Group Title: genesis of carbon sequestration in subtropical Spodosols
Title: The genesis of carbon sequestration in subtropical Spodosols
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Title: The genesis of carbon sequestration in subtropical Spodosols
Physical Description: Book
Language: English
Creator: Perez Bolivar, Juan Gerardo, 1960-
Publisher: University of Florida
Place of Publication: Gainesville Fla
Gainesville, Fla
Publication Date: 2000
Copyright Date: 2000
Subject: Soil and Water Science thesis, Ph. D   ( lcsh )
Dissertations, Academic -- Soil and Water Science -- UF   ( lcsh )
Genre: government publication (state, provincial, terriorial, dependent)   ( marcgt )
bibliography   ( marcgt )
theses   ( marcgt )
non-fiction   ( marcgt )
Summary: ABSTRACT: Multiple spodic (Bh) horizons in soils are common in the thick, acid sands of the Osceola National Forest, Northeast Florida. Spodosols samples were taken along a 200 m upland-lowland transect. Podzolization explained how the upper spodic horizon was formed. The lower one, usually extensive, and permanently saturated with water, did not follow the same mechanism of formation. The significance of this lower subsurface horizon has increased greatly as scientists study new ways of decreasing atmospheric carbon dioxide (CO2), using soils as sinks, to reduce the "greenhouse effect". Carbon (C) stored in multiple-layered Spodosols is greatly underestimated since soil scientists limit their studies to the first 2 m. Carbon-14 (14C) dating indicated that the upper spodic horizon was 1,810 +_ 40 years old; the lower B'h1 was 15,270 +_ 370 years old and the lower B'h2 was 13,820 +_ 60 years old. Aluminum (Al) illuviation occurred in the upper Bh, but not in the lower B'h horizon. Humic/fulvic acid (HA/FA) ratios were different for both upper and lower Bh horizons. The upper Bh was dominated by fulvic acids (FA)(59% vs. 41%) and the lower B'h horizon was dominated by humic acids (HA) (61% vs. 39%).
Summary: ABSTRACT (cont.): C/Al ratios decreased with depth in the upper Bh horizon, but increased with depth in the lower one. This lead to the conclusion that the mechanism that immobilizes C to form the different Bh's horizons is different. The pedogenic process of podzolization occurred in the upper Bh horizon. In the lower B'h horizon, the theory of formation was as follows: fulvic acids, after accumulating in the saturated zone, reacted with the Al in the coatings of the sand grains without stripping the coatings. The FA were responsible for darkening the sand grain. The HA reacted mostly with the Al and clays in solution. They precipitated as Al-humates and filled the space in between the sand grains as black sediment. Genesis of Spodosols is a direct manifestation of the processes dictating the terrestrial fate and transport of C. To understand these processes is fundamental in the assessment of global C dynamics.
Summary: KEYWORDS: carbon sequestration, Spodosols
Thesis: Thesis (Ph. D.)--University of Florida, 2000.
Bibliography: Includes bibliographical references (p. 180-190).
System Details: System requirements: World Wide Web browser and PDF reader.
System Details: Mode of access: World Wide Web.
Statement of Responsibility: by Juan Gerardo Perez Bolivar.
General Note: Title from first page of PDF file.
General Note: Document formatted into pages; contains vi, 191 p.; also contains graphics.
General Note: Vita.
 Record Information
Bibliographic ID: UF00100816
Volume ID: VID00001
Source Institution: University of Florida
Holding Location: University of Florida
Rights Management: All rights reserved by the source institution and holding location.
Resource Identifier: oclc - 50750574
alephbibnum - 002678738
notis - ANE5965


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I would like to thank my major professor Dr. Mary E. Collins for being a

teacher and a friend during my tenure as a student. I also thank the members of

my committee, Dr. Willie G. Harris, Dr. Hugh Poponoe, Dr. Daniel Spangler, and Dr.

William E.Puckett, for their time and guidance during my research.

I especially thank Ron Kuehl for his help and support of this research. I also

extend thanks to Larry Schwandes and to my friends in the laboratory.

I extend my deepest appreciation to my parents, Jose and Sofia, whose sacrifice,

patience, and encouragement kept me going during this long journey.



A C K N O W L E D G M E N T S ......... .................................................................................... ii

A B STR A C T ......... ..... ........................................................................... .... ........


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

O objectives of the Study..................... ........................................... .......................... 14
L literature R eview .................... ................ .................... .. .. ...... ..... .. ............ 14

2 DESCRIPTION OF THE STUDY AREA.................................... ........................ 39

Location ........................................................... 39
Clim ate ........................................ ................... 40
Physiography..................................... .............. 42
G eo lo g y ..................................................... 4 5
A von P ark L im estone.............................................................. .................... 46
O cala G group ........................................ 47
Suwannee Limestone ............................................... .............. 48
H aw thorn F orm action ................................................................................ .. 4 8
Pliocene to Holocene Undifferentiated ......................................... ............. 49
S o ils ....................................................................................................... . .......... ...... 4 9
H y d ro lo g y .............................................................. 5 1
Surficial A quifer Sy stem .................................................... .................................. 52

3 M ATERIALS AND M ETHODS .......................................................... ............... 54

F field W ork ......... .. .......... ..................................................................... ...... 54
Experim mental Plot..................................... .............. 54
Soils Studied ......................................... 57
Vegetation Study. .......... ....................................... ............. 59
Laboratory W ork........... ...... .... .......... ...................... ... ......... .... .............. 59
Routine Analysis ............................................. 59
H um ic M material ................................................................................................... 60
M in eralogy of S oils................................................................... ...... ...... .. 6 1
M icrom orphology .... .................................................. .. ........ .. ............ 62
C arbon-14 ............. ......... .................................. ....... ..... ..... .... 62

A artificial B 'h Form ation ................ ....... ................ ................. ......... 63
The Effect of Hydrogen Peroxide and Incineration on Bh and B'h Organic Matter. 64
Evaluation of Existing Characterization Data............... ......................................... 64

4 RE SU L TS A N D D ISCU SSION ......................................................................... ...... 66

M orphology................................................. ....... ......... ...... 66
Chem ical Properties .................. ................................... .. ..... .............. 73
M icromorphology ................................................................. ............ .......... .. 94
Scanning Electron Microscope (SEM) ....................................................... 97
Hydrology ............ ................................ ............... 99
V e g etatio n ................ ... .................................................. ............... 10 6
M ineralogy of the C lay Fraction..................................................... .................... 108
Carbon........................................... .............. 110
Age ............ .............. ...... ................... .............. 110
Dissolved Organic Carbon in the Filtrate ..................................... .............. 113
Organic Carbon % ................... .......... ........................ ........... 113
Humic Substances-Humic and Fulvic Acids ................................ .............. 117
A l/O C R atio ............................ ... ................... .... .................................... 12 2
Theory on the Genesis of the Soil with Multiple Bh Horizons............................. 123
Stage 1 ............................................... 124
Stage 2 .......... ....................................... 124
Stage 3 ....................... .......................... 124
S ta g e 4 ................................................................................. 1 2 6
A artificial B 'h H horizon ........... .......................................... .............. 127
Reaction of the OC from the Bh and B'h to Hydrogen Peroxide Treatment .......... 128

5 GENERAL CON CLU SION S ............................................... ............................ 132


A SO IL D E SCR IPTIO N S ...................... .... ......... ............................. ............... 135

B SO IL P R O P E R T IE S ......................................................................... ....................142

C PRECIPITA TION D A TA ...................... .... ................... ................... ............... 173

D VEGETATION .................... .................... ....... ......... 178

L IT E R A T U R E C IT E D ........................................................................... ................... 180

BIO GR A PH ICA L SK ETCH .................................... ............ .....................................191

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



Juan Gerardo Perez Bolivar

December 2000

Chair: Mary E. Collins
Major Department: Soil and Water Science

Multiple spodic (Bh) horizons in soils are common in the thick, acid sands of the

Osceola National Forest, Northeast Florida. Spodosols samples were taken along a 200 m

upland-lowland transect. Podzolization explained how the upper spodic horizon was

formed. The lower one, usually extensive, and permanently saturated with water, did not

follow the same mechanism of formation. The significance of this lower subsurface

horizon has increased greatly as scientists study new ways of decreasing atmospheric

carbon dioxide (CO2), using soils as sinks, to reduce the "greenhouse effect". Carbon (C)

stored in multiple-layered Spodosols is greatly underestimated since soil scientists limit

their studies to the first 2 m. Carbon-14 (14C) dating indicated that the upper spodic

horizon was 1,810 40 years old; the lower B'hl was 15,270 370 years old and the

lower B'h2 was 13,820 + 60 years old. Aluminum (Al) illuviation occurred in the upper

Bh, but not in the lower B'h horizon. Humic/fulvic acid (HA/FA) ratios were different for

both upper and lower Bh horizons. The upper Bh was dominated by fulvic acids (FA)

(59% vs. 41%) and the lower B'h horizon was dominated by humic acids (HA) ( 61% vs.

39%). C/A1 ratios decreased with depth in the upper Bh horizon, but increased with depth

in the lower one. This lead to the conclusion that the mechanism that immobilizes C to

form the different Bh's horizons is different. The pedogenic process of podzolization

occurred in the upper Bh horizon. In the lower B'h horizon, the theory of formation was

as follows: fulvic acids, after accumulating in the saturated zone, reacted with the Al in

the coatings of the sand grains without stripping the coatings. The FA were responsible

for darkening the sand grain. The HA reacted mostly with the Al and clays in solution.

They precipitated as Al-humates and filled the space in between the sand grains as black

sediment. Genesis of Spodosols is a direct manifestation of the processes dictating the

terrestrial fate and transport of C. To understand these processes is fundamental in the

assessment of global C dynamics.


The earth's climate is predicted to change because human activities are altering

the chemical composition of the atmosphere through the buildup of greenhouse gases-

primarily carbon dioxide (CO2), methane (CH4), nitrous oxide (N20), and

halocarbons-chlorofluorocarbons (HFCs) .

The United States is the world's largest single emitter of CO2, accounting for

about 23% of energy-related carbon (C) emissions worldwide. The U.S. share of CH4 and

N20 emissions, although uncertain, is likely to be much lower than its share of CO2

emissions, as the principal sources of CH4 and N20 emissions are more common outside

than within the United States. In the case of halocarbons and other gases, the U.S. share is

likely to be considerably larger than 23%. This is because the use of cooling and

refrigeration equipment is probably much more pervasive in the United States than

elsewhere in the world (Fig. 1).
(Data Source:

These greenhouse gases have a common singular property, they all trap heat in

the atmosphere. Although uncertainty exists about exactly how earth's climate responds

to these gases, global temperatures are rising.

The sun's energy drives the earth's weather and climate and heats the earth's

surface; in turn, the earth radiates energy back into space. Atmospheric greenhouse

gases trap some of the outgoing energy, retaining heat somewhat like the glass panels of a


HFC's and other minor gasses 2.4%
Methane 10.1%

Nitrous Oxide 2.2

Carbon (85.3%)

Figure 1. Greenhouse gas emissions in the U.S, 1996 (Source: 113097.h

greenhouse. This is the reason why this process is called the "greenhouse effect" (Fig.

2). This natural "greenhouse effect" makes life possible on earth. It keeps the planet

at an average temperature suitable to life, about 16C. However, when the atmospheric

concentration of greenhouse gases increases, climatic changes may occur (Source: An enhanced

greenhouse effect may result in significant changes in local, regional, and global

temperatures. Some climate models predict that the buildup of atmospheric greenhouse

gases will result in significant increases in the global mean temp erture, ranging from 1.5

to 4.0C by the year 2050 (Beinroth, 1996).

Vegetation changes caused by the climate change would affect the hydrologic

cycle and surface albedo. The biggest adverse impact of a CO2-induced climate change

would be caused by changing precipitation patterns that would lead to overall lower

SUN SnRm wrblr radiartin in
lreM~ted by the Earth an
Ihe aP~n sphere.

Figure 2. A simplified diagram illustrating the "greenhouse effect" (Source: stark/nasa.html)

rainfall amounts, or droughts during the growing season with increased frequency or

severity (

Since the beginning of the industrial revolution (-1850), atmospheric

concentrations of CO2 have increased nearly 30% (Fig. 3). Carbon dioxide

concentrations over the past 1,500 years, determined from ice core records (shown as

symbols), fluctuated little until 1850. Since 1958, air measurements (shown as a blue

line) taken at Mauna Loa, Hawaii, supplemented the ice core data. The smooth black

curve is based on a 100-year running mean. The inset of the period from 1850 onward

shows CO2 emissions in gigatons (billions of metric tons) per year attributed to burning

fossil fuels (shown as a blue line).


360 047
South PoCI
Mauna La
0 Fold OCO erniss" flt$
One. Gph d yi e iee i ei i e
Scr inng a ng t a 3 ar d t

atmosphere and is believed to be the primary reason for the increase in earth's


temperature (Fig. 4).
Bo 1000 1200 1d o6DO 180 20HDO
Figure 3. Graph showing the increase in atmospheric CO2 during the last 1500
years. Source: (

This increase in atmospheric CO2, during the last 30 years, due to the

combustion of fossil fuels, has enhanced the heat-trapping capability of the earth's

atmosphere and is believed to be the primary reason for the increase in earth's

temperature (Fig. 4).

The global CO2 budget is complex and involves transfer of CO2 among the

atmosphere, the oceans, and the biosphere (Fig. 5). Through the photosynthetic process,

the land removes about 100 petagrams (Pg) (10 15g) of C in the form of C02 per year.

However, about the same quantity of CO2 is added to the atmosphere each year by

vegetation and soil microbial respiration and organic decay. The world's oceans release

about 100 Pg C in the form of CO2 into the atmosphere per year and in turn absorb about

104 Pg C each year. Most of the oceanic C is in the form of sedimentary carbonates.




1880 1900 1 MD 1940 1M' 1M* 2000

Figure 4. Graph illustrating the rise of temperature (red) on earth from a reference
level that is just the average of the most recent 30 years. The reference level is
labeled zero. Source: (

Burning of fossil fuels adds about 5 Pg C and biomass burning and deforestation add

about another 2 Pg C to the atmosphere. About 3 Pg C in the form of CO2 is building up

in the atmosphere each year. The average concentration of CO2 was about 290 mg/km-1

in pre-industrial times; now it is about 350 mg/kg-1 and increasing steadily at a rate of

0.3-0.4%/yr. Since CO2 is chemically inert, it is not destroyed by photochemical or

chemical processes in the atmosphere; either it is lost by transfer into the ocean or

biosphere or it builds up in the atmosphere (

Soils are part of the pedosphere. The pedosphere is the envelope of the Earth

where soils occur and soil forming factors are active. The pedosphere only develops

where there is a dynamic interaction among the atmosphere, biosphere, lithosphere and

the hydrosphere (Fig. 6). Soils can act as sinks or sources of atmospheric C. The

exchange of CO2 between atmosphere and land plants includes soil-related efflux of 100

Pg yr1. Soil organic matter (SOM), which consist ofundecomposed and partially

decomposed organic residues and humus, is the largest and most important terrestrial C

pool in the global carbon cycle (


Global Net P nrinai i
Production and ?
Respiration ;
4.Y C ing
i /P i -Use

\ i ealilion Ii& cil, .

Carbron Flu IUicaled ByAr irow

jlanFjral =}


Fossil Fuel
SCnmbustion and
\ Cement

fa ararmn I

AnRlthropgenic Fl -----

Figure 5. A simplified diagram showing the carbon cycle and the interaction among
atmosphere, oceans and biosphere (Source:

Figure 6. Relationships among the pedosphere, atmosphere, hydrosphere, lithosphere and
biosphere. (Source:

There are two types of carbon pools in the pedosphere; soil organic carbon (SOC)

(i.e., decomposition of organic materials) and soil inorganic carbon (SIC) (i.e.,

decomposition of mineral materials). This study focuses on SOC. The current SOC

pool in world soils is estimated at 1,500 Pg (Eswaran et al., 1995). The SOC pool is

about 2 times that of the atmosphere pool and about 2.5 times that of the biotic pool

comprising land plants.

