enhanced phosphorus delivery (Brenner 1978). Unfortunately, enumerated microfossil remains from Peten sediments provide unreliable estimates of past productivity. Though amounts and accumulation rates of microfossils decreased with increasing phosphorus input to the twin basins, strong diagenesis (postdepositional destruction) makes the thanatocoenosis a poor estimator of the biocoenosis from which it was derived.

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IBE HISTOKICAL ECCLGGY OB' IHE MAYA A'i LAKES gUEXlL, SALPETEN, ANL MACANCHE ine Archaeologicai Recot a The goal of this study is to expano the geographic scope of the "Historical Ecology of the Maya" project v.estwaLQ to exanane three unexplored lake basins. With soil, archaeological, ana paleolimnological data from the nevv watersheas, seoimentation processes in the Peten lakes can be evaluateo better, and the phosphorus loaaing model developed at Yaxha and SacnaL can be testec. The new lakes considered, Quexil, Macanche, and Salpeten, differ from the twin basins in failing to aisplay the slow, steady exponential human popuiaticn growth from the Middle Preclassic until the Late Classic peak. Instead, the archaeological record shows that Maya popuiationb in the western watersheds experienceo a decline auring the Terminal Preclassic (lUO B.C. -250 A.D.) and Early Classic (25)b-55U A.D.) before risii.g once again in the Late Classic (550-850 A.D.) and finally collapsing about b50 A. I-. Archaeological study of the three watersheds was oirected L^ Don S. and Prudence M. Rice during the 1S»79 and i;>80 field seasons. To sample about k5% of the watershea area, three transects raoiating rrom the lake edge were established in each basin, and some 25% of the 55

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mounds surveyed were test-pitted to determine time ot occupation. At Quexil (Fig. 6), a single north shore transect was iaio out ana two south shore sampling plots were staked. Transects were run in a northsouth direction, and as at ^axha were U.b km wiae. In keeping with procedures used at the twin basins, the north shore transect was 2 km long, but the south shore surveys were run about o.z4 km, to the base ot the karst uplift that encloses the basin. This permitted the sampling ot a large savanna south ot the lake. Adoiticnalii , Quexil 's two islands were searched, revealing b structures on the western island and 20 on the eastern islano. At Salpeten, standard size (2 km x U.i> km) transects weie established with north-south orientation, two on the north shore and a single plot on the south shore (Fig. 6). A large, oenseiy settleo site on Salpeten's peninsula was also investigated. The site, called Zacpeten, is primarily of Postclassic age. At Macanche (Fig. 7 ) , the single north shore transect and two south shore plots were. oriented northwest-southeast. Mounds discovered within a walled site (Op 2), Muralla de Leon, were also surveyed, as were some structures between transects. In this basin, time perioo of occupation was oetermineo L^ test-pitting about 2b% of the mounds both on and off transects. Using the proportion of mounds showing occupation auring the various perious, population levels were figured based on the density of mounds found on the delimitec transects, m all three drainages, changing hay a population densities were calculated employing the assumptions used at Tikal (Haviland 1970) and at Yaxha ano Sacnab, that 84% of the mcunos were residences and each household consisted of 5.6 persons. Figure b

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Figure 5. Lake tuexil, showing the position of the aichaeciogical sampling transects and soil pits. Op = operation.

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58 Op 3 LAKE QUEXIL Archaeological Transects • Soil Pits Op 1

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Figure 6. Lake Salpeten, showing the position of the archaeological sampling transects and soil pits. Op = operation.

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60 LAKE SALPETEN Op 2 Op 1 Archaeological Transects • Soil Pits Op 3

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Figure 7. Lake Macanche, showing the position ot the archaeological sampling transects and soil pits. Gp = operation.

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LAKE MAGANCHE 62 Op 4 km 1 I I I I I Archaeological Transects • Soil Pits i?Op 2 Op 1 Op 3

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Figure 8. Crude population densities, calculatea trom housemouna densities, in the five lake basins for which both archaeological and paleolininological histories have teen studied. Population reconstructions are based on radiocarbon dated ceraiuic chronologies.

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1000 64 SACNAB 1000 200-1 « 100OUEXIL I^^ 1000 1000 1000 1000 B.C. A.D. 1000 2000 Date

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bb shows the changing population patterns for five Peten watersheds basea on mainland transect mound densities. Soil Chemistry Translocateo soils were shown to have been the tti^'cii^ai source vx phosphorus for Lakes Yaxha and Sacnab curing the period of Maya forest disturbance (Deevey et al. 197!?). In extencing the stuuy to three new watersheds, soil samples were collected from several localities in each basin to assess total phosphorus and other chemical coiicentrations and distributions in riparian soil profiles. Because bulk movement of soils is the mechanism by which phosphorus reaches the lakes, tctax phosphorus was analyzed rather than the plant-available fraction. During the ISfaO field. season, 21 soil pits were dug in the Uuexii drainage (Fig. 5), while 11 trenches were dug in both the Macanche and Salpeten basins (Figs. 6 and 7). In each case, soil pit locations were determined subjectively in order to sample several microtopographic zones as well as areas associated with haya construction. In most instances, samples were collected along archaeological transects so that Qistances from shore coula be aetermined by reference to established, staked positions in the archaeological sampling plot. Soil pits were dug to bedrock, sterile "sascab," or as oeep as was feasible. Maximum depth from site to site was variable, but none of the samplea aepths exceeaed 10(J cm. Samples were removea rrom the exposed profile wall at 10 cm intervals, each sample representing a

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composite of soil collected over the full 10 cm. About 100-200 g of soil were taken at each level and stored in indivioual plastic bags. In the lab, four levels from each soil pit {0-10 cm, 10-20 cm, an intermediate level between 20 cm and bottom, ana bottom) were removed and air-dried, though only top and bottom samples were considered in Quexil's shallow pit #4. A subsample of each air-drieo level was extracted and ground with a mortar ana pestle. A portion of the powaered soil (1-6 g) was removed, weighed, ana placeo in a 'iliermoi^ne Type 1500 furnace for two hours at 550°C to assess organic matter content by loss on ignition. Following combustion ana reweighing, a 0.3-1.5 g sample of ash was removed, weighed, and digestea in 15 ml or a heated 2:1 nitricrperchloric acia mixture. When aense, white hClU^j fumes appeared, the 250 ml beakers containing the mixture were coverea with watchglasses and the oxidation process was continueo tor an additional hour, with distilled water added periodically to prevent total drying. After digestion, samples were filterea ana the tiitrate was brought to a known volume. The filtrate was delivered to the University of Florida Institute of Food and Agricultural Sciences Soils Laboratory, where cation concentrations were determined by atomic absorption and phosphorus analyses were run on a lechnicon Auto Analyzer. I measured sulfur content in filtrate samples from surface and bottom profile levels using the turbiaimetric proceaure in StanoaLo Methods (APHA 1971). Sulfate turbidity was read on a Coleman Model 14 Universal Spectrophotometer. Prior to running sultate c.naiyses on tne digested, ashed soils, a series of paired ash-whole soil determinations

PAGE 76

67 were made to assess sulfur loss due to ignition. Measured sulfur content, as concentration per grani whole soil was shown not to oittei statistically when the two methods were compared. All soil chemical concentrations are expressed as amount per gram of air-atiea whole soil. Total phosphorus analyses run on soil profiles from ^uexil, Macanche, and Salpeten reveal that in all three watersheds a strong gradient is maintained with respect to the nutrient, surface soils clearly enriched as compared to levels deeper in the profiles (Figs. 5-12). Though exceptions ao occur, increasing depth in the profile is generally accompanied by decreasing phosphorus concentration. This trend is evident when the mean surface soil (0-10 cm) phosphorus concentration in a basin is compared to the mean value obtained for the basal (variable depth) levels of the pits. At Quexil, where the 21 soil pits were dug to an average of 74.3 cm, mean phosphorus concentration in surface soils was 178 ug P-g"-'-, or 2.
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Figure 9. Total phosphorus concentrations at selected levels in soil pits 1-12 at Quexil.

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QUEXIL 69 20 40-1 6080 < 100 PITl PIT2 I I I / PIT3 I I II Q. Q 406080100 / PIT4 PITS I I I PIT 6 I I I I 2 a. o 2040 60 80 100 PIT 7 PITS / PIT 9 -1 1 I I 20 40 6080100 PIT lO I 1 i 1 1 1 200 400 600 800 1000 PIT 11 I I I I I I I I — —I 1 200 400 600 800 1000 /igPg PIT 12 I I I I I — I — I — I — I — I 200 400 600 800 1000

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Figure 10. Total phosphorus concentrations at selecteo levels in soil pits 13-21 at Quexil.

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71 0. o o V) 1 20 40 60 80 100 QUEXIL PIT 13 PIT 14 PIT 16 PIT 17 PIT 15: PIT 18 20 406080100 / PIT 19 PIT 20 I I I 200 400 600 800 1000 r— I 1 1 r — I 200 400 600 800 1000 AigPg -1 PIT 21 I — I — I — I — I — I 200 400 600 800 1000

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Figure 11 . Total phosphorus concentrations at selected levels in 11 soil pits at Salpeten.

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SALPETEN 73 20 40 60 80 100 PIT \ PIT 2 ^ PIT 3 E a. Q 20 40 60 80 too PIT 4 i PITS PIT 6 o a. o PITS V PIT 9 20 40 60 80 \ 100 PIT 10 ^ PIT 11 200 400 600 800 1000 200 400 600 800 1000 200 400 600 800 1000 >ug Pg-'

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Figure 12. Total phosphorus concentrations at selecteu levels in 11 soil pits at Macanche. .

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MACANCHE 75 20 40-1 60 80 100 PITl I I I PIT2 PIT3 I I I I a 2040 6080 100 PIT4 PITS r" PIT6 I I I r I o o 204060 80-1 100 PIT 7 I I I I PITS PIT 9 20 4060 80 PIT 10 . PITll I I I I 1 1 1 1 1 1 -| 1 1 1 1 1 r -I r— I 1 200 400 600 800 1000 1200 200 400 600 BOO 1000 1200 200 400 600 800 1000 iug Pg -1

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To assess how organic matter and various soil chemical concentrations change with depth in the profile, mean coiicentrationt; for all of the combined top two levels (0-lU cm and 10-20 cm) in the profiles of a basin are compared to the average concentrationfa calculated for the summed bottom two levels (intermediate between 20 cm and bottom, plus bottom) of the basin pits (lable i). guexil's shallow pit #4 was excluded from this tabulation because only two levels Were analyzed, ano assessments of changing sulfur concentrations witii aepth are reliant on surface and bottom analyses only. Additionally, whole profile mean concentrations for the various soil paranieters ate given, thereby permitting a rough inter basin comparison of soil, characteristics. Organic matter distribution in the soil profiles oispiays a treno similar to that seen for phosphorus, % loss on ignition generally decreasing with greater depth. Surface soils are also enrichea in sulfur, deeper profile levels noticeably aeficient with respect to the nutrient. Similar trends in organic matter "anu sulfur concentrations suggest that much soil sulfur is present in organic form. However, ignition of the. samples at b50°C caused no apparent loss or sulfur, perhaps indicating that the bulk of sulfur is present in. mineral form, or that the organic sulfur fraction is not volatilized on burning. High inorganic sulfur content would not be unexpected, particularly at Salpeten where a gypsum outcrop overlooks the northwest shore of the , lake. Were this the case, sulfur distribution woula be expected to track magnesium and calcium in the profiles, but it does not.

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77 Table 1. summarized chemical concentrations from soil pits QU9 m the Quexil, Macanche, and Salpeten watersheds. Concentrations in the two uppermost levels ot the protile were averacjec as weie the two bottommost samples, thus giving a rough idea of chemical gradients in the soil profiles. Whole protile mean concentrations are also given for each chemical type. Sulfur concentrations were aetermined on surface ana bottom levels only. Profile Levels Profile Depth LOSS on n Ignition % Ca mg • gm -1 Mg mg*gm" Fe mg-gm -1 UUEXIL Top 2 1-10 cm Levels 10-20 cm 40 17. b 147 J. fa 2t.b Bottom 2 Levels Variable 40 10. b 212 2.3. b Whole All Profile Samples 80 14.1 160 2b. J MACANCHE Top 2 0-10 cm Levels 10-20 cm 22 lb. 7 330 23. fc Bottom 2 Levels Variable 22 fa. 9 374 24. b Whole All Protile Samples 44 12.3 3b2 24.1 3.U SALPETEM Top 2 0-10 cm Levels 10-20 cm 22 18. fa 2bb 30.1 b.4 Bottom 2 Levels variable 22 i».7 304 b.O Whole All Profile Samples 44 14.3 2b4 31.2 b.7

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lb Table 1 — extended. Al Na K P S mg'gm"'^ ug*gin~^ ug-gm"! ug«gm~^ ug-girr^ 41. b 170 648 21.0 13u 47.2 200 673 107 50 44.4 185 761 163 i^O 8.6 347 609 535 6S)0 8.0 368 453 210 440 fa. 3 358 531 373 565 13.1 2S<1 1240 545 740 16.0 319 1226 296 350 14.6 305 1233 421 545

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lb Cation distributions throughout the soil profiles are more even, without the pronounced top-to-bottom gradient seen for suitur, phosphorus and organic matter. Potassium concentrations are slightly higher in upper soils of the profiles, while sodium content is a bit richer in the deeper levels. In all three watersheds, calcium is a bit more concentrated in deeper soils, a trend that is anticipated in limestone terrain. Magnesium displays rather uniform concentration throughout the soil profiles, and though at Quexil upper level strata contain slightly higher amounts of the cation than deep soils, the trend is reversed at Macanche and Salpeten. Intra-basin variation in the chemical profiles is most apparent at Quexil, where forest soils, presumably of the iaxa series, were sampled along with Exkixil, savanna soils. Low fertility, Exkixil soils are depleted in phosphorus as compared to forest soils. Surface soils from the six savanna profiles (#1, #5, #8, #9, #10, #11) have a mean concentration of 164 ug P-g"-'-, while the 15 forest pits display an average upper level concentration about twice as high (324 ug P-g"-*-). Disregarding shallow pit #4, mean whole profile concentrations for various chemical constituents in the six savanna pits can be compared to values obtained on the 14 forest trenches. Aluminum is highly concentrated in the clay-rich savanna soils (105.4 mg Al'g~l), whereas the forest profiles contain only 18.4 mg Al'g"-'-. High iron content in the savanna soils evidently is responsible for the rich red color of the earth south of Quexil, and savanna iron levels (67. Smg pe-g-i) exceea forest soil levels

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bO (7.0 mg Fe*g~^) by nearly an order of magnituae. The lack ot calcium in grassland soils is striking, as they possess only 2.4 mg Ca-g"!. Forest soils, differing by more than two orders ot . magnitude, contain 256.1 mg Ca-g"!. Forest soils are also richer in magnesium than savanna soils, the two series containing 4.1 mg (^g.g-l and 1.7 mg hg*g~^ respectively. When mean, whole profile chemical concentrations are compared on an inter-drainage basis, several differences are apparent. Average iron and aluminum concentrations are higher at Quexil than at Macanche and Salpeten because of the high metal content of the grafaslano boils at Quexil. Likewise, calcium deficiency in the Quexil savannas is largely responsible for giving that basin an overall mean whole profile calcium value that is relatively low. Magnesium content of the Macanche and Salpeten soils exceeds that in Quexil by. 7.1 and 9.2 times respectively. The difference is not accounted for solely by the low magnesium, content of Quexil 's savanna profiles, because even forest soils at Quexil possess considerably less magnesium than encountered in samples from Salpeten and Macanche. Loloiuitizatioii in the MacancheSalpeten^district, also reflected in the water chemistry of the two lakes, is. the probable cause of high magnesium levels in the basin soils. Though it is not certain, high sulfur concentrations determined for the Macanche and Salpeten watershed soils probably point to the presence of gypsum in the unaer lying bearock of these basins. Evaporites are evidently less conunon at Quexil, and soil sulfur values

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81 from the three basins generally reflect chemical levels in the lake waters (Deevey et al. ISnSGa). Phosphorus is highly concentrated in the upper levels of Peten soil profiles, and under conditions of deforestation, erosional processes would be expected to carry large amounts ot the nutrient to the lakes. Rapid mobilization of the available phosphorus fraction is possible, but not likely, as the homogeneous aistiibution in the profiles of highly soluble sodium and potassium argues against leaching. Maya agro-engineering activities enhancea oeiivery rates ot phosphorus to the lakes not only by accelerating downhill bulk transport of soils, but perhaps by first concentrating the nutrient in surface soils through physiological cycling, interment, and refuse disposal. Ihough the aata are meager, three soil profiles oug in housemounds as well as several other pits located near construction contain extremely high levels of phosphorus suggesting an anthiopogenic source for the nutrient in enriched surface soils. At Salpeten, south shore soil pits #fc ana #7 were placed in housemounos #jfab ana tJtJ, last occupied during Late Classic times. Surface soils from these pits contain 821 ug p*g~l ana 922 ug p'g~^ respectively, much more than the overall mean value for surficial soils in the basin (596 ug P'g"-'-). On the north shore of the lake, soil pit #1 was located at the crest of a steep slope, in close proximity to rubble from collapsed construction. Ceramic sherds were encountered in the excavated soil pits, and its surface soils contained S9b ug P'g~l. Downslope from

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b2 this site, topsoil from pit #2 yielded 895 ug P«g-1. The four Salpeten soil pits within or near Maya structures had an average surface soil nutrient concentration of i»G6 ug P*g~-^, while top level soils of the remaining seven pits had a mean of only 42C ug P'g-i. At Quexil, soil pit #21 was located in south shore iiousemouno #823, a structure that was occupied during Middle and Late Preclassic times and again in the Late classic period. Surficial soils from the pit contain 467 ug P*g"^, significantly more than the overall surface soil mean of 278 ug P*g~^ for the watershed. At hacanche, pits #1 and #2 lie on the north shore slope just below construction and their highly enriched surface soils contain 1074 ug P*g~i ana 1275 ug P*g~-^ respectively, exceeding the mean surface concentration (465 ug P'g~^) found in the remaining b pits.

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PALEOLIMNOLOGY OF LAKE QUEXIL Comparing Shallow-Water and Deep-Vnater Sedimentation The primary goal of the paleolimnological research undertaken in the three new watersheds was to assess how the proximate composition c£ the sediments and accumulation rates o£ various chemical constituents of the mud varied as a function of shifting Maya population levels. The first basin considered was Lake Quexil, lying some b km east of Flores and only 1 km from Lake Petenxil (Fig. 2), the basin where Maya impact on the Peten sedimentary record was first revealed (Cowgill et al. 19b6). In 1972, H.H. Vaughan ana G.H. Yezdani useo a Livingstone piston corer (Deevey 1S65) to get a 6.5-m section in 7 m of water. The core was taken south of the lake's western islana (Fig. 13). Ihe smaii lake (area = 2.101 km^, z^ja^ = 32 m, z = 7.2 m: Deevey et al. lS»8lia) was cored again in 1978. In March of that year, M.S. Flannery, S.E. Garrett-Jones, and 1 raised a 9.2-m core from 2fc m ot watei using a modified, gravity-driven, Kullenberg apparatus (Fig. 13). This core, designated Quexil H, was one ot several long cores collecteo in the lake's deep, central basin in our effort to secure sediments of Pleistocene age. fa3

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85 o

PAGE 95

fat The shallow-water core was returned to Florida in the aluminum coring tubes, and the ^^uexil H core was transporteo to the Plorioa State Museum in the plastic tubing that lined the iron Kullenberg coring pipe, cores were refrigerated at 4°C prior to and following extrusion. Sediment chemistry and palynology of the shallow-water section were reported elsewhere (Brenner 1978, Deevey et al. 197!?, Vaughan 1979), but without accompanying aata on Maya population densities in the basin. Ihis consiaeration not only correlates sedimentary changes with shifting population levels, but by comparing two sediment columns, demonstrates the profound influence that core location and basin morphometry had on sediment chemistry and measured sediment accumulation rates. Samples were removed from the extruaed cores at b-20 cm intervals, and water content was evaluated on weighed volumetric samples by drying at 11D°C. A second set of samples was dried for total carbon and nitrogen analyses that were run on a Perkin-Elmer Model 240 Elemental Analyzer. A third series of volumetric samples was weighea ano digested in 15 ml of 2:1 nitric-perchloric acid. After oxiaation, the samples were filtered, ana the filtrate was brought to a known volume. Cation analyses were run on the filtrate by atomic absorption at the University of Elorida Institute of Food and Agricultural Sciences Soils Laboratory. Filtered digestate from the deep core samples was analyzed for phosphorus content on a Technicon Auto Analyzer at the Soils Laboratory. Aliquots of digestate from the shallow-water core were retained for phosphorus analyses, which were run colorimetrically on a

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87 Coleman Model 14 Universal Spectrophotometer following blue color development by the ascorbic acid-ammonium molybdate method in Standard Methods (APHA 1971). Sulfur content in Quexil core H was measured by assessing the quantity in the filterea digestate using the turbidimetric technique in Standard Methods (APHA 1971). When all chemical analyses were completed, chemical concentrations in dry sediment were calculated (Figs. 14 and 15), and level by level proximate compositon of the sediment was figured (Figs. 16 and 17). lo compute the chemical make-up of the mud at each level, the carbonate equivalents of magnesium and calcium were first calculated, thereby permitting the assessment of inorganic (carbonate) carbon content. Next, the inorganic carbon quantity was subtracted from the total carbon value to yield an organic carbon figure. Then, as at Yaxha and Sacnab (Deevey and Rice 1980), the organic carbon value was multiplied by 2.5 to produce a figure for organic matter content. Iron is reported as the oxide, Fe203, and Si02, likely an alumino-silicate, is the residue following subtraction of organic matter, CaC03, MgC03, and Fe203. Dating the cores was once again dependent on changes in the relative pollen diagrams. An exception was provided by numerous wood fragments that were encountered at 623-624 cm in the shallow-water core. Age determination on these allochthonous plant remains is free from the confounding effects of hard-water-lake error, and a dated sample (DAL 198) gave a ^^c age of 8410 + 180 years (Ogaen and Hart 1977). Corrected to about 9400 siaereal years (Deevey et al. 1979),

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iqure 14. The chemical stratigraphy of the Quexil shallow-water core. Fig

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89 '-org CoCOj & MgCOj N. QUEXIL Shallow -Water Core Ca Mg Fe *SiO," tot '"tot "tot mg«g"' mg«o"' mg-g"' pg-g"' mg-g~' mgg-' mg-g-' itigfl200400 200400600 200400 20 40 200400600 100200 10 10 20 30 200 600 0-1 ' ' t 1 1 1 I i I I 50100150U 300 350450500600650-1 V

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91 o ? 55 I (0 01 E — o 9 O a. « c 'o» « S o g a. S 0) o U. a E D O o ? z o _.>^^Vn/— ^ *--vA\^ o

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Figure 16. Proximate chemical composition, relative pollen abundance, and chemical accumulation rates at the Quexil shallow-water core site, as computed over archaeoloyically dateo seaiment zones. Core zones were determined palynologically.

