Present and past nutrient dynamics of a small pond in southwest Florida

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Title:
Present and past nutrient dynamics of a small pond in southwest Florida
Uncontrolled:
Nutrient dynamics of a small pond in southwest Florida
Physical Description:
ix, 158 leaves : ill. ; 28 cm.
Language:
English
Creator:
Coleman, James Mark, 1946-
Publication Date:

Subjects

Subjects / Keywords:
Pond ecology -- Florida -- Sarasota County   ( lcsh )
Genre:
bibliography   ( marcgt )
theses   ( marcgt )
non-fiction   ( marcgt )

Notes

Thesis:
Thesis--University of Florida.
Bibliography:
Includes bibliographical references (leaves 150-157).
Statement of Responsibility:
by James Mark Coleman.
General Note:
Typescript.
General Note:
Vita.

Record Information

Source Institution:
University of Florida
Rights Management:
All applicable rights reserved by the source institution and holding location.
Resource Identifier:
aleph - 000014026
notis - AAB7212
oclc - 06080674
System ID:
AA00003891:00001

Full Text












PRESENT AND PAST NUTRIENT DYNAMICS
OF A SMALL POND IN SOUTHWEST FLORIDA












BY

JAMES MARK COLEMAN


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


UNIVERSITY OF FLORIDA


1979
















TABLE OF CONTENTS


LIST OF TABLES . .

LIST OF FIGURES. .

ABSTRACT . .

INTRODUCTION . .

BACKGROUND .... ...

The Present Environment .
The Historical Environment.
Recent Trends .

BULK PRECIPITATION .... ..

introduction. .
Methods . .
Results . .
Discussion. .

GROUND WATER . .


Introduction.
Methods .


Results and Discussion.

SEDIMENTS . .

Introduction .
Methods. .
Results and Discussion.

MACROPHYTES .

Methods .
Results and Discussion.

WATER . .

Methods .
Results and Discussion.


Page

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NUTRIENT DYNAMICS OF THE POND SYSTEM. ..... .. ..

Introduction . . ..
Methods . . .
Sediment Nutrient Dynamics . .
Sediment/Groundwater Interaction . .
Available Phosphorus and Groundwater Concentrations.

THE POND SYSTEM: PRESENT AND PAST. . .

Present Nutrient Budget. ...... ..
Historical Nutrient Budget .... ..

CONCLUSIONS . .. .

APPENDICES

A CHEMICAL COMPOSITION OF BULK PRECIPITATION. .

B CHEMICAL COMPOSITION OF THE POND SEDIMENTS. .

LITERATURE CITED. ... . ..

BIOGRAPHICAL SKETCH . . .


. 90

. 90
S. 90
S 91
. 96
. 103

. 107

. 107
. 110

. 119



. 124

. 131

. 150

. 158














LIST OF TABLES


Table Page

1 Departure of post-1950 mean temperatures from pre-
1950 means and some influencing factors at six
stations in peninsular Florida. . .. 15

2 Comparison of total phosphorus in bulk precipitation
collectors at Port Charlotte, Florida .. 25

3 Comparison of total phosphorus in bulk precipitation
collectors in the study pond (North Port,
Florida). . ... 25

4 Comparison of total phosphorus in bulk precipitation
collectors in the sandy flatlands near the study
pond (North Port, Florida). ... 25

5 Comparison of total nitrogen in bulk precipitation
collectors in Port Charlotte, Florida ... 26

6 Comparison of total nitrogen in bulk precipitation
collectors in the study pond (North Port,
Florida). ... . 26

7 Comparison of total nitrogen in bulk precipitation
collectors in the study flatlands near the study
pond (North Port, Florida). .. .... .. 26

8 Comparison of total phosphorus between North Port,
Florida, sites. .. . 28

9 Comparison of total nitrogen between North Port,
Florida, sites. .... 28

10 Comparison of total phosphorus between Port Charlotte and
North Port, Florida ........ . 29

11 Comparison of total nitrogen between Port Charlotte and
North Port, Florida ... 29

12 Concentration of phosphorus and nitrogen in groundwater
input wells in 1978 .... 41

13 Concentration of phosphorus and nitrogen in groundwater
output wells for 1978 ........ . 42

iv.








Table Page

14 Groundwater movement through the study pond. ... 47

15 Percent standard deviation . 61

16 Percent standard deviation . ... 63

17 Summary of data for center sediment cores. .. 64

18 Summary of data for the first concentric ring of
sediment cores . . 65

19 Summary of data for the second concentric ring of
sediment cores . ..... 66

20 Summary of data for the third concentric ring of
sediment cores . ... 67

21 Summary of data for the fourth concentric ring of
sediment cores . .... 68

22 Plant above-ground biomass data (June-July, 1976). 75

23 Concentration of phosphorus, nitrogen and carbon in
the plant species of the pond during June and
September, 1976. ... .. 76

24 Total amount of phosphorus, nitrogen and carbon in
the plant compartment of the pond during June,
1976 . . .. 77

25 Surface hydrology of the pond (1978) ... 81

26 Nutrient data for the pond (1978) . .82

27 Regression analysis of nitrogen and phosphorus on
organic matter . ..... 92














LIST OF FIGURES


Figure Page

1 Location of the study pond . 4

2 Generalized cross-sectional view of the study pond
environs . . ... 7

3 Annual 10-year mean temperature and precipitation
changes at Tampa, Florida . .... .18

4 The study site environs. ..... . .. 33

5 Calculated groundwater equipotential contours on
July 2, 1976. . . .. 34

6 Groundwater equipotential contours and flow
directions during 1976 at Pond 11 ... 35

7 Location of groundwater wells at the study pond ... 37

8 Cross-section of the pond showing input (east) and
output (west) wells . .. 39

9 Groundwater equipotential contours and flow directions
for 1978 sampling dates . .... .43

10 Direction of groundwater flow during 1976 and 1978 46

11 Head loss during 1976 and 1978 . ... 50

12 Area of the planar section passing through the pond
center during high and low water-level periods
(mean of 1977 and 1978) . ... 51

13 Study pond water heights during 1977 and 1978. .... 53

14 Sediment sampling scheme . . 56

15 Two cross-sectional views of the study pond basin. 58

16 Total organic matter in the sediments of the pond. 69

17 Total nitrogen in the sediments of the pond. .. 70








Figure Page

18 Total phosphorus in the sediments of the pond 71

19 Nutrient concentration and water volume changes
during 1978. . . .. 85

20 Atmospheric inputs and nutrients in the water
column . ... .. 87

21 Available phosphorus distribution with depth. .... 95

22 Three-dimensional view of a quarter section of the
pond sediments showing volume changes with
distance from the center . ... 98

23 Areal view of the sediments showing bands of total
phosphorus parallel to mean groundwater flow 99

24 Distribution of total phosphorus in the sediments
encountered by the groundwater front as it
passes through the sediments . .. 101

25 A. Distribution of total phosphorus in the
sediments; B. Predicted groundwater phos-
phorus concentration down-gradient from the
pond . . 102

26 Present-day nitrogen and phosphorus inputs, outputs
and storage in grams per year ... 109

27 Sedimentation rate curve .... .111

28 Morphogenesis of the study pond basin .... ... 112

29 Amount of phosphorus that has fallen on the pond
surface since the pond began functioning .... 114

30 Amount of phosphorus lost to groundwater since the
pond began to function. . 115

31 Nitrogen and phosphorus inputs, outputs and storage
in kilograms for the life of the pond. ... 117














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


PRESENT AND PAST NUTRIENT DYNAMICS
OF A SMALL POND IN SOUTHWEST FLORIDA

By

James Mark Coleman

June, 1979

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

Nutrient dynamics of a small pond in southwest Florida were

modeled in space and time. The primary storage compartment of the

system is the sediments, and the primary sources and sinks for nutri-

ents are the atmosphere and ground water. Of the 93 g yr-l of phos-

phorus entering the pond, primarily as bulk precipitation, approxi-

mately 69 percent is stored within the system and the remainder

leaves through the ground water. About 2400 g of nitrogen enter the

pond annually, and of this, 12 percent and 5 percent exit the system

via the atmosphere and ground water, respectively.

The pond's age, determined by radiocarbon dating, is approximately

5000 years, and during this time the sediments have accumulated 124 kg

of phosphorus and 3,140 kg of nitrogen. The atmosphere and ground water

have made a net contribution (input minus output) of about 124 kg of

phosphorus and 3600 kg of nitrogen during the past 5000 years, based

on present-day rates and estimated changes in the sizes of the


viii








receiving surfaces. The remainder, in the case of nitrogen, is

assumed to be atmospheric loss.

The importance of the groundwater sink for phosphorus is demon-

strated, and its potential role as a nutrient input source for surface-

water discharge boundaries is discussed.

Comparison of the annual atmospheric phosphorus input rate to

the results of other researchers seems to indicate that the present-

day rate may be spatially constant for undisturbed regions. The 5000-

year budget for the study pond indicates that the preindustrial
-2l-
atmospheric phosphorus input rate was about 27 mg m2 yr-l, about

20 percent less than today's rate. This figure may be close to the

preindustrial global rate.


Key words:


Nutrient cycling; nutrient budgets; groundwater chemistry;

bulk precipitation; sediment chemistry.














INTRODUCTION


One of the striking features of the pine flatwoods of southwest

Florida is the number of rounded depressions or ponds which dot the

landscape. For example, in Sarasota County, excluding the coastal

strand, these ponds number an average of 15-20 per square mile. They

range in size from a fraction of a hectare to many hectares. The

ponds are shallow (one-half to a few meters deep, generally) and con-

tain water much of the year. During the dry season (spring) only the

deeper ponds retain water, but in the wet season (late summer) water

may rise above the rims of the ponds and extend many meters into the

pine flatwoods proper. Because of their relatively small size and

closed basins, these ponds are promising subjects for nutrient budget-

ing considerations.

Urbanization in this part of southwest Florida has been extremely

rapid with population growth rates approaching 6 percent per year in

1974 and 1975. It has been suggested that as the pine flatwoods are

developed, the numerous ponds could be maintained in a somewhat

natural condition and that urban runoff could be channeled into them

and held until natural processes reduce nutrient concentration in the

water column. In addition, the ponds would be connected by swales, and

a natural buffer zone would be retained around them to provide a

functional and aesthetically pleasing system.







Because of the interest in this concept, it is useful to gain a

better understanding of the system dynamics of these ponds.

