The Influence of Hydrology on Everglades Ridge And

INFLUENCE OF HYDROLOGY ON EVERGLADES RIDGE AND SLOUGH SOIL TOPOGRAPHY

ERIC JORCZAK

A THESIS PRESENTED TO THE GRADUATE SCHOOL OF THE UNIVERSITY OF FLORIDA IN PARTIAL FULFILLMENT OF THE REQUIREMENTS FOR THE DEGREE OF MASTER OF SCIENCE

UNIVERSITY OF FLORIDA

2006

Eric Jorczak

To the Florida Everglades: live long and prosper

ACKNOWLEDGMENTS

I would like to acknowledge all those who assisted me in the completion of my thesis. They include my supervisory committee chair (Mark Clark), and my supervisory committee members (Wiley Kitchens and Jim Jawitz). I would also like to thank Chris

Lewis (the best Everglades plant collector this side of the Mississippi) and all other associates of the Wetland Biogeochemistry Laboratory. I extend special thanks to my parents and family who support me in many ways.

Long days on the road and longer days amidst the Everglades merriment were shared with many field workers, with much of the help from Charles “MacGyver”

Campbell. Lastly, I thank my research site, the Everglades, for providing generally favorable field conditions. Reliable field instruments allowed this project to be completed in a relatively low-blood-pressure fashion. This research was funded by the

Critical Ecosystem Studies Initiative, administered by the U.S. Department of the

Interior, National Park Service.

TABLE OF CONTENTS

page

ACKNOWLEDGMENTS ...... iv

LIST OF TABLES...... vii

LIST OF FIGURES ...... viii

ABSTRACT...... ix

CHAPTER

1 INTRODUCTION ...... 1

Background...... 1 Historic Hydrology...... 2 Plant Assemblage ...... 2 Soil Characterization ...... 3 Current Condition...... 5 Everglades Restoration...... 6 Objectives...... 7

2 WATER FLOW AND PARTICULATE TRANSPORT ...... 8

Introduction...... 8 Hydroperiod...... 9 Water Depth...... 9 Water Flow ...... 10 Hypotheses...... 12 Site Selection ...... 12 Materials and Methods ...... 14 Flow Measurements...... 14 Total Suspended Solids (Particulate) Transport Measurements...... 15 Results...... 16 Water Velocity...... 16 Water Depth...... 16 Water Flow ...... 16 Total Suspended Solids ...... 17 Total Suspended Solids (Particulate) Transport...... 17 Discussion...... 17

v Conclusions...... 22

3 INFLUENCE OF WATER TABLE ON RIDGE AND SLOUGH CO2 AND CH4 PRODUCTION...... 34

Introduction...... 34 Aerobic Respiration...... 36 Anaerobic Respiration...... 37 Objective and Hypotheses ...... 38 Materials and Methods ...... 39 Field Collection ...... 39 Laboratory Experiment...... 40 Results...... 43 Discussion...... 44 Conclusions...... 47

4 SYNTHESIS OF HYDROLOGY EFFECTS ON RIDGE AND SLOUGH SOIL DEVELOPMENT...... 51

LIST OF REFERENCES...... 58

BIOGRAPHICAL SKETCH ...... 64

LIST OF TABLES

Table page

2-1 Coordinates of the ridge and slough study sites...... 26

2-2 Water velocity in mid-November, 2004...... 33

2-3 Total Suspended Solids values from various locations...... 33

-2 -1 3-1 Methane flux (µg CH4 cm h ) out of soil cores...... 43

-2 -1 3-2 Carbon dioxide flux (µg CO2 cm h ) out of soil cores...... 43

vii

LIST OF FIGURES

Figure page

2-1. The four study sites in the southern Everglades...... 23

2-2. Photograph of site 3A2 at the ridge and slough interface ...... 24

2-3. Aerial photograph of site ENP1 ...... 25

2-4. Photograph of site ENP2 ...... 26

2-5. Cross section of the transect at each site...... 27

2-6. Measuring water velocity using fluorescein tracer (green) in slough at ENP2...... 29

2-7. TSS were filtered in the slough at 3A1...... 29

2-8. Average water velocity +1 SD at each of the four study sites ...... 30

2-9. Seasonal water velocity +1 SD at each of the four study sites...... 30

2-10. Average water depth +1 SD at each of the four study sites ...... 31

2-11. Average water flow per meter width +1 SD at the four study sites ...... 31

2-12. Average TSS +1 SD at the four study sites...... 32

2-13. Average TSS transport per meter width +1 SD at the four study sites ...... 32

3-1. The three water-table regimes used during the soil core experiment...... 41

3-2. Cores submerged in ambient water bath ...... 42

3-3. Extracting gas from core headspace...... 47

3-4. Mean CO2 emission based on water table...... 48

3-5. Carbon dioxide emission based on water table treatment over time...... 49

3-6. Methane emission based on water table treatment over time...... 50

viii

Abstract of Thesis Presented to the Graduate School of the University of Florida in Partial Fulfillment of the Requirements for the Degree of Master of Science

INFLUENCE OF HYDROLOGY ON EVERGLADES RIDGE AND SLOUGH SOIL TOPOGRAPHY

Eric Jorczak

May 2006

Chair: Mark Clark Major Department: Soil and Water Science

The most common landscape feature of the Everglades is the ridge and slough.

Hydrology and plants of the ridge are different than those of the slough, which is only possible because of the topographic difference between the ridge and slough.