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93 OUEXIL Shallow-Water Core Proximate Composition, % Pollen, % Accumulation Rates ? I'^^l 0:0" &6: CaCOj i ^ocg '^tcOj SiOj,mgcm'.yr' P,ug cm^yr '

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•H 0) to V4 -O <0 0) cc c CO tH 0) 0) S
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95 =J Z uj S D O o o O o 2l * ""

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S>0 the age of basal sediments from the core confirms that it is a nearly complete Holocene section. Zonation of the shallow-water core was achieved by comparison of Vaughan's (1<;79) relative pollen diagrams to palynological profiles from Yaxha and faacnab (Deevey et al. 197S>). S.E. Garrett-Jones examined pollen from Quexil core H and usea percentage aiagrams from Yaxha and Sacnab, as well as the ^^uexil shallow-water section, to set zones ana attach archaeologically correlatea oates to levels in the core (Deevey et ai. lyfaUc). Ihus, the changing pollen spectrum, assumed to reflect changing population density in the basin, was usea to date the core. Dates were. assigneo to levels in the Quexil cores using ages applied to archaeologically defined periods at Yaxha and Sacnab. Proximate composition of the sediment within zones was figured after zone limits were established using the pollen spectra. Based on the dates assigned to the various horizons in the cores, chemical accumulation rates for the various archaeological periods were calculated (Figs. 16-17). The presence of a basal, high forest pollen zone in the Quexil H section that is of the same age as the bottom sediments in the shaliowwater core indicates that a near-complete Holocene profile was also obtained in aeep water. The Early Preclassic and Kiodle Pieclassic zones, distinguished palynologically in the shallow-water section, could not be separated in Quexil core H and were considered as a single zone. Unfortunately, wide interval (40 cm) sampling of the Quexil B core for pollen analysis resulted in some uncertainty in establishing zone limits. Where changes in the pollen spectrum were encountered, a

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97 horizon was designated midway between the studied levels. Lack of accuracy in defining the true levels, ana hence dates, wtiere changes occur can result in errant calculated chemical accumulation rates. This problem is most serious in dealing with zones of little thickness. Proximate chemical Composition of the Lake Quexil Seaiments The sediments of the Quexil shallowand deep-water cores are not strikingly dissimilar in chemical composition though some differences do emerge. The shallow-water section contains a higher proportion of organic matter (average of zone means = 48.1% organic matter), while Quexil H is richer in silica (average of zone means = 56. b% £)i02). Comparison of organic matter content in the two cores was achieved by assessing the zone-to-zone ratio of organic matter concentration in tiie shallowand deep-water sections. For this computation, the organic matter value of the combined Early and Middle Preclassic zone was compared to both of the palynologically distinct Early and Middle Preclassic zones identified in the shallow core. When organic mattei content (%) in the shallow-core zones was divided by the amount in the equivalent deep-core zones, the range of ratios extenoeo from an Early Preclassic low of 0.97 to a Late and Postclassic high of 2.0. The mean ratio for the seven compared zones is 1.44, indicating that the Quexil shallow-water core sediments average nearly half again as much organic matter as deep-water sediments of the same age. silica content in the two sections was compared in a similar manner, though in this case, the

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yfa zonal Si02 concentration of ^uexil h was oivided ty the shaj.lowsection Si02 value. The mean zonal ratio was 1.^7, indicating tiie higher silica content in the deep-water core. Carbonates, as CaC03 and hgC03, comprise a rather constant 5-6% of the sediment throughout all zones of Quexil H. In the shallowwater section, the content varies from j to 6% by zone until the Late and Postclassic, when carbonates made up 30% of the seaimeht. Following abandonment of the catchment by the Maya, carbonate content of the shallow-water sediments decreased slightly, but still constituted 26% of the sediment by weight. Though ostracoos are plentiful in the Late and Postclassic zone of the core, their high concentrations probably result from favorable preservation conditions, and there is little in the microfossil record to support the claim that carbonates deposited in the last 1400 years are biogenic (brenner 1978). More likely, the carbonates are of allochthonous origin ana resulted from human disturbance near the coring site. Export ot detrital carbonates from Quexil's two islands during Late and Postclassic times may explain the carbonate-rich horizon from ibU to 80 cm in the shallow-water core. The islands were evioently populatea during those perioas, all seven test-pitteo islana structures indicating Postclassic period habitation. After the close of the Postclassic, the islanos were abandoned, and carbonate content in the sediments dropped. High mean carbonate concentration in the post-Kaya section (0-80 cm) of the core is attributable to two samples taken above 25 cm in the core. High concentrations here may have resultea from wash-in when the western access roao to the lake was constructeo.

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9S» Tracking the percent composition of the sediments in the two cores from the basal zones upward, both sections show a precipitous orop in organic matter content during the Early Classic and Late and Postclassic periods, followed by an increase in the post-haya zone. While both cores show reduced organic matter content in zones dating from 250 to 1600 A.D., shallow-water sediments are about twice as rich in organic matter as deep-core seaiments in the time-equivalent sections (Table 2). Both cores display Si02 maxima in the Earli Classic as well as in the Late and Postclassic, though silica content in the zones is higher for Quexil core H. As at Yaxha and Sacnab, human aisturbance in the Ciuexil basin resulted in inorganic domination of the sediments, but the Early Classic organic matter minimum in both cores is anomalous as the watershed experiencea a population hiatus during this perioa. While the mainland remained devoid of Maya inhabitants from about 100 B.C. to 550 A.D., two mounds on Quexil 's eastern islana were occupiec during the Early Classic. This minimal disturbance can hardly account for the inorganic nature of Early Classic sediments, especially at the deepcore site. Depopulation of the drainage may not have resulted in reforestation, ana even if human activity in the watersheo ceased completely, a rapid return to a predisturbance equilibrium might not be expected. Support for the latter contention is providea by comparison of the pre-Maya and post-Maya zones. In neither Quexil core has the mean organic matter content in the post-Maya section returned to the predisturbance level. In the shallow-water core, this could be due in

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iOO Table 2. Percent composition of Lake Quexil shallow-water and deep-water core sediments. CaCOj Organic Matter + MgC03 SiO^ f'^2^j Zone Shallow Deep Shallow Leep Shallow Deep Shallow Deep Post-haya . 42 36 26 6 j(j .54 2 b. Late and Postclassic 18 Early Classic 14 Late Preclassic 66 Middle Preclassic 69 Early Preclassic 59 Pre-Maya 69 9

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101 part to dilution by large amounts of detrital carbonate. The mean organic matter percentage for the uppermost zone of the Quexil h core might have been higher if the top meter of the section had been analyzed. That portion of the core was not assesseo because the stratigraphy of the flocculent surface mud was ruined by the coring procedure. However, perfect recovery to preaisturLance conditions is not expected following the Maya downfall, as the lake waters were more effectively sealed from groundwater intrusion by a thick anthropogenic clay aquiclude. Nevertheless, the extreme inorganic nature of Early Classic sediments is anomalous and hints at improper core zonation. While human disturbance is generally associated with a shift to higher silica content in the sediments at both coring sites, aeep-watet sediments contain higher quantities of SiO^, even under pre-Kaya and post-Maya conditions. Several factors are likely responsible for this phenomenon. As allochthonous material is washea, out of the watershed and into the lake, large organic particles are deposited near shore, while siltand clay-size inorganics remain in the water column or ate resuspended and focused into deep-water locations. Furthermore, the shallow-water coring site was afforded some protection by quexil 's two islands and probably received little of the silt load that cane off the steep north shore scarp. If water levels were lower in the past, it is conceivable that the shallow-water site could have been cut off completely from direct contact with the deep basin to the east. The coring station would have been at the southern end of a shallow northsouth channel, boraered on the east by a single, flat land mass comprised of the two joined islands.

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102 Chemical Accumulation Rates in Lake Quexil Sediments Increasing riparian population density in the Quexii watershea was shown to be generally associated with a shift to inorganic domination of the lacustrine sediment matrix. Changing Maya population levels ate now compared with shifting chemical delivery rates to the lake. Modified chemical loading rates that resulted from human activity may well have altered biological processes in the aquatic realm. Additionally, nutrient export from the watershed as well as etosional consequences of human disturbance could have had an adverse effect on Maya agriculture within the drainage. Phosphorus accumulation rates are considered first, as phosphorus may have been the limiting nutrient for both lake trophic state ana . agricultural productivity. Phosphorus accumulation rates are comparea to Maya population levels as expressed by mainland population densities (Fig. 17). Comparison of changing population Densities ana phosphorus accumulation rates is complicated by the fact that designated time-specific ceramic assemblages, based on identified sherds from the Quexil catchment, are not time-equivalent to ceramic periods established at Yaxha and Sacnab. Ages attached to the twin basin ceramic sequence were correlated through palynological sequences from the paired lakes to pollen zones at quexil; thus the time zonation for occupation at Quexil is different from the time zonation applied to levels in the core. Middle and Late Preclassic ceramics from the western drainage were not distinguished in P.M. Rice's preliminary

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103 analysis of the material, but the sequence was refined to some degree in that Terminal Preclassic and Terminal classic artifacts were identified. Despite these difficulties, some general correlations between Maya population levels and chemical accumulation rates are apparent. Human intrusion in the watershea is associated with increasing phosphorus delivery rates at both coring sites (Table 3), though the maxima occur at different times. At the shallow-water site, the rate of phosphorus accumulation reachea a peak (b.& ug P'cm~2«yr~l) during the combined Late and Postclassic, a figure that is some 8.9 times the predisturbance baseline value. In deep water, the Early Classic period was the time of maximum phosphorus deposition, and the rate at which the nutrient accumulated in basin sediments (36.7 ug P'cm~^'yr~l) was 14.4 times the pre-Maya rate. Relatively high Early classic phosphorus accumulation rates measured for both cores are anomalous as the Quexil basin experienced a population decline auring that period, however, return to a predisturbance equilibrium with respect to phosphorus loading would not necessarily be expected, and high modern (post-Maya) delivery rates support this contention. Despite the evident reforestation of the watershed over the past 400 years, post-Maya phosphorus accumulation rates at the shallow-water site (4.4 ug P*cm~2«yr"-'-) and deepwater station (18.0 ug P*cm"^'yr~l) are 6.7 and 7.1 times their respective baseline values. In fact, return to a predisturbance equilibrium level may now be complete and is perhaps reflected by low modern productivity measurements. Considered as a complete unit.

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104 Table 3. Chemical accumulation rates in the Lake Quexil seaiments at the shallow-water and deep-water sites as amount per square centimeter per year. Zone *-orq (mg) CaC03 + MgC03 (mg) Si02 (mg) Ptot (ug) Shallow Deep Shallow Deep Shallow Deep Shallow Deep Post-Maya 2.2 Late and Postclassic 1.3 Early Classic 1.7 Late Preclassic 4. fa Middle Preclassic 1.8 Early Preclassic 3.3 Pre-Maya 1.3 4.8 3.1 l.i 20 4.4 16.0 1.6"

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10b however, the post-Maya section does not suggest complete recovery, and it is likely that a lag period exists between the time human disturbance ceases and phosphorus delivery rates return to predisturbance levels. High nutrient input to the lake is maintained during the post-impact phase as anthropogenically phosphorus-enriched surface soils, carried aownhill to the lake edge curing the tpisoce ot deforestation, continue to move into the lake following vegetation recovery. High phosphorus concentrations in soils associated with Maya construction support the claim that complete recovery has not occurred. A zone-to-zone comparison of phosphorus accumulation rates at the two core sites shows that the nutrient is deposited at a higher rate in deep water. In the upper four zones of the two cores, phosphorus accumulates in deep water at rates 2.&-6.4 times the age-equivalent rates measured for the shallow site. Calculated zonal phosphorus loading rates derived from the shallow-water core are all less than 7 ug P*cm~2*yr"l, the permissible value for a lake ot 5 m mean depth (Vollenweider 1968). Since Late Preclassic times, phosphorus delivery rates to Lake ^uexil, based on analysis of the aeep-water section, have exceeded permissible levels (10 ugP*cm~2'yr "'), even for a lake of 10 m mean depth, and the Early classic accumulation rate (36.7 ug P«cm~2«yr~l) is dangerously high. However, it is unlikely that eutrophication resulted from the enhanced nutrient delivery, as concentrations and accumulation rates of autochthonously produced microfossils are low in the Early Classic zone of the shallow-water core (Brenner 1978). As at Yaxha and Sacnab, much of the sedimented, disturbance-zone phosphorus in Lake Quexil was probably

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IGfe unavailable to plants and reached the lake bottom in mineral form (apatite?), having never cycled through the aquatic Liota. Other chemical components of the Quexil sediment also responded to human disturbance with higher accumulation rates. Organic carbon deposition was maximal at both coring sites during the Late Preclassic period. Within this zone, organic carbon accumulation at the shallow and deep station occurred at rates 3.& and 5.6 times the respective baseline rates. Carbonate accumulation on the lake bottom also increased with disturbance. At the shallow site, the maximum accumulation rate (5.0 mg CaC03 + MgC03*cm"2'yr"^) was . attained during the Late and Postclassic period and was 25 times the pre-Maya rate, carbonate deposition in deep water peaked in the Early Classic when 7.8 mg CaC03 + MgC03*cnr2«yr~i were accumulating, exceeding the baseline value by some 19.5 times. The Early classic was also the period of maximal silica deposition at the two sites. In shallow water, the baseline Si02 accumulation rate was increased 20-fold, while in deep water, the rate of accumulation jumped some 37 times over the pre-Maya value. In both cores, organic material as well as carbonate and silicate deposition increased following disturbance. However, the magnitude of change was greater for the carbonates and silicates, thus accounting for the highly inorganic nature of the Maya zone sediments. While human disturbance in the Quexil watershed lea to higher chemical delivery rates at both coring sites, accumulation rates at the deep station generally exceeded those measured on the shallow-water core. This has already been shown for phosphorus, but can be

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107 demonstrated for the other chemical types when equivalent-zone accumulation rates are compared. To elucidate this intra-basin difference, calculated chemical accumulation rates from the three principal, comparable Maya periods (Late Preclassic, Early classic, Late and Postclassic) in the two cores were contrasted. Deep-water deposition of silica during these per ioas rangea from 5.6 to 8.0 times the shallow-water rates, and a similar comparison of organic carbon accumulation rates shows deep-water inputs to have been l.i-2.4 times the shallow-site rates. Carbonates display a similar relationship in the Late Preclassic and Early classic when deep-water deposition exceeded shallow-water accumulation by 4.3 and 4.9 times respectively, but the trend was reversed in the Late and Postclassic, when carbonates accumulated more rapidly in shallow water than at the deep-core location. Silica accumulation rates in deep water exceea shailow-watet accumulation rates by a greater margin than that seen for organic carbon, and this is expressea in the relatively higher inorganic nature of the deep-core sediments. Higher calculated chemical accumulation rates tor the oeep-water site were not unexpected, as greater bulk sedimentation there was obvious from the differential overall lengths of the age-equivalent cores (9.2 m vs. 6.5 m). Focusing attention on the comparable, palynologically correlated disturbance zones, twice as much sediment accumulated in deep water (660-200 cm = 460 cm) as in shallow water (310-80 cm = 230 cm) from the inception of the Late Preclassic through the Late and Postclassic period. While the volume of sediment amassed in deep water during this interval was double that accumulated in

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lOfa shallow water, calculated chemical accumulation rates trom the two sites often difter by more than a factor of two. ihis is explaineo by the higher percent dry weight and higher wet weight per cm-* in the three zones of the deep core. Over the length of the three disturbance zones, the mean percent dry weight was calculated for the two cores. From 660-200 cm in Quexil H, dry weight constitutes 24.3% of the wet sediment. In the shallow-water core, dry weight makes up only 14.6% ot the sediment over the time equivalent zones. Comparing the same zones with respect to wet sediment density, guexil H mud averages 1.11 g'cm"-^ wet sediment, while the more organic deposits in shallow water display a mean of 1.02 g*cm~-^ wet sediment. Mean percent ory weight was multiplied by mean wet weight per cm-* to estimate the average dry weight content ot each cm^ wet sediment in the thtee disturbance zones of the cores. With 270 mg dry sediment'cm"^ wet sediment, the Quexil H core contains nearly twice as much dry weight per unit volume wet sediment as the shallow-water section (151 mg dry sediment 'cm"^ wet seaiment). Higher dry weight per cm-^ wet seaiment in deep-water seaiments is likely a function of several factors. Greater sediment mass deposited in deep water results in more compaction ot the mud at that site. Also, the inorganic nature of the deep deposit suggests that siliceous sediment of primarily clayana siltsize grains (Binfora, in press) is tightly packed when the overlying sediment accumulation becomes substantial, thereby removing much interstitial water. Relatively large, hydrophilic organic particles deposited at the

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10S» shallow-water site never become compacted to the degree achieved at the deep station and retain much water. It has been noted elsewhere (Brenner, in press) that phosphorus and iron concentrations in surficial (0-10 cm) soils of the i^uexil watershed do not differ statistically from levels encountered in the shallowand deep-core sediments. While this may be coincidental, or simply an artifact of aiagenetic processes, it at least suggests that the lake mud is composed largely of redeposited soils. If this is the case, and translocated soils are the primary source of seaimenteu phosphorus, carbonates, silica, and organic matter, then within-core zone-to-zone shifts in accumulation rates for any chemical pair shoulo be positively correlated, assuming there is little change in the postdepositional content of the sediment for any chemical type. Assessing the Quexil H core first, zone-to-zone phosphorus ana silica accumulation rates are highly correlatea (r = 0.94, P < b.OOb), as are phosphorus and carbonate (r = 0.96, P < 0.005) and carbonate and silica inputs (r = 0.&&, P < 0.U05). In the shallow-water core, zone-to-zone chemical accumulation rates were correlated as follows: phosphorus and silica (r = 0.72, P< 0.05), phosphorus and carbonates (r = 0.75, P < 0.05). Carbonate and silica accumulations were not significantly correlated at the 95% confidence level (r = 0.29). inis is no doubt in large part due to the unusually high carbonate accumulations registered for the two most recent zones in the core. In contrast to these highly interrelated delivery rates, both cores fail to show a significant correlation between zone-to-zone phosphorus ana

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110 organic carbon accumulation (r = 0.07, r = 0.47, P> 0.05). Perhaps zone-to-zone shifts in deposition rates for these two sedimentarir constituents were actually different, as organic matter was progressively flushed from, and thus depleted in the catchment. It is likely that differential, between-zone postdepositional loss of organic carbon also accounts for the lack of correlation. That zone-to-zone . phosphorus accumulation rates are significantly correlated with carbonate and silica rates at both core sites suggests that a comraon mechanism is responsible for delivery of these chemical types to the lake, whereas organic carbon is sedimented by a different mechanism. As at Yaxha arid Sacnab, colluviatidn or alluviation of watershed soils probably accounted for the major portion of lacustrine sedimentation, especially during the episode of forest removal. Maya deforestation in the t^uexil watershed resultec in accelerateo delivery rates of carbonates, silicates, organic matter, and phosphorus to the lake. Export of inorganic matter from the catchment was probably enhanced to a greater degree than organic matter removal, and this, along with strong diagenesis, produced oisturbance-zone muds of low organic content. The episode of vegetation removal and consequent sediment loading of Uuexil lasted about three millennia, and modern high phosphorus inputs measured in both cores demonstrate that the impact was sustained following abandonment of the watershed. calculated chemical accumulation rates for the shallowand deepwater sections elucidate the profound effect that core location ana basin morphometry had on sedimentation processes. While the shallow-

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Hi core site was protected from the erosional load coining off the steep north shore slope, the deep station was the recipient of much resuspended material. The conical bathymetry of Lake Quexil (tieevey et al. 1980a) is conoucive to the focusing of sediments into the deepest areas of the lake (Lehman 1S75, Davis ana Ford, 1982, Deevey et al. 1977). The differential accumulation of phosphorus from site to site on the basin floor makes it somewhat difficult to use the (^uexil data to refine the per capita phosphorus loading model developed at ^axha and Sacnab. Perhaps even more problematical is the inability of the zone-to-zone phosphorus loading values computed from analysis of the two cores to track short-term Maya population fluctuations derived from the archaeological record. Several factors account tor this difficulty. The cores, reliant for zonation on correlation with the discrete palynological sections distinguished at Yaxha and Sacnab, have archaeologically correlated dates that are different from the age designations applied to ceramic assemblages from the Quexil catclmient. The single Late and Postclassic sediment zone encompasses three distinguishable ceramic periods (Late Classic, Terminal Classic, Postclassic) during which time the population changed drastically as a consequence of the Classic collapse. The Late Preclassic sediment zone straddles the Middle and Late Preclassic, and Terminal Preclassic archaeological periods, again two time periods of very different levels of Maya settlement. Middle and Late Preclassic ceramics have been distinguished by P.M. Rice (Rice and Rice 1981) in a reevaluation of the Quexil sherds, but this does not resolve the association of a

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112 "no-occupation" Terminal Preclassic period with a "high-phosphorusinput," Late Preclassic sediment zone. Time designations tor the archaeological record differ from ages assigned to levels in the sediment cores, but even where time congruency is perfect (Early Classic and post-Maya), high phosphorus loadings appear anomalous as they are associated with periods of basin depopulation. Long lag periods necessary to approach a predisturbance equilibrium may explain this phenomenon. On the other hand, it is conceivable that auriiig Early classic times, the land in the Quexil drainage was constantly exploited despite the fact that the watershed remained uninhabitea. Finally, accurate age assignment to the pollen zones of the sediment cores, perhaps achieved at Yaxha and Sacnab, may not be possible at Quexil. At the twin basins, zones were set based on the assumption that the degree of deforestation reflected in the pollen spectrum was a function of the changing riparian Maya population density, known from the dateable archaeological record. At Quexil, zones were delimited by comparison with the Yaxha-Sacnab sections without archaeological data from the catchment. An assumption of slow,, steady population growth in the basin did not seem unreasonable, and the Terminal Preclassic-Early Classic hiatus could not be anticipated. If indeea the water snea had been reforested during this period, sedimentation rates would have dropped, confining accumulation during the 650-year perioo to a thin horizon. Widely spaced (40 cm) palynological sampling of the Quexil K core can be invoked to explain the failure to identity tne reforestation zone, but Vaughan's (1979) close-interval sampling of the

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113 shallow-water section does not show a horizon of vegetation recovery either. The inability to discern a 'lerminal Preclassic-Early Classic reforestation horizon in the Quexil cores is puzzling and can be interpreted in two ways. Either vegetation recovery in the basin did not occur, or if it did, evidence for forest regrowth was overwhelmed by the regional pollen rain that registered continuea deforestation. If the sediments of Lake Quexil truly record the greater regional pollen rain, then zones identified at the twin basins 50 km to the east should be contemporary with the Quexil pollen zones. However, it may. be that the pollen spectra of the iaxha and Sacnab cores reflect regional vegetation changes, while Quexil 's profiles constitute a mix of regional and local shifts, and the pollen-equivalent zones in cores from the widely separated lakes would thus not be expected to be contemporaneous, in addition to the differential settlement histories of the basins, the comparison of Quexil 's pollen profiles to the twin basin diagrams is complicated by the presence of the large savanna area south of Quexil. If the savannas are natural and of sufficient antiquity, they certainly contributed pollen to. the Quexil seaiments that can be misconstrued as evidence for human-induced deforestation. While palynological dating of the Quexil sediments probably was inaccurate, the zonation of the shallowand deep-water cores nevertheless made possible a reliable assessment of differential sedimentation at the two sites within the lake.