Of primary importance are the natural nutrient dynamics of the

pond system including the relative sizes of the constituent components.

In any future modeling of treatment capabilities, these baseline pa-

rameters are of critical importance. Secondly, assuming the ponds are

natural nutrient accumulators, it is important to know if the pond sys-

tem is tight, that is, do those nutrients which accumulate remain bound

within the system "forever" or does the system release them? Thirdly,

how has "flow through" changed over the life of the system and what are

the implications of these changes with respect to system development?

This study is designed to answer these questions and is organized

in the following manner. The present-day setting, environmental history

and recent environmental trends are presented as background information.

The next chapter discusses the primary input to the pond system, i.e.,

bulk precipitation. Ground water, which is the means by which a con-

servative nutrient, such as phosphorus, would leave the system, is dis-

cussed at this point. The following three chapters address the sizes

and some interrelationships of the pond system storage compartments.

The next chapter deals with the interaction between the major storage

compartment, sediments, and groundwater output. In the next to last

chapter the present-day nutrient budget, which is derived from ele-

ments of the previous chapters, is illustrated and discussed. Also

in this chapter the derivation of the "lifetime" budget of the pond is

presented and the "lifetime balance sheet" is discussed. The final

chapter addresses some basic considerations about nutrient cycling,

past and present, and ecosystem development of the pond system.














BACKGROUND


The Present Environment


Description, Location and Regional Physiography

The study pond is located in southern Sarasota County, Florida,

between the Peace and Myakka Rivers. It is 2.9 km north of the

Charlotte County line and 400 m east of Myakkahatchee Creek (Big

Slough) (Figure 1). Its Mercator Projection coordinates are 270 03' 33"

north latitude and 820 13' 31" west longitude. The region is in the

coastal lowlands part of the Floridian section of the Coastal Plain

province (Fenneman, 1938). According to White (1970), this physio-

graphic region is the Gulf Coastal Lowlands of the Mid-Peninsular

Zone. The province is extremely flat with a very gentle slope in a

generally southwestern direction. In the immediate vicinity of the

study pond, the slope is to the south-southwest at an approximate rate

of one meter per thousand. The province is bordered on the north and

east by the DeSoto Plain; on the south by the Immokalee Rise and

Southwestern Slope; and on the west by the Gulf Coastal Lagoons, Gulf

Barrier Chain, and the Gulf of Mexico. The Gulf Coastal Lowlands

reach their maximum areal extent in this part of the state where,in

the Caloosahatchee Valley,they follow the valley all the way to Lake

Okeechobee. From the Caloosahatchee Valley, the Lowlands gradually

narrow northward until near Bradenton, Florida, they are only about

15 km wide (White, 1970).












TAMPA

/







BRADENTON 4/YAKKA R/VER

30ARASOTA- -



STUDY



PUNTA GORDA




GULF OF FORT MYERS
kfEX/CO




0 50 km


Figure 1. Location of the study pond.








Climate


The climate of the region is typified by warm, somewhat humid

summers of long duration and short, mild winters with occasional in-

vasions of cool northern air (Bradley, 1972). This climatic type was

classified by Trewartha (1961) as humid mesothermal, humid subtropical

subgroup and by Thornthwaite and Mather (1955) as moist, subhumid with

a moisture surplus of 0 20 percent. The dominant factors controlling

the climate are latitude and proximity to the Atlantic Ocean and Gulf

of Mexico (Bradley, 1972).

Solar radiation for the region, according to Landsberg (1961),

amounts to nearly 160 Kcal cm-2yr1 at the surface and about half is

stored as net radiation (Budyko et al., 1962). The mean annual

temperature at Fort Myers, Florida, for the period 1937-1976 was

23.30C; the mean January temperature for that period was 18.1C and

mean July temperature, 27.90C. Relative humidity year-round is usually

80-90 percent at night and decreases to 50-60 percent in the early

afternoon. The mean summer wind speed is 11.6 km hr- and mean dry

season wind speed is 13.9 km hr-1. From October through December, the

direction of the prevailing wind is from the northeast; and for the

remainder of the year from the east (NOAA, 1976). The mean annual

precipitation at Fort Myers from 1937-1976 was 135.5 cm, 65 percent of

which fell during the summer months (June through September). An

average of 95 thunderstorm-days occurred each year with 78 percent of

these in the summer months (NOAA, 1976).

The thunderstorm frequency during the summer months in peninsular

Florida reaches a maximum for the United States and possibly for the

entire earth (Trewartha, 1961). This phenomenon, according to Byers








and Rodebush (1948), results from strong low-level convergence caused

by afternoon sea breezes moving into the peninsula from both east and

west. This double sea breeze convergence stimulates the vertical

growth of convective clouds. The convergence prevails up to an al-

titude of about 1,200 m with a maximum reached in the late afternoon

when the two-sided sea breeze is usually strongest (Trewartha, 1961).

Tropical storms have, at times, contributed a significant amount

of precipitation to the region. Court (1974) estimates that tropical

storms from 1931-1960 accounted for 10-15 percent of the June to

October rainfall in peninsular Florida. The chance of a storm of

hurricane intensity striking the Fort Myers area in any given year

has been estimated by Bradley (1972) to be 1 in 11.


Geology and Geomorphology


The sandy flatlands, as Parker and Cooke (1944) have called the

region, are poorly drained and dotted with shallow ponds (Figure 2).

These ponds are often nearly circular in shape, with diameters to a

few hundred meters and are generally about one meter or so in depth.

They occur in deep sands as well as in places where the sand mantle is

thin. They may be related to solution of the underlying consolidated

strata or to inequalities in the floor of a previously regressing sea

(Parker and Cooke, 1944).

The surficial sands rest uncomformably upon the Caloosahatchee

Marl which in turn uncomformably overlies the Tamiami Formation. The

surficial sands are generally medium to find grained, sometimes

mottled, and with occasional fossiliferous members (Dubar, 1962; Brooks,

1966). The Caloosahatchee, a sandy, shell marl, indurated at the top


















-JO


C~4i~\








and containing abundant fossils, is generally less than one meter in

thickness. Along the Myakkahatchee Creek, about 1 km NNE of the study

pond, it is 60 cm thick (personal observation). The Tamiami is a

fossiliferous, medium to coarse calcareous sand (Dubar, 1962; Brooks,

1966). The thickness of the Tamiami is undetermined here; however, it

is most likely relatively thin since the underlying Hawthorne is known

to outcrop a few kilometers to the north (personal observation; Vernon

and Puri, 1964).

In recent years there has been considerable discussion about the

ages and relationships of these strata. The following is a summary of

Brooks' (1968) interpretation of the Plio-Pleistocene stratigraphy of

the region. The Caloosahatchee Formation has two members. The Fort

Denaud Member is late Pliocene age and corresponds to the Okeefenokee

eustatic sea-level stand of +120-140 feet (36-43 m). The Bee Branch

Member is Aftonian in age and corresponds to the Wicomico Sea which was

at +90 to 100 feet (27-30 m). The surficial sands are divided into two

formations. The Fort Thompson Formation (three members) is of

Yarmouthian age and is related to the Penholoway (+70 feet, 21 m)

and Talbot Terraces (+42 feet, 13 m). The Sangamonian age Pamlico

Sea (+25 feet, 8 m) is represented by the Coffee Mill Hammock Formation.

Apparently, the study pond has been above sea level since the

Sangamonian interglacial period.

Soils

The dominant soil type in the sandy flatlands of the region is the

Immokalee fine sand. This type is classified as a Ground-Water Podzol

which is typified by a thin organic surface layer above a light grey,








leached layer that rests abruptly upon a black to dark greyish-brown

B horizon (USDA, SCS, 1959). In the most recent soil classification

system, this soil would be a sandy, siliceous, hyperthermic, arenic

haplaquod (USDA, SCS, 1977).

The soil (sediment) of the study pond is classified as Delray

fine sand in the center and Pompano fine sand in a concentric band

between the center and the Immokalee fine sand of the sandy flatlands

surrounding the pond. The Delray soil is a Humic Gley which is a

poorly drained, hydromorphic group of soils with dark colored organic

mineral horizons of moderate thickness underlain by mineral gley

horizons. The Pompano soil belongs to the Low-Humic Gley group of

soils. The group is characterized by poor drainage and a thin surface

horizon moderately high in organic matter which overlies undifferen-

tiated, mottled grey and brown, gley-like mineral horizons (USDA, SCS,

1959). In current soil taxonomy terminology, the Delray would be a

loamy, mixed hyperthermic gross arenic argiaquoll, and the Pompano,

an arenic or gross arenic ochraqualf (USDA, SCS, 1977).

In 1898, Dokuchaev first recognized the importance of several

environmental factors in the formation of soils. Jenny (1941), elabo-

rating on Dokuchaev's work, proposed the relationship that any soil

property was a function of climate, organisms, relief, parent material,

and time. The three soils of the study area dramatically illustrate

this relationship. High rainfall and low relief dominate the soil

forming processes for these soils. In combination, the two factors

produce a groundwater table that is near the surface year-round. The

three soils, however, represent a micro-environmental sequence of








relief which results in very different soil types. The surface of the

Immokalee is about one meter above that of the Delray. The height of

groundwater ranges from one to two meters below the surface of the

Immokalee in the dry season to just above the surface during the rainy

season. The same groundwater stand in the Delray is just above the

surface to one-half meter below the surface in the dry season, and in

the wet season a meter or more of surface water occupies the Delray

depression. This phenomenon results in the leaching of the surface

layers of the Immokalee soil as the dominant process and the accumula-

tion of the leachates in the vicinity of the mean low water level. The

acidity of the rainfall, as well as the acidity of the litter and

leachate from the dominant plants, hastens the removal of organic

matter and minerals from the surface layers of the Immokalee. In the

Delray, however, the occurrence of standing surface water for much of

the year minimizes oxidation and results in the accumulation of organic

matter in the surface layers. However, in the dry years, especially

with low winter rainfall, the water table drops below the surface and

spodosolic processes may dominate in the Delray also. In the Pompano,

neither process dominates and hence an intermediate soil type is formed.

None of the soils exhibit much pedogenic development. This is the

result of the interaction of time and parent material. It is not known

how long it takes for a well-defined soil profile to develop, and,

perhaps, under the prevailing climatic and relief regimes of the study

site, one could never develop. Other factors aside, the time required

is directly related to the resistance to weathering of the parent

material. The parent material of the study area soils is almost pure

quartz sand (Dubar, 1962) which is a highly resistant substrate. These








materials have only been exposed to the agents of weathering since the

regression of the Pamlico Sea (probably Sangamonian Age).