Pedogenic processes that affect SOC dynamics may be grouped into two

categories: SOC-enhancing and SOC-degrading processes (Fig. 7). Processes that

enhance SOC content are plant biomass production, humification, aggregation, and

sediment deposition. Processes that degrade SOC content are soil erosion, leaching, and

soil organic matter (SOM) decomposition. It is the net balance between these SOC

processes, as influenced by land use and anthropogenic factors, that determines the net

SOC pool of the pedosphere (Lal et al., 1998).

An increase in SOC, through C sequestration into the pedosphere, has two notable

positive effects. First, it enhances the soil quality by improving the soil structure and thus

the available water capacity and second, it improves the soil's environmental regulatory

capacity by affecting the emissions of gases such as CO2 and CH4 to the atmosphere.

Thus, it improves the resistance to erosion by wind and water and the transmission of

water and solutes through the soil solum (Lal et al. 1998).

As SOM is fragmented into smaller sizes and converted into humic material, soil

physical structure becomes increasingly important to the SOM decomposition rate. The

formation of soil particle aggregates and organo-mineral complexes can entrap SOM and

give rise to a physically and/or chemically stabilized soil carbon pool that can serve as a

reservoir for carbon sequestration (Garten, 1997).

Figure 7. Principal pedogenic processes affecting soil organic carbon (SOC) content (Lal
et al., 1998).

A large portion of the global inventory of SOC resides in forest ecosystems (Lal

et al. 1998); but scientists have been unable to answer many questions about the ability of

forest soils to sequester carbon and thereby ameliorate future increases in atmospheric

CO2 concentration (Lal et al. 1995a;b;c).

The state of Florida consists of 151,939 km2 of land
( site=http://www.i .html)

and "pine flatwoods" are the most extensive terrestrial ecosystem. They cover

approximately 50% of the state area.
( 16.htm)

Pine flatwoods evolved under frequent lightning and human-caused fire, and

seasonal drought and flooded soil conditions. Pine flatwoods are characterized by:

* Flat topography

* Relatively poorly drained, acidic, sandy soil

* And in the past, by open pine woodlands with frequent fires.

Pine flatwoods occur in many of Florida's National and State forests. National

forests, under the supervision of the U.S. Forest Service, extend 5,014 km2 (3.3% of the

federal land) and are located in three National Forests: Osceola, Ocala and Apalachicola

(Fig. 8).
(http://forestry.about. com/science/forestry/gi/dynamic/offsite.htm?site=http://www.fs.fed.

State Parks and State Forests (Fig. 9), under the supervision of the Florida Department

of Natural Resources, extend 3,238 km2 (2.2% of the state land) and are located in 36

different locations across the State.

Many of the soils identified in the federal and state parks are in the flatwoods

( Some of the soils are classified in

the Order of Spodosols. In Florida, Spodosols (Fig. 10) develop in sandy, acid parent

material, with poor to very poorly drained conditions and are easily recognized by the

spodic horizon (Bh). The spodic horizon is an illuvial layer with 85 percent or more

spodic materials. Spodic materials contain illuvial active amorphous materials composed

of organic matter and aluminum, with or without iron. The term "active" is used to

describe materials that have a high pH-dependent charge, a large surface area, and high

water retention. The spodic horizon normally lies below an albic horizon (a light colored

8 E



.. Gaines

f-St. P te" .

St. Petersb

W Io 5:lli


Figure 8. Location of the three National Forests in Florida.
Source: (

eluvial E horizon). Less commonly, it either is under an ochric epipedon that does not

meet the color requirements for an albic horizon or is in or under an umbric epipedon. In

~I ~-- c
~. c~~

some soils the spodic horizon is at the surface of the mineral soil directly below a thin O

horizon (Soil Survey Staff, 1999).

The pedogenic process of podzolization has been used to explain how one spodic

horizon forms but there are regions in Florida where soils with multiple spodic horizons

(Fig. 11) occur and there are doubts that the deeper spodic horizons were formed by


State Forests

SState Forest
SMajor Road
+ city
rL -A

Figure 9. Location of the 36 State Forests in Florida.
Source: (htt ://

this process. The mechanism of formation of these multi-layered Spodosols may not fit

under the classical definition of podzolization. The mechanism of podzolization requires


eluviation of Al and/or Fe from the E horizon and illuviation of these minerals in the Bh

below. This pedogenic process occurs in the upper Bh horizon, but may not occur in the

lower B'h horizon.

Most of the C stored in Spodosols occur in the A horizon (1st mineral horizon,

usually in the surface) and the Bh (spodic horizon). According to Lee et al. (1988), the

Bh horizons in selected Spodosols of Florida, sequestered, in average, 3 times more C

Oto 20cm

20 to 60cm

60 to 100cn

100 to 200c

Figure 10. Florida's State Soil-Spodosol, series Myakka (sandy, siliceous, hyperthermic,
Aeric Alaquod). Source: (

than the A horizons (8.64 mg/kg vs. 21.8 mg/kg). Carbon storage, coupled with humus

dynamics and agronomic issues, has become of global significance because of its


Figure 11. An example of a Spodosol with multiple Bh horizons near Green Cove
Springs, Florida. Photo by Mary E. Collins.

possible contribution to the reduction of atmospheric CO2 and the greenhouse effect

(Bouwman, 1990). The capacity of Spodosols to be a source or sink of atmospheric CO2

is connected strictly to the rate of SOM degradation (Dale et al., 1993). A better

knowledge of the processes that stabilize humus in Spodosols, in particular, humic

substances (the recalcitrant fraction of SOM) will play a significant role in understanding

how C sequestration is achieved.

Very little research has been conducted on the genesis of these multiple Bh

horizon Spodosols in Florida. Studying how they develop and learning the different

mechanisms of formation can help us understand the C dynamics taking place in


In general, this study investigates the pedogenic processes responsible for

forming multiple-Bh horizons in Spodosols; what are the forms of C in those spodic

horizons; how different is their morphological, physical, and chemical properties between

upper and lower Bhs and, explain through landscape evolution their genesis/kinetics.

Objectives of the Study

The objectives of this research were as follows: (a) To document the effect of

hydrology on the Bh horizon genesis and the C release with hydrological changes; (b) To

determine the differences in morphological, physical, and chemical properties among Bh

horizons; (c) To relate C sequestration to the depth of the Bh horizons in the different

Spodosols of the study area; (d) To study C sequestration by determining the forms of C

in multiple-Bh horizons in Spodosols; and (e) To propose a mechanism for the genesis of

Spodosols with multiple Bh horizons.

Literature Review

Florida has seven Orders of soils (Fig. 12). They are Alfisols, Entisols, Histosols,

Inceptisols, Mollisols, Spodosols and Ultisols. Spodosols are the dominant soil Order.

They cover 3.6 millions hectares (Fig. 13). Approximately 27% of the state land area

(Stone et al. 1992).

Spodosols in Florida are soils developed in coarse-textured parent materials under

an intense leaching environment induced by organic acids from plant litter and plentiful


The word "Spodosol" originates from the Russian term "pod" (beneath) and "zol"

(ash), or "ashy underneath." Podzol was used originally in the early Russian system of

classification to describe the forest soils that had a light-colored E horizon (Baldwin et

al. 1938).

Spodosols are probably the most photogenic soils of the world with several

kinds of horizons, each with its own color, texture, and properties. The most striking

horizon is that resulting from accumulation of black or reddish amorphous materials

Sil Orders

lni pllsl:
B spadosals
i UIeol
SUban Land

50 0 5W 100 km

Figure 12. Map of the soil Orders in Florida. Source: (

consisting mostly of organic C, Al and/or Fe. This horizon is called a spodic horizon

(Soil Survey Staff, 1999).

The formation of the spodic horizon is due to the pedogenic processes of

eluviation (mobilization) ofFe and Al from O, A, and E horizons and the illuviation

(immobilization) of these minerals in short-range-order complexes with organic matter in

the B horizon. The overall process is known as podzolization (Fig. 14). Source:

o 0 60 100 km

Figure 13. Percent land coverage of Spodosols (orange color) in Florida and Northeast
Florida. Source: (

In general, podzolization refers to those processes by which the soil is depleted of

metallic cations (alkaline materials), becomes acid, and develops leached surface layers

and lower horizons of accumulation. Podzolization is fully active only where there is acid

leaching from the surface layer of organic material. So, there must be accumulation of

organic material over the mineral soil.

A horizon
E horizon
Leached, light color,
large ly Si
-..-- Bh horizon
Accumulation of humus
AI, Fe and bases.
SC horizon
Some hunus and bases
lea che d fmm Bh Iost to
ground water.

Figure 14. Schematic diagram showing the podzolization process in the soil. Source:

The vegetation in Florida's flatwood forests, consisting mostly of slash pine

(Pinus elliottii), longleaf pine (Pinus palustris), saw palmetto (Serenoa repens)

and gallberry (Ilex glabra) (Collins et al. 1999), provides a generous amount of organic

debris with relatively low metallic cation concentration. On decomposition, this

vegetation gives rise to acid products. As the acids generated in the organic layer are

moved downward by percolating water into the mineral soil below, weatherable

destabilization occurs and metals from the sand grain coatings are released. These metals

move downward into solution. Once the coatings have been removed from the upper part

of the soil, the hydrogen ions of percolating acid waters replace many of the metallic

cations on the cation exchange complex. The metallic cations move downward in

solution, and the upper part of the soil becomes acid. Under acid conditions, many Fe and

Al compounds are unstable; and sand grain coatings containing these compounds break

down. Since quartz is fairly stable under acid conditions, it remains behind as a residue in

the upper part of the soil (E horizon). Thus, the upper layer of the soil becomes leached

(stripped) and is left in a highly acid and siliceous state. The leached material, colloidal

organic materials, metallic cations, Fe and Al oxides and clays accumulate at the lower

depth (De Conninck, 1980; Buol et al., 1997).

Spodic horizons are defined as being at least 2.5 cm thick and containing at least

85% "spodic materials". Spodic materials have a pH (1:1 water) of 5.9 or less, and at

least 0.6% organic carbon (1% organic matter). Typically, the color changes with depth

from black (the brightest chroma is near the top) to a reddish due to iron accumulation.

Colors of well-drained soils are commonly 5YR or redder; or 7.5YR with a value of 5 or

less and a chroma of 4 or less. Colors of poorly drained soils are commonly 10YR or

7.5YR with a value of 4 or less and a chroma of 4 or less. In spodic horizons that have

sandy or loamy particle size, there are commonly cracked coatings of Al, organic matter

and Fe, on sand grains (>10%) or pellets (>0.02 mm) between the sand grains (Soil

Survey Staff, 1999).

Spodic horizons are usually located under an albic horizon. Less commonly, they

are under an ochric epipedon which does not meet the requirements of an albic horizon,

an umbric epipedon, histic epipedon or simply under a thin O horizon. Spodic horizons

are commonly designated Bh, Bs, Bhs or Bsm horizons.

Two suborders of Spodosols occur in Florida, Aquods and Orthods. Aquods are

Spodosols that have a shallow, fluctuating water table and can have a histic epipedon

and/or redoximorphic features within 50 cm of the surface in an albic or spodic horizon.

If they are low in iron (<0.10%) are identified in the Alaquod Great Group. Orthods, are

Spodosols that are relatively better drained and have less than 6.0% organic C in the

spodic horizon. If they are low in iron (<0.10%) are identified in the Alorthod Great

Group. (Soil Survey Staff, 1999).

In the Florida flatwood forests (Fig. 15) Orthods and Aquods occur widely.

Orthods are usually located in the flatwood uplands and Aquods are located in local

depressions and large areas of low relief and high water table (Collins, 1990).

The flatwoods ecosystems have a nearly leveled topography. Soils quickly

become waterlogged during periods of heavy rain. Often, this period of heavy rain

produces episaturated condition (perched water table) in the soil because the restrictive

soil layers (such as the spodic horizon and, when present, the argillic horizon, which have

low hydraulic conductivity) limit water movement to lower soil horizons (Gaston, 1990).

Variations in elevation and topography affect the degree of inundation during the

rainy season. These variations result in a significant difference in the hydrology. During

the dry season, the amount of organic matter and leaf litter are the predominant factors

influencing the drought conditions of the soil. Because flatwoods is so strongly

associated with frequent fires, variation in fire regime greatly alters the amount of litter

and organic matter and thus indirectly influences the hydrology of flatwoods ecosystems.

Due to slight differences in soils and hydrology at any given location, flatwoods

communities often contain numerous other types of ecosystems, such as swamps,

marshes, hardwood hammocks, etc. This mosaic of habitats in an area can result in

a great diversity of ecotones between the flatwoods and these other communities (Sun,


Estimates of the time required for a Spodosol to develop is limited because the

time of initiation of soil-forming processes usually cannot be determined precisely. In

field experiments, Chandler (1942), used the known retreat pattern of the Medenhall

glacier in Alaska and by comparing the degree of Bh development in materials of

different ages. He estimated that a mature Spodosol would require 1,000 to 1,500 years to

Figure 15. Flatwood forest in Osceola National Forest. Photo by Mary E. Collins.

form. Russell (1974) used the drainage of Lake Ragunda, Sweden, which ended in

1796, as the beginning of soil development. He also estimated a time from 1,000 to

1,500 years for the development of a mature Spodosol. These estimates were made for

Spodosols of cold locations. Spodosols of Florida probably can form in less time since

pedogenic processes are not interrupted with the change of seasons. In contrast, in a

laboratory experiment, Harris and Hollien (2000) created an artificial spodic horizon in

81 days.

Some Spodosols develop a second or multiple Bh horizons beneath a thick E' or

Bw horizon. Holzley et al.,(1975) studied multiple Bh Spodosols in the Coastal Plains of

North Carolina. According to them these Spodosols had a dissolved organic carbon

(DOC) flux sufficient to develop a Bh horizon 7m thick in 30,000 years. He thought that

these very deep Bh horizons (up to 10 m) may be buried. But it seems more likely that

they have formed at great depth because the overlying soil materials have little Fe and Al

that could precipitate the organic C.

According to Daniels et al., (1975), in the North Carolina multiple Bh Spodosols,

there is little difficulty conceiving the formation of the upper Bh horizon within the first 2

m by the processes generally attributed to podzolization, but he thinks that there is a

serious question when considering how OC accumulates at 10 m.

Dissolved organic C originates from the decomposition of organic matter (OM).

Litter decomposition (Fig. 16) represents the sum of mass losses brought about by

catabolism (action of microbial and animal enzymes), comminution (physical

breakdown by animals and abiotic processes), and leaching of water-table materials

(Swift et al.1979).

Decomposition process


Figure 16. Simplified diagram of the litter decomposition cycle.
Source: (

As a consequence of the change in-state brought about by these processes,

soluble or particulate materials are transported down in the soil by water to sites where

different chemical conditions operate from those regulating decomposition in the soil

surface. The solubilization of litter constituents and the relocation and precipitation by

condensation reactions in mineral soil are important processes in the formation of

stabilized humus constituents (Duchaufour, 1977). The cellular material decomposes

rapidly, usually within a few months to a year or two depending upon chemical

composition. During the process of decomposition microbial cell walls and some

metabolic products are synthesized, which decompose at least 10 times more slowly than

the original litter (Lowe, 1978). In general, about 10-20% of the aboveground litter and

20-50% of the root litter is converted to humus (Nye and Greenland, 1960) and the rest is

mineralized as CO2. Within the soil, some fractions of this organic matter undergo further

biochemical stabilization and may also be complex with clays or other minerals or they

may be physically protected within clay microaggregates (Edwards and Bremner, 1967).

These biochemical and physical processes further increase the resistance of humus

compounds to enzyme attack, so that mineralization rates of some fractions may be less

than 0.1-1% per year (Campbell, 1978).

The overall C distribution of DOC, estimated by Nuclear Magnetic Resonance

(NMR) spectroscopy, has been similar for both needle and leaf forest litter (Wilson et al.,

1983; Zech et al., 1985, 1990a,b and Hempfling et al., 1987). alkyl C -H bonds comprises

approximately 10-30%, alkyl C-O bonds 50-70%, aromatic C rings 10-30%, and carboxyl

(C=O) bonds 5-10% (Kogel et al., 1988). About 50% of the C-H bonds are attributable to

extractable lipids and an additional 20% to bound lipids extractable after acid hydrolysis.