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114 Having perceived the problems associated with palynological zonation of the Quexil cores, other sedimentary parameters were examined as potential dating tools. An attempt was made to use magnetic susceptibility to establish intraana intet-basin core correlations (Oldfield et al. 1S»78, Thompson et al. 1980), but this failed as the Bison meter was not sensitive enough to recota the low level of sedimented, magnetic particles. Magnetic susceptibility measurements on Ouexil sediments are now being pursued by colleagues m England using more sensitive instrumentation. This will likely be of little help in establishing an inter-basin correlation, even when other lakes are studied, as this would demand that regional events such as ashfalls were recorded as horizons in the sediments of all the cored lakes. Magnetic susceptibility measurements taken over the length of the lake sediment cores may record changing erosion rates (J. A. Dearing, pers. comm. ) that were probably not contemporaneous from basin to basin, as surmised from the varying demographic histories. Nevertheless, the magnetic susceptibility profile, as a basin-specific indicator of human disturbance, may some day be usea in conjunction with the archaeological record to assign dates to levels in the cores. An alternative to pollen zonation at (^uexil was also sought in granulometric analysis of the basin sediments. Warwick (1980), working with sediments from the Bay of guinte. Lake Ontario, demonstrated that human disturbance resulted in an increased delivery of fine particles to the center of the lake. Binfora's (in press) particle size analysis of the Quexil H mud showed that mean particle size droppea

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lib significantly following deforestation. Within the deep-water core, fluctuations with respect to mean particle size, as well as the computed skewness and kurtosis of the measured, sampled particles were used together with the paleodemographic data to rezone and date the core (Binford, in press). Phosphorus accumulation rates were recalculatec usinc^ the granulometric zonation of the Quexil H core (Fig. lb). Ihis improves somewhat on the pollen zonation with respect to the ability of phosphorus loading rates to track short-term population fluctuations. Baseline rates more than tripled when the catchment was settlea in the Middle and Late Preclassic and fell back to nearly predisturbance levels when the watershed was depopulated in the lerminal Preclassic. The Early Classic loading rate of 21.3 ug P'cm~2'yr"^ still appears anomalously high considering that the basin remained uninhabited during that period. Dangerously high phosphorus loading was computed for the Late classic, a time of dense Maya settlement, but the high nutrient input continued into the 'ierminal Classic, when population density was greatly reduced. Sustained high phosphorus deposition rates during the relatively brief (150 years) Terminal Classic may be explained by the lag period necessary to attain a new equilibrium. As the watershed remained nearly devoid of human habitation into the Postclassic, phosphorus loading declined, but surprisingly rose again with the total abandonment of the catchment. This fine zoning of Quexil H still results in a high Early classic phosphorus accumulation rate, and it is particularly difficult to

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Figure 18. Population densities in the Quexil Viatei&hea ana total phosphorus accumulation rates at the Quexil core h site, by archaeological period. Core zones were aeliniiteo granulometrically.

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117 Archaeological Period QUEXiL Occupied Persons -km'^ Mounds 2S so 7S 100 \2S ISO Core H Accumulation Rote P, /ugcm"'.yr"' 10 20 30 40 0-

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Ufa explain considering that there is some evidence for reduced erosion in the Terminal Preclassic period. Additionally, high modern input rates are not easy to explain in that phosphorus export to the lake was low during the preceding, Postclassic period. Analysis of the stratigraphically mixed, flocculent sediments above 120 cm might have reduced the calculated post-Maya phosphorus accumulation rate. However, even if the upper section contained no phosphorus at all, the modern deposition rate would be reouced, but still in excess of ' the Postclassic accumulation rate. Thus, data from Quexil, based on palynological and granulometric fine zoning of the ceep-water cote cannot be used to refine the per capita phosphorus loading model developed for twin Lakes Yaxha and Sacnab. Paleoproductivity in Lake Quexil The Significance of Microfossils Analysis of sedimented microfossil remains can contribute to reconstructions of past lacustrine environments, especially when organisms are identified to the species level and their modern ecological requirements are known, caution must be exercised when interpreting the microfossil record, as the death assemblage examined and enumerated may have been modified significantly as compared to the original biocoenosis from which it was derived (Covich 1970). A variety of plant and animal remains are encountered in lake seoiments, but the degree of preservation for the various types is highly variable. Physical and chemical properties of the water column ana

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Hi, sediment matrix can affect microfossil preservation, as can the composition of the seaimented organism. Ihe most common remains founu in lake muds are typically resistant structures composea of alkaline earth carbonates, silica, chitin, cellulose, or pollinin (Frey li»7t). Many of the most useful algal types for trophic state characterization are not fossilizea. Nitrogen-tixiny cyanophytes, indicators of lake eutrophy, are notably absent from the fossil recoru (Brugam 1976), but their former presence can be aocumentea it myxoxanthin, myxoxanthophyll, or oscillaxanthin can be detected by seaiment pigment analysis (Wetzel 1975). The five principal invertebrate groups that leave body parts or resting eggs in lake seaiments and are used tor environmental reconstructions are the Cladocera, miages, molluscs, ostracods, and rotifers (crisman 197ba). Adaitionai groups, such as rhizopoos, neorhabdocoeles, sponges, and several other insect groups besides midges, leave iaentifiable remains at the lake bottom aiic may eventually prove to be useful indicators of past lacustrine conditions (Frey 1976). Stratigraphic shifts in numbers or species composition for the various taxonomic groups can, in conjunction with other evaluated sedimentary parameters, proviae information concerning past conditions with respect to productivity, water chemistry, lake level, and oxygen content of the water. As with all paleolimnological studies, accurate interpretation of the sedimentary record is Dependent on the analysis of an array of physical, chemical, anc biological aspects of the profile. With several kinds of data from the profile.

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120 hypotheses about past conditions can be constructed and tested. Inferences about past lake conditions that fail to explain all data sets can then be rejected (Pennington 1981). The Microfossils of the Quexil Cores Microfossil concentrations in the oi^exil shallow-v«ater core (Fig. IS) were reported, and accumulation rates were compared on a 2ohe-to-2one basis to total phosphorus deposition rates (Brenner 1978). Phosphorus accumulation was positively correlated with microfossil accumulation from the earliest, pre-Maya section of the core through the Late Preclassic (Fig. 20). The trend ceased in the Early classic when phosphorus deposition was high, but calculated microfossil delivery to the sediments was low. The inverse relationship between microfossil accumulations and phosphorus deliveiy was sustained into the Late and Postclassic, though ostracods were sedimented at a rapid rate in the carbonate-rich zone ot thecore. Following depopulation of the basin, microfossil accumulations were once again high in the organic, post-Maya section of the core, while phosphorus input dropped to 75% of the Late and Postclassic rate. As phosphorus was thought to be the limiting nutrient for lacustrine productivity, explanations were sought to resolve the enigmatic inverse relationship between high phosphorus Deposition ana low microfossil accumulation, a situation that prevailed for more than a millennium. As the combined carbonate and silicate oelivety rate was

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Figure 19. Microfossil concentrations in the Quexil shallovv-vvate): core.

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QUEXIL Shallow-Water Core 122 I I ' I r ' I I 05 U) fiS> \a 25 50 75 100 Remains • cm"' Wet Sediment («io'

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•H

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124 tUui o X _o (da) a^BQ

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125 maximal in the Early classic and still high through the Late and Postclassic, siltation may have been severe enough to limit light penetration in the water column and thereby reduce productivity. The inorganic sediments of the two disturbance zones probably constitute a microenvironment that is not favorable for microfossil preservation. Low calculated microfossil accumulation rates for the Early Classic and Late and Postclassic zones may be inaccurate estimates of original deposition rates, and perhaps simply reflect severe diagenesis in ttie clayand carbonate-rich sediments. Total pollen accumulation in the inorganic sections of the core was also low, and though this may have been a function of increased deforestation, postdepositional destruction of pollen grains can be invokea. Ihe claim is supporteu by the very poor pollen preservation encountered in the clay-rich sediments of Lake Yaxha (Vaughan, pets. comm.). Estimated gross sedimentation rates used to calculate zonal microfossil accumulation rates can affect zone-to-zone changes in the delivery rates computed for the remains. The Early classic sedimentation rate (0.17 cm*yr~^) was slightly higher than the Late Preclassic rate (0.16 cm'yr"^). Nevertheless, Late Preciassic microfossil accumulations were much higher, indicating the higher numbers of remains per cm-^ encountered in mua from that zone. While gross sedimentation rates influence computed microfossil accumulations from zone-to-zone, they do not explain the inability of microfossil accumulations to track computed phosphorus inputs as the chemical ana fossil rates are calculated employing the same zonal gross sedimentation rates.

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126 Apparent zone-to-zone positive correlation between changing phosphorus accumulation and inicrof ossil accumulation from the pre-haya section of the core until the Late Preclassic may be simply a function of changing estimated gross sedimentation rates. More likely, howevei, is the possibility that increasing phosphorus delivery to Lake Ouexil, associated with initial clearing and burning of the cliraax forest, qiq enhance productivity. The plant-available forms of the nutrient, delivered following initial land clearance, were utilizeo by macrophytes and aquatic microflora and ultimately sedimented on the lake bottom. After the major portion of the phosphorus originally tiea up in the vegetation and litter of the basin finally reached the lake, subsequent phosphorus delivery was associated with bulk transport of watershed soils deficient in plant-available phosphorus. Even if soluble phosphorus delivery to the lake continued into the Early Classic, it is possible that the nutrient was rapidly scavenged and coprecipitated with the carbonates that were also being supplieo at a great rate (Wetzel 1970, Otsuki and Wetzel 1972, Manny et al. 1978). Despite the realization that postaepositional aestruction ot mictofossils might affect inferences about past levels of productivity in Lake (iuexil, counts were made on the Ouexil H section to supplemeiit information that :had emerged from analysis of the shallow core. Accumulation rates calculated tor the shallow-water section may t-e biased indicators of lake-wide productivity as a consequence of the unique position of the coring site. This would certainly be the case if lake levels were lower in the past and the locality had been

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127 isolated from the rest of the basin. Accumulation rates based on counts from Quexil H might be expected to proviae better estimates of changing basin-wide production. Comparison of zone-to-zone microfossil accumulation rates in the two cores can provide additional evioence for the resuspension and focusing of remains into the deep areas of the lake, a phenomenon already documented by seaiment trap studies at Lakes Yaxha and Sacnab (Deevey et al. 1977). Zone-to-zone chemical and microfossil accumulation rates can be compared to test the hypotiiesis that productivity was phosphorus-limited. The question can be addressed on a finer scale it level-by-level concentrations of phosphorus and microfossils are examined. The instantaneous, bulk sedimentation rate is the same for any given level, whether chemicai or microfossil accumulation rates are being calculated. Thus, assessment of level-by-level changes in the concentration of microfossils ana phosphorus essentially evaluates the correlation between accumulation rates for the two parameters. If the microfossil accumulation were dependent on and linearly related to phosphorus accumulation (supply), the ratio of microfossil concentration to phosphorus concentration from level to level should remain about the same over the length of the core. samples for microfossil analysis were removed from the tiuexil cores at 20 cm intervals. In the shallow-water section, sampling began at the mud-water interface, and volumetric plugs of seaiment were taken over the length of the core, except at 620 cm, where the core haa been previously sampled for radiocarbon dating. Sampling of Quexil E began

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128 at 120 cm, and samples were collected every 20 cm down to yoo cm, the only exception being a gap at 860 cm where a large section was removeo for ^^C analysis. The volume of sediment removed from each level of the shallow-water section was 0.452 cm-^, while Q.316 cm^ of sediment was taken from Quexil H. Volumetric sediment samples were transferred to lb ml Nalgene centrifuge tubes and 8 ml of 10% KOH was added. The tubes were placed in a hot water bath for 15-20 minutes, and the sediment was simultaneously disaggregated with a glass rod. Following the heating procedure, the samples were centrifuged and the supernatant was at awn off with a pipet. Distilled water was added to the tubes and the sediment was stirred with a glass rod. Again the samples were spun down and the overlying liquid was drawn off the top. After three such rinses, the mud was transferred to polystyrene tubes and centrif ugea. Liquid was once again drawn off and water was added until a volumetric level marked on the tube wall was reached, samples from Quexil H were brought to 0.95 cm-^ while the tubes containing hydrophilic organic samples from the shallow-water core were filled to l.b cm-^. When samples were brought to a known volume, magnetic stirring bars were placed in the tubes and the samples were mixed usiny a ColeParmer Mark I magnetic stirrer. While the samples were being homogenized, microscope slides were cleaned and placed on a hotplate. Two drops of glycerine jelly, lightly stained with safranin were applied to the slides at two positions. A subsample of lfa.t)3 ul was removed from the stirred sediment slurry. with a micropipet and added to

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12S> each of the glycerine jelly drops on the slide. The subsamples were mixed into the glycerine jelly with a fine needle, and following evaporation of water from the mixture, cover slips were applied, thus making good permanent slides. Enumeration of microfossil remains was accomplished by scanning slides at 200X magnification. As each slide contained two samples prepared from a given core level, left and right samples on the sliae were both examined and microfossil concentrations were figured from the average of the ouplicate counts. At levels where microfossiis were not plentiful, the entire area below the cover slip was studied, but where remains were abundant, fractions of the slide were examined. In the latter case, transects were scrutinized over the entire slide to account for possible non-random distribution of remains below the cover glass. Microfossil concentrations for levels in the cores were figured as remains -cm'^ wet sediment (Figs. 19 and 2i). Within the delimited pollen zones, average concentration in the sediment for each microfossil type was computed and multiplied by the zonal sediment accumulation rate to calculate the zonal microfossil accumulation rate as remains 'cm'^-yr-l (Figs. 20 and 22). There is a degree of subjectivity involved in the enumeration of microfossiis and criteria must be establishea with respect to tallying the remains, so that consistency is maintained over the length of a core and between cores. A brief discussion of what actually was counted in the two Quexil cores is appropriate. Cladocera carapaces are here reported as total carapaces (whole animals), ano the

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131 oo (uio) ejoQ uj M)dea

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132 concentrations are based on the enumeration of all complete half carapaces. Bosminid remains are presumably from the common moaetn plankter, Eubosmina tubicen , while chydorid parts are likely from several species, at least one of which is Alona atfinis . Cladocera headshields, hot reported for the Quexil shallow-water core, were counted in Quexil H and represent intact remains. Ostracod remains in the Quexil sediments are reported as complete valve pairs, though single valves were tabulated. Additionally, ostracod mandibles were counted in the Quexil sediments and were generally associated with a mass of tangled appendages, ihe intact mandible-appendage complex or mandible pair was assumed to be equivalent to. a valve pair for reporting purposes. Botryococcus , originally considered a member of the Xanthophyceae, but now assigned to the Chlorophyceae (Hutchinson 19b7), possesses cells that grow within or protruding from a gelatinous matrix (Thompson 1959). Each, cell clump was enumerated as an entity. Desmias, representing several species of Staurastrum were tallied each time a semi -cell or radiating arm was encountered, frediastrum cf . ouplex was counted when at least half of the colony was present. Reported sponge spicules represent all complete remains as well as fragments encountered. Most sponge spicules were intact and of the acerate type. No attempt was made to separate hyphal strands ana . fungal spores when counting, and reported values in the "fungal elements" category are for total combined indiviaual spores ana hyphal fragments. Centric and pennate diatoms were enumerated as indiviaual

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133 cells. Some broken pennate remains were seen, and in such cases they were counted if at least half the cell was present. Finally, the "chitin fragments" category represents incomplete bosminid, chydorid, and ostracod pieces, as well as some rarer insect remains. Quexil H microfossils are now considered using the core zonation based on the palynological record. While dates assigned to levels in the core may be erroneous, dependence of microfossil accumulation rates on phosphorus delivery can be tested, as both parameters ate subject to the same error. Pollen zonation also permits inter-core comparison of microfossil concentrations and accumulations at the shallow and deep stations. Changing microfossil concentrations (Fig. 21) in the sediment are discussed starting with the basal, early Holocene levels and working upward in the core. Botryococcus , likely an important primary producer in modern Lake Quexil, increases steadily in abundance per cm^ from the bottommost sample through 780 cm. Thereafter, concentrations in the sediment fluctuate a bit, reaching a peak level (1.64 x 10^* cm"-^) at 680 cm. While Botryococcus increases its concentration in the sediment, desmid abundance declines. Desmids are nearly absent by 800 cm, but show a resurgence at 760 cm, a level at which Botryococcus concentration drops, suggesting perhaps that these algal types were replacing each other in the early Holocene as the principal primary producers in the phytoplankton. Diatoms were encountered in low concentrations and only in the bottom two core levels. Pediastrum was identified at only four levels in the core and displays low

PAGE 143

134 concentrations in those samples. Like Botryococcus , Peoiastrum concentrations in the sediment are generally inversely relatea to desmid abundance, but the Chlorococcales drop out above 680 cm. Inferences about changing trophic state auring the early holocene history of the lake are tentative due to the lack of knowledge concerning the ecological requirements ot these algal types in tropical situations. If the presence of Pediastrum cf . duplex reflects more eutrophic conaitions in the lake, as it does for instance in Minnesota lakes (Crisman 1978b), the parallel rise in Botryococcus might suggest that it too is indicative of higher productivity . This is contraaicted by the importance of Botryococcus in modern Lake CiUexil where measureo productivity is low. however, the contemporary assessment ot trophic state was based on only a single light-dark bottle experiment. Though some species of Staurastrum are characteiistically touna in eutrophic systems, the majority of species are encountered in the plankton of oligotrophic lakes (Hutchinson 1967), ano the aesmio decline moving upward through the bottom 2 meters of the core perhaps reflects increasing nutrient supply and lacustrine productivity. That conditions changed is evident not only in the shifting phytoplankton species composition of the mud, but in the gross stratigraphy of the sediments. Laminations indicative of meromixis show up below 800 cm in the core and persist until about the 590-cm level when the aeposits become increasingly inorganic. The onset of meromixis might argue against increasing productivity, as nutrients trapped below the chemocline would not have been recirculated into the photic zone.

PAGE 144

135 Above 680 cm, Botryococcus is the only primary producer leaving a significant number of remains in the sediment, ahereafter, concentrations decline fairly steadily until 480 cm, interrupted only by small peaks at 600 cm and 540 cm. At 480 cm, the planktei neatly disappears in the inorganic sediments of the Early Classic zone. Fungal element concentrations fluctuate over the bottom 3 m of the core but display a general increasing trend until midway through the Late Preclassic zone when concentrations drop precipitously between 600 cm and 580 cm. Concentrations increase slightly at 560 cm and rise again at 540 cm in a similar manner to Botryococcus , ana then decline steadily to 480 cm, paralleling the phytoplankter . Sponge spicules, like diatoms, are found in great abunoance in the bottom two levels of the core. However, a relatively high concentration is seen at 7^0 cm, following the aisappearance ot oiatoms from the record. Above this level, spicule concentrations are low, fluctuating until 600 cm, when numbers in the sediment fall to a value two orders of magnitude lower than the 900-cm peak concentration. Rather than reflecting high production rates, high concenttationb ot siliceous remains in the basal levels of the core might be inoicative of low pH and optimal preservation conaitions in tne organic muo. Falling levels of siliceous remains are perhaps explained if the desmid decline does indicate increasing lake trophic state. Greater utilization of dissolved CO2 would have raisea the pH in the water column, thereby contributing to the dissolution of siliceous remains prior to their deposition on the lake bottom. Vvith a transition to

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136 more inorganic sediments at 590 cm, low concentrations of sponge spicules were maintaineu for nearly 3 n. above this level, with only a slight rise in abundance seen at 5fc0 cm. ' The pattern of oeclining concentration associateo with increasing inorganic content of the sediment is seen for several microfossil types. While chitin fragment concentrations fluctuate consioeraLly from 900 cm up to 600 cm, their mean abundance per cm^^ in the organic, bottom 3 . of the core is more than twice as great as the mean calculated for the succeeding, overlying 2.6 m. Likewise, Botrvococcus , fungal elements and sponge spicules display low concentrations in the more than two and a half meters of highl, inorganic sediment from 590 cm in the core up to 325 cm depth. About midway into the palynologically defined Late and Postclassic .one, Botrvococcus , fungal elements and chitin fragments show a peak at 320 cm associated with higher organic content of the sediments. All three microfossil types show a slight decline at 300 cm, a resurgence at 280 cm, and thereafter a drop in concentration to very low levels .y 240 cm. The bimodal peaks (320 cm and 280 cm) occur during the granulometrically oefinea terminal Classic pe.xoo. V,ith the return of more organic sediments, desmids reappear with a small peak at 300 cm. sponge spicules too were more numerous in the organic sediments, displaying higher concentrations at 300 cm and 280 cm. bponge spicules and desmids were absent from samples collecteo at 240 cm and 220 cm. With the Maya abandonment of the drainage and a return to organic sedimentation at about 210 cm, Botrvococcus, oesmio, fungal element.