The Historical Environment


The pond system is four-dimensional, and the fourth dimension,

time, may be the most critical for understanding the nature of the sys-

tem. The agents of time are environmental conditions, which may be

static or changing in the time frame of the pond's existence. Static

conditions have a chronic effect upon the system, tending to drive it

in one direction, and given sufficient time the end result will be the

filling in or drying up of the pond with complete oxidation of sedi-

ments. Changing environmental conditions can have the same effect if

the change is unidirectional, thereby intensifying the effects of

static conditions. However, if the change is reversible, the effect

will be preservation of the system as long as the period of any one

direction does not exceed the system's capacity for resilience.

The pond system came into being about 5000 years ago (4565 120,

University of Miami Radiocarbon Dating Laboratory--#UM1494). Since

that time, it has been subject to the influences of sea level and

climate as they affect groundwater height. Sea-level changes are the

subject of much controversy today. Several authors (Shepard, 1963;

Scholl and Stuiver, 1967; Milliman and Emery, 1968; Scholl et al.,

1969) believe that sea level has risen continuously for at least the

last 5000 years. The effect of a continuously rising sea level, and

hence ground water, would be an increasing sedimentation rate. How-

ever, using the Scholl et al. (1969) curve, the increasing rate would be








decelerating for the past 5000 years and approaching stasis at the

present.

A second group of investigators (Fairbridge, 1961; Morner, 1969;

Fairbridge, 1974) have indicated that sea level reached its present

stand at about 6000 BP and has been fluctuating since then.

The effect of fluctuating sea level, and hence groundwater height,

upon the pond would be to establish the sedimentary process as dominant

during relatively high stands, but during low stands, an oxidizing

environment would prevail and the pond would act more like a periodi-

cally flooded soil. The interaction of these two regimes would result

in a pond system with a very slow net sedimentation rate. Several

shallow Florida lakes and ponds are known to have very slow sediment

accumulation rates, for example, Mud Lake's recent history, 0.39 mm
-l -
yr (Watts, 1971), Spanish Pond, 0.17 mm yr-l (Deevey and Brenner,

unpublished),and Site No. GDF-125, 0.2 mm yr-1 (Clausen et al., 1979).

Climatic fluctuations, instead of sea-level changes, may explain

the peculiar sedimentary histories of these ponds. During periods of

high precipitation and low evaporation, the sedimentary system would

dominate in the pond and, the reverse being true, the oxidation process

would dominate. It can be inferred from Denton and Karlen (1973) and

LaMarche (1974), among others, that there have been alternating warm

and cool periods during the late Holocene. The link between cooler

temperatures and decreased precipitation is fairly well documented in

late-glacial times (Damuth and Fairbridge, 1970; Bonatti and Gartner,

1973; Parmenter and Folger, 1974; Williams et al., 1974; Deuser
at al., 1976; Gates, 1976), and Simpson and Hebert (1973) and Moran

(1975) believe that in peninsular Florida this link may be due to the








inhibitory effect of decreased sea-surface temperatures on hurricane

formation. From recent work in the Caribbean and equatorial Atlantic,

several researchers have, in fact, reported differences in paleo-

temperatures ranging from 2 to 6C, between glacial and nonglacial

stages (Emiliani, 1966; Shackleton, 1967; Dansgaard and Tauber, 1969;

Lynts and Judd, 1971). A decrease in hurricane activity would not

only result in decreased precipitation but also a decrease in cloud

cover during the high evaporation season of summer and early autumn.

Seasonal variation in precipitation and evaporation, apart from

long-term climatic or sea-level changes, may be the dominant causal

agent in the sedimentation pattern of the pond. A wet and dry cycle

with the very short period of one year would have the same effect on

total accumulation as long-term cycles.

It seems likely that some combination of seasonal and long-term

climatic and sea-level changes have caused variations in groundwater

heights which have resulted in an alternating accumulation-decomposition

system in the pond. Following Scholl et al., (1969), sea-level rise

would be a unidirectional environmental change in the experience of the

pond. Long-term climate, on the other hand, is bidirectional and con-

tains the nested bidirectional set, seasonal variation.

The influence of these patterns on the past nutrient dynamics of

the pond has probably been considerable. It is evident that in the

decomposition mode nitrogen and phosphorus would become available for

exchange between components of the system. Perhaps less obvious is the

fact that with changing groundwater heights, the sizes of the inter-

faces between components would also change and, hence, so would rates

of exchange.








Recent Trends


We have seen that environmental conditions have been different in

the past, and it is interesting to speculate on what may be in the

future for this region. The pattern of glacial and interglacial

cycles is well documented (Prell, 1974; Shackleton and Opdyke, 1973;

Imbrie et al., 1973; Kukla, 1970; Hays et al., 1969) as is the pattern

of cold and warm periods between major events, especially in recent

times (LaMarche, 1974; Dansgaard et al., 1971; Lamb, 1969; 1966).

According to Mitchell (1963; 1972),Reitan (1971), and Bryson (1974),

we are headed toward another cool period. Whether it is just a cool

fluctuation or a more pronounced cold period is unknown, as are the

effects of man-made interference.

The annual mean temperature change at Tampa, Florida, was compared

to the average change for the Northern Hemisphere (Reitan, 1971;

Mitchell, 1972) with relatively good agreement. The Tampa record

extends sporadically into the 1820's, but no records exist from the

late 1850's to the mid-1880's. From the available record, it can be

seen that temperatures rose rather rapidly in the 1840's; there was a

decline around the turn of the century and then another relatively rapid

rise; a leveling-off occurred in the 20's and 30's and then a slight

rise in the 1940's; and finally a post-1950 decline. Bryson (1974) has

described the 1940's as a period of unprecedented warmth in the past

millennium and both the Tampa and Northern Hemisphere curves seem to

substantiate this claim for recent times.

With this in mind, the post-1950 temperature regimes for six

peninsular Florida stations were compared to the 1940's thermal maxi-

mum (Table 1). The annual mean temperature for peninsular Florida













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decreased by 0.12'C, but the winter temperature declined by 0.53C

and the summer by only 0.01C.

One possible scenario for this pattern of temperature decline is

the interaction between long-wave radiation flux and the CO2 content

of the atmosphere. Rasool and Schneider (1971) have shown that tempera-

ture increases as the logarithm of atmospheric CO2 contentand Machta

(1971) and Machta and Telegadas (1974) have shown a rapid rate of in-

crease in CO2 content in the last 40 years. Dansgaard et al. (1971)

believe that, as indicated by the Camp Century ice core cycles, we

should be in a cooling period, but Broecker (1975) says that the in-

crease of CO2 in the atmosphere has interferred with the natural cycle

and modified the decline in temperature. This interference may be

more significant in the summer when the long-wave radiation flux is

13 percent greater than in winter in peninsular Florida (Table 1).

As a result, summer temperatures have changed little, but winter

temperatures have declined at about the rate predicted by the Camp

Century core. The net result is an annual change very close to that

predicted by Broecker's (1975) combined effect of CO2 and the Camp

Century cycles.

Hydrologic evidence from peninsular Florida indicates that a

dry period is approaching. Moran (1975) and Coleman (in preparation)

have demonstrated that peninsular Florida has experienced unusually

arid conditions in recent times and have attributed these to the

decline in hurricane activity (Hope, 1975) in recent years due to a drop

in low latitude sea-surface temperatures and persistently stronger

upper-level westerlies over the Caribbean Sea (Simpson and Hebert,

1973). Supportive evidence of this hypothesis can be found in the








decline in river flow volumes in peninsular Florida. Coleman (in

preparation) established that a sharp decrease in river flow in the

Peace and Kissimmee Rivers had begun in the early 1960's. In addi-

tion, ten rivers, representing a combined drainage area of over

20,000 km2 and a range in period of record from 27 to 46 years,were

compared using post- and pre-1960 averages. The result was a 16-38

percent decrease in flow after 1960 (USGS, 1978). The implication is

that peninsular Florida is experiencing drought conditions when

compared to recent records.

A link between temperature and precipitation changes is evident

at Tampa, Florida (Figure 3). A rapid warming occurred in the 1840's

followed 40 years later by a substantial increase in precipitation.

Temperature declined in the 1890's and precipitation 10 years later.

This same pattern reappears later with temperature increasing rapidly

from 1900-1920 and decreasing in the 1950's. Precipitation increase

lags temperature again by 40 years and the decrease by only 10. Ap-

parently, the response time for temperature-linked precipitation

increase is about 4 times the response time for decreases.

With regard to the sea-surface temperature/hurricane activity

hypothesis, it appears that the warming of the sea surface is a slower

process than cooling. It is interesting to note that there has been

little change in summer air temperatures in peninsular Florida in the

last 40 years, but there has been a one-half degree centigrade drop in

winter temperatures (Table 1). Since there has been little change in

summer temperatures, it would seem that the evaporative and convective

forces which control the growth of thunderstorms may not have changed.










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19


This indirectly tends to support the sea-surface temperature/hurricane

hypothesis.

In summary, peninsular Florida appears to be cooling and drying

with man-made factors interfering with the trend.














BULK PRECIPITATION


Introduction


The atmospheric input of nutrients to aquatic systems has been

considered insignificant in relation to that contributed by terrestrial

runoff. However, with increasing atmospheric pollution from various

man-made sources, this may no longer be valid (Wetzel, 1975). Gambell

and Fisher (1966) suggested that in areas where surface waters are low

in dissolved materials, atmospheric inputs may be a major determinant

of chemical composition. Likens and Bormann (1972) found that in some

relatively oligotrophic, mountainous regions atmospheric fallout is a

major contributory source of nutrients. At Lake Weir, Florida, the

rainfall input of phosphorus and nitrogen was estimated to be about

15 percent of all surface runoff (Brezonik and Messer,,1977). In the

sandy flatlands of Southwest Florida where topographic relief is almost

totally absent, surface runoff is insignificant and groundwater move-

ment is extremely slow. Atmospheric bulk precipitation (rainfall and

dry fallout) is expected to be the major source of nutrient input to

the small ponds of this region.