The remaining C-H bonds may be ascribed to cutin-like macromolecules (Ziegler, 1989).

Polysaccharides (cellulose and hemicellulose) accounts for most of the O-alkyl C

resonances. Minor contributions are due to oxygen-substituted lignin side chains, lignin

methoxyl groups, and ester carbons in cutin and waxes. Aromacity carbon is mainly due

to lignin (Kogel et al., 1988). Most of the DOC infiltrates the soil and moves through the

soil matrix. This movement is caused by the negative charge of the acidic organic

compounds that are not balanced by sorption of Al or Fe so, the hydrophilic organo-

metallic compounds repel each other, disperse and migrate (Skjemstad, 1992).

McDowell and Likens (1988) studied the origin composition and flux of DOC in

the Hubbard Brook Valley in central New Hampshire. Cronan and Aiken (1985) studied

the chemistry and transport of soluble humic substances in forested watersheds of the

Adirondack Park, New York and, Yavitt and Fahey (1985) studied the organic chemistry

of the soil solution during snowmelt leaching in Pinus contorta ecosystems, Wyoming.

All these scientists observed that mobilization of DOC varies strongly during the course

of the year through the soil. The common maximum DOC mobilization occurred at first

leaching events after dry and warm periods (Guggenberger and Zech, 1993a; Vance and

David, 1991) probably because OM had time to accumulate in the surface of the forest


According to Daniels (1975), vegetation affects the movement and relative

age of DOC through the soil. When vegetation removes soil water via evapotranspiration,

the DOC that is left behind would be "young". If this DOC is not used by plants or

microorganisms, it would be free to move downward with the ground water. The

horizons below would receive only that C that would precipitate by chemical or

biological means. If the flux of that C is greater than the loss of it, C would accumulate.

Dawson (1978) studied Spodosols in the Cascade Mountains of Washington. He observed

that, in general, large quantities of DOC were leached into the mineral soil from the

forest floor, producing solution concentrations up to 122 mg C L1.

Cronan (1990) observed in a forested watershed located in New York, that the

concentrations of DOC typically decreased sharply with increasing soil depth. Solutions

in the B horizons had concentrations, on average, about one-fifth of values observed

in forest floor solutions. Similar observations were made by Dalva and Moore (1991) in a

forested swamp catchment in Westland, NewZealand. They observed that DOC

average for B horizons was, on average, one-sixth of the values observed in forest floor


As DOC moves through the soil, it interacts with clays. Humus-clay interaction in

soils is a dynamic process. Both humus and clay act as centers of activity around which

chemical reactions occur. Furthermore, by attracting ions to their surfaces, they

temporarily protect the ions from leaching. Because of their surface charges they also act

as "contact bridges" between larger particles, thus helping to maintain stable granular

structure ( Soil/03-10.htm).

Many processes take place in soils, but adsorption is probably the controlling step

in the formation of microaggregates in the soil. Adsorption on soil colloids depends on

the nature and properties of the surfaces available for interaction with ions and molecules

present in the soil solution. Active sites on soil clays, for instance, are frequently masked

by the presence of hydrous oxide material coating their surfaces and much of these

surface particles are coated with humic substances. In this way, the complex soil colloid

would show surface properties attributable to clay, hydrous oxide, and humic compounds

(Cornejo, 1996).

The capacity of metal oxyhydroxides to adsorb humic substances was reported by

Evans and Rusell (1959). They indicated that adsorption decreased as the pH of the soil

increased. On the other hand, Schnitzer and Skinner (1963) reported that fulvic acids

(FA), the smaller molecules of humic substances, were able to chelate (complex) with Fe

and Al from goethite, gibbsite and soil samples rich in "free" Fe and Al. According to

Theng and Scharpenseel (1975) and Theng (1976), the hydrous oxides of Fe and Al are

the most efficient substances in linking acidic organic molecules to clay surfaces.

By using X-ray diffractrometry and 13C-NMR spectroscopy Theng et al. (1986)

detected evidence of the occurrence of interlayer-clay-organic complexes in two New

Zealand soils with low microbial activity and a high acid reaction. In these soils, the

complex analyzed was formed by a regularly interstratified mica-smectite. The organic

species was a humic substance with a polymethylene chain structure containing little or

no aromatic C.

Schnitzer et al. (1988), using IR, NMR, and GC-Mass spectroscopy

techniques, re-examined previous results obtained by Kodama and Schnitzer (1971) in a

Canadian Spodosol. They concluded that about half of the clay-associated OM consisted

of humic materials and the other half was mainly composed of long-chain aliphatics.

Catroux and Schnitzer (1987) reported aromacity of SOM extracted from silt to be

higher than that extracted from clay. While aromatic structures appear to be concentrated

in silt-size separates, organic substances in clays seem to be dominated by aliphatic


The quantity of DOC sequestered in the flatwood ecosystems is significant.

Stone et al. (1992) estimated that 809 Tg of OC was sequestered in Florida Spodosols;

431 Tg residing in Bh horizons. Spodosols in Florida have about 0.05% of the estimated

global SOC pool estimated by Post et al. (1982) but, these data are underestimated

because subsurface C sequestration also occurs in the deep Bh horizons of Florida's

multiple Bh Spodosols.

Daniels et al. (1975) was the first to study multiple Bh Spodosols in coastal plain

soils of North Carolina. These North Carolina Spodosols contain some feldspars.

Northern Florida Spodosols differ from these North Carolina counterparts in that they are

formed from coastal plain sediments (mostly quartz) that do not have weatherable

minerals (Brasfield et al., 1973). The source of metals for complexation and mobilization

is restricted to relatively resistant secondary minerals which occur mainly as sand-grain

coatings (Harris et al., 1987; Harris and Hollien, 2000). Podzolization in Florida's

Spodosols require the presence of a water table, but the relationship between depth to

water table to the upper spodic boundary is not direct (Harris, 1998).

Farmer (1983), how also studied multiple-layered Spodosols in New Zealand,

think that despite these differences, the mode of formation of the Bh horizon has been

considered essentially similar. The traditional view is that Al and Fe are

released by weathering in the A horizon and are translocated as organic complexes and

deposited in the B horizon where there is an increase in sesquioxides. If reducing

conditions prevail, the iron is "lost" from the soil in Fe (II) form. However, most

Spodosols in Florida have formed in sands with very low initial contents of sesquioxides

and/or lack weatherable minerals that might provide continuing inputs of Fe and Al.

Therefore, while free sesquioxides are essential to the formation of Bh horizons in freely-

drained Spodosols, a different process is probably involved in the development of Bh

horizons in Florida because of the poorly drained conditions.However, major differences

in morphology and micromorphology between Bh's suggest different mechanisms of

precipitation (Harris, 1998).

Farmer (1983) observed that in hydromorphic Spodosols organic precipitates

filled the space between uncoated quartz sand grains in a manner that suggests

precipitation from solution. Also he observed that in freely drained Spodosols the sand

grains were coated with darker organic matter and paler (yellowish) sesquioxide coatings,

and the spaces between the grains were largely unfilled. He suggested that these

differences were due to different mechanisms in the podzolization process.

Daniels et al. (1975) thought that moving ground water is the mechanism for

distributing OC through the deep B'hs horizons. According to the Soil Characterization

Data of Florida (Carlisle, 1978, 1981, 1985, 1988 and 1989) deep B'h spodic horizons

have a lower hydraulic conductivity than the superficial Bh. Low hydraulic conductivity

would allow more time for the DOC to react with the Al/Fe in clays and solution.

In reassessing the processes that forms Spodosols, it has been proposed that, in

humus-Fe Spodosols formed on coarse parent materials, organic matter migrates through

the E horizon in soluble and colloidal form and is adsorbed or precipitated at the top of

the B horizon. This occurs on surfaces that initially carried coatings of sesquioxides; or as

OM moves down in the leaching water. OM takes up more and more Fe and Al from the

lower sesquioxide-rich horizons until its original charge is neutralized; thus, leading to

the mutual precipitation of the metals and OM.

Both processes imply the availability of both Fe and AL compounds

(sesquioxides) in the B and lower horizons. However, the parent material of Florida's

Spodosols initially contain only small amounts of Al sesquioxides and only trace amounts

of weatherable minerals, there is no evidence of sesquioxide coatings (enrichment), and

could not form in the zone of permanent saturation.

In their study of the multiple Bh horizons soils in North Carolina, Holzley et

al. (1975) postulated that with little Fe and Al the OM was not rendered immobile. It

moved deeper and even through the soil systems into streams. Kaurichev and

Nozdrunova (1964) reported that there were differences in Spodosols that are

"overmoistened". These differences are: (1) There is an alteration of oxidation and

reduction phases. (2) A transformation on the structure of the OM. (3) A reduction

of the components of the mineral soil constituents. (4) The translocation of substantial

amounts of OM down to a substantial depth.

Tolchel'nikov (1983), studied Spodosols with multiple Bh horizons in Russia. He

thought they occurred because the OM present in the lower B'h horizon originated during

the Holocene epoch. According to his theory, the humus accumulated deep in the soil

because the soils at that time were devoid of clay particles. After the deep B'h horizon

was formed, new material was deposited over it, and a new Bh horizon developed over

the old one.

The formation of spodic horizons is directly related to SOM. SOM consist of

humic substances and nonhumic substances. Nonhumic substances are all those materials

that can be placed in one of the categories of discrete compounds such as sugars, amino

acids, fats and so on. Humic substances are the other, unidentifiable components.

The formation of humic substances is one of the least understood aspects of

humus chemistry and one of the most intriguing. The study of these macromolecules has

been a challenge to the ingenuity of scientists for more than 200 years, and in spite of the

application of almost all available analytical instrumentation developed over the past four

decades, knowledge of their nature and composition is still limited (Saiz-Jumenez, 1996).

Humic acid (HA) is defined as the fraction of humic substances that is not

soluble in water under acidic conditions (pH less than 2) but is soluble at higher pH

values. HA is the major extractable component of soil humic substances. It is dark brown

to black in color (Schnitzer, 1982). The formation of HA during the decomposition and

transformation of plant residues is often accompanied by increases in alkyl-C and

carboxyl-C and decreases in ether-C, acetal-C, and aromatic-C in the molecular structure

of the acid (Zech et al. 1985).

Fulvic acids (FA) are the fraction of humic substances that are soluble in water

under all pH conditions. They remain in solution after removal of humic acid by

acidification. FA are light yellow to yellow-brown in color (Schnitzer, 1982).

Several pathways exist for the formation of humic substances during the decay of

plant and animal remains in soil (Fig. 17). The classical theory, popularized by

Waksman, (1936) is that humic substances represent modified lignins pathwayyl. The

majority of present-day investigators (Stevenson, 1982) favor a mechanism involving

quinones (pathways 2 and 3). In practice, all four pathways must be considered as likely

mechanisms for the synthesis of HA and FA in nature, including sugar-amine

condensation (pathway 4). These four pathways may operate in all soils, but not to the

same extent or in the same order of importance. A lignin pathway may predominate in

poorly drained soils and wet sediments, whereas synthesis from polyphenols may be of

considerable importance in certain forest soils. The frequent and sharp fluctuations in

Figure 17. The mechanisms for the formation of soil humic substances. Numbers
represent pathways from 1 to 4. (Stevenson, 1982).

temperature, moisture, and irradiation in terrestrial surface soils under a harsh continental

climate may favor humus synthesis by sugar-amine condensation.

Humic substances are widely considered to represent the most stable fraction of

SOM. Their stability is attributed variously to their chemical structure and heterogeneity

as well as to being caught within soil aggregates and interactions with metal cations and

clay minerals. The recalcitrance of humic substances may owe more to the latter than to

the former mechanisms, since it has been shown that when extracted HA are incubated

with fresh soil, they rapidly decompose unless polyvalent cations are present (Juste et al.,


Carbon-dating methods have shown that HA have mean residence times of

thousand of years compared with hundreds of years for the humin fraction. The FA

fraction contains polysaccharides with fast turnover and are generally contemporary

with the humin fraction or are of more recent origin (Paul and van Veen, 1979). If FA

move down in the soil, however, they can be among the oldest fractions (Goh et al.,


Ugolini et al. (1977) used lysimeters to study the migration of organic matter and

mineral particles in a subalpine Swiss Spodosol. He observed that the Bh horizon of this

Spodosol was friable with a high content of humins and HA that formed aggregates. He

calculated that it would remain hydrophilic with an average OC turnover of 200 years.

He concluded that if decomposition rate was less than the rate of eluviation from OM,

organo-metallic compounds would accumulate. The horizon would become hydrophobic

and FA would predominate.

Many investigators now believe that all dark colored humic substances are part of

a system of closely related, but not completely identical high-molecular-weight polymers.

According to this concept, differences between HA and FA, can be explained by

variations in molecular weight, number of functional groups carboxyll, phenolic OH),

and extent of polymerization. The postulated relationships are depicted in Fig. 18.

The low-molecular-weight FA have higher oxygen but lower C content than high-

molecular-weight HA. FA contain more functional groups of an acidic nature,

particularly COOH. The exchangeable acidities of FA (900-1400 cmol/kg) are

considerably higher than HA (400-870 cmol/kg).

Another important difference is that while the oxygen in FA can be accounted for

largely in known functional groups (COOH, OH C=O), a high portion of the oxygen in

HA seems to occur as a structural component of the nucleus. Electron microscope

observations revealed that the HA of different soils have polymeric structure. This

structure appears in form of rings, chains, and clusters (Saiz-Jimenez, 1996). The size of

these macromolecules ranged from 6-50 nm depending upon the humification


HA are thought to be complex aromatic macromolecules with amino acids, amino

sugars, peptides, and aliphatic compounds involved in linkages between the aromatic

groups. The hypothetical structure for HA, shown in Fig. 19, contains free and bound

phenolic OH groups, quinone structures, nitrogen and oxygen as bridge units, and COOH

groups variously placed on aromatic rings

The hypothetical model structure of FA (Buffle's model) contains both aromatic

and aliphatic structures, both extensively substituted with oxygen-containing functional

groups (Fig. 20).

Humic substances
(pigmented polymers)

Fulvic acid Humic acid Humin

Light llow
yellow bt o-n -

increase in intensity of colour >
increase in degree of polymerization >
2 000 increase in molecularweight )300 000 ?
45% increase in carbon content >62%
48% decrease in oxygen content )30%
1 400 decrease in exchange acidity >500
decrease in degree of solubility -

Figure 18. Chemical properties of humic substances (Stevenson, 1982)

cc -, co' m, <, H i
a "A CQ O. HN
>1 i. a11 1'14

0' re

Figure 19. Hypothetical structure of humic acids. (Stevenson, 1982)

Bracewell and Robertson (1987) showed that aliphatic (polymethylene) chains,

heavily substituted with hydroxyl and carboxyl groups, occurred in soils in which

biological activity is high and OM turnover is rapid. In contrast, relatively unsubstituted

aliphatic chains are characteristic of OM in soils in which biological activity is restricted,

\ / / "'/ "C/

Figure 20. Model structure of fulvic acids. (Buffle, 1977 )

for example, by low temperature or excess moisture. In general, the smaller FA

molecules are also more mobile and accumulate more sesquioxides per unit C before

precipitating as Al or Fe-fulvates. For this reason, they have been considered the primary

agent of Fe and Al translocation in the soil (McKeague and Day, 1968).

HA molecules can range to a considerable size, but those in Spodosols are slightly larger

than FA molecules. The continually moist and acid conditions characteristic of many

Spodosols are not conductive to the development of larger humic molecules characteristic

of other regions (Kononova, 1966). These small HA molecules are also similar to FA in

that they are mobile and able to complex Fe and Al. With regard to the theory of Bh

horizon formation, their behavior differs from FA only in that their precipitation

threshold occurs at a lower level of Fe and Al loading. They should, therefore,

accumulate closer to the surface than FA complexes. Thus, the upper B horizon of

Spodosols should be characteristically richer in humic acid complexes, while the more

mobile FA should move deeper into the B horizon.