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137 chitin fragment, and sponge spicule concentrations are all seen to rise between 220 cm and 200 cm in the core. Sponge spicule and desmia concentrations remain low and fluctuate in the postdisturbance section of the core while Botryococcus , fungal elements, and chitin fragments display concentrations more indicative of recovery to predisturbance conditions. Comparison of microfossil concentrations as expressed by remains 'cm'^ wet sediment, between pre-Kaya anci post-Maya levels is confounded by more compaction and greater dry weight per unit volume down core. Correction tor differential water content can be achievea by expressing microfossil concentrations as numbers pet gm dry weight. Presented in this manner, abundances are seen to have nearly returneu to predisturbance levels. The mean concentration of botryococcus in the upper (120-200 cm) section of the core is 219 x 10^ remains* gm"'^ dry sediment, approaching the value computed tor the basal organic portions (600-900 cm) of the core (242 x 10^ remains •gm"-'dry sediment). Ostracods are found in small numbers and at only a tew levels in the bottom 3 m of the core, but display a bit of a peak at 600 cm, in the uppermost organic mud lying just below the thick clay-rich 2one. Following the transition to inorganic sediments, ostracods show a small rise at 540 cm only to drop out until 320 cm, where theit concentrations rise coincident with the increase seen for many other microfossil types. Encountered at 320-280 cm, ostracod remains disappeared once again at 260 cm only to increase in abundance when more organic sedimentation commenced following the haya abanaonment ot the watershed.

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13b Bosminids, unlike the microfossil types already discussed, are rare below the transition zone trom organic to inorganic seuiment at 590 cm, though many tallied fragments from the basal 3 m appeared to be bosminid mucrones. Intact carapaces and heaashields of what is likely Eubosmina tubicen increase in concentration during the Late Preclassic. It is perhaps noteworthy that bosndnics became an important component of the zooplankton community in Lake guexil at about the same time that Bosmina rose in importance in Lake Valencia, Venezuela (Bradbury et al. 1981). About 10^ carapaces are found in each cm^ of wet sediment throughout the inorganic 2,one of the core, though higher concentrations were detected at 540 cm and 440 cm. Abundance per cm-^ is maximal at 320 cm and stays cathet hiv,h until 260 cm, rising once again in the post-haya segment of the core. Bosminid headshields generally follow the trend seen for carapaces anc might have tracked the carapace concentrations more closely if the headshield abundances were not reliant on small sample sizes. The graphs for chydoria remains are based on a small number of enumerated carapaces and headshields. Ihe presence ot remains throughout the bottom 6 m of the core is spotty, but as for nearly all other .microfossil types, concentrations are high from 320 cm to 2&L) cm in the core, dropping in the inorganic levels above 260 cm, and showing a general increase again in the post-Maya sediments. Chydorid carapaces and headshields reached peak abundance in the sediment at 140 cm. Focusing on bosminid carapace and headshieiu concentrations throughout the Quexil H core, it is clear that posterior portions of

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i3S the animals accumulated at a greater rate than anterior exuviae. Ihere are 20 levels in the core in which both carapaces and heaoshields wete found. At each of these levels the whole carapace concentration was divided by. the headshield concentration, and the mean ratio calculatea for all 20 levels was 4.9 carapaces per headshield. This gives a minimal estimate of the differential oegree to.whicn the boay parts were subject to accumulation in deep water, as nine sampled levels contained carapaces, but no heaashields, while only the bottom-most (900 cm) sample displayed the reverse situation. For the six levels containing both anterior and posterior portions of chyaorios, the mean ratio was three carapaces per headshield. Five levels haa carapaces but no headshields, while only three levels possessed heaashields only. Several processes might account for the higher relative concentrations in the mud of posterior claooceran remains as comparea to anterior portions. Exuviae are evidently transported long distances before final. deposition on the lake bottom, and presumably. the chydorio remains found in the deep-water sediments originated in distant, littoral areas. In a conical basin like wuexil, there is aitteLential deposition of sediment over the basin bottom, with sediments preferentially laid down in deep trenches. This occurs because there is a greater amount of water and hence more suspended material above deep spots, and because particles that settle in shallow areas are resuspended and carried into deep water. Vvhen remains are focused into deep water, a winnowing process may be responsible for the preferential deposition of carapaces. This is contrary to the sorting of eroaea

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i4U particles that reach the lake as alluvium or colluvium, that ultiniately results in smaller particles being depositea at the lake center. It anterior and posterior portions of Eubosmina obey stokes* Law, as Vallentyne and Swabey (1955) suggest Bosmina longirostris parts do, intact shells should be less prone to resuspension than smaller fragments and headshields. But such an assumption ignores the consideration of the hydrodynamics of the differentially shapea anterior and posterior boay parts. Carapaces may simply preserve better than headshields, and even it deposited in similar numbers at the deep-water coring site, fragility of the anterior sections may have relegated them to the chitin fragments category. While Vallentyne and Swabey (1955) argue that shells are more easily broken into unrecognizable fragments tiiai. headshields, antennules are easily lost resulting in a low proportion of complete anterior to posterior remains. Bosminid remains outnumber chydorid remains in the Quexil H core. In eight levels between 120 cm and 320 cm, the mean ratio of carapaces was 6.3 bosminids per chydorid, and three levels contained only bosminid remains. This probably reflects the great aistance of tlie deep-water coring site from the littoral habitat preferred by chydorids and perhaps the overall high ratio of planktonic to littoral habitat in the lake. Interpretation of the chitin fragment category is oifticult as all pieces were enumerated, regardless of size. While the bottom 3 m contain twice as many fragments per cm^ as the succeecing 2.6 m, this

PAGE 150

141 does not necessarily imply that half as many whole animals are represented in each cm^ of the overlying inorganic mud. No effort was made to assess how many fragments constitute an individual. The decline in chitin fragments associated with the appearance ot whole bosminid parts at 600 cm is somewhat anomalous as postdepositional destruction (break-up) of remains might be expected to be more severe in the clay-rich sediments above 590 cm. If a large proportion of the fragments were bosminid pieces, whole carapace ana fragment concentrations should probably rise together in the inorganic section of the core. That chitin fragment concentrations decline may be explained by the dilution effect of a high inorganic sedimentation rate. The concurrent rise in bosminid aensity probably implies that their production rates were increasing. While many of the fragments from the deepest section of the core appeared to be mucrones of bosminids, it is conceivable that they are not. They may be parts of cladocerans whose shells are poorly preserved. After mechanical breakage, these fragments may have been protected from further chemical destruction by deposition m deep water under anoxic conditions maintained by persistent meromixis. This would support the contention that bosminids may have only become common in the Quexil plankton about 2000 years ago. Microfossil Accumulation Rates and Phosphorus Loading Phosphorus and microfossil accumulations are now evaluated on a zone-to-zone basis to explore the dependency of microfossil production

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142 rates on the nutrient supply {Fig. 22). Even if dates employed for calculations are wrong, the error affects each parameter equally ana similar zone-to-zone changes for two variables might at least suggest that delivery rates to the sediment are correlated. Botryococcus was the most common alga found in the Quexil H core, and as remains were encountered over the length of the section, changing accumulation rates that might be indicative of shifting primary productivity were compared to phosphorus accumulation rates. Phosphorus delivery increased from pre-Maya times through the Late Preclassic, and the rise was tracked fairly well by Botryococcus accumulations in the sediment. Between the Late preclassic ana Early Classic, phosphorus accumulation rate nearly doubled, but Botryococcus input to the sediments fell to about one-third the Late Preclassic level. When Late and Postclassic phosphorus input dropped to 45% of the maximal Early classic rate, botryococcus accumulation declined also, but only to 77% of the Early Classic level. Late and Postclassic phosphorus loading was nearly equivalent to delivery rates computed for the Late Preclassic, but Botryococcus accumulation haa dropped to about one-fourth the Late Preclassic rate. With the Maya depopulation of the catchment, phosphorus accumulation changed little, but Botryococcus production rose more than three-fola. Zonal changes in fungal element accumulations look similar to shifts in Botryococcus , with fungal remains tracking the phosphorus inputs until the Late Preclassic, only to have their accumulation rates drop substantially in the succeeding Early Classic ano Late and

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u

PAGE 153

144 O O X UJ D O (IU3) mdOQ I I I 1 1 I L < 5 111 o lU 00 > m S z S ^ o < < o 2 Ul ui (da) eiBQ

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145 Postclassic zones. The return to more organic post-Maya sedimentation saw an increase in fungal element accumulation, the rate approaching that calculated for the maximal Late Preclassic. Maximal sponge spicule accumulation occurred during pre-Maya times and was associated with very low phosphorus accumulation. In the succeeding Middle and Early Preclassic section of the core, spicule deposition dropped substantially, though phosphorus accumulation increased slightly. As for Botryococcus and fungal elements, the Late Preclassic was a periou of high spicule accumulation. Spicules were supplied to the sediments at slow rates from about 250 to 1600 A.D., but show a resurgence associated with the Maya depopulation of the basin. Zone-to-zone changes in desmid accumulations look much the same as sponge spicule deposition rates, with the exception that desmids fail to display a high Late Preclassic value. Chitin fragments accumulateo at very low rates until the Late Preclassic. The relatively high level of deposition achieved in the Late Preclassic was sustainec over the next 13 centuries and then displayed a four-fold increase in the post-Maya sediments. The Late Preclassic was a perioo of high accumulation rate for animals, and except for chydorid carapaces, accumulation rates for all entomostracan remains were greater in the Late Preclassic than in the preceding underlying zone. Ostracods, like many other fossil types showed reduced delivery to the sediments in the succeeoing Early classic ana Late and Postclassic zones, but post-Maya inputs were an order of magnitude greater than those calculated for any preceding period.

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14b Bosminid parts were accumulating at their highest rates in the post-Maya section of the core, and are distinguished from other microfossil types in exhibiting a relatively high Early classic deposition rate. Intact half carapaces of chydorids were absent in the Late Preclassic sediments, while headshields dropped out in the Early Classic. Anterior and posterior portions of these littoral cladocerans were delivered to the sediment at maximal rates in the post-Maya period. High, computed post-Maya microfossil accumulations are undoubtedly in excess of the true postdisturbance values. Additionally, post-Maya inputs are exaggerated with respect to accumulation rates calculated for the earlier time periods. In the post-Maya section, microfossil concentration was assessed in the 120-200 cm levels only, had the top meter been analyzed, the loosely packed, water -rich upper levels would likely have contained fewer remains per cm^ wet sediment. Thus, the mean number of remains per cm^, that was multiplieo by the gross sedimentation rate to compute microfossil accumulation rate, was too large. While this error makes comparison of post-Maya accumulation rates with previous period rates somewhat dubious, computed phosphorus accumulation in the post-aisturbance section of the core is. presumably affected similarly, and zone-to-zone correlation of nutrient and microfossil delivery throughout the core is valid. If zone-to-zone changes in accumulation rates for total phosphorus and microfossils are inversely related, deposition rates for microfossils are likely independent of the supply rate for the nutrient. Even if total phosphorus and microfossil accumulation rates

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147 increase and decrease together on a zohe-to-zone basis, correlation is demonstrated only if the magnitude ot change from one zone to the next is similar for both variables. Botryococcus , fungal elements and chitin fragments generally track phosphorus accumulations from the pre-Maya period through the Late Preclassic zone. But the Early Classic accumulation rates for these microfossil types are relatively low despite the dangerously high phosphorus loading ratie. Only the Cladocera demonstrate a positive response to enhanced Early classic phosphorus input. Modern microfossil accumulation rates are all at least twice as high and some many times higher than Late and Postclassic rates, while phosphorus delivery increased only 8% over the value for the preceding period. The association of high phosphorus delivery with low microfossil inputs to the sediment during the Early classic is somewhat anomalous if productivity is assumed to have been phosphor us-limitea. It is possible that other factors may have restricted photosynthesis during this period, if siltation were sufficiently severe, high phosphorus loading rates may have had little effect on primary productivity. Production may have aeclined as a consequence of reduced plantavailable phosphorus delivery. Vvhile the total phosphorus accumulation was maximal in the Early Classic, a small proportion of the delivered element may have been usable for phytoplankton growth. Finally, the Early classic sediments are highly inorganic (!>2% inorganic content), and probably constitute a poor preservation medium for sedimented microfossil remains. If diageriesis of deposited microfossils were

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14& particularly severe in the inorganic section of the core, calculateo accumulation rates for the remains are poor estimators of the original organismal production rates. The transition from the Late and Postclassic to the post-haya period saw a great increase in microfossil accumulation and only a small change in phosphorus loading, suggesting that there was a change in the delivery rate of available phosphorus and/or better preservation conditions. The increasingly rapid deposition rate of organic matter as compared to inorganic matter, resulted in a higher organic proportion in the proximate composition of the sediment, thereby creating better conditions for microfossil preservation, increasing calculated microfossil accumulations would thus seem to result from a positive feedback system. As more fossils are deposited on the lake bottom, the organic content of the sediment matrix increases, resulting in better preservation of remains and high counts. Zone-to-zone changes in the average accumulation rates for phosphorus and microfossils may provide some insight into the reliance of microflora ana microtauna production on the nutrient supply. However, because average concentrations and mean sedimentation rates are employed in the calculation of the zonal accumulation rates, the true relationship between the parameters can be obscured. A level-by-level comparison of the two variables can evaluate better the reliance of microfossil production rates on the rate of phosphorus supply. The dependency of microfossil accumulation rates on the total phosphorus input can be tested by calculating the ratio of microfossil

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149 numbers to phosphorus concentration at every level over the length of the Quexil H core. Both variables must be expressed in the same units, as amount per gram dry weight or as amount per cm-^ wet sediment. Instantaneous gross sedimentation rates are the same at a given level whether laicrofossils or chemistries are being considered. Thus, dilution of one variable by clays, for instance, dilutes the second variable equally. Therefore, the ratio between the accumulation rates for any two variables at a given level is the same as the ratio between their concentrations. If the accumulation rate of a microfossil type is dependent on and linearly related to the total phosphorus supply in a positive manner, the, ratio of microfossil numbers to phosphorus concentration should remain relatively constant over the length of the section. Large variations in the computed ratios suggest that microfossil accumulation rates are independent of or inversely related to the rate of total phosphorus supply. Botryococcus is the most prevalent primary producer whose remains are abundant in the Quexil H sediments. Botryococcus concentrations, expressed as numbers per cm-^ wet sediment, were divided by the corresponding total phosphorus concentrations, expressed as ug P per cm^ wet sediment. The calculation was run on 38 levels in the core, and the resultant ratios display a wide range, varying from 6.4 to 1060. The mean ratio is 318, and the standard aeviation for the computed values is 2S4. High variability in the ratios, ranging over more than two orders of magnitude implies that Botryococcus

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IblJ accumulation in the sediments is not reliant on the total phosphorus supply. Lack of Botryococcus dependence on the total phosphorus supply was suspected at the outset when concentrations for the two parameters were assessed over the length ot the core. Total phosphorus and Botryococcus concentrations fluctuate to different degrees throughout the section, suggesting that inputs to the seoiment of the two variables are independent or at least not linearly related in a positive way. Phosphorus concentration averages 70.9 ug p'cm"^ wet sediment over the length of the core, with a standard deviation of 19.0. Botryococcus concentrations in the core range over two orders ot magnitude, displaying a mean value of 24.1 x 10^ remains-cm"-^ wet sediment and a standard deviation of 29. S x 10^. When the level-by-level Botryococcus -total phosphorus ratios were computed for the Quexil h core, a trend became evident. Higher ratios were encountered in the more organic sediments. Means and standard deviations of the ratios were computed for three major aones in the core, distinguished simply by their different organic matter content. Fourteen samples collected from the organic horizons between tOO cm and 900 cm yielded a mean ratio of 516 ±_ 294. Post-Maya organic sediments above 210 cm gave a similar value of 481 ^^ 201. In the preoominantly inorganic mud between 220 cm and 580 cm, 19 samples produced a mean ratio of only 129 +^ 173. When the ratios in the more organic levels between 280 cm and 320 cm were deleted, the remaining 16 levels had a mean of only 7 2 ±_ 95. Lower numbers of algae relative to phosphorus in

PAGE 160

151 the inorganic disturbance-zone sediments might suggest diagenetic loss of cells in this region of the core. Alternatively, available phosphorus in the clay-rich zones may constitute a smaller proportion of the total phosphorus supply. The data suggest that Quexil's trophic state, as inferred from Botryococcus concentrations, was not dependent on the total phosphorus supply. Such a conclusion must be qualified. Botryococcus is an important component of the modern phytoplankton, but may have been replaced in the lake during the past, by other, poorly preserved algae. Even the claim that Botryococcus production was not phosphorus limited is stated tentatively. Vvhile some other nutrient may have limited the chlorophyte production rate, it is possible that total phosphorus levels measured in the seaiment provide little insight into the amount of plant-available phosphorus delivered to the lake. If the proportion of available nutrient as a traction of the total remainea the same through time, conclusions about the phosphorus limitation of Botryococcus might be valic. however, there is little reason to believe that plant-available phosphorus constituted a constant proportion of the total phosphorus reaching the lake, especially following forest clearance and subsequent, prolonged soil erosion. Even if Botryococcus production rates were dependent on the total phosphorus rate of supply, postdepositional destruction of sedimented remains may have obscured the relationship.

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Ib2 Carbon-Nitrogen Ratios in Quexil Core H Carbon and nitrogen values may revealinformation about past levels of lacustrine productivity when their ratio is considered over the length of the core. In the organic-rich segment of the core below 590 cm, C:N ratios are high (18-22) and are adjusted downward only minimally by subtraction of inorganic carbon, which makes up a small fraction of the total carbon pool in this section of the core (Fig. 15). Low productivity, slow sedimentaton rates, and conseciUent prolonged diagenesis of surface muds may have allowed for relatively greater removal of nitrogen, thereby producing the high C:N ratio. A similar explanation has been proposed to account for high C:N ratios in surface sediments of Florida's oligotrophic lakes (Flannery et al. 1982). Thin laminations throughout the basal 3m of the Quexil H core support the claim that sedimentation was slow during the early Holocene. While the presence of undisturbed laminae implies hypolimnetic oxygen depletion and less rigorous chemically oxiaiiing conditions, loss of nitrogen from the organic matter may have occurred rapidly when the material was suspended in the warm waters of the photic zone. Appreciable inputs of allochthonous material with a high C:N ratio (Hutchinson 1957) might be responsible for the measured elemental relationship. This contention is supported by the abundance of terrestrial leaf, twig, and seed remains in the basal part of the core. With the conunencement of inorganic sedimentation came a drop in the C:N ratio. If only the organic carbon fraction had been

PAGE 162

153 considered, ratios would be even lower, as inorganic carbon constitutes a significant amount o£ total carbon in the clay-rich zones. Several processes may have reduced the C:N ratios throughout the inorganic, disturbance sediments. Following deforestation of the catchment and depletion of the terrestrial organic matter reservoir, autochthonous organic carbon deposition may have increased relative to allochthonous organic carbon input to the sediments. Additionally, rapia sedimentation rate during the perioa of inorganic deposition may have precluded diagehetic nitrogen loss. As the episode of inorganic sedimentation was associated with high levels of human population density, export of human effluent rich in nitrogen. may have reduced the C:N ratio, however, the terminal Preclassic-Early Classic population hiatus does not show up unless it is the C:N peak at 540 cm. Finally, the rise in abundance of . bosminia remains may in part be responsible for the downward shift in C:N ratio. Chitin is a polymer of N-acetylglucosamine (Barnes and barnes 1978), and higher bosminia concentrations relative to algal remains would tend to depress the C:N ratio in the inorganic portion of the core, assuming that the stability of nitrogen containing compounds in the animal remains is greater than that occurring in plants. With the return of organic sedimentation in the post-Maya period, C:N ratio rose to an average value of 13.8. Though perhaps indicating some terrestrial contribution, the ratio is not much greater than the 12:1 ratio expected from the decomposition of lake plankton (Wetzel 1S75).

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154 Comparing Microfossil Accumulation Rates at the Two Quexil Coring Sites Micro£ossil accumulation rates at the shallow and deep-water coring sites are now compared on a zonal basis revealing differences in sedimentation at the two stations. Accumulation of bosminid and chydorid carapaces proceeded at similar rates in shallow water. During the Late and Postclassic, bosminids accumulated only z.3S times faster than chydorids, and in the modern sediments bosminids and chydcrids accumulated in a ratio of 1.19:1. In deep water, the Late and Postclassic bosminid:chydorid ratio was 9.6:1 and dropped to only 6.11:1 in the post-haya seoiments. The lower bosminid:chydorid ratio in shallow water sediments reflects the proximity of the coring site to littoral habitat preferred by chydorids. conversely, the cieep coring station is surrounded by planktohic habitat, while littoral zones are a distance away. Deep water accumulation rates for each fossil type were divided by the corresponding shallow-water zonal accumulation rates to assess the magnitude of differential deposition at the two localities (Table 4). Despite the position of the Quexil H coring site with respect to the littoral areas, resuspension ana focusing of chydorid remains into deep water resulted in higher chydorid accumulations there than in shallow water. Late and Postclassic and post-Maya aeep-water chydoria accumulation proceeded at rates 4.10 and 3.35 times faster than shallow-water accumulation. At the same time, differential deposition of bosminid carapaces was more pronounced, and deep-water accumulation

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Ibb Table 4. A comparison of microfossil accumulation rates in Quexil shallowand deep-water localities. C^uexil H 2,onal microfossil accumulation rates were divided by corresponding Quexil shallowcore accumulation rates, h indicates the fossil was found only in deep-water sediments of the specified zone. A dash indicates the fossil was absent from the zone of both cores. Archaeological Fungal Chitin Period Ostracods Bosmina chydorids Botryococcus Elements Fragments

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Ib6 rates were 16.44 and 17.12 times the corresponding shallow-core rates in the two recent zones. Valid comparison of post-Maya accumulation rates in the two cores is doubtful, as calculated modern accumulation rates for Quexil H are excessively high because water-rich, and presumably microfossil-poor , sediments in the top meter of the core were not analyzed. Botryococcus accumulated more quickly in deep water, except during the combined Early and Middle Preclassic period when gross sedimentation at the shallow site was greater than that measured for the deep site. Higher sedimentation rate in shallow water occurred during the time when laminations were forming in deep-water sediments, implying meromictic lake conditions. Productivity in the deep central basin may have been restricted if nutrient regeneration from deep waters was impeded by the chemocline. Productivity may not have declined in the shallow areas to the south and west of the t^uexil islands, it is conceivable that this morphometrically distinct region of the lake was not affected by the meromixis detected in the central basin. Resuspension and focusing of remains from shallow to deep water may have been prevented by the presence of a chemically inducea density gradient, and fossils would have been preferentially deposited at the monimolimnion boundary. Fungal elements accumulated at much higher rates in aeep water, particularly during Early Classic and Late and Postclassic times. Again, comparison of post-Maya accumulation rates is invalia as moaern deep-water accumulations are excessively high, ivo processes probably

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157 contributed to greater fungal element accumulation in deep water.. The small paricles are easily resuspended from the sediment surface and redeposited at the deep site. While focusing of fungal remains may account for some of the differential deposition, order of magnitude differences at the two sites require further explanation. Silicates, delivered as particles of primarily clay and silt size, are also preferentially deposited in deep water. During early Classic and Late and Postclassic times, silicates were deposited in deep water at rates 5.6 and 5.S times faster than shallow water rates. The biological remains show an even greater tendency for deposition in deep water and fragmentation of hyphal strands in the deep-water inorganic sediments probably contributed to the very high counts. Ostracod remains only became common in the Quexil sediments curing Late Preclassic times. Individuals, as measured by mandibles, were deposited in deep water 4.95 times faster than whole organisms were sedimented in shallow water, as determined by valve enumeration. But the ratio of deep-water to shallow-water accumulation rates droppea below unity in the Early classic (0.67) and tell even lower (0.25) in the subsequent Late and Postclassic period, indicating higher shallowwater accumulation rates for about 13 centuries. It is possible that the low oxygen content of deep, benthic waters may have restricted ostracods to shallower areas. Additionally, highly inorganic deepwater sediments may have provided a poor habitat for benthic species of seed shrimp. Thus, deep-water production rates of ostracods may have '• been reduced with the onset of inorganic sedimentation.