Methods


The sampling of bulk precipitation is subject to two major sources

of error in the field: error due to poor sample preservation and that

due to biological contamination. In order to have confidence in
20








nutrient analyses, EPA (1974) states that samples should not be held

for more than 24 hours. Therefore, unless a daily sampling program is

instituted, sample preservation can be a problem. Some researchers

have attempted to circumvent this problem by employing refrigerated

samplers (Gambell and Fisher, 1966; Pearson and Fisher, 1971; Mattraw

and Sherwood, 1976). Refrigerated samplers are generally based on a

modification of one described by Gambell and Fisher (1966) and consist

of a glass funnel connected to a reservoir by tubing. The reservoir

is contained in a commercial refrigeration unit or ice chest, and the

temperature is artificially maintained at about 4C. These collectors

are expensive to install and maintain, and the samples, according to

EPA (1974), should still not be held for more than 24 hours. In

addition, the funnel is not the best receptacle for dry fallout. Dry

particles falling on a dry surface are subject to removal by wind

action.

In my study, due to economic constraints and the uncertainty of

refrigerated preservation, I decided to use open polyethylene buckets

with several centimeters (actual amount depended on the season) of

acidic water in them. The pH (3.9) of this water was the same as the

mean pH, i.e., x of -log [H+], of the study pond. This pH was ob-

tained by adding 0.01 N HC1 todistilled, deionized water. The

rationale behind this method is that, although the ponds and buckets

differ considerably in physical, chemical and biological properties,

by mimicking the acidity the receptacles could approach the functional

regime of the pond. With respect to phosphorus, this method was con-

sidered to be adequate. Since phosphorus does not have a gaseous

phase and since the particulate and soluble phases of total phosphorus








are used to determine the final number, the interchange between these

two components was considered for this study to be unimportant. As

for total nitrogen, the results should be viewed more critically. In

the absence of clear knowledge of the interplay between gaseous and

soluble phases of nitrogen, I cannot be sure that nitrogen exchange was

not occurring at the air-water interface, and hence the nitrogen

results should be interpreted as indicative of nitrogen inputs.

With regard to biological contamination due to bird feces, it was

predetermined to discard those samples that were apparently contaminated.

Samples with insects in them were analyzed to be compared with those

without insects to see if there was a consistent and significant dif-

ference. Chlorophyll content was measured in several samples as a

check for algal contamination.

Six bulk precipitation collectors were installed in duplicate on

wooden platforms about 1.5 m above the ground surface at three sites

in the study area. Two side-by-side collectors were installed in the

study pond, two in the sandy flatlands about 20 m from the western

edge of the pond and two in downtown Port Charlotte about 18 km south-

east of the study pond.

Samples were collected biweekly from the beginning of June to the

end of October, 1978. Samples were transported, on ice, to the labora-

tory where they were filtered immediately. The filter papers were

oven dried and stored in jars to await sediment analysis. The

filtrate was analyzed for nutrients by the following methods:

for TP: Persulfate digestion
Automated Colorimetric Ascorbic Acid
Reduction Method (EPA, 1974)








for TKN: Sulfuric acid digestion
Automated Selenium Method (EPA, 1974)

for NO3+ NO2: Automated Cadmium Reduction Method (EPA, 1974)

Filter papers and filter paper blanks were digested on a block

digester in FisherR high temperature bath oil. The oil is used to

allow uniform heating of the digestion tubes. The filters were

digested by the sulfuric acid-hydrogen peroxide method (modified from

EPA, 1974; see discussion in chapter on sediments). The digested

sample was then analyzed by the same methods as the solution phase.
-2 -l
Concentration raw data were converted to mg m2 yr by the

following formula:


N (mg m2 yr-l) =


C (mg 1-1) x V (1) x 10,000 cm2 m-2 x 365 days yr-1

A (cm2) x D (days)


where:


N = amount of nutrient

C = concentration of nutrient

V = field volume for solution phase; digestii
volume for particulate phase

A = area of the plane defined by the top of
receptacle (374.11 1.72 cm')

D = number of days sample was exposed to the
atmosphere


on tube


the


Results


The nutrient data were averaged over the sampling period with the

result that one number was obtained for each phase (solution, particu-
late and total) in each of the six collectors (raw data appear in
Appendix, Tables A-1 A-6). Several samples, however, were less than








detection limits, and these presented somewhat of a problem. The

first impulse is to exclude them from the mean. However, this has the

effect of establishing an unrealistically high mean since all the ex-

cluded values are at the low end of the range. A better estimate of

the true mean can be achieved by including them. But what is the

best way to deal with values that are less than detection limits?

The bestestimate of the true values for these samples can be obtained

by narrowing the range as much as possible and then taking the mid-

point. The range was narrowed, in the case of phosphorus, using the

orthophosphate phosphorus value as the low end of the range when this

value was above detection limits. As for nitrogen, the low end was

established by the total value of ammonia and nitrate+nitrite when

these were above detection limits. In some cases, the measured con-

stituents of total phosphorus and total nitrogen were also less than

detection and zero was used as the low end of the range.

The first priority of data analysis was to determine if statistical

differences existed between duplicate collectors. The differences be-

tween the mean of duplicate collectors were compared using a t-test.

At an a of 0.05 there is no difference between duplicate collectors at

any of the three sites for either phosphorus or nitrogen (Tables 2-7).

Based on this conclusion, duplicate collectors were lumped at each

site, increasing the N (number of samples), and thereby allowing for

more sensitive intersite comparisons.

The next question to consider is: Do the ponds receive different

amounts of phosphorus and nitrogen than the sandy flatlands? To

answer this question, the new means, achieved by averaging the results

from intrasite collectors, were compared using the t-test of the









Table 2. Comparison of total phosphorus (mg m-2 yr-1) in bulk precipi-
tation collectors at Port Charlotte, Florida.


Phase North Collector South Collector
t a
x s n x s n

Solution 75.9 48.6 8 52.3 +29.5 8 1.174 0.272
Particulate 46.8 20.8 8 33.6 19.9 8 1.297 0.220
TOTAL 122.7 42.6 8 85.9 33.7 8' 1.916 0.080








Table 3. Comparison of total phosphorus (mg m2 yr -) in bulk precipi-
tation collectors in the study pond (North Port, Florida).


Phase North Collector South Collector
t a
x +s n x s n

Solution 11.9 + 6.0 9 9.8 7.8 7 0.610 0.558
Particulate 20.6 11.7 9 16.2 6.8 7 0.882 0.394
TOTAL 32.5 14.5 9 26.0 10.3 7 1.002 0.344






Table 4. Comparison of total phosphorus (mg m2 yr- ) in bulk precipi-
tation collectors in the sandy flatlands near the study pond
(North Port, Florida).


Phase East Collector West Collector
t a
x +s n +s n

Solution 21.3 19.0 11 17.1 11.2 11 0.632 0.539
Particulate 17.9 14.5 11 14.2 + 9.1 11 0.717 0.483
TOTAL 39.2 26.0 11 31.6 16.9 11 0.813 0.427








Table 5. Comparison of total nitrogen (mg m-2 yr- ) in bulk precipita-
tion collectors in Port Charlotte, Florida.


Phase North Collector South Collector
t c
x +s n +S n

Solution 1,231 269 8 1,470 967 8 0.673 0.513
Particulate 238 164 8 200 166 8 0.461 0.664
TOTAL 1,470 +328 8 1,670 989 8 0.543 0.606






Table 6. Comparison of total nitrogen (mg m-2 yr ) in bulk precipita-
tion collectors in the study pond (North Port, Florida).


Phase North Collector South Collector
t a
x s n x +s n

Solution 776 300 9 571 282 7 1.391 0.189
Particulate 77 48 9 95 71 7 0.606 0.561
TOTAL 853 317 9 666 298 7 1.201 0.260






Table 7. Comparison of total nitrogen (mg m2 yr-) in bulk precipita-
tion collectors in the sandy flatlands near the study pond
(North Port, Florida).


Phase East Collector West Collector
t a
x +s n x s n

Solution 752 528 11 788 559 11 0.155 0.880
Particulate 81 92 11 76 54 11 0.155 0.880
TOTAL 833 546 11 864 +580 11 0.129 0.899








difference betweentwo means. Once again, with an a of 0.05, no dif-

ferences were observed in either phosphorus or nitrogen, and hence all

four collectors at the two sites were combined to establish a new mean

for a relatively undisturbed natural area in North Port, Florida

(Tables 8 and 9). These means were 104.3 41.7 mg m2 yr and

33.0 18.5 mg m-2 yr-l of total phosphorus at Port Charlotte and North

Port, respectively. Total nitrogen was 1,569 717 mg m-2 yr- at Port

Charlotte and 816 461 mg m-2 yr-1 at North Port (Tables 10 and 11).

These means were then compared to see if there is a difference

between atmospheric nutrient input to a small but rapidly growing urban

area, Port Charlotte, and a relatively undisturbed area, North Port.

The results are illuminating indeed. The differences between both

phosphorus and nitrogen are very highly significant and approximately

three times as much phosphorus and twice as much nitrogen are falling

on Port Charlotte as on North Port, near the study pond (Tables 10

and 11). The nitrogen to phosphorus ratio is also different between

Port Charlotte and North Port. The N:P ratios in the soluble, particu-

late, and total components of bulk precipitation are: 21.1, 5.4 and

15.0 for Port Charlotte and 46.8, 4.7 and 24.7 for North Port (Tables

10 and 11).

Discussion


According to Brezonik and Messer (1977), studies on nutrient

inputs in the subtropics are extremely scarce. However, there is one

study in peninsular Florida which can be compared to these results.

At Gainesville, Florida, 290 km north of this study, Brezonik et al.

(1969) reported rainfall input values of 44 mg m-2 yr-l of phosphorus















Table 8. Comparison of total phosphorus (mg m-2 yr ) between North
Port, Florida, sites.


Phase Pond Collectors Flatlands Collectors
t a
x s n x s n

Solution 11.0 6.7 16 19.2 15.4 22 1.991 0.056
Particulate 18.7 9.8 16 16.2 11.8 22 0.691 0.495
TOTAL 29.7 12.8 16 35.4 21.8 22 0.933 0.364













Table 9. Comparison of total nitrogen (mg m2 yr ) between North
Port, Florida, sites.


Phase Pond Collectors Flatlands Collectors
t a
x s n x s n

Solution 686 302 16 770 531 22 0.568 0.582
Particulate 85 58 16 79 74 22 0.269 0.797
TOTAL 771 313 16 849 550 22 0.509 0.624















Table 10. Comparison of total phosphorus (mg m-2 yr ) between Port
Charlotte and North Port, Florida.