The percentage of the humus, which occurs in the various humic fractions, varies

considerably from one soil environment to another. The humus of forest soils is

characterized by a high percentage of FA (50.7 to 66.6%) while the humus of peat and

grassland soils is high in HA (53.8 to 68.7%) (Stevenson, 1982) (Fig. 21).

1 FA

Grassland soils Forest soils
FA-fulvic acid
HA- humic acid

Figure 21. Distribution of humus forms in grasslands and forest soils (Stevenson, 1982).

A system, devised by Kumada (1987), classified HA into four types: Rp, P, B and

A. These HA are then related to soil properties, vegetation type, and land use. Rp-type

HA represent an early stage in the humification process (e.g. rotting wood), whereas the

P-, B-, and A-types represent stable forms in strongly acid (P), moderately acid (B), and

weakly acid-to-alkaline soils (A). Spodosols developed under forest produce P-type HA.

This HA carbon occurs mainly as chemically aromatic (benzene ring) structures (Higashi,


The current spodic horizon definition is based on the presumption that amorphous

weathering products accumulate in the B horizon through the agency of relatively low

molecular weight (approximately 800) acid organic completing polymers (Soil Survey

Staff, 1999). These polymers are products of organic decomposition under acid

conditions. They are presumed to readily complex Fe and Al from the mineral fraction

and remain soluble and mobile until a critical amount of Fe and Al has been completed

after which they precipitate (Schnitzer and Khan, 1972). The Bh horizon is considered

to be a zone of organic Fe and Al precipitation.

Although the current definition emphazises the organic forms ofFe and Al, it is

recognized that inorganic amorphous forms are also present (Stobbe and Wright, 1959).

These may be decomposition products of the organic forms or they may have moved to

the horizon as inorganic colloids (Farmer et al., 1980).

Both Fe and Al are known to accumulate. McKeague and Day, (1968) suggested

that Al was the most distinctive marker in some Canadian Spodosols; and there have been

suggestions that Al alone could be used to define a Bh horizon. Southard (1994)

discussed that Fe and C distributions parallel each other in both the well-drained and

poorly-drained soils, suggesting that they probably occur together. The Al content in

well-drained and poorly-drained soils accumulate at a greater depth than either the Fe or

C, suggesting the possibility that the Al is not completed and may have been translocated

as an inorganic ion.

It seems that the critical factor for immobilization is the ratio of C to metal ions

(McKeague et al., 1983). With a high ratio, compounds are dispersed and mobile. As

the ratio decreases, due to additional complexation of metal ions during transport, the

complex is immobilized by precipitation or flocculation.

Holzhey et al. (1975) stated that HA were the principal organic components of

thick lower Bh horizons in the North Carolina Coastal Plain. Since FA usually dominate

most Bh horizons, he conceptualized a model that involved an environment of migrating

organic that accumulate and apparently polymerize to HA in sands until some maximum

OM content was attained. Beyond that maximum, there is little accumulation, although

migration continues. More recently, Anderson (1982) reported data for five Scottish Fe

humus Spodosols in which Bh horizons were distinguished by higher content of humic

acids (in average 2X more) than the B horizons below). According to Anderson (1982),

colloidal and soluble organic acids move in the soil until they encounter the sesquioxide-

coated-surfaces of the B horizon. Here, the negatively charged colloidal OM is filtered

out or precipitated on the positive charged oxide surfaces at the top of the B horizon. HA

concentrate in the top whereas, FA move further before becoming absorbed. He

conceptualized that Spodosols with more HA than FA have a wetter moisture regime.

The occasional moisture saturation in the Bh horizon, together with accumulation of OM,

could lead to reducing conditions. Ferric iron would change to ferrous iron, which would

rapidly re-oxidize in larger pores to form ferric species which would be immediately

trapped by OM.

The HA/FA ratio usually, but not always, decreases with increasing depth. Lee,

(1988), observed that, in selected Florida Spodosols, this ratio increased with depth in the

non-orstein Spodosols of St. Lucie and St. Johns Counties.

Multiple Bh genesis is a direct manifestation of processes dictating the terrestrial

fate and transport of DOC. These processes are fundamental in the assessment of global C

dynamics, but details of reactions and the role of water table in triggering them is still

uncertain (Harris, 1998).

This dissertation will serve as a source of information and understanding about

the processes that act upon the formation of multiple Bh horizons in Spodosols. An

improved understanding on how these soils sequester C is essential to cope with the

postulated global temperature change on our planet.



The research area was located in Baker County, northeast Florida (Fig. 22)



i n
2 0


'- -

Map Scale: cm = 3.13km

Figure 22. Location of research site, Baker County, Florida.

Baker County is bordered on the west by Columbia County, on the south by Union and

Bradford Counties, on the east by Nassau, Duval and Clay Counties, and on the north by

the St. Mary's River and the State of Georgia. The research site is located north of the

Olustee Battlefield in the southeastern part of the Osceola National Forest (Fig. 23).

This site was choose to represent Spodosols with multiple Bh horizons in northeast




S" -*

Research Site
Olustee Battlefield
Map Scale: icm 1.47km

Figure 23. Location of the research site in Olustee Battlefield near the Osceola National


Baker County is in the southern boundary of the thermic soil temperature regime

(Soil Survey Staff, 1999). It is characterized by long, warm summers and relatively mild

winters. The Atlantic Ocean, Gulf of Mexico, and large inland lakes moderate the


The total annual mean precipitation is 1376.2 mm (Watts, 1996). The average

monthly precipitation and the actual precipitation received during the study in the Olustee

Battlefield is presented in Table 1. There was a deficit of 427.8 mm of precipitation

during the hydrological field study due to the drought caused by La Nioa.

Table 1. Average monthly precipitation and actual precipitation for February 1999 to
July 2000.

Month Mean Actual Difference

Feb-99 98.80 34.80





Total after 1376.20 948.40 -427.80
12 months
Feb-00 98.80 52.60 -46.20
Mar-00 101.10 100.60 -0.50
Apr-00 83.30 17.80 -65.50
May-00 109.20 7.20 -102.00
Jun-00 179.80 169.20 -10.60
Jul-00 178.60 164.40 -14.20
Total after
18 months 2127.00 1460.20 -666.80

A large part of this rainfall occurs in summer as locally heavy afternoon or

early evening thundershowers. As much as 51 to 76 mm of rain can fall in an hour.

Daylong rains in the summer are rare and generally accompany tropical depressions.

Some tropical depressions intensify into tropical storms or hurricanes. These

storms normally occur between June and mid-November. Hurricane-force winds rarely

develop because of the inland location of the county. Extended dry periods can occur at

any time during the year but are most common in spring and fall (National Climatic

Center, 1996)


Florida is part of the Coastal Plain Province as defined by Fenneman (1938) and

Thombury (1965). The Coastal Plain Province is a subaerial inland extension of the

continental shelf. The Florida peninsula lies principally on the Florida Platform. This

platform extends nearly 640 km north and south and nearly 640 km in its broadest width

west to east. More than one-half of the Florida Platform lies under water leaving a

narrow peninsula of land extending to the south from the North American mainland

(Scott, 1992).

The peninsula is divided into three physiographic zones (White, 1970). Baker

County is located in the Northern physiographic zone. The Northern zone extends

northward to Georgia and to the south, through an imaginary cross peninsular line which

would pass approximately through the cities of St. Augustine, Palatka, Hawthorne, and

Gainesville in Florida. The Northern zone is distinguished by continuous high ground

forming a broad upland which extends eastward to the Eastern Valley, and westward

continuously into the Western Highlands of Florida. In Baker County, two geomorphic

subzones are recognized: the Northern Highlands, which dominate in the County, and

the Atlantic Coastal Lowlands which, in Baker County, consists of a small area of the

Duval Uplands (Fig. 24) (Cooke, 1945).

The Northern Highlands in Baker County were formed by sea terraces in the Early

Pleistocene. These terraces occurred at different elevations above the sea level (Fig. 25).

The Sunderland (65.5 m above sea level) and Coharie (51.8 m above sea level) (Cooke,

1945) terraces are the highest in the county. The Okefenokee terrace (MacNeil, 1949)

was formed when sea level was about 45.7 m above the present level and includes the

basin of the present Okefenokee Swamp. The Okefenokee Swamp ranges in elevation

from about 27.4 to 39.6 m above sea level and was once occupied by a shallow

intracoastal bay (MacNeil, 1949). The Wicomico terrace (30.4 m above sea level)

separate the Northern Highlands from the Atlantic Coastal Lowlands.

Remnants of the Coharie and Sunderland terraces form the Lake City Ridge

(Figs. 24 and 26), that passes through Olustee and trends to the northeast toward the

southwestern part of Charlton County, Georgia.

The Trail Ridge, located in the eastern part of the county (Fig. 24) is part of the

lower Coastal Plain and consists of a series of Quaternary beach complexes that parallel

the modem coast and are younger nearer the coast. These beach complexes made subtle

ridges of which the Trail Ridge was the crest of the Wicomico beach complex

Elevations of the Lake City Ridge range from 45.7 to 65.5 m and are similar to

those associated with Trail Ridge (30.5 to 61 m). Both Ridges probably existed as a chain

of islands, which formed the southern boundary of the Okefenokee Sound.

The Atlantic Coast Lowlands subzone extends to the land adjacent to the Atlantic

coast line of Florida. The Atlantic Coastal Lowlands includes a number of geomorphic

Map Scale I cm = 3. 14km

Figure 24. Physiographic areas of Baker County, Florida.

subdivisions. Only one of these subdivisions occurs in Baker County: the Duval Upland

(Fig. 24). The Duval Upland (White, in: Puri and Vernon, 1964), occurs in southeastern

Baker County adjacent to the boundary of Baker and Nassau Counties. It is bounded to

the west by the Trail Ridge and is part of a larger coast-parallel landform which extends

eastward into Nassau and Duval Counties. The small part of this feature that occurs in

Baker County ranges in elevation from approximately 15.2 to 30.4 m.


- Ok'EFENOKEE 45 7m

* WICOMICO 30.4m

Map Scale lcm=3.82 km
Figure 25. Marine terraces and highest elevation of those terraces identified in Baker
County, Florida.


Baker County is underlain by hundreds of meters of alluvial and marine sands,

clays, limestones, and dolomites (Clark, 1964). The Lake City Limestone is the oldest.

Next oldest rock is middle Eocene limestone (42 to 49 million years before the present)

in the Avon Park Formation. The youngest sediments are undifferentiated surficial sands

and clays of Pliocene to Holocene in age (5 million years old and younger). The Avon




1 04km
0 2 4 6 8 10 12 14 16 18 20

Figure 26. Topographic map of the Lake City Ridge and the research site.

Park Formation and the younger limestone units overlying it are important freshwater

aquifers. The discussion of the geology of Baker County will be confined to sediments of

Eocene-age and younger. Fig. 27 illustrate the underlying stratigraphy of a cross section

from west to east (U.S. Geological Survey Staff, 1962).

Avon Park Limestone

The Avon Park Limestone of the middle Eocene-age overlies the Lake City

Limestone and is similar in lithology. It is about 44 m thick in southwestern Baker

,*; C~'C"





County and thins to less than 15 m in the eastern part of the county. The top of the

formation ranges from 94 m below sea level in southwestern Baker County to more

than 187 m below sea level in the eastern part (U.S. Geological Survey Staff, 1968).






10 -21 -

-270',- --

West East

Figure 27. Stratigraphy of cross-section near Lake City Ridge, Baker County.

Ocala Group

The Ocala Group of Late Eocene consists of three limestone formations of similar

character (Fig. 27). From the oldest to youngest, they are the Inglis, Williston, and the

Crystal River Formations (Puri, 1957). These formations are differentiated generally on

the basis of lithology and fossil content. In Baker County, however, they consist of fairly

homogeneous sequence of cream to light gray, medium soft, chalky to granular marine

limestones that contain thin beds of hard, massive dolomitic limestone, and dolomite. The

Inglis and Williston Formations are generally more granular in texture than the overlying

Crystal River Formation and the Inglis Formation generally is more calcitic and slightly

darker in color than either the Williston or the Crystal River Formations. The thickness of

the Ocala Group ranges from 69 to 96 m in Baker County. The average thickness of the

Crystal River Formation is about 47 m and the average thickness of the Willinston and

Inglis Formations is about 15 m each. The altitude of the top of the Crystal River

Formation ranges from about 30 m below sea level in southwestern Baker County to

about 110 m below sea level in the eastern part (U.S. Geological Survey Staff, 1968).

Suwannee Limestone

The Suwannee Limestone consists of tan, white, or cream marine limestone, which in

many areas is dolomitic and coquinoid in parts, and varies considerably in hardness

(Cooke, 1936). In some locations this limestone is lithologically similar to the Ocala

Group limestone and is identified mainly by the last occurrence of the foranifera

Dictyoconus cookei (invertebrate animal). The thickness of the limestone ranges from 4

to 15 m, and the beds can be discontinous in the subsurface. In Baker County, the

Suwannee Limestone is a freshwater-bearing unit of the Floridan aquifer system (U.S.

Geological Survey Staff, 1968).

Hawthorn Formation

The Hawthorn Formation (5 to 24 million years old) overlies the Suwannee

Limestone in the western part of Baker County, The Hawthorn Formation is dominantly a

series of marine deposits consisting of varying and interbedded lithologies and

characterized by phosphatic sands, granules, and pebbles. The Hawthorn Formation

ranges from approximately 38 to 107 m in thickness (Scott, 1988)

Pliocene to Holocene Undifferentiated

Deposits of unconsolidated and poorly consolidated quartz sand that contains various

amounts of clay overlie the Hawthorn Group in Baker County. According to the Florida

Geological Survey (Leve, 1986), these sandy deposits generally range from about 7 to

30 m in thickness in the Northern Highlands area of Baker County. Sandy deposits in the

vicinity of Trail Ridge and Lake City Ridge are twice as thick than those of the Northern


Sands in the Northern Highlands are fine grained or medium grained and has only

trace amounts of heavy minerals (Johnson, 1986), especially titanium ore. In contrast,

sands in the Trail Ridge area are characteristically fine grained and has common heavy

minerals. Sands in the Trail Ridge are mined for their heavy minerals, especially


The Undifferentiated Sands, as described by geologists, are where the different

soils are formed.


The majority of the soils identified in the Osceola National Forest in the Baker

County Soil Survey report, (Watts, 1996), occur in the flatwoods, and are classified as

Spodosols. For the Florida Soil Characterization Data, one series with multiple Bh

horizons was sampled in the study area, Leon. This multiple Bh horizon Spodosol is in

the suborder Aquods. During this study, another series with multiple Bh horizon was

sampled in the Osceola National Forest, Mandarin. This multiple Bh horizon Spodosol

along with the Spodosols with one Bh horizon are classified in the suborder Orthods.

Aquod Spodosols differ from Orthods in that they have evidence of wetness

(redoximorphic features) within 50 cm of the soil surface. Orthods do not have evidence

of wetness above a depth of 50 cm. Therefore, no redoximorphic features are noted in

Orthods above a depth of 50 cm.

Aquods that have <0.10% iron (by ammonium oxalate extraction) in 75% or

more of the spodic horizon are further subdivided in the Great Group Alaquods.

Alaquods occur primarily in the southeastern U.S. and are the dominant Great Group in

Spodosols in Florida (Collins, 1990). Their water table fluctuates within the upper 50 cm,

and in the process, Fe is reduced, is soluble and, moves out of the soil. The spodic

horizon is dark-colored and consists mainly of an accumulation of organic matter and Al.

The spodic horizon often has a wavy upper boundary. An eluvial layer called the albic or

E horizon normally overlies the Bh horizon. The eluvial layer is light-colored as the Fe

and other metals have leached out as the result of the fluctuating water table. This E

horizon isgenerally thick, but can be thin in the wettest Alaquods.

Most of the Alaquods in the Osceola National Forest can be further subdivided

into Ultic Alaquods, Aeric Alaquods, or Arenic Alaquods. Ultic Alaquods have an

argillic horizon that begins above a depth of 200 cm; Aeric Alaquods have a spodic

horizon above a depth of 75 cm and, Arenic Alaquods have a spodic horizon that occurs

at a depth between 75-125 cm.