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156 Even if ostracod production in deep-water areas declined, focusing of remains into deep trenches might tend to raise computed deep-water accumulation rates, it is likely that many remains deposited in deep water were lost through mechanical break-up and dissolution. The extreme rarity of "valves in deep water. suggests that carbonates there are readily solubilized, probably under conditions of high CO2 concentration and low ph. Ostracod shells are only present in deepwater sediments of high organic matter content. Under such conditions, physical destruction is less likely/ and the presence of organic matter may reflect less aerobic and anaerobic loss of carbon and hence less CO2. Chitin fragments were preferentially accumulating in shallow water during the Early Classic and Late and Postclassic. Large numbers of ostracod shell fragments were encountered in the shallow-water sediments, while deep-water remains assigned to the fragment category were dominated by pieces of cladocerans. High carbonate content of the shallow-water Late and Postclassic sediments might be invoked to account for the excellent preservation of ostracods in that zone, especially if the presence of aetrital carbonates buffers conditions at the sediment surface. As the shallowwater site shows high carbonate content into the post -Kaya period, much higher ostracod accumulation in deep water is unexplained. As for other remains, modern deep-water ostracod accumulations are too high, because the flocculent sediments above 120 cm were not analyzed. Even if ostracod remains were absent in the top meter of the core, the computed deep-water accumulation rate would exceed the shallow-water

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Ib5> accumulation rate by more than an order of magnitude. Relatively greater deep-water ostracod accumulation is associated with the return to organic sedimentation and probably resulted from the improvement of the deep-water benthic habitat, resuspension and focusing of remains, and enhanced preservation at the deep site.

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TESTING THE PHOSPHORUS LOADING MODEL DEVELOPED AT YAXHA-SACNAB Coring in Lakes Saipeteriy hacanche, and ^uexil, lS>bC . coring operations at Lakes Salpeten, Macanche, and Quexil were undertaken curing the spring of 1980. Long ceres tromaeep water were sought in order to clarify the picture of regional haya disturbance in the Peten and to obtain sediments of pre-holocene age that couiu verity the existence of arid Pleistocene climates in the Central American lowlands. Proxy data documenting such Pleistocene conaitions were unknown between Florida (Watts 1&75, Watts and Stuiver 196U) and northern South America (Wijmstra ana van oer Hammen Ibbb, braobury et al. 1981). Deep trenches of the Central Peten lakes Were suspected of being probable repositories of Pleistocene-age sediments, as the depressions may have held water even during perioas of lower sea levels and water tables. The belief that Pleistocene lake deposits could be retrieved from the Guatemalan lowland basins prompted the 1S77 and 1978 Kullenberg coring attempts in Lakes Macanche ana guexil. In 1977, a 5.4-m core (Mac D) was obtained in deep water at Lake Macanche, but the section desiccated and shrank to 4.2 m prior to extrusion. Bottoming in organic-rich mud, the core just managed to penetrate the thick clay lens deposited as a consequence of Maya-induceo erosion. Further attempts to obtain even older material from Macanche were thwarted when ibO

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lol the core lift motor was stolen, bringing the 1977 fiela season to a premature close. The following year, three, long, deep-water sections were raisea from the central basin of Lake uuexil (Fig. 13), but all the cores evidently bottomed in early Holocene deposits. Even wnen loadeo with 220 kg of lead drive weight, the gravity corer was slowed considerably on passage through the thick anthropogenic clai aquiclude anu couio not penetrate beyond the early Holocene organic deposits below. The Kullenberg corer proved to be incapable ot raising Pleistocene sediments and consequently, a professional drilling company was contracted to obtain sections in 1980. Daho Pozos ot Guatemala City conducted coring operations in Lakes Quexil, Salpeten, and Macanche between 22 April and 22 May 1980. The arilling equipment was boltea to a 6.1 m X 9.1 m raft, and samples were taken with a 45.7 cm split-spoon sampler, bearing a 5.08 cm cutting edge or nose cone. The split spoon was lined with plastic pipe and as samples were brought on deck, the tubes were labeled, stoppered, and wrappea in heavy plastic to prevent drying of the sediments. Nose cone samples were packaged separately in Whirl-pak bags. Iron casing pipe was usea to guarantee that successive core sections came from the same hole, and the casing was washea out prior to each stepwise lowering. Gore samples were stored in wooq boxes and returned to the Florida State Museum in September 1980 where they were refrigerated at 4°c before and after extrusion. At Salpeten (area = 2.62b km^, Zj^^^ = 32 m, z = 7. fa m; Deevey et al. 1980a), a deep-water core (Sal 80-1) was obtained in 26.1 m of water (Fig. 23) and penetrated to 15.1 m below the mua-water

PAGE 171

lt}2 interface. Flocculent, organic surface sediments were not retained in the split-spoon sampler, and the uppermost, clay-rich niuc retrieved was thought to lie about 1.6 m below the sediment surface. However, a 1.67-m mud-water interface core taken several meters from the Sal 80-1 site contained a higher water and organic matter content at 1.6 m than the topmost sediments of the Sal 80-1 core. This indicates a probable small gap in the section, but the exact size of the missing section remains undetermined. This difficulty is unresolved as a result of the inability to measure accurately the depth of the loosely packed surface mud. Continuing the work at Salpeten, a shallow-water section, designated Sal 80-2, was taken in 6.4 m of water (Fig. 23) to compare deepand shallow-water seaimentation in the saline lake. The top 2 m of the core were obtained with a Livingstone piston-corer (Deevey 1965) and subsequent sections were collected with the split-spoon sampler, thus raising a complete 5.39 m profile. The Sal 80-1 core was sampled at 52 levels over its total length and Sal 80-2 was sampled at 28 levels. At each sampling point in the cores, two 1 cm-^ volumetric plugs of sediment were removed and weighed to determine wet weight per unit volume. These samples were next dried at 110 °C to evaluate percent dry weight, and then burnea at BBCC in a Thermolyne Type 1500 furnace to assess organic matter content by loss on ignition. A second set of samples was driea at llCC and ground to a fine powder with a mortar and pestle. Weighea aliquots of the pulverized sediment were usea for total carbon analyses

PAGE 172

a. CO S

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164 Zo 9 O cd o c ^' o o o a o 9 CO ol E E »a u> « TlO I I 09 O CM E E (0 «o CM O 2 a> o» o o OO CO col o o a a a "S CO CO

PAGE 174

165 that were run in a LEGO induction furnace. Another portion of the ground sediment was weighed and digested in 15 ml of a 2:1 nitric-perchloric acid mixture. The digested samples were filtered ana the filtrate was brought to a volume of 50 ml. Sulfur determinations were run on the digestate turbidimetrically according to Standard Methods (APhA 1981). Cation analyses were aone Ly atomic absorption and total phosphorus was run on a Technicon Autoanalyzer at the University of Florida Institute of Food ana Agricultural Sciences soils Laboratory, chemical concentrations in the mud were then figured as amounts per gram of dry sediment (Figs. 25 and 2t>). At Lake Macanche (area = 2.166 km^, ^n^iax = 57.5 m, z = 25.1 m; Deevey et al. 1980a), more than 10 m of sediment was retrievea in 55.8 m of water. Coring began about 0.61 m below the mud surface ana terminated 10.77 m below the mud-water interface. The seaiment profile, designated Mac 80-1, was obtained in deep water soutnwest of the island in the basin and south of the 1977, Mac D coring site (Fig. 24). Sampling and processing of the 39 samples taken over the length of the core were similar to the treatment of salpeten samples, with minor exceptions. Cation determinations on aigestate were run by atomic absorption at the University of Florida Department of Environmental Engineering and total phosphorus analyses were run manually on a Coleman Model 14 Spectrophotometer, after blue color development by the ascorbic acid-ammonium molybdate technique. As at Salpeten, chemical concentrations were figured as amounts per gram of dry sediment (Fig. 27).

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167 E o 5 S " o o Q ' 9 "O O «< CO CB O >o o ev N o *d lo eo K O h> eo O X 9 9 £ JZ o o c c (B CO o o CO CO 2 2

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c

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169 *2 UJ 00 i £ < o CO o o o o o o o o ^ N m o o o o NCO o o o o o o o o o o o o O »CM CO ^ U) (uio) djoQ uj iiidaa

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171 (uio) 8JO0 uj MtdaQ

PAGE 181

a. CO

PAGE 182

173 (uio) ejoo uj M^dea

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174 Lake Quexil yielded two deep-water (29 m) profiles of differing length, core Que 80-2 comes from 4.b7-9.b5 m below the mua surface and the unextruded uppermost sediment from the profile contains a high clay content. This inorganic deposit is anthropogenic and is assigneo a Maya-period age by gross stratigraphic correlation with Quexil core H. At about 5 m depth, there is a transition to mote organic seaiments and this condition prevails until about 8.i> m depth in the profile where the deposits are again dominatea by inorganics that mark the Pleistocene-Holocene boundary. Core Que &0-1 began in organic. sediment 7.49 m under the mua surface and drilling endeu 12.19 m below this depth. Basal, sediments itpm the section were taken from 19.68 m below the mud-water interface, extending the Quexil E core sediment record bi more than 10 m. Core Que 80-1 has been analyzed mineralogically and the bottom 10 m are rich in calcite and gypsum, presumably deposited when lake levels were low during late Pleistocene times (Deevey et al., in press) . Lying above and in contact with the inorganic Pleistocene deposits of Que 80-1 are humified organic sediments, at some levels rich in leat and wood fragments. Small bits of wood were removed from a 7 cm portion of the core (8.94-9.01 m) and pooled as a sample for radiocarbon dating. The sample (SI-b257) was run by Robert stuckenrath at the Smithsonian Institution Radiation Biology Laboratory and produced a radiocarbon age of 10,7 50 + 460 B.P. Though the error on the determined age is large, the terrestrial wood date is free from the confounding problem of the hard-water-lake effect. Gross stratigraphic

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17b correlation of Que 80-1 with the 1978 CiUexil H section contirms the claim that a near-complete holocene profile was otitained L^ . the Kullenberg corer. Ihe 1980 Quexil cores await further chemical ana palynological examination. Sediment chemistry of the Macanche and Salpeten cotes Proximate composition of the Macanche and -Salpeten sediments was figured on a level-by-level basis. Carbonate content was assesseo by calculating the carbonate equivalents of magnesium and calcium ano summing the two chemical types. Iron was assumec to be present as Fe203 and organic matter content was obtainea directly by the loss on ignition procedure. Silicates, presumably present as alumino-silicates, were assumed to be the resioue toliowing subtraction of organic matter, CaCOj, MgC03, and Fe203 (Figs. 215-27). In computing the proximate composition of the Salpeten sediments, some error was introduced by assuming all calcium ano magnesium to be bound with carbonate. In the sulfur-rich inorganic sections of the cores, much of the calcium and magnesium is doubtless bound with sulfate. Thus, because silicates are figured by difference and carbonate has a lower molecular weight than sulfate, Si02 values are probably overestimated in the sulfurous levels of the cores. The computation of proximate composition .assumes that organic matter , CaC03, MgC03, Fe203, and SiU2 comprise 100% of the sediment. Most of the aluminum reported for the Salpeten cores represents a

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17fc fraction of the Si02 value, and is presumed to have Leen extracted, in part, from clays. Other chemical constituents of the mud probably amount to less than 1% of the sediment dry weight.. Sulfur is the exception, and in the basal, sulfur-rich levels, proximate make-up of the sediment is grossly miscalculated, as sulfur comprises more than 5% of the sediment by weight in several levels of both cores. Palynological zonation of core t^uexil h proved inerfective for refining the phosphorus loading model developed at Lakes Yaxha and Sacnab. Cores obtained at Lakes Macanche ana Salpeten dULing the 1980 field season have not yet been studied palynologically, but as these water sheas also experienced a Maya population hiatus in the Early Classic (Fig. 8), anticipated phosphorus loading figures based on palynological fine-zoning may be poor estimates of the true loaoing values. With sediment chemistry completed on shallowand deep-water cores from several lakes, an alternative, cruae test of the phosphorus loading model was formulated. Rather than testing the response of phosphorus inputs to incremental Maya population changes in a single basin (intensively), the total phosphorus load attributable to Maya disturbance can be assessed and compared to integrated Maya population curves in several basins (extensively). Lacking pollen data from the Salpeten and Macanche cores, alternative parameters were employed for zonation of the profiles from these lakes and for rezoning the Sacnab core, tiUexil h, and the t^uexil shallow-water section. At Sacnab and Quexil, Maya agro-engineering activities were shown to have caused a shift in the proximate

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177 composition of the sediment to an overwhelming domination by the inorganic components, ana abandonment of the catchments resultea in a resumption of more organic deposition. While the palynological record may represent a mix of regional and local vegetation changes, shifts in the chemical composition of the sediments indicate changing erosional processes withinthe drainage. Thus, the major inorganic-organic transition horizons are considered to be reliable basin-specific markers that identify the inception and termination of Maya occupation in the watersheds. In Quexil and Salpeteh, where the corer penetrateo beyond the organic, pre-Maya sediments, the calcite and gypsum-rich underlying deposit distinguishes a aated, climatically-induced change in sediment composition that marks the Pleistocene-Holocene bounoaty (Deevey et al., in press). With dates attached to three levels in the cores (Pleistocene-Holocene transition, initial Maya disturbance, Maya disappearance), and complete chemical profiles, pre-Maya, baseline chemical accumulation rates can be computea as can disturbance period chemical delivery rates. Using this type of dating procedure, several questions can be addressed. Export of inorganic matter from terrestrial areas is accelerateo by human disturbance, and the magnituoe of change over baseline rates can be evaluated. Delivery of phosphorus to the lakes presumably increased as a consequence of vegetation removal, ana the degree of change attributable to human perturbations can be measured. Annual per capita phosphorus export to Lakes iaxha anc sacnaL was estimated at about 0.5 kg (Deevey et al. ISlb). Together with

PAGE 187

17b archaeologically derived demographic histories from the watersheds, the chemical stratigraphy can be used to test this proposed figure. Finally, withinand between-lake comparisons of phosphorus accumulation rates permit an assessment or the influence that cote location and lake morphometry have on estimating the lake-wide phosphorus accumulation rate. Assessing the Maya Annual Per Capita Phosphorus output Zoning the cores Chemically To test the phosphorus loading model developed at Yaxha ana Sacnab, the procedure employed at the twin basins was essentially reversed. In the easternmost twin lakes, the effective riparian area was delimited and phosphorus outputs from theMaya populations auring any given archaeological period were calculateo, assuming' export from the watershed to have equalled the phosphorus input values derived from the study of the sediraent cores. On tnese assumptions, export was at a rate of 0.5 kg*capita~-^*yr~i. The new back-calculation procedure assumes export at this per capita rate and abandons the fine-zoning technique used at the twin lakes. The entire aisturbance-zone sequence is considered as a single unit. The rate at which phosphorus accumulated on the lake bottom as a consequence of disturbance was computed by calculating the disturbance-zone phosphorus accumulation rate and subtracting the pre-Maya baseline rate. This rate was multiplied times the span of

PAGE 188

lib Maya time and the lake area, to compute the total amount of phosphorus deposited on the basin floor as a result ot human disturbance. It was assumed that the disturbance phosphorus load reached the lake at a rate of 0.5 kg "capita"^ "yr"^, and the number of person-years necessary to generate the disturbance phosphorus load was computed. Next, the population density graph for a watershed was integrated, to provide a figure that represents the number of per son-years lived per km'' over the span of Maya time. The number of person-years necessary to generate the disturbance phosphorus load was then aiviaed Ly the number of person-years*km~2 lived throughout Maya time, ihis proceoute provides a value representing the area that must have been occupied throughout Maya time to account for the disturbance phosphorus input. If the estimated annual per capita phosphorus export figure (0.5 kg) is reasonable, the calculated effective riparian area should approximate the true source area for eroded soils, the region enclosed by nearest high ground. Zones in the cores were delimitea baseo on changes in the organic matter concentration of the sediment. Thus, changes in loss on ignition or calculated organic carbon figures were employed to distinguish horizons. The bottommost, Pleistocene-Holocene transition was assigned a date of about 10,000 B.P., or 8000 B.C., for calculating pre-Maya accumulation rates. As wooa from the basal portion ot the Quexil shallow-water core gave an age of b410 + IbO radiocarbon years (Ogden and Hart 1S77) and the climatically-induced sediment transition was dated at 10,750 + 460 radiocarbon years in core uue 80-1

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IfaG (Stuckenrath, pers. comm), the assigned age for the inception of the Holocene is not unreasonable. The age is consistent with the 10,bU0 B.P. estimates for the early Holocene lake level rise of Lake Valencia, Venezuela (Bradbury et al. 1981, Binfora 1982), ano with ^*C dates: for the inception of "Early Holocene moist periods" in tropical Africa (Butzer et al. 1972) and southern Australia (Bowler et al. 197b). The age of the Pleistocene-Holocene transition is perhaps slightly underestimated. Ihis has the effect of reducing by a small amount the number of years allowed for pre-Maya sedimentation, and thus causes a minor overestimation of pre-Maya chemical accumulation rates. Computed predisturbance chemical accumulation rates are based on a pre-Maya time span of 7000 years, so it post-Pleistocene organic seoimentation truly began as early as 11,000 B.F., the calculated predisturbance chemical accumulation rates would be too high by a factor of only 14%. As predisturbance chemical accumulation rates are generally small relative to delivery rates calculated for the Maya aisturbance 2,one, the chemical accumulation rate due solely to human impact (Waya zone rate-baseline rate) is changea little by adjustment of the Pleistocene-Holocene transition age. Initial Maya intrusion in the Peten watersheds is detectea in the cores by a reduction in sediment organic content (Figs. 14, 15, 25, 26, 27), and the horizon was assigned an age of 1000 B.C. Ihe olaest ceramic sherds encountered at Lakes Yaxha and Sacnab were relegated to the Ah Pam complex, while Amanece ceramics are the olaest artifacts encountered in the western watersheds (Rice and Rice 1981). As both

PAGE 190

181 the ceramic complexes are of Middle Preclassic age (1000 B.C. -250 ; B.C.), the inception of Maya settlement in the drainages was aatea at 1000 B.C. Earlier studies at Sacnab and Quexil (Deevey et al. 1979) pushed the Middle Preclassic boundary to 1500 B.C. to accommodate possible pioneer settlement in the catchments, but this test of the model hews to the archaeological record and uses the olaest,. generally accepted Middle Preclassic age. It is certainly possible that initial settlement in the basins postdated 1000 B.C. Nevertheless, assigning the earliest disturbance-zone sediments the maximum archaeologically supported age of 1000 B.C. allows the longest period of time for the accumulation of Maya-zone sediments. This results in the lowest possible calculated Maya-period chemical accumulation rates, and computed increases over baseline rates can be considered minimal, further reduction of the Maya-period chemical accumulation rates could be accomplished by using an even older date for the organic-inorganic transition. However, lacking archaeological evidence for earlier human activity in the drainages, the 1000 B.C. date provides the most conservative estimate of human impact consistent with other data. Maya abandonment of the Peten watersheds caused the resumption of organic sedimentation and this horizon was assigned a date of 1600 A.D., some 75 years after colonial contact ana nearly a century before the Spanish conquest of the Itza Indians in the Central Peten (Stuart and Stuart 1977). Thus, Maya occupation of the Peten watersheds is registered as a 2600-year inorganic interruption in the Holocene,

PAGE 191

182 lacustrine, organic sediment record. Post-Maya, deep-water sediment accumulations in the Peten lakes range trom a minimum ot rougly 80 cm (Macanche) to 210 cm (Quexil), and it is thought to be unlikely that the onset of organic sedimentation postdates 1600 A.D. An argument might be made for dating the resumption of organic sedimentation at about 860-900 A.D., concurrent with the Classic haya collapse. However, reforestation apparently commenced following the end of the Postclassic phase of occupation (Vaughan ano Deevey 1981), and in the Quexil shallow-water core, Quexil H, and Macanche core D, forest recovery and organic sedimentation begin at nearly iaentical levels in the sections. Use of the more recent date (1600 A.D.) allows more time for Maya-period sedimentation. The tendency is to bias on the low side all chemical accumulation rates in the disturbance zone. Increases over predisturbance rates, which constitute a measure of human impact, are thus considered to be minimum values. Six sediment sections from four lakes were useo to reevaluate the phosphorus loading model developed at Yaxha and Sacnab: Quexil H, the Quexil shallow-water section, Sal 80-1, Sal 80-2, Mac 80-1, and the Sacnab profile. Some of the sediment sections do not span the entire Holocene, and a brief discussion of the problems associated with each is appropriate. The Quexil cores bottomed-out above the Pleistocene boundary, thus pre-Maya, baseline phosphorus accumulation rates are underestimated slightly if the basal age of the cores is truly under 10,000 years old. It has been argued elsewhere that the Lottoitiiii&st levels of the Quexil sections are likely about 9400 calendar years old

PAGE 192

183 (Deevey et al. 1979; Brenner, in press), implying that calculatea predisturbance phosphorus accumulation rates are ott by no more than about 10%. AS pre-Maya accumulation rates are small, relative to Maya period rates, the computed accumulation rate due to disturbance alone is altered minimally by the error in the baseline estimation. At Sacnab (area = 3.897 km-^, z^i^x = 13 ni, z = b.b m; Deevey et al. 1980a), the pre-Maya phosphorus accumulation rate is grossly underestimated if the bottom of the core is assigned an age ot 8000 . B.C., as the Livingstone piston-corer failed to even reach the pre-Maya pollen zone known from analysis of the ^iuexil cores. Ihe consequence is an overestimation of the phosphorus accumulation rate due to Maya activity alone. Macanche core 80-1 did not reach the Pleistocene bounaary, but is thought to be a fairly complete Holocene section. A basal, bulk sediment sample' (SI-5254) yielded a radiocarbon, age ot 9855 _+ 230, but is subject to hard-water-lake error and is too old to be corrected for possible atmospheric ^^C enrichment using the bristlecone pine chronology. If atmospheric levels of '^C remained high as far back as the Pleistbcene-Holocene transition (Stuiver 1970), the two principal phenomena contributing to dating error would tend to cancel each other. The radiocarbon age of the bottommost Mac 80-1 sediments may be roughly equal to the sidereal age. At Salpeten, both cores penetrated the Pleistocene boundary and the pre^-Maya portion of the Holocene sequence is complete.