Phase Port Charlotte North Port
t a
Ss n x s n

Solution 64.1 +40.7 16 15.7 13.0 38 6.641 <0.001
Particulate 40.2 20.8 16 17.2 11.0 38 5.314 <0.001
TOTAL 104.3 41.7 16 33.0 18.5 38 8.765 <0.001













-2 -1
Table 11. Comparison of total nitrogen (mg m2 yr ) between Port
Charlotte and North Port, Florida.


Phase Port Charlotte North Port
t a
X +s n X +s n

Solution 1,351 696 16 735 446 38 3.897 <0.001
Particulate 219 161 16 81 67 38 4.483 <0.001
TOTAL 1,569 717 16 816 461 38 4.617 <0.001








and 580 mg m- yr of nitrogen. It is not known whether these values

include dry fallout. Pearson and Fisher (1971) studied atmospheric

nutrient inputs in New England, New York and Pennsylvania and found an

annual input of 16 mg m-2 of phosphorus and 297 mg m-2 of nitrogen.

The nutrient input of phosphorus at North Port is greater than

that of the New England study, but peninsular Florida is thought to

be a high phosphorus area. The nitrogen input at North Port is

greater than either of the above studies, but the variance around

my mean is more than half of the mean, and the variance in the two

comparative studies is unknown. In addition, my study only encom-

passes about half of a year, although it includes elements of both

wet and dry seasons.

The Port Charlotte nutrient inputs are high when compared to the

North Port results and the northern studies. The Port Charlotte

values, however, are low by comparison to those obtained in a recent

study of bulk precipitation (East Central Florida Regional Planning

Council Report, unpublished). In an improved pasture, based on one

sample, a rateof200mg-pm-2 yr-1 was calculated and at Tampa, Florida,
-2 -1
based on two samples, 300 mg-p m yr














GROUND WATER


Introduction


In light of the almost total absence of relief and high soil

permeabilities of this region, it was suspected that the surface of the

water table is the major sink for nutrients, particularly phosphorus,

which does not have a gaseous phase in its cycle. Data on the nutrient

composition of the water-table aquifer of the region are not abundant,

and data on Sarasota County are unknown to the author. However, the

U. S. Geological Survey (1978) has monitored wells, tapping various

aquifers in surrounding counties and found that phosphorus and nitrogen

are highly variable, ranging from a few hundredths of a milligram per

liter to several milligrams per liter. Sutcliffe (1973) has analyzed

the chemical composition of several wells in Charlotte County and found

nitrates in the water-table aquifer in the Cape Haze area to average

0.8 mg 1-1 (two observations) but has no data on phosphorus in this

aquifer. In the shallow artesian aquifer (sampling interval = 20-26 m),

he reports values of 0.14 and 5.8 mg 1-1 of phosphate and nitrate,

respectively, based on a single observation. The need for more exten-

sive nutrient composition studies on this important sink seems fairly

obvious.








Methods

In 1976, four shallow groundwater wells (1.2 m below ground sur-

face) were installed around pond 11 (about 850 m northeast of the study

pond, Figure 4) at the major compass points. Water height was measured
in these at varying intervals from July to November, 1976, and once in
June, 1977. With these data, the direction and strength of the head

can be calculated. For example, on July 2, 1976, the groundwater

height in the south well was 7 cm above the water height in the east,
23 cm above the north and 30 cm above the west. In order to determine
the groundwater equipotential contours for this date, it is necessary

to find the point on the north-south transect at which groundwater

height would be 7 cm below the water height in the south well (Figure 5).
The same is done on the west-south transect, then a line is drawn
through the two points and the east well, giving a 7 cm equipotential
contour relative to the south (highest groundwater stand) well (Fig-
ure 5). Subsequent contours are represented by lines equidistant from
the original contour at all points. Groundwater flow direction is
perpendicular to the contours at any point.

Figure 6 shows the groundwater contours and flow direction

for all 1976 sampling dates (variation in flow direction is dis-

cussed later). The direction of flow was generally east to west in

1976. Based on this analysis in April, 1978, ten wells were in-
stalled at the study pond in the following configuration: four
replicate wells were placed two meters apart on a line perpendicular

to the east-west transect on the eastern edge of the pond; four

wells were placed on a line perpendicular to the same transect

with the same spacing on the western edge of the pond; and one

well each on the western end of the northeast-southwest transect






















U.S. HIGHWAY 41


GULF OF
MfEXICO2


SI Jkm
O I0 km


CHARLOTTE HARBOR


The study site environs.


Figure 4.






464
KEY
Calculated GW contour
S Equidistant supplementary contours
Points of equal potential with
E-well relative to S-well
0 Pond center
IZj GW well with height (m msl)
-> Direction of GW flow


I p
0 30m


/
/


/
4;
/
/
/
/
/
/
/


/
/


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/ /



/
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/ t


Calculated groundwater (GW) equipotential contours on
July 2, 1976.


Figure 5.


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and the southeast-northwest transect (Figure 7). These last two

served a double purpose: to provide more than two points so that

the groundwater surface could be quantified in the manner described

above; and to insure that the groundwater flow results obtained from

the pond 11 wells, upon which the placement of the study pond wells is

based, were not anomalous.

All ten wells were placed at a depth of about 1.5 m (Figure 8).

This depth was approximately 0.5 m below the bottom of the center of

the pond insuring that the wells would be receiving water that had

passed through the pond sediments. All wells were screened for 0.5 m

of their length, i.e., the region below the bottom of the center of

the pond. The east group of wells, therefore, would monitor inputs of

water and nutrients to the pond sediments and the west group the

outputs from the sediments.

The wells were sampled monthly from April through November, 1978,

by the following method. Water heights were measured by dropping a

weighted tape in the wells and recording the difference between the

top of the well and the surface of the water in it. The wells were

then pumped dry and allowed to refill before taking a water sample to

avoid sampling the possibly contaminated water standing in the pipe.

Water samples were placed on ice and returned to the laboratory for

nutrient analyses.

Nutrients were analyzed by the same methods described in the bulk

precipitation chapter. Groundwater contours and flow direction were

calculated by the method described for pond 11 wells.












Pine-Palmetto


GW Flow


Pine-Palmetto


i

0 20m


Location of groundwater (GW) wells at the study pond.
X = groundwater well.


Figure 7.


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Results and Discussion


Analysis of the nutrient data from the groundwater wells indicates

a substantial difference in the total phosphorus concentration but not

in the total nitrogen concentration between the east and west well

groups (Tables 12 and 13). Before the wells were grouped, they were

tested for differences within the group, and when none was found for

either parameter, the four east wells were combined and likewise the

west. Mean total phosphorus concentration in the east wells was

0.16 mg 1-1 and in the west, 0.338 mg 1- This difference was tested

for statistical significance and was found to be so at an a of 0.0019.

Mean total nitrogen concentration was 2.09 mg 11 in the east and

2.04 mg 1-1 in the west. These were rather obviously not significantly

different from one another.

Figure 9 shows groundwater contours and direction of flow at the

study pond for the 1978 sampling dates. (The August-October contours

are missing because surface water was standing at the wells during

this period.) The direction of flow is generally westward toward

Myakkahatchee Creek discharge boundary; however, there is considerable

variation in the direction of the flow. This was also seen at pond 11

in 1976. This variation is believed to be the result of manipulation

of surface-water levels in Snover and Cocoplum Waterways (Figure 4).

Both of these canals have numerous control structures, and if, for

example, water is held in Snover and released from Cocoplum, the

groundwater gradient would swing around toward the south. Conversely,

if surface water is held in Cocoplum and released from Snover, the

direction of maximum head loss would tend to be more northerly. The

ancestral flow patterns are, therefore, apparently interrupted
























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periodically, but these manipulations have only occurred since the

waterways were constructed several years ago. Also, they have ap-

parently not significantly affected the basic east to west flow of

phosphorus, as is evidenced by the concentration differential between

the east and west wells and is not evident between the east and south-

west or northwest wells.

The results from Figure 9 were plotted (Figure 10), and the

monthly areas under the curve calculated and used to obtain the monthly

means (Table 14). Also plotted on Figure 10 is the curve for July to

November, 1976, which was developed from data on pond 11.

The mean annual direction of flow in 1978 was 2820, between west

and west-northwest. The mean dry season (April-June) direction was

2200 or southwest and the mean for wet and intermediate seasons

(July-March) was 3020, between west-northwest and northwest.

The generally westerly direction of groundwater flow supports the

phosphorus concentration differential and indicates a net movement of

phosphorus by groundwater through the pond,elevating concentrations down-

gradient from the pond.

In order to quantify this effect in terms of amount of phosphorus

moved, it is necessary to know the discharge (m3 year- ) of water mov-

ing through the pond. Discharge (Q) can be calculated by Darcy's Law:

Q = PIA

where:

P = permeability of the water-table aquifer
(m3day-lm-2)

I = head loss (m m-1)



































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A = area (m2) of the planar section passing through
the center of the pond and sediments perpendicu-
lar to the line of flow.


The first term of the equation (P) was obtained from the Soil Interpre-

tation Record for the Immokalee Soil Series (National Cooperative Soil

Survey, 1977) and field inspection and personal communication with

Warren Henderson, the regional soil scientist. Permeability was de-

termined to be 3.66 m3day-m-2.

The head loss at the study pond for each sampling date was ob-

tained by calculating the difference in water height between ground-

water contours along a line perpendicular to the groundwater contours

(Figures 5 and 9). The values for each date are then plotted and the

area under the curve gives monthly means (Figure 11). The average

head loss at pond 11 was obtained in the same manner and plotted on

Figure 11. Apparently during the wet season, high-water months, there

is a decrease in gradient steepness that was not recorded in 1978 since

water level was above the surface at all four sets of wells. This

gradient change was incorporated into the 1978 data (Table 14) by using

the area under the dashed line (Figure 11), an approximation of 1976,

for these months. The mean annual head loss is 1.84 mm m-l

The third term of the equation (A) is somewhat more difficult to

obtain. Area (A) is defined as that planar section which passes through

the center of the pond perpendicular to the line of flow and limited

on the bottom by the bottom of the sediments, and on the top by the

surface of the sediments (Figure 12). The bottom of the sediments was

located at several points along a transect perpendicular to mean flow

direction. Water height varies throughout the year. Two years, 1977































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and 1978, of water height data are plotted in Figure 12; 1977 was a

relatively dry year and 1978 relatively wet. The areas under the

curves were calculated per month, and the months averaged to give a

representative year (Table 14). The mean water heights were then

drawn on figures like Figure 13 and the enclosed area calculated

(Table 14).