Orthods are generally better-drained Spodosols. They have <6% organic carbon in

the spodic horizon, and do not have evidence of wetness within 50 cm of the soil surface.

Orthods have a thick E horizon that lacks redoximorphic features above 50 cm depth.

Orthods are further subdvided at the Great Group level into Alorthods. The Alorthods

have <10% Fe (by the ammonium-oxalate method) in the Bh horizon. They have a high

accumulation of Al in comparison to Fe.

Alorthods that are saturated with water in one or more layers within 100 cm of the

soil surface for 20 consecutive or 30 cumulative days per year are placed into the

subgroup called Oxyaquic Alorthods. The "aquic" prefix is an indication of wetness, and

the prefix preceding aquic, "oxy", indicates the presence of oxygen and drier conditions.

Most of the Spodosols that occur in the Lake City Ridge (Fig. 28) area are in the

suborder Oxyaquic Alorthods. These soils have a spodic horizon that begins within

100 cm of the soil surface. If the spodic horizon begins within a depth of 125 to 200 cm

of the soil surface and, has 3.0 percent or less OC in the upper 2 cm of the Bh horizon, it

is classified as Entic Grossarenic Alorthods. "Grossarenic" is a term used to indicate thick

(>125 cm), leached sandy layers. "Entic" is the term used to indicate little or no evidence

of development in the soil.

At the study site the soils were classified as Centenary (sandy, siliceous, thermic,

Entic Grossarenic Alorthods) in the upland; Mandarin (sandy, siliceous, thermic,

Oxyaquic Alorthods) in the upper and lower midslope, and Leon (sandy, siliceous,

thermic, Aeric Alaquods) in the upper and lower lowland.


Rain is the source of most groundwater. The occurrence of groundwater is controlled

primarily by the subsurface texture of the soil. Rocks that are sufficiently permeable to

yield usable quantities of water to wells are called aquifers. The aquifers serve as

conduits that distribute and store groundwater. There are two types of aquifers in

Baker County: (1) the surficial aquifer, which is not overlain by an impermeable layer

Interte a-

Sca k

Figure 28. Soil map of Lake City Ridge and the research site. Spodosol extension
in blue; Ultisol extention in red; others in gray. Source: Baker County
Soil Survey, 1996.

and the water table is free to rise and fall and, (2) the artesian aquifer, which is overlain

by an impermeable bed and water is confined under pressure (U.S. Geological Survey

Staff, 1968). Discussion will be focused on the surficial aquifer which is the one

pertinent to the study.

Surficial Aquifer System

The surficial aquifer system is the permeable hydrologic unit contiguous with the

land surface that is comprised principally of unconsolidated (silicic)clastic deposits

(Southeastern Geological Society, 1986). It contains the water table, and the water

within it is under mainly unconfined conditions; but beds of low permeability may

cause semi-confined or locally confined conditions to prevail in its deeper parts. The

lower limit of the surficial aquifer system coincides with the top of the Hawthorn

Formation. The permeable beds of the aquifer are generally within the upper 15.5m of


the surface. Water is discharged from the aquifer through evapotranspiration and

seepage into streams, lakes, and swamps if their water levels are lower than the water

level of the aquifer (Leve, 1986).

In many areas, the surficial aquifer is used for small yield agricultural and

domestic water supplies, but usually it has bad taste due to the high iron content


Field Work

Experimental Plot

The field site was located north of the Olustee Battlefield in the Osceola

National Forest. This site was selected to represent Spodosols with multiple Bh horizons.

Spodosols with multiple Bh horizons in the area were originally identified and studied for

the research project titled "Ecological Inventory of the Osceola National Forest" (Collins,

1999). A 200 m long x 18 m wide experimental plot, extending from the uplands to the

lowlands was chosen. Water table depth was determined using water wells. The plot was

divided into 8 rows (Fig. 29). Each well was made of 5.1cm diameter PVC pipe that was

2.5 m in length. Along the lower 25 cm, 40 holes with 8 mm in diameter were drilled to

allow water to enter. A screen mesh covered the holes to prevent sand from filling the

holes. Each well was backfilled with sand to ensure a tight fit of the well and the

surrounding soil. Around each well, at surface level, a plastic mat, sealed with silicon,

was placed to prevent water from seeping down. Each well was covered with a plastic

cap. Using a flashlight and a tape measure, water table depth was determined regularly.

The regional office of the Forest Service in the Osceola National Forest collected the

daily precipitation data that occurred near the research site. The weather station was

located next to the entrance of the Olustee Battlefield. The data used for this project was

taken from February 1999 to January 2000.

The topographic map of the experimental plot is illustrated in Fig. 30. The

elevational difference between the uplands and the lowland was 1.42 m.

Between each row of wells, four probes (Fig. 31) were installed (Fig. 29). The

probes were used to extract water to measure DOC. The probes were made of 5.1 cm

diameter PVC pipes. Each probe went to a different horizon; E, Bh, E' or Bwl and B'h.

The depths to each horizon are shown in Table 2.



Figure 29.Experimental design of the water wells and probes.

There were 4 treatments (E, Bh, E' or Bw and, B'h), and 8 replicates, totaling 32

probes; and a total of 24 water table wells. One extra well and 4 more probes were

installed, 50 m to the north of the transect, inside the nearby wetland.


The length of each tube was determined as the depth to the horizon + 50 cm. At

the lower end of the pipe, a 10 cm long stainless steel needle was installed. A

polyethylene tubing was attached to the needle inside the PVC tube. The tubing was of

the same length as the PVC tube + 15 cm. Surrounding each probe, a plastic mat, sealed

.iiive Ele.l.T,,, . lufflSWlMKBr~tit,, #
cm ,"i'"
t ~ ~~..:..r'::".",-", :
i i. '
.. . ,- .:i _;,i!.._.'_- _' ,, .? ... :":."
., ^;: .i
,^ _' -,_,. I.* .,,.. . ...

xW s 1: 25m
0 1 2
Yaos 1: 3m
S 1 2

Figure 30. Topographic map of the experimental plot.

Stainless Steel



PVC tube 5. Icm diameter

Figure 31. Probe design.



Table 2. Depth to different horizons in the experimental plot.

Soil Series E Bh E' or Bw B'h

Centenary 70 173
Centenary 70 157
Upper Mandarin 12 22 70 150
Upper Mandarin 15 27 72 168
Lower Mandarin 20 38 66 160
Lower Mandarin 31 56 80 164
Upper Leon 30 58 83 165
Lower Leon 34 60 102 162

with silicon, was placed to prevent water from seeping in from the surface. A small

opening was made atthe upper end side of the PVC tube to allow the tubing to come out.

Each probe was covered with a cap. The depth to each horizon was determined by hand


Using a manual vacuum pump (Fig. 32), 50 mL of water was extracted from

the different horizons. Each water sample was filtered, in the laboratory, with a 45

micron carbon free filter the same day it was taken. They were stored in a freezer until

the DOC was measured.

Soils Studied

A soil transect was made from the upland to the lowland (Fig. 33). Detailed

descriptions of the five soils (uplands, upper mid-slope, lower mid-slope, upper lowlands

and lower lowlands) were made (Appendix A).

Vacuum Pumv

12" VaIcum
Purmp -ose

Figure 32. Actron III vacuum pump.


Figure 33. Location of the soils that were sampled in the transect (Countour line 10cm).

The soil from the upland was a sandy, siliceous, thermic, Entic Grossarenic

Alorthods Series Centenary. Both soils from the midslope were classified as sandy,

siliceous, thermic, Oxyaquic Alorthods Series Mandarin. Both soils from the lowlands

were classified as sandy, siliceous, thermic Aeric Alaquods Series Leon.

Vegetation Study

A detailed map of the understory vegetation was made. The "line-intercept

method" (Browner, 1989) was used to determine vegetation frequency and coverage.

A perpendicular line 100m long was selected randomly between rows #3 and #7. A

yellow tape was stretched along the line. The line was subdivided into 10 intervals. Every

other interval (n=5) was counted. Along the line, and for each interval, plant species were

recorded and the distance they covered along that portion of the line in number of

decimeters (dm). Only the plants touched by the line or lying under or over it were

considered. Frequency was calculated as the number of intervals in which a particular

plant species occurred divided by 10 (number of intervals sampled). Cover range was

calculated as the total intercept length of a particular plant species divided by the total

line length sampled. Frequency rank was calculated as the frequency of a particular

species divided by the total frequency for all species. Cover rank was calculated as the

total intercept length for a particular plant species divided by total intercept length of all

species. All trees, within a 5 m radius of any of the wells were mapped.

Laboratory Work

Routine Analysis

Particle-size analysis was determined using the pipette method (Day, 1965). Soil

reactions (pH) were measured in 1:1 solid liquid ratio using water and KC1.

Exchangeable bases were extracted by NH40Ac at pH 7.0 and the concentration

measured using atomic absorption spectrometry; Extractable acidity was extracted using

BaCL2-TEA at pH 8.2. Cation exchange capacity (CEC) was calculated as the sum of

exchangeable bases and extractable acidity (EA); and the percentage base saturation (BS)

was calculated as the percentage of CEC attributable to bases x 100. OC content was

determined by a modification of the acid dichromate digestion method (Soil Survey Staff

(2), 1996). To measure organically completed Fe and Al, the sodium pyrophosphate

extractable method (Franzmeier et al., 1965) and the sodium citrate-dithionite method

(Soil Survey Staff (2), 1996) were used. These two methods are used together as criteria

for spodic placement. For a more reliable and accurate estimation of the soil properties

and a better understanding of soil exchange complex, ammonium oxalate (McKeague and

Day, 1968) was also used, in conjunction with the other procedures, to measure C, Al and

Fe contents.

Humic Material

Dissolved organic carbon in the soil groundwater was measured using a high

temperature total organic carbon (TOC) analyser (Dohrman DC 190; Santa Clara, CA).

The percentages of the different humic substances (FA and HA) in the Bh

horizons were calculated using the organic matter fractionation method (Schnitzer, 1982)

(Fig. 34). Ten grams of air-dry soil was place inside a 200 mL propylene flask, 100 mL

of 0.5NNaOH was added. The air was displaced from the flask with N2. The mixture

was shaken for 24 hrs at room temperature. The dark-colored supernatant was separated

from the residual soil by centrifugation (10,000 rpm for 10 min.). Ten-mL aliquots from

each sample were placed inside 40 ml test tubes. The samples were acidified to a pH 2

with 2NHC1. The samples were left to sit for 24 hrs, then the soluble material (FA) was

separated from the coagulate (HA) by centrifugation (2,000 rpm for 2 min.). The

fractions were transferred to 20 mL test tubes and freeze-dried. After dryness, they were

tightly sealed with wax paper and placed in a desiccator. The sample and test tube were

weighed. Afterward, the tubes were cleaned with potassium dichromate and HC1 and

weighed. The difference x 100 was accounted as percentage FA or HA in the sample.



insoluble sIoluble
ppt soln.

Figure 34. Diagram showing the extraction and fractionation of humic substances.

Mineralogy of Soils

Mineralogy of the clay fraction of the lower Mandarin soil (representative soil of

the area with multiple Bh horizons) was determined. Three hundred grams of soil from

each horizon studied was treated with 100 mL of sodium hypochlorite to remove all

organic material. The silt and clay were separated from the sand using a 270-mesh sieve.

The silt and clay were separated by centrifugation (Whittig and Allardice, 1986)

following Na saturation to promote dispersion. The clay fraction was prepared for x-ray

diffraction analysis (XRD) by depositing approximately 250 mg as a suspension onto a

ceramic tile under suction. K and Mg saturation were performed directly on the tiles by

washing with the respective Cl- salts and rinsing. Glycerol was added to the Mg-saturated

sample. Samples were scanned at 20 2e min1 with CuKa radiation.


The micromorphology of the spodic horizons was studied using undisturbed

samples from the upper and lower Bh horizons. A thin section impregnation

technique (personal communication with Dr. W. Harris) was used to prepare the

samples. Undisturbed samples were taken from the transect. The clods were trimmed to a

size of 7.5 cm high by 5.0 cm diameter and air-dried for 2 weeks. After drying, the

samples were placed in aluminum cans and oven-dried for 4 hrs. The 2 components of

the epoxy resin (Scotch Cast Resin #3) were poured in equal amounts in two separate

beakers and heated with the clods at 95C for 2 hours. The two epoxy components were

mixed together and poured over the clods. They were placed in a vacuum desiccator

equipped with a cold trap to protect the pump, and subjected to a vacuum for about 45

minutes. They were taken out of the desiccator and put back in the oven at 95C and left

overnight.The aluminum can with the impregnated clod was then cut into 2 cm slices

with a diamond saw. The slices were send to Burham Petrographics in Monrovia, CA for

preparation of the thin sections.

Al-C distribution in the Bh horizons was compared using optical microscope and

Scanning Electron Microscope (SEM) techniques. Optical microscope photos were taken

using a digital camera. Then the micromorphology slides were coated with Au-Pb and

SEM photos were taken at the exact same location in the slide.


Lower Mandarin soil samples from the Bh and B'hl and B'h2 horizons were

obtained for 14C dating. The samples were carefully handled and wrapped in aluminum

foil to prevent any contamination. To isolate 14C pre-treatment was applied to the

samples. Each sample was dispersed in deionized water and then given hot HC1 acid

washes to eliminate carbonates. NaOH washes were conducted to remove secondary

organic minerals. The NaOH washes were followed by a final acid rinse to neutralize the

solution prior to drying. The soil samples were analyzed by the radiometric technique.

This technique synthesized soil C to benzene (92%C), measuring C14 content in a

scintillation spectrometer, and then the radiocarbon age was calculated. 14C conventional

age was the result after applying 13C/ 12C corrections to the measured age. The analysis

was done by Beta Analytic Laboratories, Miami, FL.

Artificial B'h Formation

An experiment was conducted to observe how soil from the Bw horizon (the

horizon above the B'h) and the E horizon (the horizon above the Bh), would react with

FA and HA. Eight clear PVC tubes of 2.54 cm in diameter were cut to 60 cm pieces. A

stopper with a 5 cm x 0.5 mm glass tube was placed in the lower end of the PVC tubes. A

flexible tubing was inserted in each glass tube. The flow of water was controlled with a

pressure clamp. The upper end of the pipe had a stopper to prevent contamination.

Soil from the Bw horizon was placed inside four of the PVC tubes up to 30 cm. Four

additional PVC tubes were filled with soil from the E horizon up to 30 cm. A liter of

water was mixed with 30 mL of FA and another liter was mixed with 30 mL of HA. Two

tubes with Bw soil were saturated with the mixture of FA; two more were saturated with

the mixture of HA. The same procedure was done with the tubes with soil from the E

horizon. The experimental water table was set to 40 cm height. The mixture of acids and

water flowed through the soil at a rate of 5 cm/day. The experiment was done for 2 days.

The Effect of Hydrogen Peroxide and Incineration on Bh and B'h Organic Matter

A second laboratory experiment was conducted to measure the effectiveness of

hydrogen peroxide and the incineration technique to remove the organic matter from the

different spodic horizons. Four samples of the Bh and B'h horizons were taken from the

Mandarin soil. Five grams of oven-dry soil (95C) were placed in crucibles already

weighted. Two soil samples of each of the horizons were treated with hydrogen peroxide.

The other soil samples were left untreated. After 4 days, they were dried on a hotplate

and weighed again. The difference in weight between the oven-dry soil and the treated

and untreated samples x 100 was calculated as percentage organic matter loss. Then all

eight soil samples were incinerated to 6000 C for six hours to remove all organic matter.

After cooling to room temperature inside a desiccator they were weight again. The

difference in weight between oven-dry samples and incineration samples was accounted

as total organic matter. The soil weight difference between the incineration method and

the hydrogen peroxide treatment x 100 was accounted as percentage organic matter loss

due to treatment.

Evaluation of Existing Characterization Data

The Soil Characterization Program was established in the University of Florida in

1970. The purpose of this program was to sample, analyze and describe soils throughout

Florida. The data of more than 1000 pedons, covering over 300 soil series, have been

published in seven separate records covering the physical, chemical, mineralogical and

morphological data of each soil (Calhoun et al., 1974, Carlisle et al., 1978, 1981, 1985,

1988, 1989; Sodek et al., 1990).