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Ib4 The inorganic Maya disturbance zone is complete in all the cores except Sal 80-1. As the topmost sediments of the section are inorganic, no post-Maya mud was recovered, and the latter part of the Postclassic sequence is apparently missing. Nevertheless, the incompleteness of the section is thought to have a negligible effect on the computed Maya zone sediment accumulation rate, reducing it by less than 10%. The split-spoon sampler, lowered 50.76 cm with each successive drive, was unable to retrieve post-Maya organic material because it was loosely packed and simply fell from the coring tube. Inorganic deposits, rich in clay, were helo without the aia of a core-catcher, and it is unlikely that an entire drive segment of disturbance zone mud was lost. Even if 50 cm of the section aid fall from the sampler, 685 cm of Maya zone mud was obtained, and the missing portion represents, at most, 7% of the oisturbance zone segment. When zonal chemical accumulation rates for the cores were computed, it was evident that both phosphorus and inorganic matter were delivered to the basins at accelerated rates as a consequence of Maya activity in the catchments (Table 5). Focusing on phosphorus, it is apparent that the measured increases in accumulation rates over baseline levels range from 16% at Macanche to more than an oraer of magnitude registered in shallow water at Salpeten. Baseline phosphorus accumulation rates were subtracted from Maya zone rates to compute the rate of accumulation on the lake bottom due to disturbance alone. Assuming the disturbance rate to have been uniform over the basin floor, the entire phosphorus load aeposited as a consequence of human

PAGE 194

Ibb Table 5. Total phosphorus and inorganic matter accumulation rates for six long cores. Core zones Viere delimited taseci on changes in the organic matter (LOI) or Cqiq content ot the profiles.

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186 activity was calculated for each lake. Testing of the model then required the integration of the archaeologically oerived, Maya population density curves. The reconstruction of prehistoric Maya population density curves for the Peten watersheds has been briefly discussed. The procedure is detailed here to point out slight between-watersheo differences in the integration process used to compute person-years •km"'^ liveo in each basin over Maya time, and to explain the treatment of the isolatea island populations in Quexil and the peninsula inhabitants at Salpeten. P.M. Rice's preliminary analysis of ceramic sherds from test pits dug in mounds at Quexil, Salpeten, and Macanche permitted the assignment of each artifact to one of six chronostratigraphic periods. In the earlier study at ^axha ana Sacnab, ceramic material from the housembunds was relegated to one of five archaeologically defined zones (Table 6), though Postclassic occupation of the twin basin region was confined to the Yaxha island sites. Within each basin, the percentage of mounds occupieo during a given archaeological period was calculated by dividing the number of time-specific occupations, as derived from the ceramic record, by the total number of test-pitted mounds. The density of housemounds in a watershed was figured by assuming that fc4% of the structures on transects were residential, while some 16% were adjunct constructions, as had been done at Tikal (Haviland 1970). The proportion of time-specific occupations was then multiplied by the total residence density to obtain the number of residences occupied per km^ during

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187 Table 6. Ceramically defined archaeological periods of the Peten watersheds. Ceramics from housemounas in the catchments were assigned to the various periods, thus dating the occupation of a structure. Quexil, Salpeten, Macanche Yaxha-Sacnab Archaeological Period Age Duration Archaeological (Ye&ts) Period Age Duration (Years) Postclassic

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Ibfa each of the designated archaeological time periods. The residence density ( residences •km"'^) for each time span was then multipliea by the number of persons per residence (5.0) to calculate the number ot persons per km^, which by convention is the population density for the end of a time peripd. Vvhile Hayiland (1972) has argued that a figure of 5.0 inhabitants per structure might -be more appropriate, this crude test of the model employs his earlier (1970) value to be consistent with the phosphorus loaaing model oevelopea at iaxha ana Sacnab,; . The mean population density for each defined archaeological period was figured as the average level between the end of the preceding : period and the end of the time span being consiaered. Ihe mean population density for a period was then multiplied by the number of years in the zone to obtain the number of person-years -km";^ lived during the time interval. Ihis was done for each archaeologically-def ined time period and the values were sumiiiea, essentially integrating the population density graphs and producing a figure that represents the total number ot person-years •km"'^ livea in a basin over Maya time (1000 B.C.-16C0 A.D.). The integration procedure was modified slightly when dealing with Sacnab's population. As Sacnab supported no postclassic settlement, and the classic period collapse in population likely occurred over a span of 50-100 years, a mean Postclassic population level intermediate between the classic peak value (168 persons •km~2) and zero grossly overestimates the density in the basin following the Classic period termination. Thus, for

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169 calculating purposes, the mean population density after 850 A.D. was assumed to be 14 persons'km"^ or about 1U% ot the Late Classic mean (135 persons 'km-^). Ihis allows tor the persistence in the basin of some Terminal Classic habitation, or use of the catchment by some of Yaxha's Postclassic inhabitants. In any case, the ^itegrated postcollapse population density at Sacnab accounts for only about 10% of the total integrated Maya period population oensity in the basin. The rate of phosphorus accumulation on the lake floor attributable to human activity was calculateu by subtracting the baseline rate from the Maya zone rate. Assuming sediment accumulation to be uniform over the basin bottom, the disturbance phosphorus accumulation rate was multiplied by the lake area and 2600 years of Maya time. This computation produced a figure equal to the entire oisturbance-generatea phosphorus load on the lake bottom. To calculate the number of person-years necessary to produce this phosphorus input, the load was expressed in kg and divided by the proposed per capita loading rate (0.5kg*person-year-l). ihis procedure was used to compute the number of riparian person-years necessary to generate the disturbance load at Sacnab and Macanche. At Quexil, the two islands were occupieo ano the phosphorus generated by the island inhabitants had to be considered prior to the determination of the "mainland" person-years required to proauce the "mainland-derived" phosphorus load. The proportion of test-pitted island mounds showing occupation during the archaeologically defined time periods was multiplied by the total number of residences on the

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19U islands to obtain the total number of housemounds occupied during each ceraniically identified time period, 'ihe total number of occupiec residences tor each period was multiplied by 5.6 persons* residence"^ to obtain the maximal islana populations tor the close of each archaeological time period. Mean population levels for the time periods were determinea and multipliec by the number of years in each period to calculate the number of person-years lived on the islanas by time period. The sumiiiation of these values provioes the total integrated number of person-years lived on the islands throughout Maya time. This figure was multiplied by U. 5 kg phosphorus*person-year~^ to obtain the total cisturbance phosphorus load contributed by the island inhabitants. This value was subtracted from the total Quexil disturbance phosphorus loaa to produce a figure equal to the total disturbance phosphorus input attributable to the "mainland" populations. This number was then aiviaed by the per capita loading rate to obtain the number of person-years required to account f or . the nutrient input originating on the "mainlana." For Salpeten, the peninsula site of Zacpeten, that was densely settled in the Postclassic, was treated in the same manner as the tiuexil islands in order to compute the number of person-years required to account for the phosphorus brought in from the land surrounding the basin. To accomplish this, the phosphorus generated by the peninsula inhabitants was subtracted from the total disturbance phosphorus load before the number of "mainland" person-years necessary to produce the "mainland-derivea" phosphorus input was calculatea.

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ISl For each basin, the number of riparian person-years required to generate the phosphorus load was divided by the archaeologically derived figure for the number of person-years •km"'' lived throughout Maya time. This produced a computed riparian area that was evidently occupied to account for the measured "mainlano" disturbance phosphorus load. If the annual per capita phosphorus loaaing value (0.5 kg) is reasonable, the computed riparian area shoulo match the sii,e ot the true drainage, the region from which colluvium could have been derived. A model was constructed that assumes the lakes are circular and considers the occupied riparian region to have been a concentric band surrounding the lake (Fig. 28) . 'ihis permits the calculation of the approximate distance from shore that would have been occupied (effective riparian distance) in each watershea. The Impact of sediment Focusing The two Quexil cores have already been usea to document the effects of sediment focusing in the conical basin. The differential, calculated effective riparian areas derived from study ot the two sections again reflect the impact of sediment focusing. Evidently, single cores from conical basins can be poor estimators of the integrated, mean lake-wide sedimentation rate. The Quexil H core undoubtedly overestimates the true riparian area, as the cote site received much of the Maya-induced colluvial load emanating from the steep north slopes as well as redeposited material originally

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Figure 28. Sensitivity of the phosphorus output mooel aevelopea at Yaxha-Sacnab to inaccurate estimates of lake-wide phosphorus accumulation resulting from seoiment focusing. Deep-water cores in conical Lakes Salpeten and t-uexil overestimate the riparian area while shallow-watei cores underestimate the region. Cores from ellipsoid Lakes Macanche and Sacnab most closely approximate the true riparian area.

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193 MACANCHE80-1 ^fejS' km 1 2 3 4 S SACNAB SALPETEN 80-1 j!r:l-
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194 sedimented in shallow areas. The deep-water core demands the occupation ot 8.68 km^, thus resulting in a drainage to lake ratio ot 4.23:1. This requires that settlement as far from the lake shore as 1.05 km be considered truly riparian, which is unlikely as nearest high ground is encountered much closer to the lake edge in most areas. The Quexil shallow-water core site, by virtue of its protected position southwest of the islands and its shallow water location, producea a section that underestimates lake-wide phosphorus sedimentation. Requiring the occupation of less than 0.5 km^ to account for the disturbance phosphorus load, the core implies a drainage to lake ratio of 0.22:1, ana allows riparian settlement to have extended only 90 m from the lake shore. It is likely that the phosphorus accumulation rates due to disturbance, as computea from these two cores, bracket the true, integrated mean accumulation rate that could have been employed to compute the actual phosphorus load delivered to the lake as a consequence of Maya activity. Sediment accumulation is not uniform over the bottom of conicaily shaped basins as can be noted from a comparison of the two Quexil cores. This conclusion is corroborated by consideration of the two Salpeten profiles. The riparian area (46.61 km^) calculated using Sal 80-1 as an estimator of lake-wide phosphorus accumulation is clearly excessive, requiring that Maya inhabitants living more than 3 km from the lake shore be considered riparian. If the computed occupied region is assumed to define the true catchment, the resulting drainage to lake ratio is 17.83:1, again much too high for this karsted

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195 area where nearest high ground is often close to the lake edge. Accumulation of phosphorus at the Sal 80-1 coring site is greater than the mean lake-wide accumulation rate by virtue of the station's proximity to the steep north shore slopes and its position in a deep trench. At both coring sites in Salpeten, the Maya zone phosphorus accumulation rate was about 10 times greater than the baseline accumulation rate. Comparing the two stations, zonal phosphorus accumulation rates for the deep-water site are more than an order of magnitude higher than rates computed for equivalent zones in Sal 80-2 (Table 5). The computed effective riparian area as calculated using the deep-water core, overestimates the area that defines the drainage. When the shallow, Sal 80-2 core disturbance phosphorus accumulation rate is used to calculate the basin-wide disturbance phosphorus load, it is not possible to even account tor the phosphorus export expected from the peninsular site of Zacpeten alone. The two profiles, taken in deep and shallow water, again demonstrate the differential distribution of sediment over the bottom of trumpet-shapeo basins. Having considered multiple sections from the conical Quexil and Salpeten basins, it was shown that deepor shallow-water cores respectively overestimate or underestimate the integrated lake-wide mean sedimentation rate, the degree of error being a function of lake morphometry and core position. In situations where sediment deposition is more likely to have been uniform over the entire lake bottom, a single core can be used to assess basin-wide sediment accumulation more

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196 accurately. Ellipsoid basins meet this criterion, and calculated riparian areas should approximate most closely areas trom which phosphorus-enriched colluvium was derived (true, occupied riparian area), when computed using cores from pan-shaped lakes. Thus, determined occupied areas surrounding the more elliptical Sacnab and Macanche basins (Deevey et al. 19&0a) should delimit the true source areas for eroded topsoil. The only caution is that the Sacnab area is probably overestimated due to the incompleteness ot the core.lhe baseline phosphorus accumulation rate is underestimated, resulting in a computed nutrient accumulation rate due solely to human activity that is too high. Predictions about the effect of lake morphometry on sedimentation are fulfilled by a basin-to-basin comparison of computed occupied areas and maximal distances from shore considered to be riparian. Calculations based on the Mac 80-1 core require Maya occupation. of a 1.78 km2 land area, or a -riparian band extenuing . Q .25 km from the lake shore. Morphometric considerations, based on hypsimetric curves developed for the Peten lakes (Deevey et al. -ISaGa) , would predict a smaller calculated riparian area for Lake Sacnab. However, the incomplete pre-Maya sequence in the Sacnab core results in overestimation of the disturbance phosphorus accumulation rate, thereby exaggerating the computed occupied riparian region (5.76 km^) and the distance from shore contributing colluvium (0.64 km). When the PleistocenerHolocene transition date of faOUO B.C. is abandonee in favor of the admittedly questionable -'^C age of the basal Sacnab sediment

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197 {QL-1029, 6410 ± 100; Deevey 1978), the calculated occupied riparian area is reduced. Using this procedure, Sacnab's ef tective riparian region is shown to be 1.36 km^ or an area extending 0.18 km from the shore. Quexil's hypsimetric curve closely approximates the curve £pr an idealized conical basin and focusing of sediments into deep water is not surprising. Computed sediment accumulation rates based on the study of deep-water core Quexil H are excessive and lead to the computation of an effective riparian area that is too large. As expected, the computed riparian area for Quexil exceeds values calculated for the more ellipsoid Macanche and Sacnab basins. Ihe occupied region around Quexil is nevertheless smaller than that computed for trumpet-shaped Salpeten, based on the study of the deep-water, Sal 80-1 core. While conical like Salpeten; Lake Quexil may have been subject to less intense sediment focusing because the deep central basin of the lake, though steep-sided, possesses a large flat area enclosed by the 28 m contour. The Salpeten deep-water core (Sal 80-1) demands the extension of the riparian area to 3.06 km from the lake shore, encompassing an area (46.81 km^) that certainly exceeds the true region from which disturbance-zone sediments were derived. This is expected, as Salpeten was shown to be the most hypercbnical of the studied Peten lakes (Deevey et al. 1980a). The deep trench where the core was taken, was only discovered in 1980, and its contours are not known well enough to warrant a revision of the hypsimetric curve for the basin. The

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>4-l

PAGE 208

199 (uj) mnaa

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200 interpretation is not altered by the presence of this depression, and the coring site, in 26.1 m of water, was located just south of the maximum trench depth. The limited, deep-water region undoubtedly receives much focused sediment (Pig. 29). While hypsimetrtic curves may provide insight into the expected degree of moaern sediment focusing in Peten basins, it is difficult to assess the past impact of the process, as deep trenches and sinks may have been obliterated by infilling during 10,000 years of deep-water Holocene sedimentation. In order to verify that the assumed haya annual per capita export figure of 0.5 kg P is reasonable, it is necessary to compare computed occupied riparian areas to the true drainage areas from which colluvium could have been derived. The validity of the test is weakenea somewhat by the inability to delimit objectively the true drainage area. The karst terrain is deeply dissected and maps do not resolve the problem as contour intervals are often widely spaced, thereby failing to identify nearest high ground. Despite this oitticuity, maps and personal observations suggest that the potential source area for colluvium probably extends to an average aistance of about O.b km around each lake. This figure is approximated by computed riparian areas based on cores from the ellipsoid hacanche and Sacnab basins. The vagaries of sediment focusing are apparent at tiuexil and salpeten where deep-water cores overestimate lake-wiae sedimentation rates, thereby resulting in excessive computed riparian areas. Nevertheless, phosphorus accumulation rates computed from dual borings in the two conical basins apparently bracket the integrated mean accumulation rate, as computed riparian areas based on the shallow-water sections underestimate the true drainage.

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201 Crude sensitivity testing of the model was accomplishea by calculating riparian areas and distances from shore considereo riparian employing annual per capita phosphorus export figures of 0.05 kg ana 5.0 kg, or an order of magnitude lesser and greater than the proposeo value. A 5.0 kg annual per capita export figure cannot account for the sedimented nutrient derived from the Quexil islands or the peninsular site of Zacpeten, while at Macanche and Sacnab, the computed areas considered riparian extend only 30 m and 80 m, respectively, from the lake shore. Use of the 0.5 kg figure enlarges the distance considered riparian to excessive degrees, from a minimum distance of 1.47 km using •the Quexil shallow-water core, to 11.86 km employing Sal 80-1. Zoning the Cores Palynologically The estimated per. capita phosphorus output figure was originally proposed based on studies at Yaxha and Sacnab, where cor.es were . , fine-zoned using pollen. As pollen zonation was stiown to be unreliable for dating sediments at Quexil, the changing chemistry of the sediment was used as a dating tool to test the phosphorus loading model in. four basins. The changing proximate composition of the lake sediment is thought to be a better basin-specific indicator of disturbance. Nevertheless, it can be demonstrated that crude zonation of the cores using pollen, has little influence on the outcome of the model testing. At both Quexil and Sacnab, the palynologically determined inception of the Middle Preclassic lies below the organic-inorganic

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2U2 transition. If pollen is used to identify the Kiddle Pceclassic boundary (1000 B.C.)/ the Maya disturbance zone is expanded and the pre-Maya zone is reduced, in Quexil H, the Early and Middle Preclassic zones were not distinguished palynplogically, so the beginning of the Middle Preclassic was assigned to the 720 cm level, about midway into the 1-m thick zone. The resumption of organic sedimentation and palynological evidence for reforestation used to identify the Maya abandonment of the watersheds occur concurrently in the Sacnab core as well as in the Quexil shallow-water section. In Quexil B, the post-Maya zone is chemically identified at 210 cm and placed at 200 cm palynologically. Where changes in chemical composition or relative pollen percentages occurred, the midpoint was selected as the limit between zones. The slightly different chemical and pollen horizons marking the inception of the post-Maya period may simply reflect the wide spacing of samples taken for pollen analysis. Having rezoned the cores cruaely into pre-Maya and Maya zones using pollen, the phosphorus loading model was again tested by calculation of effective riparian areas (Table 7). For Sacnao, palynological zonation requires the effective drainage be expanded to 19.11 km^, extending the source area for redeposited soil to l.t>i» km from the shore. This apparently overestimates the true arainage area. In Quexil, rezonation of the shallow-water core increases the computed riparian area, demanding that land up to 0.49 km from the lake shore be considered part of the true drainage. The already excessive riparian area determined by chemical zonation of the Quexil H core is expanded even more by palynological identification of the Middle Preclassic boundary.

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203 Table 7. Testing the phosphorus loading model using pollen zonation o£ the cores. Kaximum Depth Phosphorus Effective Riparian Years in Accumulation Kiparian Distance In Core Rate Area From Shore Zone (cm) ug^cm'-^^yr"^ (km'') (km) Core Zone Quexil Shallowwater Quexil H Sacnab Maya 2600 375-bO 4.8 PreMaya 7000 624-375 l.U Maya 2600 720-200 15.9 PreMaya 7000 920-720 1.6 Maya 2600 590-100 10.5 PreMaya 7000 625-590 0.3 3.27 14.86 19.11 0.49 1.51 1.59

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204 An alternative approach to assessing the effect of rezonation was tried. Riparian areas, as calculated from the chemical zonation of the cores, were held constant, and new per capita phosphorus export values were computed based on pollen zonation. As palynolcgical zonation expands the disturbance zones in the cores, the computed annual per capita export rates were raised above the O.b kg figure originally useo in the riparian area calculations. For core guexil H, the annual per capita phosphorus loading rate was raised to O.b kg, while the shallow-water core required that each person contribute 1.42 kg of phosphorus annually. For Sacnab, the new computeo per capita loaaing rate was 1.65 kg of phosphorus per year. Though somewhat higher than the proposeo annual per capita phosphorus export value of O.b kg, the figures are not inconsistent with the range of zonal per capita delivery rates measured at /iaxha and Sacnab (U.2b-1.4b kg'capita"l*year~l) based on seven zones. Reliance on pollen as opposed to chemistry for gross core zonation and testing of the model does not alter dramatically the computed riparian areas. Differences are compensated for by small, conceivable changes in the annual per capita phosphorus loading rate. Calculated effective riparian areas, or regions from which colluvium was derived during haya occupation of the Peten watersheds, in some cases approximate the true drainage areas enclosed by nearest high ground. The equivalency of the computed and true drainage is approached most closely using cores from pan-shapeo lakes, while deep-water' sections from conical basins overestimate the occupiec

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2Ub riparian region contributing slopewash, and shallow-water profiles underestimate the area. Phosphorus export from the watersheds ma^ well have had an impact on Maya agriculture, and presumably the effect of colluviation was not confined to lake watersheas. Wherever forest clearance occurred, it no doubt precipitated soil erosion from the karsted hills and nutrients were likely sequebtered in "bajos" or dry depressions. , Assessing the Impact of Soil Nutrient Loss Rates of phosphorus delivery to the Peten lakes increased as a consequence of human disturbance, and large amounts of the nutrient were sequestered on the basin bottoms due to Maya agro-engineering practices. Up to this point, the human-meaiated transfer of phosphorus from land to water has been discussed from the limnological viewpoint, that is, with respect, to the rate of nutrient supply or total amount of nutrient delivered to the lakes. At Lake Quexil, as at Yaxha and Sacnab, the microfossil record was examined to determine whether lacustrine productivity changed in response to the alterea rate of phosphorus income. Nothing has yet been saia about the consequences of nutrient removal from the riparian region. Phosphorus delivered to the lakes as a consequence of disturbance was pihosphorus removed from the drainages, and quantification of the terrestrial nutrient loss might provide a crude measure of the environmental impact sustained by the watershed soils and vegetation.