The mean daily discharges for each month were computed using the

formula Q = PIA (Table 14). These were then multiplied by the days in

the month which gives mean monthly discharges which when summed give

total annual discharge. The total discharge per year was 54.53 m3

(Table 14).

An approximation of the net amount of phosphorus leaving the pond

per year can be obtained by multiplying the concentration difference

between east and west wells by the volume of water passing through the

pond. This difference is 0.178 mg 1-1. The amount of phosphorus lost

is 9.7 g.

















SEP-OCT


N 4M


JUN


N 4M


E
Lo

10 M


Figure 13.


Area of the planar section (hatched) passing through the
pond center during high and low water-level periods (mean
of 1977 and 1978). Note: dashed line equals water height.


~I~














SEDIMENTS


Introduction


In an earlier, preliminary study it was determined that the great

majority of nutrients was contained in the sediments of these pond

systems (unpublished). This is, of course, expected since the sedi-

ments are the oldest and most functionally conservative component of

the pond. Most analyses of sediment deposition have been based on a

single core from the deepest point of a basin (for example, Davis,

1969; Kerfoot, 1974; Likens and Davis, 1975). This approach was con-

sidered to be inadequate for this study. Several researchers have

shown that sediment deposition is not uniform throughout a basin but

rather that more sediment is deposited in the deeper portions than in

the shallower (Wilson and Opdyke, 1941; Deevey, 1955; Lehman, 1975).

This observation is compounded by varying decomposition rates which

are expected to be greater in the shallower parts of a basin than in

the deeper. Particularly, this should be true, given their inter-

mittent nature, of the shallow ponds of southwest Florida.

A second criticism of the single core approach is that it does not

address the problem of area distribution in sediments. The homo-

geneity or lack thereof can be determined only by a multiple core

approach.








Methods


Figure 14 is a representation of the sediment sampling scheme

that was determined to define most adequately the sediment compartment,

given the economic constraints imposed upon the study. The basic plan

is three replicate center cores and four concentric rings, with four

cores each, at 20 cm intervals of elevation. The center cores are

within 1.5 m of the deepest point in the pond. The placement of cores

on the concentric rings alternates between cardinal and minor points

of the compass. Three additional center cores were obtained for

radiocarbon dating, but only one was needed since it contained suffi-

cient carbon for reliable dating.

The center and inner three rings of cores were collected in the

spring of 1978 and the outermost on August 30, 1978. The cores were

collected using a rig which consisted of a tripod with an adjustable

chain fastened at the top. A piston, composed of two rubber stoppers

and an eyebolt with washers and adjustable nuts, was connected to the

end of the chain. The coring tubes were of U. S. Plastics Corp.,

1/16" (0.16 cm) thick, clear Lexan polycarbonate tubing.

When the appropriate place for a core was located, the piston was

inserted into a clean tube and the nuts tightened until a good seal was

obtained. The chain was then adjusted until the piston rested on the

top of the sediment. The tube was then pounded gently into the sedi-

ment down to and slightly beyond the point at which significant re-

sistance was encountered. This occurs in nearly pure sand or clay,

which was interpreted to be the bottom of the pond sediments. The

remainder of the tube was then filled with water to equalize pressure,












Pine-Palmetto


Pine-Palmetto


SI I2
0 20 m


Figure 14.


Sediment sampling scheme.
NOTE: (-) = sediment core; (-) = 20 cm-interval surface
elevation contours; and (---) = the edge of the pine-
palmetto association.


t


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~4\ 3L
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pulled up by hand, and capped at the end. The tube was sawed off at

the piston and this end also capped. The advantage of clear plastic

tubes, although some strength must be sacrificed, is that the core can

be immediately inspected to insure that the maximum amount of informa-

tion with regard to stratigraphy, etc., has been preserved.

The cores were returned to the laboratory for extrusion and sec-

tioning. The cores were extruded by pushing a rubber stopper through

the tube with a wooden rod. All cores were inspected and the top 3 cm

removed as it was determined that this was a well-defined root-mat

zone. The three center cores were sectioned at 5 cm intervals below

the top three. The three radiocarbon cores were also measured. The

six center cores all displayed rather well-defined sediment/underlying

material boundaries. The boundaries were defined by a rather abrupt

lightening in color and increase in sand and particularly clay. The

range in occurrence of this boundary was from 78-87 cm with a mean at

82 cm.

The outer cores exhibited less well-defined boundaries. The color

gradient was more gradual, and there was little increase in clay. This

was expected, however, since the clayey underlying material is essen-

tially flat and the bottom of the sediments curve up away from the

center (Figure 15). The approximation of the bottom of these outer

sediments was made on the basis of color change, and the cores below

the top 3 cm were sectioned into the same number of intervals (16)

or multiple thereof as the center cores. This was done in order to

equate all cores in depositional time as more sediment accumulates in

the deeper parts of the basin (Lehman, 1975; etc.). The outer two

concentric-ring cores contained so little pond sediment (in all but














































O E
0
lo0m


Figure 15. Two cross-sectional views of the study pond basin.








one case 6 cm or less below the top 3 cm) that it was impractical to

follow this scheme.

After sectioning, all segments were measured to determine volume,

placed in labelled jars and oven-dried at 105C for 20 hours. Some

samples were dried for longer periods with no additional change in

weight (Black et al., 1965, Methods of Soil Analysis, specifies an

overnight drying time is sufficient for soil analyses). The dried

sediment samples were weighed and their bulk densities (dry weight in

gm/volume in cm3) recorded.

The organic matter content of the samples was determined by loss

on ignition. This technique was deemed acceptable since previous

ground and surface water analyses showed negligible amounts of

inorganic carbon. The difference in sample weights before and after

one hour in a muffle furnace at 550C was determined to be the weight

of organic matter in a sample. Several samples were tested with

longer ignition times, but no additional weight loss was obtained

and so one hour was found to be adequate.

Several digestion techniques for phosphorus were tried using a

block digester. It had been predetermined that a precision error of

10 percent of the mean and a recovery of 90 percent would be acceptable

and allow for a meaningful interpretation of the results. Three

methods were tried on the block digester: perchloric acid (after

Black et al., 1965), perchloric acid nitric acid (modified from

Jackson, 1958) and sulfuric acid hydrogen peroxide selenium

dioxide modifiedd from EPA, 1974); but all three yielded poor repro-

ducibility or recovery.








It was thought that the problem might lie in nonuniform heating

capacity of the block digester. To overcome this problem, FisherR

high-temperature bath oil was added to the block digester prior to in-

serting the digestion tubes. With this new technique, the simplest

and safest digestion method, sulfuric acid hydrogen peroxide, was

attempted with favorable results. During the three months that the

nutrient analyses were run, 24 samples of National Bureau of Standards

(NBS) Standard Reference Material (SRM) green cement were analyzed.

This standard was chosen because its phosphorus content was at the

upper end of the range of phosphorus in the pond sediments. The re-

sults of the NBS cement analyses were as follows: recovery 99.6

percent; standard deviation, 7 percent of the mean. As a double-check

on the method, a sample of Lake Michigan sediment, which closely ap-

proximated the texture of the pond sediments, was analyzed in dupli-

cate, and 0.0080 and 0.0082 percent phosphorus were found. The

Canadian Center for Inland Waters had analyzed the same sample and

reported 0.0089 percent phosphorus.

One advantage of the method is that it can be used simultaneously

for nitrogen determinations. The quality of the nitrogen data was

periodically checked by analyzing samples of orchard leaves (NBS, SRM).

Eight samples were analyzed during the three-month period with a mean

recovery of 116 percent and a mean standard deviation of 3 percent of

the mean. The concentration of nitrogen in the orchard leaves was at

the high end of the range of nitrogen in the pond samples.

After digestion, the samples were analyzed using the Single

Reagent Method (EPA, 1974) on a Technicon autoanalyzer. In this

method the reaction of orthophosphate with ammonium molydate followed








by reduction with ascorbic acid produces a blue color which can be

colorimetrically measured. For nitrogen, the reaction of ammonia,

sodium hydroxide, alkaline phenol and sodium hypochlorite develops a

blue color designated as indophenol (EPA, 1974).


Results and Discussion

The basin appears to be hypersinusoidal in shape and basically

symmetrical along the east-west transect (Figure 15). On the north-

south transect the basin floor slopes more gradually toward the north

than the south, and consequently there is more accumulated sediment

on the north side of the center.

The raw data, converted to mg cc-1 by multiplying by the bulk

densities, aretabulated in Appendix Tables B-l B-19. As to the

reliability of the data, several samples were run in triplicate for

organic matter, nitrogen and phosphorus. Table 15 shows the standard

deviations about the means of these samples expressed as percent of

the means. It had been predetermined that the percent standard devia-

tion should be less than or equal to ten in order for the analyses to

be of maximum use. This criterion was met; however, the median is

probably a more useful measure of the precision of the chemical

analyses since the mean tends to overweight outliers.

Table 15. Percent standard deviation


ParameterNumberof Range (%) x (%) Median (%)
Triplicates
Organic matter 27 0.8 23.3 4.9 3.9
Nitrogen 34 1.5 21.3 7.4 5.1
Phosphorus 37 0.4 18.5 6.2 5.6








In addition, two samples were run in triplicate for nitrogen and

phosphorus on several different days to test for day-to-day sources of

error. One sample was run on five different days, and the standard

deviation as percent of the mean was 6.6 for phosphorus and 13.7 for

nitrogen. The other sample, run on six days, was 7.1 percent for

phosphorus and 8.7 percent for nitrogen. It appears from these

analyses that the between-day error is greater than the within day

error, and the nitrogen is more sensitive to between-day error than

phosphorus.

As previously mentioned, the sediment/underlying-substrate boundary

was well defined at the pond center, but away from the center the

boundary is somewhat indistinct. I decided to use organic matter con-

tent to determine this boundary away from the center. The mean or-

ganic matter content immediately below the boundary in the center was

43 mg cc-1 (Appendix Tables B-l B-3). Therefore, it was decided

that if organic matter content drops below this concentration for two

successive segments, the boundary had been passed. The two successive

segments rule was chosen to preclude the possibility that sand lenses

in the sediment would be considered as the boundary.

In light of this definition of the bottom of the sediments, the

reliability of the data from the sediments only was analyzed with

somewhat better reproducibility for nitrogen and phosphorus than was

found in all samples (Table 16).