Data for multiple Bh Spodosols appearing in the Soil Characterization data was merged

to the data obtained in the present study to determine certain relationships between upper

and lower Bh horizons. The data used from the Soil Characterization Data include total

bases, extractable acidity (EA), cation exchange capacity (CEC), extractable Al vs.

extractable acidity, extractable Al vs. pH, and weighted average organic carbon content.



Soil morphology is defined as (i) The physical constitution of a soil profile as

exhibited by the kinds, thickness, and arrangement of the horizons in the profile, and by

the texture, structure, consistence, and porosity of each horizon. (ii) The visible

characteristics of the soil or any of its parts. Source: (http://www.
bin/gloss search.cgi?OUERY=MORPHOLOGY&SOURCE= 1).

Three different soil series were identified and classified. These soils were:

Centenary sandy, siliceous, thermic, Entic Grossarenic Alorthods

Mandarin sandy, siliceous, thermic, Oxyaquic Alorthods

Leon sandy, siliceous, thermic, Aeric Alaquods

Selected morphological properties, the landscape position, and the drainage class

of the soils studied are shown in Table 3. The complete description of the soils in the

transect can be seen in Appendix A. All these soils had mostly fine quartz sand as parent

material and a single grain structure in the A horizon that promoted high infiltration rate.

In general, the upland soil, Centenary, had a "salt and pepper" color, 70% light

gray (10YR 7/1) and 30% dark gray (10YR 4/1) A horizon, followed by a yellowish

brown (10YR 5/4) Bwl and a yellowish brown (10YR5/4) Bw2 horizons. Below the Bw2

horizon, a pale brown (10YR6/3) El and a very pale brown (10YR 7/3) E2 horizons

occurred. A fluctuating water table over the permanent water table created periodic

Table 3. Selected morphological properties, geomorphic position, and drainage of the
soils studied.

Series Horizon Depth Color Texture Landscape Drainage
(cm) (moist)1 position class

Centenary Ap 0-10 70% 10YR fs2 Upland Somewhat
7/1 poorly
30% 10YR
Bwl 10-18 10YR 5/4 fs
Bw2 18-40 10YR 5/4 fs
E1 40-64 10YR 6/3 fs
E2 64-104 10YR 7/3 fs
Eg 104-143 10YR 8/2 fs
Bg 143-153 10YR 5/2 fs
Bhl 153-168 10YR 3/2 fs
Bh2 168-190 10YR 2/2 fs
Bh3 190-212 7.5YR 2.5/1 fs
Upper Ap 0-10 50% 10YR fs Upper Mid- Somewhat
Mandarin 7/1 slope poorly
50% 10 YR
E 10-22 10YR 6/1 fs
Bh 22-38 10YR 4/4 fs
E' 38-63 10YR 7/3 fs
Egl 63-96 10YR 8/2 fs
Eg2 96-130 10YR 8/1 fs
Bw 130-157 10YR 5/4 fs
B'hl 157-190 10YR 4/2 fs
B'h2 190-200 10YR 3/3 fs
Lower Ap 0-2 70% 10YR fs Lower Mid- Poorly
Mandarin 8/1 slope
30% 10YR
E1 2-20 10YR6/1 fs
E2 20-36 10YR 7/1 fs
Bhl 36-45 10 YR 2/1 fs
Bh2 45-55 10YR 2/2 fs
Bh3 55-64 10YR 3/3 fs
BE 64-72 10YR 7/3 fs
Egl 72-106 10YR 7/1 fs
Eg2 106-160 7.5YR 7/1 fs
B'hl 160-180 10YR 3/1 fs

Table 3-continued.

Series Horizon Depth Color (moist)1 Texture Geomorphic Drainage
(cm) position

B'h2 180-192 10YR 2/2 fs
B'h3 192-200 10YR 2/1 fs
Upper Leon Ap 0-10 70% 10YR fs Upper Poorly
5/1 Lowland
30% 10YR
Ap/Eg 10-19 70%10YR fs
30% 10YR 5/1
Eg 19-47 10YR 5/1 fs
Bhl 47-52 10YR 2/1 fs
Bh2 52-68 10YR 3/2 fs
Eg/Bw 68-105 10YR 8/1 fs
10YR 3/4
Bw 105-120 10YR 4/4 fs
10YR 5/4
Bw/Eg 120-130 10YR 4/6 fs
10YR 6/4
B'w 130-180 10YR 4/2 fs
B'h 180-200 10YR 2/1 fs
Lower A 0-10 60% 10YR 3/1 fs Lower Poorly
Leon 40% 10YR 5/1 Lowland
A/E 10-16 70% 10YR 3/1 fs
30% 10YR 5/1
Egl 16-28 10YR 6/2 fs
Eg2 28-52 10YR 5/2 fs
Bhl 52-60 10YR 2/1 fs
Bh2 60-83 7.5YR 3/2 fs
Bh3 83-98 7.5YR 4/2 fs
Bwl 98-116 10YR 5/3 fs
Bw2 116-130 10YR 6/3 fs
Bg 130-137 2.5YR 5/2 fs
B'hl 137-157 7.5YR 4/4 fs
B'h2 157-177 7.5YR 3/2 fs
B'h3 177-200 10 YR 2/1 fs
Munsell color notation
2 Fine sand

anaerobic conditions under the E2 horizon making the next horizon a very pale brown

(10YR8/2) Eg horizon. Gleying was caused by the process of reduction. Under this Eg

horizon a grayish brown (10YR5/2) Bg horizon occurred. Below 153 cm a very dark

grayish brown (10YR 3/2) Bhl to black (7.5YR 2.5/1) Bh3 horizons occurred.

The upper mid-slope soil, Mandarin had a "salt and pepper" color, 50% light gray

(10YR7/1) and 50% gray (10YR5/1) Ap horizon, followed by a gray (10YR 6/1) E

horizon that consists mostly of stripped sand grains. Under the E horizon, a dark

yellowish brown (10YR 4/4) Bh horizon was formed. This Bh is an accumulation

horizon of humus and Al. Under this horizon, a very pale brown (10 YR 7/3) E'followed

by a very pale brown (10YR 8/2) Egl and a white (10YR 8/1) Eg2 horizons occurred.

Under these horizons a yellowish brown (10YR5/4) Bw formed. Under the Bw a dark

grayish brown (10YR 4/2) B'hl to dark brown (10YR 3/3) B'h2 occurred.

The lower mid-slope soil, Mandarin had a "salt and pepper" color, 70% white

(10YR8/1) and 30% dark gray (10YR4/1) thin Ap horizon, followed by a gray (10YR

6/1) Eland a light gray (10YR 7/1) E2 horizons. Under these E horizons, a black (10YR

2/1) Bh horizon was formed. The value and chroma of the Bh increased with depth from

black (10YR 2/1) in the Bhl to dark brown (10YR 3/3) in the Bh3 horizon. Under the

Bh3, a very pale brown (10YR 7/3) mixed, thin BE horizon occurred. Below this, a light

gray (10YR 7/1) Egland a light gray (7.5YR 7/1) Eg2 formed. Below 160 cm a very dark

gray (10YR 3/1) Bhl to black (10YR 2/1) B'h3 occurred.

The upper lowland soil, Leon, has a "salt and pepper" color, 70% gray (10YR5/1)

and 30% light gray (10YR7/1) Ap horizon, followed by a combination of 70% light gray

(10YR 7/1) and 30%gray (10YR 5/1) Ap/Eg horizon. Following this combinational

horizon a gray (10YR 5/1) Eg horizon was formed. Under this Eg horizon, a black (10YR

2/1) Bh horizon occurred. The value and chroma of the Bh increases with depth from

black (10YR 2/1) in the Bhl to very dark grayish brown (10YR 3/2) in the Bh2. Below

the Bh2, the following horizons occurr: a combination white (10YR 8/1) and dark

yellowish brown (10YR 3/4) Eg/Bw horizon, a dark yellowish brown (10YR 4/4) and

yellowish brown (10YR 5/4) Bw horizon, a combination dark yellowish brown

(10YR4/6) and light yellowish brown (10YR 6/4) Bw/Eg horizon and, a dark grayish

brown (10YR 4/2) Bw horizon. Below 180 cm a black (10YR 2/1) B'h horizon occurred.

The lower lowland soil, Leon, had a "salt and pepper" color, 60% very dark gray

(10YR 3/1) and 40% gray (10YR 5/1) A horizon, followed by a combination 70% very

dark gray (10YR 3/1) and 30%gray (10YR 5/1) A/E horizon. Following this combination

horizon, a light brownish gray (10YR 6/2) Egl and grayish brown (10YR 5/2) Eg2

horizons were formed. Below the Eg2 horizon, a black (10YR 2/1) Bh horizon occurred.

The value and chroma of the Bh increased with depth from black (10YR 2/1) in the Bhl

to brown (7.5YR 4/2) in the Bh3 horizon. Below the horizon the following horizons

occurred; a brown (10YR 5/3) Bwland pale brown (10YR 6/3) Bw2, a grayish brown

(2.5Y 5/2) Bg horizon, and below 137 cm, a brown (7.5YR 4/4) B'hl to black (10YR 2/1)

B'h3 horizons occurred.

A fairly common feature of the soils' morphology was the occurrence of multiple

spodic horizons, one much deeper than the other. The soil with only one Bh horizon

(Centenary) corresponded to the deeper B'h horizon in the Mandarin and the Leon. The

shallow Bh horizon did not form in the uplands (Fig. 35).

The transition from the dry Spodosol, Centenary, to wet Spodosol Leon, within

the transect was accompanied by an increasing water-table fluctuation influence. The

transition from the lower Mandarin, a poorly drained soil, to upper Mandarin, a

moderately well drained soil, was accompanied by an upward-trending, decreasingly

pronounced Bh, which faded as one approached the Centenary. The light-gray (10YR

7/1) E horizon persisted laterally above the Bh until both, the Bh and the E disappeared

Entic Grosarenic

Figure 35. Topo-pedo morphological sequence of the transect.

and a Bw appeared in the Centenary. The Centenary Bw sands had pale brown (10YR

6/3) to brownish yellow (10YR 5/4) colors indicative of grain coatings.

In general, the horizons above the B'h did not indicate any stripping. The sands

remained mostly coated. The colors remained pale brown (10YR 5/2) to brownish yellow

(10YR 4/4).

A photograph of the horizons in the lower Mandarin shows the color changes in

the different horizons (Fig. 36). One distinct characteristic between the upper Bh and the

lower B'h horizons was the development of color. In the lower Mandarin and the upper

and lower Leon, the Bh horizons were black (10YR 2/1) becoming generally browner

(10YR 2/2 to 7.5YR 3/2) and slightly redder (10YR 3/3 to 7.5YR 4/2) with depth. The

. -. *!^ . . . ..:,

,. ... ..... .....

Ap El E2 Bhl Bh2 Bh3 BE Eq1 Eg2 B'hl B'h2 B'h3

Figure 36. Soil colors by horizon in the lower Mandarin soil.

B'h horizon was dark gray (usually 10YR 3/1) becoming blacker (10YR 2/1) with

increasing depth.

The texture of all the horizons was fine sand (Table 4) with only small amounts of

silt and clay. Silt content ranged from 1.5% in the Bw2 of the lower Leon to 8% in the

Ap of the Centenary. Clay content ranged from 0.2% in the E of the upper Mandarin to

3.8% in the Bh2 horizon of the lower Leon. A trend can be seen where silt and clay

increased in the upper Bh horizon (Table 4). In the lower Mandarin the silt increased

from 2.8% in the E2 to 7.8% in the Bhl horizon; the clay increased from 0.5%in the E2

to 2.4% in the Bhl horizon. In the upper Leon the silt increased from 4.1% in the Eg to

6.8% in the Bhl horizon; the clay increased from 0.4% in the Eg to 1.6% in the Bhl

horizon. In the lower Leon the silt increased from 0.5% in the Eg2 to 2.9% in the Bhl

horizon. This increase of clay could be attributable to enrichment of the Bh horizon via

mechanical translocation of silt and clay particles from the E horizon to the Bh horizon.

The same trend was reported in an earlier assessment of Florida Spodosols (Calhoun and

Carlisle, 1973). This trend supports the view that clay-and silt-sized particles migrate

downward and deposited on the sand particles. Soluble OM then adsorbs to the Al

and Fe coated surfaces to form the Bh horizon. This trend is not evident in the second B'h

horizon. It appears that there is no mechanical translocation of finer particles from the

horizons above to the B'h.

The most common method to identify lithological changes in soils is to analyze

depth distributions of the stationary particle, sand. When the fine sand-size distribution of

the site was studied, no abrupt changes in texture, indicating discontinuities, were

determined (Fig.37).

Chemical Properties

Soils are dynamic systems. They regularly undergo a number of biogeochemical

reactions that alter their characteristics. Some of the chemical reactions that happen in

Spodosols are: decomposition, humification, mineralization, gleization, oxidation-

reduction and. podzolization. These biogeochemical reactions give rise to a number of

different soil chemical properties that can be used as criteria to explain soil genesis and


The chemical properties from the soils sampled in the experimental plot are

shown in Table 5. A trend can be seen from the upper Mandarin to the lower Leon. Total

bases decreased with depth from A horizon to the E horizon then, total bases increase in

the Bh horizon. Total bases in the upper Mandarin decreased from 3.41 cmol/kg-1 in the

Table 4. Particle-size distribution of soils along the transect.

Series Horizon Depth VC1 C2 M3 F4 VFb %Total %Silt %Clay
(cm) % % % % % Sand

Centenary Ap 0-10 0 1.4 18.6 66.9 4.4 91.3 8.0 0.7
Bwl 10-18 0 1.4 22.6 64.6 5.8 94.4 4.9 0.7
Bw2 18-40 0 1.4 20.4 69.2 4.8 95.8 3.7 0.5
E1 40-64 0 1.2 20.2 67.0 6.2 95.6 3.9 0.5
E2 64-104 0 1.2 20.0 69.2 5.6 96.0 3.5 0.5
Eg 104-143 0 1.2 13.6 74.8 6.4 96.0 3.1 0.9
Bg 143-153 0 1.2 17.4 69.2 5.2 93.0 4.7 2.3
Bhl 153-168 0 1.2 20.4 66.4 5.6 93.6 5.7 0.7
Bh2 168-190 0 1.6 18.2 70.6 4.8 95.2 4.0 0.8
Bh3 190-212 0 1.8 21.6 69.0 3.6 96.0 2.8 0.6

Upper Ap 0-10 0 2.0 25.0 64.3 2.8 94.1 5.4 0.5
Mandarin E 10-22 0 1.7 26.1 63.9 3.7 95.4 5.4 0.2
Bh 22-38 0 2.1 24.5 63.0 3.4 93.0 4.2 2.8
E' 38-63 0 1.5 25.8 64.4 3.2 94.9 2.2 2.9
Egl 63-96 0 1.9 22.7 67.3 1.7 94.5 3.1 2.4
Eg2 96-130 0 1.5 22.5 68.1 4.5 96.6 2.7 0.7
Bw 130-157 0 1.4 22.5 65.3 5.0 94.2 2.6 3.2
B'hl 157-190 0 1.4 21.6 64.3 4.7 94.8 4.4 0.8
B'h2 190-200 0 1.3 23.0 68.0 3.0 95.3 3.9 0.8

Lower Ap 0-2 0 1.4 26.0 60.8 4.8 93.0 6.4 0.6
Mandarin E1 2-20 0 1.7 30.6 61.0 3.7 97.1 2.4 0.5
E2 20-36 0 1.7 26.4 63.6 5.0 96.7 2.8 0.5
Bhl 36-45 0 1.8 17.2 65.0 5.8 89.8 7.8 2.4
Bh2 45-55 0 1.6 20.0 61.6 6.0 89.2 7.5 3.3
Bh3 55-64 0 1.4 17.0 66.2 6.4 91.0 6.3 2.7
BE 64-72 0 1.2 20.8 65.8 5.8 93.6 4.4 2.0
Egl 72-106 0 1.9 24.9 64.5 4.6 95.8 2.6 1.6
Eg2 106-160 0 1.7 25.1 65.4 4.7 96.9 2.1 1.0
B'hl 160-180 0 1.4 18.4 72.8 4.0 96.6 2.6 0.8
B'h2 180-192 0 1.4 20.6 71.2 3.6 96.8 2.4 0.8
B'h3 192-200 0 0.8 19.2 72.0 4.2 96.2 3.1 0.7

Table 4-continued.