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206 The proportion of phosphorus removed from the watersheds and transferred to thei lakes as a result of 26U0 years of Maya occupation was computed in an effort to quantify roughly the impact of human-induced nutrient export from the terrestrial sector. Soil concentrations were known and the effective riparian areas had been delimited. These figures, together with values for the total phosphorus load delivered to the lakes as a consequence of "mainlana" disturbance, permit the calculation of the exported portion of the predisturbance soil phosphorus standing stock. The test assumes that physical translocatipn of soils was the mechanism by which phosphorus entered the lakes. Furthetmore, it is accepted that soil phosphorus concentrations have returned to nearly : predisturbance levels during the four centuries since the haya abandoned the catchments.. While very .high nutrient concentrations arfe; encountered near Maya construction, the presence of climax forest, and a modern pollen rain with similar relative proportions to the pre-Maya pollen spectrum indirectly suggests the attainment of a new soil equilibrium that approximates the predisturbance state, 'ihe potentially disturbed regolith was considered to extend to a depth of 50 cm and the soil was assumed to have a specific gravity of 1.1 (Deevey et al. 1979). The mean, whole profile phosphorus concentration from all the pits in a basin was then used to calculate the standing stock of total phosphorus in the top 50 cm of the riparian soils. For Sacnab, the computed value is based on a small sample of ; three pits, and for Quexil, the mean whole profile concentration was computed

PAGE 216

207. omitting shallow pit #4. The sedimented, disturbance phosphorus load emanating from the riparian area was divideo by the total phosphorus stock in the riparian soils. This calculation provides an estimate of the proportion of soil phosphorus transferred to the lake as a consequence of human disturbance (Table 8). While core location affects the computed lake-wide disturbance, phosphorus accumulation, it in turn influences the calculated riparian area. Thus, though deep-water cores from conical basins may exaggerate the disturbance phosphorus load on the lake bottom, the occupied area and riparian soil phosphorus stock are also overestimated, ihe computed proportion of soil phosphorus exported to the lake as a consequence of Maya activity remains the same whether the Quexil shallow-water core and small riparian area are used, or Quexil h and the larger riparian area are employed. The average annual riparian disturbance phosphorus input to each lake was figured by dividing the total "mainland" derived phosphorus load by the 2600 years of Maya time. This value was then divided by the amount of phosphorus in the riparian soil compartment, yielding the proportion of the riparian soil phosphorus stock removed annually by the Maya (Table 8). In the four basins considered, some .20-54% of the riparian soil phosphorus stock was transferred to the lakes as a consequence of human activity. The mean proportion of transferred soil phosphorus for the four watersheds is 40.8%. This value is undoubtedly too high, as

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20b Table 8. Soil phosphorus depletion attributable to Maya agroengineering activities. Core

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20S» felled trees and litter on the forest floor contributea to the sedimented phosphorus load. At Hubbard Brook, New Hampshire, the above and below ground biomass and forest floor stocks of phosphorus amount to 0.0165 kg phosphorus -m"^ (Likens et al. 1977), a value that includes some nutrient contained in surficial soils. Rodin and Bazilevich (1967) estimate that tropical rain forests contain about 0.03 kg phosphorus 'm'^ in the plant biomass. Jordan (1970) reports that woody tissue and leaves of the Puerto Rican rain forest possess 0.0071 kg phosphorus •m~2. Lacking data on the phosphorus content of the Peten forest and litter, the literature values are relied upon as a crude estimate. Using the mean of the average whole profile soil phosphorus concentrations for the four Peten basins, the top 50 cm of watershed soils are shown to contain 0.1675 kg phosphorus •m~2. it was assumed that the vegetation of Peten is comparable to the rain forest with respect to its phosphorus . content (0.03 kg*m~2). ihe forest floor phosphorus content measured at Hubbard Brook (0.0076 kg'm"^), which includes some soil nutrient, was used to estimate the phosphorus content of Peten 's litter, summing the vegetation, litter, ana soil values, it is surmised that the Peten forest contains about 0.2053 kg phosphorus •m~2 down to 50 cm in the soil profile. The vegetation and litter account for about 18.4% of this phosphorus pool. Thus, even when using the maximal reported value for vegetation phosphorus, and adding to it a figure for the phosphorus content of litter, the calculated proportions of soil phosphorus exportea to the lakes as a

PAGE 219

21U consequence of disturbance (Table 6 J are adjusted downward by a small amount. Accounting for the phosphorus contained in the living ana aead biomass of the forest, the mean proportion of exported soil phosphorus for the four watersheds is reduced from 40.8% to 33.3%. While a significant proportion of the soil regolith was ultimately transported to the lakes during 2600 years of Maya occupation, the process occurred at a very slow rate. The average annual disturbance phosphorus load delivered to the lakes (Table 8) amountea to between 0.008% (Salpeten) and 0.021% (Quexil) of the soil compartment phosphorus stock. These values are shitted aov.nwara minimally byconsideration of the vegetation and litter contribution to the sedimented phosphorus load. The mean annual rate at which phosphorus was exported from the basins during Maya time was evidently rather low. however, the rate of soil removal in any given year was certainly a function of Maya population density and land use. Luring periods of high population density, annual soil losses may have been consiuetably higher than the computed mean value. Maya population levels may have, in turn, responded to the increased erosion rates it soil loss reducea agricultural yields or had an indirect, negative impact on harvests of aquatic resources. Erosion Rates tor the Peten Watersheds The proportion of soil phosphorus transported to the Peten lakes as a consequence of Maya activity is impressive ana implies significant

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211 landscape reduction. Predisturbance and Maya period erosion rates were calculated for comparison with published values trom other forested ana disturbed watersheds. While erosion has been quantified in a number of temperate studies, there is a paucity of literature on tropical catchments. Erosion of the Peten soils was assessed by looking at the inorganic load deposited in the lake basins. The sedimented inorganics are believed to be of primarily alldchthonous, terrestrial origin, with little deposition resulting from biological processes within the lake (eg. carbonate sedimentation). While a portion of the siliceous ana carbonaceous sediments (the bulk of the inorganic fraction), may have been delivered to the lakes in soluble form, the majority of the ^ material presumably arrived as particulates. During episodes of deforestation, nearly all the inorganic material likely reached the lake shores via soil creep. Sedimented organic material was ignored in the erosion calculations, as allochthonous organics may have been lost through diagenesis and are inseparable from autochthonous organic . remains. Erosion rates are generally calculatea by measurement of dissolved, suspended and bedloads in streams or rivers draining catchments. Alternatively, erosion has been assessea directly by measurement of soil loss around dated archaeological ruins or age-old trees (Judson 1968a). These latter methods> like the paleolimnological approach, provide a long-term evaluation of the erosion rate, while stream loads vary with rainfall and must be monitored over a long period of time.

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212 Erosion rates were figured based on data from four cores: Quexil H, Sal 80-1, Mac 60-1, and Sacnab. Initial computations ignorfc special consideration of the Quexil islands or the peninsular site of Zacpeten, and assume all inorganics came from the computed riparian area. For each lake, the annual predisturbance and Maya period inorganic loads were computed by multiplying the zonal inorganic accumulation rates times the lake area. The annual load of inorganics delivered to the lake was then divided by the calculated effective riparian area, the region from which colluvium was derived. (As was argued for phosphorus, while deep-water cores from conical basins exaggerate the lake-wide sediment accumulation, the riparian region from which the redeposit'ed soil came is also overestimated). Ihis computation yields pre-Maya and Maya period inorganic export rates. The erosion rates are expressed in metric tons'km~^*yr~^, and landscape reauction, presented as cm'lOOO yrs~^ was computed assuming the soil has a specific gravity of 1.1 (Table 9). Predisturbance rates of inorganic loss for the four wateisheos are variable, but with the exception of Macanche, the catchments all display baseline rates that are comparable with rates measureo elsewhere. Predisturbance export of inorganics from the Brains and Murray Lake watersheds in Michigan proceeded at rates of nine tons*km"2»yr~^ and 20-30 tons'km~2«yr~^ respectively (Davis 1976). Predisturbance erosion rates were computed based on Bonatti and Hutchinson's paleolimnological study of Lago di Monterosi, Italy. In that watershed, and throughout Italy, erosion prior to human intervention proceeded at rates of about 52-78 tons*km~2*yr~-'.

PAGE 222

213 o +J O (0 04 >i H iH -a P -H C ... U nj X (S '^ O W CP w s # a >4 >t-i O .ii >4 o c: u J3 ft H en

PAGE 223

214 (Judson 1968b). Forested watersheds of the Maryland Piedmont yield less than 35 tons'kin~2«yr~l as a consequence of erosion (Wolman 1967), while Mississippi catchments covered in mature pine-hardwood forests lose some 2-9 tons*km~2.yr-l (Ursic and Dendy 1965). In . Kenya, studies of forested drainages produced erosion rates ranging from 20-30 tons'km'^'yr-^. Quexil, Salpeten, and Sacnab erosion rates are consistent with the literature values and are revised upward minimally if organic material is considered, as the whole soil profiles; average some 14% organic matter down to 50 cm, and soils are the presumed source of the sediment. Macanche's predisturbance inorganic export rate (361.4 tons'km~2-yr-l) appears anomalously high. Unlike the other lake sediment cores that contain pre-Maya deposits of uniformly high organic matter content, Macanche's predisturbance muds possess a high proportion of inorganic matter below 705 cm. The inorganic sediments at the base of the section may indicate very early human activity in the catchment, predating the inception of the Middle Preclassic. There is, however, no archaeological evidence to support this notion. Alternatively, it might be suggested that the inorganic-rich muds below 705 cm are of Pleistocene age. If this were the case, the pre-Maya Holocene sequence would be confined to only 120 cm of organic material between 585 cm and 705 cm in the core. Rezoning the core in this manner produces a pre-Maya bulk sediment accumulation rate of 0.017 cm«yr~^, a value that seems quite slow. The phosphorus loading model was tested using 705 cm as the Pleistocene-Holocene

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2i; boundary. The calculated riparian region (11 km-') overestimates the true source area for colluvium, permitting the extension ot the effective riparian area to a distance 1.22 km from the lake shore. Ihe overly large computed riparian area probably results from the underestimation of the baseline phosphorus accumulation rate. The predisturbance rate is no doubt too small because the Pleistocene boundary in fact lies well below 705 cm. Placement of the Pleistocene-Holocene contact at 705 cm was also rejected using the basal radiocarbon date from the core. Lying more than 3.5 m below the proposed boundary, the bulk sediment at 1060-1072 cm has a radiocarbon age of nearly 10,000 years. In order for the 705 cm level to possess a sidereal age of 10,000 years, the basal sediments would have to be much older. There is no reason to suspect that the radiocarbon age of the bottommost portion of the core is grossly underestimated or substantially younger than the calenarical age. Ultimately it may be possible to assign a rough age to the inorganic-organic transition at 705 cm using the pollen profile trorfi the section. . As the Macanche core is thought to be a near-complete faolocene profile, an alternative hypothesis was sought to explain the inorganic nature of the predisturbance mud below 705 cm. A dry stream Lea opens into the eastern end, of the lake, ana the shallows east of the island may be the result of accumulated oeltaic deposits. Some of the streamload, particularly small clayand silt-size particles may have been carrieo as far as the deep-water coring site. The accuiuulation

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21b rate of the stream-transported material was undoubtedly influenced by a number of factors. Lake level fluctuations may have changea the position of the stream discharge point relative to the coring site, and the streamload probably varied with rainfall and runoff, '.here is no reason to believe that the stream-carried sediment accumulation rate at the coring site was the same during pre-Maya and Maya times. Nevertheless, high predisturbance and disturbance period accumulation rates for both inorganic matter and phosphorus suggest that preferential sediment deposition at the coring locality has occurred throughout most of the Holocene. The highly organic material underlying the earliest Middle Preclassic mud may have been depositee during a period of reduced stream flow or when stream-delivered suspended material was impeded from transport to the coring site. in testing the phosphorus loaning model at Macanche, the calculated riparian area was found to extend 0.29 km from the lake shore, slightly underestimating the true source area for colluvium. underestimation of the disturbance generated phosphorus load might have causea the discrepancy between the computed and actual riparian areas. It is possible that the pre-Maya stream-delivered phosphorus accumulation rate was higher than the stream-carriea phosphorus accumulation rate during Maya times. Subtraction of the inflated baseline value from the Maya period phosphorus accumulation rate woula have resulted in an anthropogenically derived accumulation rate that is underestimated by a small amount. Erosion rates computed for the Macanche .catchment using core; Mac 80-1 are almost certainly overestimated, as the coring site was the-

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217 repository for much inorganic material brought in by stream flow. Nevertheless, pre-haya erosion rates can be roughly comparea to disturbance perioa rates in all four Peten basins. Erosion rates for the Maya period exceed baseline rates in the Peten watersheds, though the magnitude of change differs for the four basins. At hacanche, where baseline rates were high, the disturbance period erosion rate was only 2.3 times the pre-Maya rate. At the other extreme, Salpeten's Maya period erosion rate was 24.2 times greater than the baseline value. The mean Maya period-baseline ratio for the four drainages is 10.6, indicating that disturbance resultea in erosion rates an order of magnitude greater than baseline values. At Frains Lake, the postdisturbance watershed erosion rate was 10 times the baseline figure and in the Murray Lake drainage, human intrusion caused a five-fold increase in erosion over the predisturbance level (Davis 1976). At Lago di Monterosi, human disturbance resulted in erosion rates about an order of magnitude greater than predisturbance rates (Judson 1968b). Evidently the increase in erosion resulting from human activity is highly variable and in part dependent on land use. Ursic and bendy (1965) indicate that erosion from cultivated agricultural catchments in Mississippi may be as much as three orders of magnitude greater than that registered for forested watersheds. Vvolman (1967) argues that agriculture raises erosion rates by about an order of magnitude over the baseline condition. It is noted, however, that active construction projects on exposed land may lose more than 1000 times the material exported from forested watersheds.

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218 Alternatively, erosion can be assessed by calculating the proportion of inorganic matter in the riparian soils that was transported to the lakes as a consequence of Maya activity. The baseline inorganic accumulation rate was subtracted from the Maya zone rate to compute the accumulation rate due to disturbance. This value was then multiplied by the area of the lake to obtain the annual lake-wide inorganic load. As some inorganic loading emanated from the Quexil islands and Salpeten's densely settled Postclassic peninsular site, an adjustment in the annual loading rate was made in an effort to compute the load derived from the "mainland," or effective riparian area. Phosphorus generated by Quexil's island inhabitants accounted for 10.7% of the total disturbance phosphorus loaa, ano it was assumed that the islanders contributed an equivalent proportion of the total disturbance inorganic loaa. Thus, the average annual inorganic load derived from the "mainlana, " or calculated effective riparian area, is 89.3% of the total annual disturbance input. The site of Zacpeten generated 8.9% of Salpeten's disturbance phosphorus load and the annual disturbance inorganic loading figure was aajusted downward by tnis amount to compute the amount coming from the calculated effective riparian area. The annual inorganic loading rates attributable to mainlana disturbance were then divided by the respective calculated effective riparian areas. This computation provides values tor the annual rate of inorganic export from the watersheds resulting from disturbance. The annual "mainland" derived inorganic loading rate was also

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219 multiplied by 2600 years of Maya time to compute the entire inorganic yield attributable to riparian Maya populations. Assuming that soils have returned to a near predisturbance equilibrium with respect to their inorganic content, the inorganic stock in the contemporary watershed soils was figured for each basin. In each basin, the mean whole profile inorganic percentage was used for calculation. Loss on ignition was not run on soils from the three Sacnab pits, so the average of the mean percent inorganic values tor the other three basins was employed to evaluate the total stock in the Sacnab basin soils. As mean whole profile inorganic proportions in Salpeten, Quexil, and Macanche range from only 85.7% to 87.7%, the Sacnab estimate is likely reasonable. Assuming soils have a specific gravity of 1.1, the inorganic material contained in the top 50 cm of the regolith was computed on a km'' basis.. Then, multiplying this factor times the computed effective riparian area, the total inorganic stock in the top bO cm of the riparian soils was figured. For each basin, the total inorganic yield delivered to the lake as a consequence of Maya disturbance was divided by the inorganic stock present in tjfie riparian soils. This provides an estimate of the proportion of soil stock inorganics transferred to the lake during 2600 years ot Maya lano use (Table 9). At Quexil, the proportion ot phosphorus removed from the soils as a consequence of Maya-induced erosion (54%) exceeds slightly the inorganic fraction transported (40%). The near equivalence ot the values is not surprising as zone-to-zone changes for phosphorus

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220 accumulation rates in Quexil core H were shown to be correlated with both carbonate and silicate accumulation rates, when the cote was zonea palynologicaliy. The positive correlations suggested a common delivery mechanism for the three chemical types and bulk soil transport was proposed. Mean, soil prof ile concentrations were used to calculate phosphorus and inorganic stocks in the riparian soils, but it phosphorus-rich, organic topsoils comprised the bulk of the eroded material, a slightly higher proportion of phosphorus as opposeo to inorganic removal might be expected. Additionally, if the standing vegetation contains a significant portion of the watersheo phosphorus stock, but relatively little of the inorganic material in the catchment, detorestation would contribute a relatively higher traction of the phosphorus compartment as compared to the inorganic stock. in the Salpeten, Macanche, and Sacnab watersheds, the con.putea proportion of soil inorganics transported to the lakes over Maya time exceeds the fraction of soil phosphorus moved. At Salpeten, the soil phosphorus stock was depleted by 20%, while 37% of the soil inorganic compartment was transferred to the lake. Macanche soils lost b2% ot their phosphorus supply, but evidently 244% of the soil inorganic stock down to 50 cm was carried to the lake. At Sacnab, too, more than all (112%) of the inorganic material in the top 50 cm of the riparian soils was lost to the lake, while only 37% of the phosphorus stock crossea the drainage-lake interface. The discrepancy in the computed proportions of transported phosphorus and inorganics is not surprising. The sedimented

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221 disturbance inorganic loads in hacanche and Sacnab exceed the total inorganic stock in the top bO cm of the riparian soils. This suggests that there may be an error in restricting the potentially erodable regolith to the uppermost 50 cm for calculating purposes. The high, measured proportions of transferred inorganics may indicate large losses of deep, inorganic-rich and phosphorus-poor "sascab.If inaeea subsoil below 50 cm were transported to the lakes, the erodable inorganic stocks in the watersheds were underestimated ano consequently, the proportions exported to the lakes were overestimated. Lowering the erodable boundary to 100 cm ana measuring loss on ignition throughout the profiles would likely more than double the calculated inorganic stocks figured for the watersheds, as only surficial soils contain appreciable organic matter and -sascab" probably has a higher specific gravitythantopsoil. Inclusion of the deep, subsoil levels in the assessment of the riparian phosphorus stock would change the computedMaya-transporteo phosphorus fraction by only a small amount. This would hold if phosphorus concentrations were n>easured over the entire profiles oown to 100 cm, and the concentration curves were integrated to evaluate the total phosphorus content in the soil compartment. The phosphorus content in the subsoil from 50-100 cm would undoubtedly amount to a small fraction of the total regolith phosphorus stock, and, therefore, would add little to the amount measured in the half meter of topsoil. It is likely that the depth to which the soil was erodea variea : between watersheds and from place to place within a catchment. This

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222 being the case, arbitrary limitation of the erodable regolith to the upper 50 cm for calculating purposes would be expectea to result in differential exports of phosphorus and inorganic matter. High proportions of calculated inorganic matter transport might be expecteo in watersheds where urban construction or other engineering endeavors mobilized large amounts of phosphorus-aepleted inorganic material from deep in the soil profile. At Macanche, much silt was sedimented as a result of the construction of the defensive wall, Muralla de Leon, near the northeastern shore of the lake. The small site of Cerro Ortiz, overlooking the southeastern edge of the lake, may have contributed much inorganic material. At Salpeten, the peninsular site of Lacpeten very likely contributed a substantial inorganic load to the lake during Postclassic times. While the total Maya period inorganic load was adjusted downward by 8.9% to compute the -mainlanaderived load, the correction is probably insufficient to allow for the massive silt output from the urbanized peninsular site. At Sacnab, construction efforts cannot be invoked to explain the large export of inorganics as the catchment never hosted urban development. Maya activity in the Peten watersheds accelerated phosphorus and inorganic matter delivery to the lakes, and both chemical types probably reached the waters' edge in eroded soil. Nevertheless, when the erodable soil section is assumed to extend to bO cm, it is shown that differential proportions of phosphorus and inorganics were removed from the soil compartment of each watershed. With only four

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223 lake-watershed systems studied, and cores grossly zoned, explanations for the unequal proportions of Maya-erodea soil inorganics and phosphorus remain speculative. The problem may be resolved partially by future fine-zoning of the sediment profiles, particularly if relative changes in phosphorus and inorganic loading rates are compared with archaeologically documented shifts in social organization or lana use. Massive exports of inorganics resulting from ceremonial, urban, or defensive construction could then be aemonstrated not only by between-catchment comparisons, but within a watershed.