The data in Appendix Tables B-l B-19 were averaged and totaled

for each parameter. The means for the center cores and within concen-

tric rings were compared for each parameter using a "t" test of the

two most different means within a group. No significant (a = 0.05)








Table 16. Percent standard deviation


Parameter Number of Range (%) x (%) Median (%)
Triplicates

Organic matter 24 0.8 23.3 5.3 4.2
Nitrogen 28 1.5 13.1 5.3 4.1
Phosphorus 31 0.4 13.4 5.1 4.4



differences were found for any parameter between the center cores or

within concentric rings. It was determined to combine the center cores

and the cores within each ring, resulting in an average center core and

an average core for each ring (Tables 17-21).

The mean totals for organic matter, nitrogen and phosphorus in the

center and each ring (Tables 17-21) were plotted against distance from

the center (Figures 16-18). Carbon was not plotted since its value was

derived fromorganic matter and nitrogen. To calculate the total amount

of each substance in the sediments, the formula for computing the vol-

ume of a solid of revolution was borrowed from solid geometry and

modified as follows:

V 2r Ar
1000

where:

V = Total amount (kg)

A = Area under the curve (g cm-l)

r = Distance from the axis of symmetry to the
center of gravity (cm)


The axis of symmetry in this case is a line passing through the center

of the sediments (Figures 16-18). The center of gravity for any plane













































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A = 13,467 g cm1
r = 1,014 cm
V = 85,800 kg-OM


Figure 16.


10 20 30 40 50
DISTANCE (m)


Total organic matter (OM) in the sediments of the pond.
S = axis of symmetry; G = line through the center of
gravity; A = area under the curve; r = distance from S
to G; and V = total amount.


6




5




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200


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40


A = 484.28 g cm1
r = 1,032 cm
V = 3,140 kg-N


10 20 30 40 50
DISTANCE (m)


Figure 17.


Total nitrogen (N) in the sediments of the pond.
S = axis of symmetry; G = line through the center of
gravity; A = area under the curve; r = distance from
S to G; and V = total amount.









14




12




10



E
08

C
c:
01

E
6




4




2


10 20 30 40
DISTANCE (m)


Figure 18.


Total phosphorus (P) in the sediments of the pond.
S = axis of symmetry; G = line through the center of
gravity; A = area under the curve; r = distance from
S to G; V = total amount.


A = 22.36 g cm-
r = 879 cm
V = 123.5 kg-P








passing through the center of the sediments lies on a line parallel to

the axis of symmetry and at a distance from that axis such that one-

half of the area of the plane (A) lies on either side of the line

(Figures 16-18).

By this method, it was determined that 85,800 kg of organic

matter, 3,140 kg of nitrogen, and 124 kg of phosphorus were contained

in the sediments. By the formula,

carbon = (organic matter nitrogen) 0.444


where 0.444 is the percent carbon in the cellulose molecule and assum-

ing the composition of organic matter to be primarily cellulose, the

total carbon in the sediments was found to be 36,701 kg.














MACROPHYTES


Methods


Macrophyte above-ground biomass was harvested in June, 1976. One

meter square plots were clipped, bagged and taken to the laboratory to

be oven-dried (at 60C) and weighed.

Plant samples from each of the subcompartments of the macrophytes

in the ponds were collected in June and again in September of 1976.

These samples were returned to the laboratory, separated into roots,

shoots and leaves, oven-dried, ground in a Wiley mill and stored to

await chemical analysis.

Phosphorus in the macrophytes was obtained by sulfuric acid

digestion (APHA Standard Methods, 1976) followed by automated colori-

metric analysis. Nitrogen and organic carbon percentages in the

macrophytes were obtained by combustion and subsequent thermal con-

ductivity measurement by the use of a Perkin-Elmer elemental analyzer.


Results and Discussion


The following vegetation pattern generally prevails in the pond.

NuphaA tuteum (L.) Sibthorp and Smith (yellow pond-lily) occupies the

pond center. Also in the center but occurring over a larger area is

the spike-rush (sedge) EZeocha iA baLdwinii (Torrey) Chapman. In a

more or less concentric ring outside of the spike-rush grows Panicum

hemitomon Schultes (maidencane). From the edge of the Panicum to the

73







pine-palmetto association a somewhat diverse community occurs. This

community is dominated by Hypelicum abeicczttumt Lamarck (sand-cypress),

Eupatotium capillioium (Lamarck) Small (dog-fennel) and Andpopogon

glomeratuw (Walter) BSP (beardgrass).

Above-ground biomass data, nutrient concentration data and total

amounts of nutrients are presented in Tables 22, 23 and 24, respectively.

Amounts of nutrients in the plant compartment of the system are rela-

tively insignificant when compared to those found in the sediment

compartment. The total amount of phosphorus in the plants was 1.1 per-

cent of the total in the sediments; total nitrogen was 0.7 percent;

and total carbon, 2.4 percent. This is not unexpected since the plants

are a short-term storage compartment by comparison to the sediments.

A comparison of seasonal differences in nutrient concentrations

in the macrophytes lead to some interesting conclusions. The concen-

tration of phosphorus increased rather substantially in all macrophytes

between June, the end of the dry season, and September, the end of the

rainy season (Table 23). This "luxury" consumption is greatest in

those species which occupy the center (deepest part) of the pond and

appears to be related to the species niche. The greatest luxury con-

sumption (September concentration equal to 3.9 times June) was found

in Eleochaics, a submerged aquatic; followed by the floating-leaved

NuphaA (3.3 times in the leaves); and the emergent Panicum (3.0 times

in the leaves). The basically terrestrial Eupatoiium doubled its

concentration, and the woody Hype~icum exhibited only a small increase

(Table 23). This pattern suggests that submerged plant parts have the

ability to absorb phosphorus and that the more of the plant that is

submerged, the greater the absorptive capacity, i.e., increasing the















Table 22. Plant above-ground biomass data (June-July, 1976)


Plant spp. Area Ocupied Biomass Total Weight
S(m (g m-2) (kg)

Nuphar 221 15 6 3.3
Eteochacis 548 a a
Panicum (live) 1085 179 70 194.2
Panicum (dead) 1085 732 263 794.2
Hypericum 7222 0.75 1.9 5.4
Eupatotium 7222 44 27 317.8
Andropogon (live) 7222 46 44 332.2
Andropogon (dead) 7222 27 46 195.0

TOTAL 9076 1842.1

aBiomass for EteochariA was not obtained.










Table 23. Concentration (%) of phosphorus, nitrogen and carbon in the
plant species of the pond during June and September, 1976.


Phosphorus Nitrogen Carbon
Plant spp. Jun Sep Jun Sep Jun Sep


NuphaA
leaves 0.242 0.796 3.04 4.06 44.0 48.2
petioles 0.223 0.576 1.08 1.37 37.2 42.5
Eleochwahi 0.220 0.864 1.75 1.75 46.6 45.7
Panicum
leaves (live) 0.122 0.368 2.82 2.88 46.6 48.5
stems 0.109 0.250 0.67 0.33 43.7 46.9
leaves (dead) 0.064 a 0.84 a 46.0 a
HyfpeAicum
leaves 0.110 0.141 1.63 1.45 56.2 63.5
stems 0.033 0.051 1.64 0.59 50.3 50.6
roots 0.054 a 1.83 a 50.2 a
Eupatorium
leaves 0.143 0.287 3.06 2.97 52.2 54.0
stems 0.085 0.192 1.22 1.55 46.8 47.1
roots 0.087 a 1.10 a 47.2 a
Andropogon
shoots (live) 0.082 a 1.12 a 48.9 a
roots 0.032 a 1.07 a 46.9 a
shoots (dead) 0.014 a 0.30 a 46.9 a

aData not collected.















Total amount (kg) of
plant compartment of


phosphorus, nitrogen and carbon in the
the pond during June, 1976.a


Plant spp. Phosphorus Nitrogen Carbon

Nuphar. 0.008 0.07 1.3
E.eocha.hi b b b
Panicum
live 0.224 3.39 87.7
dead 0.508 6.67 365.3
HypeAicwn 0.004 0.09 2.9
Eupatoiwum 0.362 6.80 157.3
Andtopogon
live 0.272 3.72 162.4
dead 0.027 0.59 91.5
Total live 0.870 14.07 411.6
Total dead 0.535 7.26 456.8
TOTAL 1.405 22.83 868.4

aBased on mean concentration in above-ground parts.
bNo biomass data for EZeochaui6.


Table 24.








surface to volume ratio with respect to phosphorus appears to be

directly related to concentration of phosphorus in the plant.

There is substantial evidence to support this contention. For

example, Twilley (1976) and Twilley et al. (1977) found that Nuphaw

tuteum does, in fact, absorb phosphorus through its leaves, and other

researchers (McRoy and Barsdate, 1970; Bristow and Whitcombe, 1971;

DeMarte and Hartman, 1974) have reported this phenomenon for other

submerged and emergent macrophytes.

Another interesting phenomenon is the apparent phosphorus con-

servation mechanism implied by the difference in concentration in liv-

ing and dead plant parts (Table 23). Panicum apparently translocates

48 percent of the phosphorus from dead leaves to other living parts of

the plant whereas Andropogon translocates 83 percent. This may be

controlled by an evolutionary mechanism which is related to the species'

ability to occupy aquatic habitats. The basically terrestrial

Andropogon retains considerably more of its phosphorus than the

emergent Panicum since the former must meet its phosphorus needs

through root absorption only.

Seasonal differences in nitrogen concentrations are slight with

the exception of Hype4icum stems which lose about two-thirds of their

nitrogen between June and September. Nitrogen is mobile in plants

(Gauch, 1972), and this change may reflect transport of nitrogen from

the stem to actively growing plant parts as the season progresses.

This hypothesis is supported by the fact that both Panicum and

Andropogon tend to conserve about two-thirds of the nitrogen in

dead plant parts (Table 23).

Carbon concentrations are interesting in the fact that nearly all

parts of all species increased in carbon content as the season progressed







(Table 23). This may be the result of an increasing amount of lignin

production later in the growing season. The starch and cellulose

molecules are 44 percent carbon, and most common sugars and organic

acids are about 40 percent carbon. However, the three primary aro-

matic alcohols in all angiosperm lignins, coniferyl alcohol, sinapyl

alcohol and p-courmaryl alcohol (Salisbury and Ross, 1969), contain

67 percent, 63 percent and 72 percent carbon, respectively

(Freudenberg, 1965). The increased production of these "carbon

heavy" compounds could account for the increase in carbon content

observed in September (Table 23).