Series Horizon Depth VC1 C2 M3 F4 VF5 %Total Silt Clay
(cm) % % % % % sand % %

Upper Ap 0-10 0 1.5 29.3 57.7 2.8 91.3 7.9 0.8
Leon A/Eg 0-19 0 2.1 25.6 64.8 2.4 94.9 4.7 0.4
Eg 19-47 1.8 27.3 63.8 2.6 95.5 4.1 0.4
Bhl 47-52 0 1.8 28.4 62.8 4.0 91.6 6.8 1.6
Bh2 52-68 0 2.1 26.2 63.9 3.2 95.4 3.9 0.7
Eg/Bw 68-105 0 1.9 23.5 66.4 4.1 95.9 3.8 0.3
Bwl 105-120 0 1.6 22.2 65.4 5.2 94.4 5.2 0.4
Bw/Eg 120-130 0 1.7 20.8 67.2 4.7 94.4 5.1 0.5
Bw2 130-180 0 1.6 20.7 66.8 5.3 94.4 1.6 4.0
B'h 180-200 0 1.0 23.6 65.5 4.6 94.7 4.8 0.5

Lower Ap 0-10 0 1.4 22.6 64.2 4.6 93 6.2 0.8
AE 10-16 0 1.4 25.4 62.4 5.2 94.4 5.0 0.6

Egl 16-28 0 1.4 23.4 64.8 6.4 96.0 3.5 0.5
Eg2 28-52 0 2.4 22.4 64.8 4.2 93.8 5.7 0.5
Bhl 52-60 0 2.6 21.0 62.4 4.0 90.0 7.1 2.9
Bh2 60-83 0 2.2 24.4 61.4 4.8 92.8 3.4 3.8
Bh3 83-98 0 2.4 24.6 65.6 3.2 95.8 2.0 2.2
Bwl 98-116 0 2.0 25.8 63.6 4.4 95.8 2.5 1.7
Bw2 116-130 0 1.8 23.2 65.8 5.6 96.4 1.5 2.1
Bg 130-137 0 1.8 19.2 66.4 5.6 93.0 4.6 1.5
B'hl 137-157 0 1.6 25.0 64.8 4.0 94.8 3.7 0.9
B'h2 157-177 0 1.8 22.4 67.6 3.6 95.4 3.8 0.8
B'h3 177-200 0 1.4 25.6 65.4 3.2 95.6 3.8 0.6
'VC =very coarse sand


coarse sand
medium sand

4F = fine sand
5VF = very fine sand

Figure 37. Fine sand to total sand ratio against depth for all the soils of the research area.

Ap horizon to 1.15 cmol/kg-1 in the E horizon until the upper Bh is reached then, total

bases increased to 2.0 cmol/kg-1. Further down the slope, in the lower Mandarin, total

bases decreased from 5.13 cmol/kg-1 in the Ap horizon to 0.36 cmol/kg-1 in the E2

horizon until the upper Bh is reached then, total bases slightly increase to 1.94 cmol/kg1.

Continuing down the slope, in the upper Leon, total bases decreased from 5.53 cmol/kg-1

in the Ap horizon to 0.49 cmol/kg-1 in the Eg. In the upper Bh horizon total bases

increased to 1.58 cmol/kg-1. Finally, in the lower Leon, total bases decreased from 7.2

cmol/kg-1 in the A horizon to 1.27 cmol/kg-1 in the Eg2 horizon. As in the other soils, in

the upper Bh horizon total bases increased to 2.11 cmol/kg-1.

When the weighted average of the total bases is compared between the upper and

lower Bh horizons the upper Mandarin Bh has 7.3 times more total bases than the B'h; the

lower Mandarin Bh has 3.5 times more total bases than the B'h; the upper Leon Bh has

3.7 times more total bases than the B'h; and the lower Leon Bh has 3.6 times more total

bases than the B'h. Total bases were higher in the upper Bh horizons than in the lower

B'h horizons.

All Soils

0.8 Centenary
S0.6 - Upper Mandarin
!. -Lower Mandarin
u- 0.4- Upper Leon
0.2 --- Lower Leon
0 50 100 150 200 250
Depth (cm)

When the total bases of the E horizons are plotted against the total bases of the Bh

horizon by location, using Soil Characterization Data (Appendix B), the same increase

trend from E horizon to Bh horizon (Fig. 38) is seen for the multiple Bh Spodosols of

NE Florida, and the soils of the study site Central Florida also had the increasing trend.

The trend is not clear in the Northwest multiple Bh Spodosols because there was little

data available. When total bases from the E horizon are compared with the total bases in

the B'h horizon there is no clear trend (Fig. 38). Only in the Spodosols of the Northwest

the total bases increased. Total bases usually do not increase from E to B'h (Table 5).

Decrease in extractable acidity (EA) from the A horizon to the E horizon

and then, increase in extractable Al in the Bh horizon is also seen from the upper

Total bases relationships between E and Bh, Total bases relationships between E and Bh,
E and B'h horizons-NE Florida E and B'h horizons-NW Florida

o035 ,-'- a A 04-351 __ .
030 A 035-082
S025 -A 03
020 002 0

o cmolkg E

Total bases relationships between E and Bh, Total bases relationships between E and Bh,
E and B'h horizons- Central Florida E and B'h horizons-Study Site

3 5
010 y5- 13_ _5793,_04399
2 y 01 10 1
000- u

o-: --2"X- | 26E- - -- Q
Euu 0 u5 ulu ulS u2u u25 u3u u35

0 01 02 03 04 05 06
cmollkg E cmol/kg E

Figure 38. Total bases (E vs. Bh) from multiple Bh Spodosols in Florida's soil
characterization Database by location
characterization Database by location

Mandarin to the lower Leon (Table 5). In the upper Mandarin, the EA decreased from

9.16 cmol/kg-1 in the Ap horizon to 4.11 cmol/kg-1 in the E horizon. When the Bh was

reached, the EA increased to 10.89 cmol/kg-1. Down the slope, in the lower Mandarin,

the EA decreased from 9.29 cmol/kg-1 in the Ap horizon to 3.03 cmol/kg-1 in the E2

horizon. In the Bh horizon EA increased to 13.4 cmol/kg-1. Further down the slope, in

the upper Leon, EA in the Ap horizon decreased from 9.9 cmol/kg-1 to 3.77 cmol/kg-1 in

the Eg horizon. When the Bh was reached, the EA increased to 13.35 cmol/kg-1. Finally,

in the lower Leon, EA decreased with depth from the Ap horizon, 9.45 cmol/kg-1, to 4.04

cmol/kg-1 in the Eg2 horizon. Then, EA increased to 11 cmol/kg-1 in the Bh. The

decrease in EA from A horizon to E horizon and the increase from E horizon to Bh

horizon occurred in all the multiple Bh Spodosols in the Soil Characterization Data except

in the Leon series in Bay County and the Myakka series in Volusia County. Another

exception is where the multiple Bh Spodosol has no E horizon (Appendix B).

Extractable acidity from the E horizons was plotted against the EA of the Bh

horizons using the data for multiple Bh Spodosols of the Soil Characterization Data

according to Spodosol location (Fig. 39). No clear trend was shown except for the

Spodosols located in the NE of Florida. Probably there is insufficient data in the other

locations. Also E horizons were plotted against B'h horizons looking for trends (Fig.

39). The results obtained in this research indicated that EA decreased with depth in the

B'h (Table 5). The B'h horizons usually had lower EA than the horizons above. Contrary

to the results for B'hs in the Soil Characterization data (Appendix B)

Figure 39. Extractable Acidity of multiple Bh
Characterization Database.

Spodosols (E vs. Bh) by location -Soil

Cation exchange capacity from the upper Mandarin to the lower Leon decreased

with depth from the A horizon to the E horizon and then increased in the Bh horizon.

CEC in the upper Mandarin decreased from 12.57 cmol/kg-1 in the Ap horizon to 5.26

cmol/kg1 in the E horizon, then the CEC increased in the Bh to 12.89 cmol/kg-'. Further

down the slope, in the lower Mandarin CEC decreased from 14.42 in the Ap horizon to

3.39 cmol/kg4 in the E2 horizon until the upper Bh was reached then, the CEC increased

to 15.34 cmol/kg-'. In the upper Leon CEC decreased with depth from 15.43 in the Ap

horizon to 4.26 cmol/kg-1 in the Eg horizon. When the Bh horizon was reached, CEC

increased to 14.93 cmol/kg-1. Finally, the CEC in the lower Leon also decreased with

depth from 16.65 in the A horizon to 5.31 cmol/kg- in the Eg2 horizon until the upper Bh

was reached then, CEC increased to 13.11 cmol/kg-1. A similar decrease in CEC from A

Extractable Acidity relationships between E Extractable Acidity relationships between E
and Bh, E and B'h horizons-NE Florida and Bh, E and B'h horizons-NW Florida

S30 25 Y.
25 A A .0-3 20 R--43..
5 20- 15
!5 A. y0 1-895x, 13 154

S0 0 1 2 3 4
0 1 2 3 4 5
cmol/kg E
cmol/kg E
Extractable Acidity relationships between E Extractable Acidity relationships between E
and Bh, E and B'h horizons-Central Florida and Bh, E and B'h horizons-Study site

a 25
-45953_15332_ 20 ------12__2,__14313_
m 20 4 15
010 y__ _- i 10 .........
-- 0------------" -------------
E 0 0
0 1 2 3 4 0 1 2 3 4 5
cmol/kg E cmol/kg E

horizon to E horizon and, then an increase in CEC in the Bh horizon occurred in the

multiple Bh Spodosols characterized in the Soil Characterization Database (Fig. 40).

There also a similar increasing trend from E to the B'h horizon (Fig. 40).

Contrary to the results of the Soil Characterization data, the results obtained in this

research indicate that CEC decrease with depth in the lower B'h (Table 5).

The increase of total bases, extractable acidity and CEC in the upper Bh probably

occurred because the Bh is a horizon of accumulation of humus and Al. Humus has

colloidal properties which react, in terms of cation exchange, almost identically to

mineral colloids. However, humus can have a far greater capacity to adsorb cations

(bases, H+ and Al3+) than clay ( hums.htm).

All the soils were acidic, and most of the samples had a pH of <5. pH's in water

ranged from 3.8 to 5.2. pH's in KC1 ranged from 2.9 to 4.7.(Table 5). Range of the soil's

pH was lower with KC1 because the salt displaced the hydrogen ions (HF) and the

Aluminum ions (Al3+) from the soil. Al3+ ions reacted with the water to form more H+ by

the reaction: Al3+ + H20 -> Al(OH)3 + 3 H+ acidifying more the solution and thus

decreasing the pH.

The pH increased slightly with depth. In all soils with more than one Bh the

upper Bh horizon had a lower pH than the second B'h horizon. This difference is

probably due to the different moisture conditions in each of the horizons. In the first Bh

oxidized forms of chemical species (Fe3+, SO42-, CO) dominate, while in the second B'h

reduced forms (Fe2+, S2-, CH4, H2) dominate (Reddy, 1997). In saturated conditions there

is absence of oxygen. The oxidized forms are converted into reduced forms through

several microbially mediated catabolic processes. These alterations in chemical reactions,

CEC relationships between E and Bh, E and CEC relationships between E and Bh, E and
B'h horizons-NE Florida B'h horizons-NW Florida

i 40 20
A y=2;9733x+ 13 306 (0
. 30 15

1 y 1 440 1 2 3 87

cmol/kg E cmol/kg E

CEC relationships between E and Bh, E and CEC relationships between E and Bh. E and
B'h horizons-Central Florida B'h horizons-Study site

__1_______________-___ .__ -_ 0Q in-25
o 20 0 R2 0 1 .

1 ..... 1 -
S10 o -
E 0 E 0O

S02 4 6
0 1 2 3 4

0 1 2 3 4 5
cmol/kg E cmol/kg E

CEC Figure 40. Cationships between E and Bh, E and CEC relationships between E and Bh. E and-Soil

Characterization Database.

as the results of soil anaerobiosis, affects soil pH. In general, saturated soil conditions

results in increase of pH and a decrease in redox potential. The increase of pH with depth

in these acid soils will depend on the proton consumption during reduction of the
oxidi zed forms u under satural Florida B'h horizons-Study siteitions.

Exchangeable Al ions are characteristic of acid soils. Exchangeable Al pduced

the acidity by hydrolyzing further to Al(OH)3 and releasing H to the soil

solution. Al is present in appreciable amounts at pH > 5.8. While other major

exchangeable cations are generally leached from soils during soil formation, Al is

retained in soils ultimately as Al(OH)3, the Al end-product of soil weathering (Bohn et
25 0 - .

cmol/kg E cmol/kg E

Figure 40. Cation Exchange Capacity of multiple Bh Spodosols (E vs. Bh) -Soil
Characterization Database.

as the results of soil anaerobiosis, affects soil pH. In general, saturated soil conditions

results in increase of pH and a decrease in redox potential. The increase of pH with depth

in these acid soils will depend on the proton consumption during reduction of the

oxidized forms under saturated conditions.


Exchangeable Al ions are characteristic of acid soils. Exchangeable A13+ produced

the acidity by hydrolyzing further to AI(OH)3 and releasing H'to the soil

solution. Al is present in appreciable amounts at pH > 5.8. While other major

exchangeable cations are generally leached from soils during soil formation, Al is

retained in soils ultimately as AI(OH)3, the Al end-product of soil weathering (Bohn et

Table 5. Chemical properties of the soils sampled

Extractable Total Extractable CEC* Base pH pH
Series Horizon Depth Ca Mg Na K bases Acidity Saturation (water) (KCI)
cm 1 cmol %
Centenary Ap 0-10 2.35 0.41 0.09 0.05 2.90 9.72 12.62 23.0 4.0 2.9
Bwl 10-18 1.00 0.25 0.04 0.03 1.32 4.07 5.39 24.4 4.6 3.8
Bw2 18-40 0.55 0.25 0.13 0.00 0.93 2.65 3.58 25.9 5.0 4.4
E1 40-64 0.25 0.08 0.13 0.00 0.46 1.58 2.04 22.7 5.2 4.5
E2 64-104 0.20 0.08 0.13 0.00 0.41 1.6 2.01 20.5 5.2 4.6
Eg 104-143 0.15 0.16 0.13 0.00 0.45 1.12 1.56 28.5 5.1 4.6
Bg 143-153 0.30 0.33 0.13 0.05 0.81 2.06 2.87 28.2 5.1 4.5
Bhl 153-168 0.20 0.16 0.09 0.03 0.48 2.97 3.45 13.8 5.0 4.6
Bh2 168-190 0.25 0.16 0.13 0.00 0.55 2.61 3.16 17.3 5.0 4.6
Bh3 190-212 0.10 0.16 0.04 0.00 0.31 1.81 2.12 14.5 5.2 4.7

Upper Ap 0-10 2.60 0.53 0.20 0.08 3.41 9.16 12.57 27.1 4.2 3.5
Mandarin E 10-22 0.82 0.26 0.06 0.01 1.15 4.11 5.26 21.9 4.4 3.6
Bh 22-38 1.50 0.28 0.13 0.09 2.00 10.89 12.89 15.5 4.4 4.1
E' 38-63 0.87 0.23 0.13 0.03 1.26 2.98 4.24 29.7 4.7 4.5
Egl 63-96 0.25 0.08 0.13 0.04 0.5 1.18 1.68 29.7 4.7 4.6
Eg2 96-130 0.20 0.08 0.13 0.02 0.43 1.13 1.56 27.6 4.7 4.6
Bw 130-157 0.20 0.08 0.13 0.05 0.46 5.76 6.22 7.4 4.6 4.3
B'hl 157-190 0.15 0.08 0.09 0.02 0.34 3.21 3.55 9.6 4.7 4.5
B'h2 190-200 0.05 0.10 0.04 0.02 0.21 1.68 1.89 11.1 4.9 4.7