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SUMMARY . Paleolimnological data from Peten lake sediment cores were used in conjunction with paleodemographic information on riparian Maya populations to elucidate the environmental impact of prolonged human settlement in the watersheds of the karsted Guatemalan lowlanos. Palynological study of sediment profiles from central Peten Lakes Quexil (Vaughan 1979, Deevey et al. 1980c), Petenxil (Isukaoa 1961)), Macanche (Garrett-Jones, pers. comm. ) , and the easternmost twin Lakes Yaxha and Sacnab (Deevey et al. 1979) revealed the widespread extent or deforestation associated with Maya occupation of the region. Forest clearance may not have proceeded at identical rates in all basins. Nevertheless, in each core the mix of regional and local pollen recorded evidence of increasing forest removal continuing until Late Classic times, when Maya population densities were maximal throughout the area. Following the Classic collapse, the human-inauced savanna conditions were sustained by the small, nucleated Postclassic populations. At Sacnab and Quexil, where retrieved basal sediment levels are sufficiently old, human-influenced vegetational changes were detected in horizons predating the inception of the Middle Preclassic perioa (1000 B.C.). At Yaxha (Deevey et al. 1979) and Petenxil (Tsukada 1966) coring efforts failed to obtain muds antedating Middle Preclassic age. 224

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225 but the episode of grassland expansion was amply documented. High forest pollen comprised a progressively smaller proportion of the pollen sum through Late and Postclassic times. In all five lakes assessed palynologically, the uppermost sediments contain a record of forest recovery that commenced at the close of the Postclassic, some 400 years B.P. Deforestation and subsequent Maya agro-engineering practices within the Peten catchments changed sedimentation processes in the lakes. As people moved into the drainages, predisturbance organic sedimentation was supplanted by the accumulation of deposits dominated by clay-rich inorganics. The general, gross stratigraphic pattern of Holocene sedimentation in the Peten basins is known from four lakes: Macanche, Salpeten, Quexil, and Sacnab, the latter two lying some 50 km apart. Maya period anthropogenic, inorganic sediments are intercalated between Holocene organic muds of pre-Maya and post-Maya age. At Lakes Petenxil and Yaxha, borings failed to penetrate through the "Maya clay" deposit. Coring at Yaxha was impeded by the thickness (> 6 m) of the clay lens, which stopped the small piston corer. The tremendous thickness of the erosional load that blankets the Yaxha basin is attributable to the archaeologically documented dense Classic occupation of the drainage as well as substantial urban construction in the watershed. It is suspected that the anthropogenic clay aquiclude is underlain by organic lacustrine deposits in both Yaxha and Petenxil. Land clearance caused an increase in the sediment accumulation rate as erosion carried large amounts of soil into the lakes. Organic

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226 matter contained in the felled vegetation, litter, and uppermost soil horizon was quickly flushed from the catchments, and subsequent, rapio sediment accumulation was dominated by inorganics. The depletion of the allochthonous organic matter pool, together with decreased lacustrine productivity and severe diagenesis of any sedimented allochthonous or autochthonous remains, resulted in disturbance-zone muds with low organic content. At Lake Quexil, a prolonged episode of predistuibance meromixis was inferred from the undisturbed laminated sediments underlying the anthropogenic clay section. Forest clearance may have disrupted the stable chemical stratification as the consequent soil erosion supplied the mixolimnion with large amounts of dissolved and particulate matter. Additionally, increased wind movement over the lake surface would have resulted following tree removal, thereby enhancing the possibility of holomixis. Alternatively, it is conceivable that turnover was inhibited following riparian disturbance, but evidence tor the continued meromixis was obliterated by the high rate of colluviation that overwhelmed the short-term (annual?) organic-inorganic cycle of sedimentation responsible for producing the laminae. The paleolimnological record has been used to aetermine past levels of phosphorus loading to the Peten lakes. As phosphorus is often the limiting nutrient tor primary productivity in lacustrine systems, paleoproductivity can sometimes be inferred from past rates of phosphorus supply. Furthermore, phosphorus sequestered in basin

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227 sediments represents a potential nutrient supply deflected from cycling within the terrestrial sector. Phosphorus transported to the lakes as colluvium was no longer potentially available for Maya agricultural production, and an increasing rate of accumulation in the lake sediments can be equated with decreasing riparian soil productivity. Inputs of i^C-deficient, carbonate carbon to the Peten lake sediments made reliable radiocarbon dating of the profiles impossible. At Lakes Yaxha and Sacnab, dates were assigned to levels in the cores where major changes in the pollen spectra were detected (Vaughan and Deevey 1981). The paleodemography of the basins was known, and it was assumed that the degree of forest removal detected in the pollen profiles was a reflection of changing population density in the watersheds. Maya populations in the twin basins grew at a slow, steady exponential rate from the Middle Preclassic through the Late Classic period. When phosphorus accumulation rates were computed based on palynological dating of the cores, phosphorus supply to the lakes, ; delivered primarily as colluvium, was shown to be Maya densitydependent (Brenner 1978). Mot only did phosphorus input to the basins track population growth, but the per capita contribution was shown to be about 0.5 kg«yr-l, a value that perhaps coincidentally matches the annual physiological flow of phosphorus through human bodies (Leevey et al. 1979). Lacustrine productivity, as inferred from microfossil enumerations, evidently rose with initial human intrusion in the watersheds, but by Early Classic and Late and Postclassic times, when phosphorus was

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228 supplied to the lakes at very high rates, microfossil accumulations dropped precipitously. During periods of massive colluviation, the bulk of the phosphorus delivered to the lakes probably arrived at the waters in unavailable mineral form (apatite?) and bypassed the biota en route to sedimentation on the basin bottom. Productivity may have actually been inhibited by the severe siltation, and any phosphorus delivered in available form may have been rapidly scavenged and coprecipitatea with carbonates or clays. It is also likely that microfossils buried in the anthropogenic clay sediments were subject to severe mechanical abrasion and aiagenesis, so that the remains retrieved and enumerated represent only a small proportion of the microfossils originally deposited. Shallowand deep-water cores from Lake tuexil were studied to test the phosphorus loading model developed for the twin basins. Unlike the Yaxha and Sacnab catchments, guexil experienced a lerminal Preclassic-Early classic Maya population decline that was undetected in the pollen record. Pollen zonation of the guexil cores was achieved by matching with the discrete assemblages from the twin basin profiles. Phosphorus loading rates derived from palynological zonation of the two sections failed to track the human population changes in the basin. This is in part due to the lag period between the time that soils are anthropogenically phosphorus-enriched following vegetation clearance, and the time they are delivered to the lake by colluviation. Additionally, ages assigned to pollen horizons in the Quexil cores are probably incorrect. Lake Quexil lies about 50 km west of the twin

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229 lakes, and while core zones from the three basins were matched by equivalency of pollen proportions, the delimited zones are not necessarily contemporaneous. Ages applied to the pollen zones in the Quexil cores might be inaccurate, but the horizons are useful zonation tools for testing the dependence of microfossil accumulation rates on the rate of total phosphorus supply, and for intra-basin core correlation. As at Yaxha and Sacnab, microfossil accumulation rates appear to have been independent of the supply rate of total phosphorus. Nevertheless, phosphorus limitation is not disproven, as the plant-available phosphorus delivery rate is unknown, and postdepositional loss of microfossils in the clay-rich zones of the cores makes the enumerated thanatocoenosis a poor estimator of the biocoenosis from which it was derived. Comparison of the Quexil shallowand deep-water sections revealed between-site sediment differences. The shallow-water core site lies in a subbasin of the lake. Located south of the islands in the lake, it was sheltered from the colluvial load coming off the steep north shore slopes. Consequently, zones of the shallow-water section contain more organic matter than equivalent zones of the deep-water profile. Direct deposit of north shore slopewash, as well as resuspension and focusing of fine, siltand clay-size inorganics into deep water, accounts for the high silica content of the deep-water core. Comparing zonal chemical and microfossil accumulation rates at the two sites demonstrated the profound effect of sediment focusing in this conical

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230 basin. The reconstruction of ancient phosphorus budgets for lakes with conical morphometry is. thus confounded by the unequal distribution of sediments over the basin floor, i single cores from such basins can provide inaccurate estimates of mean lake-wide chemical accumulation rates. As pollen was shown to be an unreliable tool for dating the tjiiexii cores, alternative methods were sought for fine-zoning the profiles. The Quexil H core was rezoned using particle size analysis, but phosphorus accumulation still failed to track population levels closely. Ultimately, fine-zoning was abandoned in favor of cruae division of the profiles from four lakes (Quexil, Macanche, Salpeten, Sacnab) into pre-haya and Maya zones. Zones were delimited by the organic matter content of the sediments, as the changing chemical stratigraphy of the profiles was thought to be a good basin-specific disturbance indicator. Maya period phosphorus and inorganic matter accumulation, rates exceeded predisturbance, baseline values in all six cores from the four lakes. Gross stratigraphic correlation of a shallowand deep-water section from Lake Salpeten again demonstrateo the consequences of sediment focusing in conical basins. The phosphorus loading model developed from the iaxha-Sacnab stuay was reevaluated by crude zonation of the six long cores from. four lakes (Quexil, Salpeten, Macanche, Sacnab). Multiple cores (deep-water ana. shallow-water) from conical basins Quexil and Salpeten verified pre;dictions concerning the influence of lake morphometry on calculated annual per capita phosphorus inputs. Deep-water sections, containing

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231 large amounts of resuspended and focused material, overestimated annual per capita loading rates, while shallow-water sections underestimateo ' the true value. In ellipsoid Lakes Macanche and Sacnab, single cores proved to be more reliable estimators of the lake-wide sedimentation rate. Despite the vagaries of sediment focusing, it was shown that riparian populations in the watersheds did supply phosphorus to the lakes at a rate of about O.b kg*capita~i«Yr~l. Testing of the phosphorus loading model was complicated by several, factors, some of which might be resolved by futurie work. Acoustic reflection profiles from the basins can provide a three dimensional picture of sediment distribution over the lake bottom (Schubert 19faU). Using this technique, calculated chemical accumulation rates derived from single cores could be corrected to account for the effects of unequal lake-wide sediment deposition. Testing of the model was reliant on the accurate delimitation of the true drainages surrounding the Peten lakes. Lacking detailed topographic maps of the watersheds, it was necessary to settle for rough estimates of thfe arainage areas. Intensive surveys of the basins might better define the true source area for colluvium, the riparian land area enclosed by nearest high ground. Between-basin differences in topography may influence actual per capita phosphorus inputs to the lakes. Individuals living on steep slopes certainly contribute more colluvium per year than persons occupying level terrain. For model testing purposes, it was assumed that basin-to-basin topographic differences were negligible and that

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Maya populations showed no inter-basin difference with respect to topographic preference. Detailed surveys ot the geographic features, in conjunction with settlement data, might explain between-lake differences in computed annual per capita phosphorus output figures. Riparian soil phosphorus concentrations and soil erodibility can also affect the per capita delivery rate of phosphorus to the lakes. Microregional differences in the local geochemistry are reflected in basin-to-basin chemical differences. Ihese dissimilarities are detected in lake waters, sediments, and catchment soils. Iron concentrations are notably higher in Quexil soils ana sediments than in soils or miids from Salpeten and Macanche. In the dolomitized SalpetenMacanche district, magnesium concentration is higher in soil, lake water, and sediment samples as compared to levels measured in the various compartments at quexil. Lake uuexil woula be expectea to have received a somewhat lower annual per capita phosphorus supplement than the other Peten lakes because a portion of the lake shore is contacted by phosphorus-deficient Exkixil soils that are resistant to erosion. Maya agro-engineering activities transported a large proportion ot the riparian soil phosphorus stock to the Peten lakes. Correcting tor the sedimented phosphorus load contributed by foiest vegetation and litter, it is estimated that 2600 years of human activity depleted the soil compartment phosphorus pool in the basins by a mean value ot about one-third. In computing the proportion of phosphorus lost from each basin, it was assumed that the disturbance-generated ioao originatea in the soils, litter, and vegetation lying within the computed riparian

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area. The watershed-lake system was assumed to have been closed with respect to this transfer ot phosphorus into or out ot the drainage. The only obvious external phosphorus source, that delivered-in precipitation, was accounted for by the subtraction of the baseline phosphorus accumulation rate prior to the computation of the disturbance load. i i During the 2600 years of Maya occupation in the Peten watersheds, the drainage-lake ecosystems may not have been closed in terms of phosphorus movement. Food grown outside the drainage may have been imported into the catchment for consumption. Nutrients contained within the comestibles would have been delivered to basin soils in refuse, excreta, and human burials. Ultimately, following a period of retention in the soils, the imported nutrients would have reachea the lakes in colluvium. It cannot be determined whether there was a net flow of phosphorus into the catchments. While the import of tooo might suggest the net centripetal movement of phosphorus to riparian population centers, this may have been partially balancea by the exoaus of large numbers, of Late Classic inhabitants who exported phosphorus sequestered in their bodies. If indeea there were a net flow ot phosphorus into the catchments, the computed fraction of phosphorus removed from basin soils by human disturbance might be overestimateo. Regardless of provenience, the sedimented phosphorus load represents a huge potential nutrient supply deflected from possible agricultural production.

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Maya populations of the central Peten drainages stressed the ecosystems through forest clearance and subsequent agro-engineering activities. There is ah irresistible temptation to link the consequent environmental strain to the eventual Classic Maya collapse. Forest removal, eroision, and rapid nutrient sequestering are documented in the paleolimnological recora. Further questions must be addressed betore these processes can be invoked to account for the Classic decline. Erosion and soil nutrient loss in the context of a tropical karst environment can certainly have a negative impact on agricultural output. Modern agronomic studies in the Peten could provide a quantitative measure of the long-term yield limitations imposed by extensive and intensive agricultural strategies. It is conceivable that ancient Maya agriculturalists perceived the loss of soil as a problem, and they may have taken steps to retain soils in some localities. Potential soil conservaton schemes should be postulated, and archaeological evidence for their. practice might be sought, though remnants of these agricultural. techniques may lie buried beneath thick beds of colluvium. Maya food procurement may have been limited not only. by, terrestrial nutrient loss, but by the massive siltation of the lakes. The microf ossil record suggests that lacustrine productivity declined during Early classic and Late and Postclassic times. Aquatic resource availability may have declined too. At Ttaxha and.Sacnab, archaeological recoveries of snail shells, turtle remains, and net sinkers are maximal in Middle Preclassic and Postclassic contexts (Rice

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23b 1976). The data suggest that aquatic animal populations declined in the Late Preclassic, perhaps due to habitat destruction ana over harvesting, recovering only after the Classic collapse. This study comprises one aspect of the "Historical Ecology of the Maya" project. Maya occupation of the Peten watersheds was shown to have drastically modified rates of material flow in the arainage-lake ecosystems. Models designed to explain the prolonged persistence or sudden disappearance of Maya civilization in the tropical lowland setting must consider the impact of human disturbance on the environment. The paleolimnological record has shed some light on the environmental history of the Peten. While elucidating the past, the information may prove to be valuable for preaicting the consequences of future human-induced stresses on the environment. The human population of the Peten is growing rapidly, doubling every 3-7 years (Schwartz 1977, Castellanos 1980). Modern population densities for the Peten as a whole remain minuscule (6 persons 'km'^) compared to Late Classic population levels deduced for several sites. However, the contemporary doubling time for the Peten population is about two orders of magnituoe shorter than the value computed for the ancient Maya population inhabiting the combined Yaxha-Sacnab drainage. Peten's natural resources are again being exploited, and as forest removal proceeas, the terrain will be utilized for crop production, cattle grazing, and silviculture. Development schemes for the region will likely be formulated to fulfill the economic objectives of a

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23(3 select few. The rapid deforestation that is anticipated may maximize profits in the immediate future, but the approach is myopic with respect to hopes for long-term resource exploitation, it has been suggested that Central American lowland forests on arable land will be completely removed by the year 2000, the rapidity of their demise being a function of the interaction between the demand for food production and the costs of clearing, drainage, and disease control (CEQ and DOS 1981). Ihere is no reason to believe that the Peten will be exempt from this scenario. The findings of this paleolimnological study support the recommendation that future development of the Peten proceed with as little perturbation of the natural forests as possible. Strip cutting of vegetation (Jordan 1962) ana other soil retention schemes should be implemented where forest clearance is necessary. These techniques should minimize erosion and nutrient loss. Unless far-sighted management proceaures are institutea, it may be possible over the next two decades to assess again the impact of wiaespread human-induced deforestation on Peten's tropical karst environment.

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BIBLIOGRAPHY Adams, R.E.W. 1973. The collapse of Waya civilization: A review o£ previous theories. Pp. 21-34 iri I'.P. Culbert (ed.). Ihe Classic Maya collapse. Univ. New Mexico Press, Albuquerque. 549 p. . 1977. The origins ot Maya civilization. Univ. New Mexico Press, Albuquerque. 465 p. . 1980. Swamps, canals, and the locations of ancient Maya cities. Antiquity 54: 206-214. , W.E. Brown, Jr., and l.P. Culbert. 1981. Radar mapping, archeology, and ancient Maya land use. Science 213: 1457-1463. , and T.P. Culbert. 1977. The origins of civilization in the Maya lowlands. Pp. 3-24 i£ R.E.Vii. Adams (ed.). The origins of Maya civilization. Univ. New Mexico Press, Albuquerque. 465 p. Altschuler, M. 1958. On the environmental limitations of Mayan cultural development. Southwestern J. Anthrop. 14: 189-198. American Public Health Association. 1971. Standard methods for the examination of water and wastewater. 13th Ed. Washington, L.C. 874 p. Anonymous. 1980a. Tendra solucion el problema ael Lago Peten-Itza? Peten-Itza 21: 9. Anonymous. 1980b. Algunas voces Mayas y su significado en Castellano. Peten-Itza 21: 24. Back, Vii. 1981. Hydromythology and ethnohydrolog^ in the New Wotlo. Water Resour. Res. 17: 257-287. Barnes, M.A., and W.C. Barnes. 1978. Organic compouncs in lake sediments. Pp. 127-152 in A. Lerman (ed.). Lakes: Chemistry, geology, physics. Springer-Verlag, New York. 363 p. Binford, M.W. 1982. Ecological history of Lake Valencia, Venezuela: Interpretation of animal microfossils and some chemical, physical, and geological features. Ecol. Monogr. 52: 307-333. . In Press. Paleolimnology ot the Peten lake District, Guatemala, I. Erosion and deposition of inorganic sediment as inferred from granulometry . Develop. Hydrobiol. 237

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239 Cooke, C.W. 1931. Why the Mayan cities of the Peten district, Guatemala, were abandoned. J. Washington Acad. Sci. 21: 2b3-2S7. Council on Environmental Quality and the Department of State. 1961. The global 2000 report to the President: Entering the twentyfirst century. Vol. 1 and 2. Blue Angel, Inc., Charlottesville, Virginia. 766 p. Covich, A. P. 1970. Stability of molluscan communities: A paleolimnologic study of environmental disturbance in the Yucatan Peninsula. Ph.D. thesis, Yale Univ., New haven, Connecticut. 163 p. Cowgill, U.M. 1962. An agricultural study of the southern Maya lowlands. Amer. Anthrop. 64: 273-286. , and G.E. Hutchinson. 1963a. Sex-ratio in childhood ana the depopulation of the Peten, Guatemala. Human Biol. 35: 90-103. , and G.E. Hutchinson. 1963b. Differential mortality among the sexes in childhood and its possible significance in human evolution. Proc. Natl. Acad. Sci. 49: 425-429. _, and G.E. Hutchinson. 1964. Cultural eutrophication in Lago di Monterosi during Roman antiquity. Internatl. Assn. Theor. Appl. Limnol. Proc. 15: 644-645. , and G.E. Hutchinson. 1973. El Bajo de Santa-Fe. Amer, Soc, Trans. 53(7): 1-51. Phil. _, G.E. Hutchinson, A. A. Racek, C.E. Goulden, R. Patrick, and' M. Tsukada. 1966. The history of Laguna de Petenxil, a small lake in northern Guatemala. Connecticut: Acad. Arts Sci., hem. .17: 1-126. ' , . Crisman, T.L. , 1978a. Interpretations of past environments from lacustrine animal remains. Pp. 69-101 iji D. Walker and J.C. Guppy (eds.). Biology and Quaternary environments. Australian Acad. Sci. , Canberra. . 1978b. Algal remains in Minnesota lake types: A comparison of modern and late-glacial distributions. Verh. Internatl. Verein. Limnol. 20: 445-451. Culbert, P.T. 1973. The Maya downfall at Tikal. Pp. 63-92 iin P.T. Culbert (ed.). The Classic Maya collapse, tini v. New Mexico Press, Albuquerque. 549 p. Davis, M.B. 1976. Erosion rates and land-use history in southern Michigan. Environ. Cons. 3: 139-148.

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BIOGRAPHICAL SKETCH Mark Brenner was born on March 3, 1952, in New York City. He attended high school at Rockland Country Day School in Congers, New York, and graduated in 1969. His undergraduate years were spent at Grinnell College, where he received a B.A. in Biology in 1973. Prom 1973 to 1975 he worked for the Department of Biological Oceanography at Lamont-Doherty Geological Observatory. He was involved with mariculture research at field stations in Queens, New York, and In St. Croix, U.S. Virgin Islands. From February 1975 through June 1975 he traveled extensively in central America. He began graduate school at the University of Florida in September 1975 and worked in tropical paleolimnology, receiving his M.S. in 1978. His M.S. and Ph.D. field work took him to Mexico, Belize, and Guatemala, where his primary interests were tropical ecology, limnology, and paleolimnology. 249

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I certify that I have read this study and that in my opinion it conforms to acceptable standards of scholarly presentation and is fully adequate, in scope and quality, as a dissertation for the degree of. Doctor of Philosophy. ( Cjhj^CL ''^ S. ^=^ Edward S. Deevey, Chairman Graduate Research Professor of Zoology and Graduate Research Curator, Museum I certify that I have read this study and that in my opinion it conforms to acceptable standards of scholarly presentation and is fully adequate, in scope and quality, as a dissertation for the degree of Doctor of Philosophy. Frank G. Nordlie Professor of Zoology I certify that I have read this study and that in my opinion it conforms to acceptable standards of scholarly presentation and is fully adequate, in scope and quality, as a dissertation for the degree of Doctor of Philosophy. %M^ Carter R. Gilberft Associate Professor of Zoology and Associate Curator, Museum I certify that I have read this study and that in my opinion it conforms to acceptable standards of scholarly presentation and is fully adequate, in scope and quality, as a dissertation for the degree of Doctor of Philosophy. Thomas L. Crisman Associate Professor of Environmental Engineering

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I certify that I have read this study and that in my opinion it conforms to acceptable stanaards of scholarly presentation and is fully adequate, in scope and quality, as a dissertation for the degree of Doctor of Philosophy. /'Ktf^ Cytrtq^iM^ )>^J-^-[ Douglas S. Jonesi Assistant Prof esEOE>^f Geology This dissertation was submitted to the Graduate Faculty of the Department of Zoology in the College of Liberal Arts and Sciences anu to the Graduate School, and was accepted as parial fulfillment of the requirements for the degree of. Doctor of Philosophy. April 1983 Dean for Graduate Studies and Research