WATER


Methods


Nitrogen and phosphorus in the pond water were collected and ana-

lyzed according to the methods described in the bulk precipitation

chapter. Total organic carbon in a sample was converted to carbon

dioxide by catalytic combustion in an Oceanography International R

total carbon analyzer. The carbon dioxide formed is measured directly

by an infrared detector. The measured carbon dioxide is directly pro-

portional to the concentration of carbonaceous material in the sample

(EPA, 1974).

Results and Discussion


Table 25 contains water height, surface area and volume data.

Water height was measured directly. Surface area was determined by

plotting the respective water heights on a predrawn.figure of the

basin shape and then calculating from the diameter. Volumes were cal-

culated by addition of frustra for several water heights and then

plotting a water height-volume curve from which the remaining volumes

were obtained. Table 26 contains the nutrient data for the pond

water during 1978.

Unlike static surface water features where changes in concentra-

tions of nutrients usually reflect planktonic population "blooms" and

"crashes," the study pond's biological dynamics are confounded by

80









Table 25. Surface hydrology of the pond (1978).


Water
Date Height Area Volume
(m) (mi) (m3)


Jan
Jan
Feb
Feb
Mar
Mar
Apr
Apr
Apr
May
May
Jun
Jun
Jul
Jul
Aug
Aug
Aug
Sep
Sep
Oct
Oct
Nov
Nov
Dec
Dec


.47
.50
.59
.70
.74
.80
.68
.55
.43
.27
.34
.21
.21
.61
.85
1.20
1.21
1.10
.93
1.05
.99
.89
1.00
.91
.85
.76


1,512
1,653
2,073
2,734
3,043
3,685
2,574
1,934
1,345
452
915
244
244
2,124
4,286
9,076
9,076
9,076
5,558
7,815
6,866
4,855
6,977
5,153
4,286
3,217


220
275
475
822
950
1253
775
365
170
45
85
18
18
525
1525
4366
4484
3522
2025
2800
2490
1775
2520
1875
1525
1080








Nutrient data for the pond (1978).


Amount Concentration (mg 1-1)
Date .
TP (g) TN (kg) TOC (kg) TP TN TOC


Jan
Jan
Feb
Feb
Mar
Apr
Apr
Apr
May
May
Jun
Jun
Jul
Jul
Aug
Aug
Aug
Sep
Sep
Oct
Oct
Nov
Nov
Dec
Dec


46.42
105.05
53.68
<279.48
145.35
<60.45
<40.15
87.38
6.44
15.98
2.27
2.81
19.43
74.73
183.37
98.65
186.67
125.55
89.60
59.76
<81.65
40.32
155.63
111.33
19.44


.47
.42
1.34
1.45
1.68
1.67
.71
.67
.17
.22
.08
.09
.99
2.44
5.02
5.29
6.52
2.90
4.54
3.66
3.11
3.40
3.00
1.77
1.74


5.61
7.38
10.76
19.11
27.82
34.49
13.87
7.46
2.37
3.77
1.28
1.24
17.59
65.27
152.37
129.14
138.77
84.65
88.48
92.13
N.A.
83.16
94.69
63.75
41.26


.211
.382
.113
<.340
.116
<.078
<.110
.514
.143
.188
.126
.156
.037
.049
.042
.022
.053
.062
.032
.024
<.046
.016
.083
.073
.018


2.12
1.52
2.83
1.76
1.34
2.16
1.94
3.92
3.68
2.55
4.60
5.10
1.89
1.60
1.15
1.18
1.85
1.43
1.62
1.47
1.75
1.35
1.60
1.16
1.61


25.5
26.9
22.7
23.3
22.2
44.5
38.0
43.9
52.6
44.4
71.2
68.7
33.5
42.8
34.9
28.8
39.4
41.8
31.6
37.0
N.A.
33.0
50.5
41.8
38.2


TP = Total Phosphorus
TN = Total Nitrogen
TOC= Total Organic Carbon
N.A.=contaminated


Table 26.








changes in water volume. To understand this relationship, assume that

there is a constant amount of some substance in the water. When water

volume increases, the concentration of the substance would decrease,

and conversely a decrease in volume of water would show an increase in

concentration. Therefore, changes in concentration do not necessarily

reflect changes in productivity rates. These rate changes can be

ascertained by comparing the magnitude of volume and concentration

changes (Figure 19). For example, total organic carbon triples from

March to June, but water volume decreases by two orders of magnitude

and so an apparent bloom is, in fact, a crash.

When concentrations are converted to amounts, changes in productiv-

ity become readily apparent (Figure 20). There are three population

blooms: one large summer increase and two smaller ones in early spring

and late fall. The pattern very closely follows changes in water vol-

ume which appears to be a dominant population controlling mechanism.

As volume increases so does productivity, to fill the new habitat;

but as volume declines, the population crashes as many more individuals

are removed from the water column than are added. The net effect of

this pattern is to keep concentrations relatively constant. The ratio

of maximum to minimum water volume is approximately 250 to 1; for

amount total organic carbon, it is about half of this; and for nitro-

gen and phosphorus, about 82 to 1. By contrast, concentration maxima

of carbon and nitrogen are only 3 to 4 times their respective minima

and phosphorus 32 times.

Another interesting effect of fluctuating water height and its

consequent changes in surface area is the change in the area available

for receiving atmospheric inputs. Figure 20 shows the total amounts
































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of nitrogen and phosphorus falling on the pond water surface during

sampling intervals. The changing amounts reflect both changes in

atmospheric input rates and changes in pond water surface area. It

should be noted that changes in the amounts of nutrients in the water

column are generally an order of magnitude greater than the at-

mospheric inputs for respective intervals. However, the mean amounts

of nitrogen (2.1 kg) and phosphorus (80 g) in the water column for

the year are not very different from the total yearly inputs of nitro-

gen (3.1 kg) and phosphorus (120 g). It appears that the pond water

may achieve steady state with atmospheric inputs over relative long

duration, but in the short term,regeneration from the sediments

probably plays the dominant role in supplying nutrients for seasonal

changes in productivity.

This is consistent with the work of other researchers who have

found that both the decomposition of dead aquatic macrophytes and the

active "pumping" by living specimens contribute substantial amounts of

phosphorus to the water column. Reimold (1972) found that a SpaAtina

marsh on the coast of Georgia released 601 mg-P m-2day-1; McRoy et al.

(1972) reported that ZosteAa in an Alaskan lagoon added 62 mg-P m-2

day-1 to the water column; and Twilley (1976) showed that Nuphax was

capable of adding only 2 mg-P m-2day-1. The large differences observed

are most likely related to biomass (Twilley, 1976) since the biomass

of Spattina, a grass, is considerably greater than Nupha&.

If we take the amount of phosphorus added to the water column

between 21 June and 4 August (approximately 180 g) (Figure 20) and

divide by the number of days and by the average surface area (Table 16),
we can calculate an addition rate of about 1 mg-P m-2day-. By
we can calculate an addition rate of about 1 mg-P m day1. By







subtracting that amount added as bulk precipitation (approximately

0.1 mg-P m-2day-l) (Figure 20), it is estimated that, for the period

under consideration, 0.9 mg-P m-2day-l were regenerated from the

sediments by some combination of mechanisms. This is about one-half

of Twilley's (1976) results and considerably less than Reimold (1972)

and McRoy et al. (1972). These differences may in part be due to

biomass differences. For example, when converted to a dry weight basis,

Nupha. contributed 210 mg-P g-lday-l, whereas ZosteAa added only about
90 mg-P g-day-1 (Twilley, 1976). As stated above, ZosteAa appeared

to contribute 30 times more phosphorus than Nuphat. Differences may

also be attributed to water chemistry, plant characteristics, etc.

(Twilley, 1976).














NUTRIENT DYNAMICS OF THE POND SYSTEM


Introduction


In the chapter on bulk precipitation we found that the pond re-

ceives a substantial amount of nitrogen and phosphorus from atmospheric

fallout. There is an additional smaller input from ground water.

Nitrogen entering the system can leave through the groundwater sink

and by nitrification or denitrification, also exit the system in the

gaseous state via the atmosphere. Phosphorus, on the other hand,

rarely exists in the gaseous state, and, therefore, phosphorus can only

exit the system through the groundwater sink (see background chapter

for discussion of surface-water runoff). This chapter will discuss the

dynamics of these nutrients, particularly phosphorus, as they pass

through the system.

Methods


Only one additional method needs to be presented here. Available

or movable phosphorus orthophosphatee phosphorus and poly-phosphorus),

that which can be removed by leaching of the sediments, was determined

for several samples from the cores of concentric rings 1 and 2 and the

center cores. Samples were analyzed according to the method of Black

et al., 1965 (part 2, p. 1043). Solution pH was adjusted to 3.9 (the

mean pH of the pond water and ground water).

Methods pertaining to all other parameters discussed here can be

found in the preceding chapters.








Sediment Nutrient Dynamics


Although intuitively it might seem that the pathway of nutrients

through the water column to the sediments ought to be perpendicular to

the water surface, in reality there is directional transport of sedi-

ment and its constituents toward the deepest part of a basin (Deevey,

1955; Rigg, 1958; Pewe et al., 1965; Lehman, 1975), i.e., sediment

focusing (Likens and Davis, 1975). These studies, however, have dealt

with static lake basins, in general, and not seasonal ponds such as

the study pond, and although the study pond exhibits an hypersinusoidal

sediment deposition pattern (Figure 15), it is not known whether some

nutrients are deposited during the dry season along the continuously

receding pond edge. A comparison of the wet and dry season nutrient

concentrations (see chapter on pond water) does indicate a concentrat-

ing effect during the dry season implying transport toward the center.

However, the concentration and amount values are highly variable and

are confounded by those amounts which are bound-up in macro-organisms.

The problem of whether some phosphorus escapes the sediment focusing

mechanism and is transported directly downward near the periphery of

the pond probably cannot be addressed in this study. Suffice it to say

that a substantial amount of sediment and its constituent nutrients is

focused toward the pond center.

Not only is the sediment deeper toward the center of the pond

and, therefore, total organic matter, nitrogen and phosphorus greater,

but also mean phosphorus increases toward the center of the pond

(Tables 17-21). Mean organic matter and nitrogen do not exhibit a

regular areal trend and appear to be fairly constant.