Table 5-continued.
Extractable Total Extractable CEC* Base pH pH
Series Horizon Depth Ca Mg Na K bases Acidity Saturation (water) (KCI)
cm cmol %

Lower Ap 0-2 3.9 0.74 0.44 0.05 5.13 9.29 14.42 36.0 4.2 3.1
Mandarin E1 2-20 1.7 0.49 0.22 0.03 2.44 4.72 7.16 34.0 4.5 3.8
Bh3 55-64 0.35 0.08 0.22 0.00 0.65 20.03 20.68 3.1 4.5 3.9
BE 64-72 0.15 0.08 0.13 0.10 0.47 3.59 4.06 11.5 4.9 4.5
Egl 72-106 0.05 0.08 0.13 0.01 0.27 3.70 3.97 6.8 5.1 4.6
Eg2 106-160 0.10 0.08 0.13 0.01 0.32 4.59 4.91 6.5 5.1 4.5
B'hl 160-180 0.10 0.16 0.09 0.03 0.38 3.30 3.67 10.3 5.1 4.7
B'h2 180-192 0.15 0.16 0.13 0.00 0.45 2.78 3.23 13.8 5.4 4.6
B'h3 192-200 0.05 0.16 0.09 0.00 0.30 2.69 2.99 10.1 5.0 4.6

Upper Ap 0-10 4.41 0.67 0.40 0.05 5.53 9.90 15.43 35.8 3.9 3.0
Leon A/Eg 10-19 2.04 0.41 0.18 0.02 2.65 5.66 8.31 31.8 4.2 3.2
Eg 19-47 0.30 0.08 0.10 0.01 0.49 3.77 4.26 11.5 4.5 3.6
Bhl 47-52 1.30 0.08 0.20 0.00 1.58 13.35 14.93 10.6 3.8 3.5
Bh2 52-68 0.75 0.04 0.20 0.00 0.99 26.32 27.31 3.6 3.9 3.6
Eg/Bw 68-105 0.15 0.11 0.25 0.00 0.51 2.95 3.46 14.7 4.3 3.8
Bwl 105-120 0.05 0.08 0.09 0.00 0.22 3.08 3.30 6.7 4.3 3.7
Bw/Eg 120-130 0.05 0.08 0.08 0.01 0.22 2.34 2.56 8.6 4.3 4.0
Bw2 130-180 0.05 0.16 0.20 0.01 0.42 6.61 7.03 6.0 4.5 4.2
B'h 180-200 0.15 0.16 0.40 0.00 0.35 4.80 5.15 6.8 4.6 4.3

Table 5-continued.
Extractable Total Extractable CEC* Base pH pH
Series Horizon Depth Ca Mg Na K bases Acidity Saturation (water) (KCI)
cm 1 cmol %

Lower Ap 0-10 5.2 1.56 0.44 0.00 7.20 9.45 16.65 43.2 4.0 2.9
Leon AE 10-16 2.75 0.91 0.17 0.00 3.83 5.71 9.54 40.1 4.1 3.0
Egl 16-28 0.95 0.41 0.13 0.00 1.49 3.39 4.88 30.6 4.4 3.5
Bwl 98-116 0.15 0.25 0.13 0.00 0.53 19.94 20.47 2.6 4.5 4.0
Bw2 116-130 0.10 0.16 0.09 0.00 0.35 2.22 2.57 13.7 4.7 4.2
Bg 130-137 0.35 0.33 0.13 0.02 0.83 3.41 4.24 19.6 4.6 4.2
B'hl 137-157 0.10 0.25 0.09 0.02 0.46 6.73 7.19 6.4 4.8 4.5
B'h2 157-177 0.15 0.25 0.09 0.00 0.49 5.39 5.88 8.3 4.8 4.5
B'h3 177-200 0.15 0.08 0.09 0.01 0.33 3.95 4.28 7.8 4.8 4.5
*CEC = Cation Exchange Capacity

al., 1979) the extractable Al contents of the five soil series are shown in Table 6 along

with extractable Al (sodium-pyrophosphate), extractable Al (citrate-dithionite) amounts,

and the Al/OC ratio for the different Bh horizons.

From the upper Mandarin to the lower Leon, the numbers show (Table 6) that

extractable Al (KC1) was probably accumulating in the Bh horizons. In the upper

Mandarin, the Al (KC1) increased from 0.28cmol/kg-1 in the E horizon to 0.59 cmol/kg-1

in the Bh horizon; in the lower Mandarin it increased from 0.32 cmol/kg-1 in the Eg2 to

1.02 cmol/kg-1 in the Bhl.Down the slope, in the upper Leon, the Al (KC1) increased

from 0.06 cmol/kg-1 in the Eg horizon to 1.01 cmol/kg-1 in the Bhl horizon. Finally, in

the lower Leon the Al (KC1) increased from 0.02 cmol/kg-1 in the Eg2 to 0.6 cmol/kg-1 in

the Bhl. This accumulation did not occur in the lower B'h horizon. Apparently, in the

upper Bh, Al, the binding agent, was dissolved by the action of the organic acids which

were produced during the decomposition of the vegetation, and the fluctuation of the

water-table. This resulted in the stripping of the sand grains in the E horizon and the

movement of Al to a deeper depth. This process did not occur in the soils located in the

upper part of the experimental plot because there was less influence of the water table

(Fig. 41a-f)) so, the effectiveness of the Al to accumulate in the first Bh, may be

associated with water table dynamics.

This accumulation of extractable Al (KC1) does not occur in the lower B'h. There

is no stripping of the upper E' or Bw horizon. Extractable Al (KC1) is not released from

the sand coatings. In fact, extractable Al decreases. This difference in Al(KC1) could

indicate that there is no translocation of aluminosilicates from the sand grain coatings of

the horizons above the B'h. Nevertheless, Al probably does exist in the water saturated


Aluminum extract, from the Bh horizons, with sodium pyrophosphate was higher

(Table 6) than the Al extracted with citrate diothinite because most of the Al in the Bh

horizon was in Al-organic complex form. Citrate dithionite removed only the cristalline

forms of Al. Aluminum (KC1) to OC ratio (Table 6) increased with depth in the upper Bh

horizon and decreased with depth in the lower B'h horizon. This decrease in the upper Bh

Al/OC ratio was probably due to the sequestration of most of the C in the Bhl, the first

illuvial horizon. The increase of Al (KC1) to OC ratio in the lower B'h horizon was

probably due to the lack of translocation of Al from the horizons above the B'h. With no

translocation of Al, OC accumulated. Al in situ remained constant and the ratio increased.

To study the form of Al -C complex in the soils, pyrophosphate-extractable

Al to oxalate-extractable Al ratios were calculated. The oxalate extraction removes both

inorganic and organic complex Al. Pyrophosphate removes only organic complex Al.

The pyrophosphate-extractable Al to oxalate-extractable Al ratio indicated that Al existed

mostly as organic complexes in both, Bh and B'h horizons in all the soils. The C

pyrophosphate to %OC ratio indicated that the C present in the Bh and B'h horizons is

organic in origin (Table 7). The lower B'h horizon had, on average, less than 0.6%

organic carbon. Only the B'h3 on the lower Leon soil had more than 0.6% (0.63%)

organic carbon. The actual definition for spodic horizons establishes a minimun of 0.6%

O.C. in the horizon to be called a Bh horizon. The Bh horizon in the Centenary and the

corresponding B'h horizons in the two Mandarins and two Leons, classified previously as

B'h horizons, did not meet the 0.6% O.C.criteria.

Table 6. Extractable Al by potassium chloride, sodium pyrophosphate, and sodium
citrate-dithionite of the different soil horizons and the Al/OC ratio.

Series Horizon Depth AI(KCI) Al Al (CD) AI(KCI)
(cm) cmol/kg (Pyr)1 cmol/kg /OC
cmol/kg ratio
Centenary Ap 0-10 0.21

Bwl 10-18 0.14
Bw2 18-40 0.10
E1 40-64 0.08
E2 64-104 0.08
Eg 104-143 0.04
Bg 143-153 0.17
Bh1 153-168 0.24 0.19 0.15 0.63
Bh2 168-190 0.16 0.11 0.13 0.36
Bh3 190-212 0.07 0.05 0.10 0.13

Upper Ap 0-10 0.34
Mandarin E 10-22 0.28
Bh 22-38 0.59 0.23 0.06 0.47
E' 38-63 0.21
Eg1 63-96 0.12
Eg2 96-130 0.08
Bw 130-157 0.24
B'hl 157-190 0.16 0.18 0.10 0.35
B'h2 190-200 0.09 0.08 0.04 0.16

Lower Ap 0-2 0.24
Mandarin Egl 2-20 0.25
Eg2 20-36 0.32
Bhl 36-45 1.02 0.13 0.25 0.76
Bh2 45-55 1.07 0.29 0.50 1.16
Bh3 55-64 1.12 0.31 0.58 2.00
BE 64-72 0.26
E'gl 72-106 0.05
E'g2 106-160 0.07
B'hl 160-180 0.20 0.14 0.21 0.48
B'h2 180-192 0.16 0.11 0.17 0.32
B'h3 192-200 0.12 0.09 0.15 0.21

Table 6---continued.

Series Horizon Depth Al (KCI) Al Al (CD)2 AI(KCI)
cmol/kg (Pyr)1 cmol/kg /OC
cm cmol/kg ratio

Upper Ap 0-10 0.14
Leon A/Eg 10-19 0.04
Eg 19-47 0.06
Bh1 47-52 1.01 0.17 0.08 0.73
Bh2 52-68 1.15 0.60 0.19 1.13

Lower Ap 0-10 0.14
Leon AE 10-16 0.09
Eg1 16-28 0.04
Eg2 28-52 0.02
Bhl 52-60 0.6 0.1 0.2 .41
Bh2 60-83 0.83 0.16 0.21 .79
Bh3 83-98 0.94 0.26 0.24 1.24
Bwl 98-116 0.2
Bw2 116-130 0.11
Bg 130-137 0.32
B'hl 137-157 0.28 0.29 0.46 .61
B'h2 157-177 0.21 0.23 0.44 .36
B'h3 177-200 0.19 0.21 0.12 .29
1Sodium pyrophosphate
2 Sodium citrate-dithionite

Rela e Elevaion

Fig. 41

Relative Depth
' 1. . : : -. .

Fig. 41b ,..
:. ::- ; '
i::~ C
bC~ ~** :

1 2
X axis 1: 25m
Y axis 1: 3 m

Figure 41a. Topographic map of the research area.
41b. Water table depth on February 11, 1999.


; . .~


-: '

;. :


~.: ::


li -[L.
'' 3.
''' i:



: ;
-~-~: :-
"' : :

Fig. 41c

Relative Ceps n



-Ifitil ...*J'

. .- t '

. .... . . ..
." 0 ; :..

r !

--. .. ,. ,- '. -. ._'.. ... . .
,: .... . .-. -...-. .:..-... ;: c.. .. .
.I ''i" ." -" .:. --":,- .'o "-r ".. '

Fig. 41d

Figure 41c. Water table depth on May 10, 1999

41d. Water table depth on August 27, 1999.

i )
...: ~....
:: i:
:: I:




Relative depth

.- ^ *; .
.. . . ..... ;.: "C ..'-" '" '
!::-^"" *'-""^ ^ ** --: .
) i..

'' ,*s!* ; "^^ "*- .,*T'1 '. .
,. -," .K ^ -^ .y^^ .'v ; *' ,.,. .. ;
^^*^,<^^ ^^:.^,,,. ^

Fig. 41e

Relative depth

^^ '^ -*"^-. .,- !**s : E ;*',,o
.. ift:f ^;.5/ -. ,L .
...!.. $

"*^^""'-.^*' :^-n.!i'^':L:;--,_

-,,:: :'." ", 2 '
;.:' ".^- .- **/ ^ t .--'r. '- _-' ... '
.. I ... L .-..:.:.
; *- i ; :::.'7-- __C-.."r. .i

Fig. 41f

Figure 41e. Water table depth at September 24, 1999
41f Water table depth at December 1, 1999.

Table 7. Percentage of organic C (OC), pyrophosphate-extractable C and Al, pyrophosphate-oxalate ratios.

Series Horizon Depth % % C % Al (Pyr) %AI (NH40x) Al (Pyr)/ C (Pyr)/
O.C. (Pyr)1
(cm) Al (NH40x) % O.C.

Centenary Bhl 153-168 0.38 0.35 0.19 0.25 0.76 0.92
Bh2 168-190 0.44 0.41 0.11 0.16 0.69 0.93
Bh3 190-212 0.52 0.50 0.05 0.08 0.63 0.96

Upper Bh ... 22 38 ........ 25 ............. ....................... 0.26 ....0.88 ..0.96
Mandarin B'hl 157-190 0.46 0.42 0.18 0.21 0.86 0.91
B'h2 190-200 0.58 0.58 0.08 0.13 0.62 1.00

Lower Bhl 36-45 1.35 1.21 0.13 0.15 0.87 0.90
Mandarin Bh2 45-55 0.92 0.86 0.29 0.33 0.88 0.93
Bh3 55-64 0.56 0.52 0.31 0.35 0.89 0.93
B'hl 160-180 0.42 0.32 0.14 0.18 0.78 0.76
B'h2 180-192 0.50 0.37 0.11 0.12 0.92 0.74
B'h3 192-200 0.56 0.52 0.09 0.11 0.82 0.93

Upper Bhl 47-52 1.38 1.24 0.17 0.18 0.94 0.90
Leon Bh2 ------.-52=68.....2.....------102 .-------0 92-....... .0,60........................... 80............................. 75------------- -.- 0 90
B'h 180-200 0.48 0.48 0.31 0.34 0.92 1.00

Table 7-continued.

Series Horizon Depth % % C % Al (Pyr) %AI (NH40x)3 Al (Pyr)/ C (Pyr)/
O.C. (Pyr)1
(cm) Al (NH40x) % O.C.

Lower Bh1 52-60 1.48 1.42 0.10 0.19 0.53 0.96
Leon Bh2 60-83 1.05 0.96 0.16 0.22 0.73 0.91
..... B h 3 ............... 83- 9 8 .......... Z 6 ........Q.0 Z .1................... .2 6 ........................... ..3 1 ............................... 84 ............................ .9 3
B'hl 137-157 0.46 0.40 0.29 0.35 0.83 0.87
B'h2 157-177 0.58 0.51 0.23 0.27 0.85 0.88
B'h3 177-200 0.66 0.63 0.21 0.24 0.84 0.95
pyrophosphate extractable


"Soil micromorphology" is the study of soil morphology by microscopic (light

optical and less frequently by submicroscopic) methods, often using thin-section

techniques. Source:
( SOURCE= 1.

To study the micromorphological features of Bh and B'h horizons under the

microscope, thin sections were prepared of the Bh and B'h horizons of the upper

Mandarin soil, lower Mandarin, and lower Leon. These soils were selected because

they occur very close to each other, but have different water table dynamics.

Comparisons between the Bh and B'h horizons in the upper Mandarin soil (Fig. 42)

showed that the sand grains (skeleton grains) of the upper Bh horizon were slightly

coated with dark organic matter and paler (yellowish) sesquioxides coatings (cutans); the

space between the sand grains (chambers) was largely unfilled. This horizon was very

brittle since little OM was present to serve as aggregate agent for the skeletal grains. In

the lower B'h horizon, the skeletal grains were darker than the first Bh, they had more

cutans. Some organic precipitates (plasma) filled the chambers in a way that suggested

precipitation from solution. When this B'h horizon was dry, it became slightly brittle.

These results are similar to those of Brandon (1977), for the soil series Leon, sampled in

Florida. According to him, the brittleness was associated with complete macropore filling

with opaque OM containing many silt-sized mineral particles. Also, these results were

similar to those of Farmer (1983), who studied the hydromorphic humus podzols in

Cooloola, Queensland. His results showed that in these podzols organic precipitates filled

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