Maintaining this topographic difference between the ridge and slough is necessary to maintain the biological diversity of the Everglades. This research examines hydrologic parameters that may play a role in maintaining this topographic difference.

The first part of this research consists of a hydrologic survey of the ridge versus slough to assess differences in water velocity and suspended-solids transport. Results from this research indicate that although water velocity between ridges and sloughs was not significantly different, there was a significant difference in suspended-solids transport, with most sloughs having higher suspended-solids transport compared to ridges. This was because sloughs have deeper water, and a greater concentration of total suspended solids.

ix The second part of this research assesses the influence of water table on ridge versus slough CO2 and CH4 production. Forty-eight soil cores were collected from ridges and sloughs with different hydrologic regimes. Cores were subjected to either a flooded

(+5 cm), saturated (0 cm), or drained (-15 cm) water table; and CO2 and CH4 emission was analyzed using gas chromatographs. Results from this research indicate that ridge and slough gas emission do not differ significantly, but lowering the water table results in significantly more CO2 emission.

The importance of hydrology for ridge and slough soil decomposition cannot be overstated. This research concludes that hydrologic parameters such as hydroperiod and water depth are very important in regulating soil decomposition. It is important to provide the correct hydropattern when implementing Everglades restoration, to optimize soil-accretion processes to maintain the ridge and slough topography.

CHAPTER 1 INTRODUCTION

Background

The Everglades is a 600,000 hectare subtropical freshwater wetland composed of an extensive marsh dotted with tree islands (Davis, 1943; Loveless, 1959; Gleason,

1974). The predominant landscape feature is known as the ridge and slough. It consists of higher-elevation ridges dominated by sawgrass (Cladium jamaicense Crantz); and lower-elevation sloughs containing plants accustomed to deeper water, such as

Nymphaea odorata and Eleocharis spp. This topographic difference between the ridge

and slough is important for maintaining the biological diversity that popularized the

Everglades. Plants and soil topography are influenced by subtle variations in hydrology

(DeAngelis and White, 1994). In this thesis, hydrology is used synonymously with

hydropattern and includes hydrologic components such as water flow, water depth, and

hydroperiod, among others. Hydrology selects for plants by influencing soil

composition, oxygen availability, and amount of woody structure needed to support plant

growth.

Anthropogenic changes in hydrology over the past several decades have decreased

soil elevations in many areas, causing a deleterious change in the shape, distribution, and

biological diversity of the ridge and slough (Science Coordination Team, 2003).

Everglades restoration seeks to improve and preserve the integrity of the ridge and slough landscape; therefore it is important to maintain the elevation difference between the ridge and slough, which sustains its diversity. There is a limited understanding about which

1 2 hydrologic parameters influence the development and maintenance of ridge and slough topography. Another unknown is the importance of hydrologic parameters versus biotic factors in regulating soil decomposition (one factor controlling the rate of soil accretion).

This research seeks to explore the influence of hydrology on ridge and slough soil topography.

Historic Hydrology

Historical Everglades hydrology was much different than what currently exists. In the wet season, water would overflow the southern rim of Lake Okeechobee and sheet flow southward throughout the ridge and slough, with most of the water emptying into the Gulf of Mexico (Science Coordination Team, 2003). Water depths were sometimes over 1 meter deep in Water Conservation Area 1 (Andrews, 1957). Hydroperiod was long (Science Coordination Team, 2003), therefore minimizing soil oxidation, and allowing extensive accretion of organic soils. All of these hydrologic parameters have been altered in the ridge and slough, due to drainage of the Everglades.

Plant Assemblage

The three common habitats in the ridge and slough are ridges, sloughs, and wet prairies. Of the three, ridges have the highest elevation, and therefore, the shortest hydroperiod and shallowest water depth when compared to its adjacent slough or wet prairie. Wet prairies are more similar to sloughs than ridges, since both have lower elevations than ridges, and often contain similar plants such as Eleocharis spp. (personal observation). Compared to wet prairies, sloughs tend to contain a greater proportion of floating-leaved aquatic plants; while wet prairies tend to contain a greater proportion of emergent plants such as Eleocharis cellulosa, Rhynchospora tracyi, and Panicum

hemitomon (Loveless, 1959). Characterizing the difference in topography and plants

between a ridge and slough was one goal of this research.

Composition of the ridge and slough differs with location. In most of Water

Conservation Area 3A (WCA-3A), ridges are adjacent to sloughs. In Everglades

National Park (ENP), ridges are typically adjacent to wet prairies (hereafter called

sloughs, for ease of comparison with other sloughs).

Soil Characterization

Within a ridge and a slough, the soil topography is relatively flat. One can discern

soil topography by simply looking at the plants on a ridge or slough; a similar plant

species in an area indicates a similar soil topography there. Since the topography is

similar, hydrology is similar, so a monospecific stand of plants often exists. This

especially holds true for ridges, where C. jamaicense typically accounts for almost all of

the plant biomass present (personal observation). The greatest change in topography

occurs along the ridge and slough interface, where topography rises noticeably when

transitioning from a slough onto a ridge.

Everglades soil can reach 3 meters deep in northern portions (such as Water

Conservation Area 1); and becomes progressively shallower heading south, with some

locations having soil only a few centimeters deep (Qualls and Richardson, 2002). An

initial survey of this study’s research sites measured average soil depths of 59 to 118 cm,

soil pH from 6.5 to 7.5, and soil bulk density from 0.01 to 0.63 g cm-3 (unpublished data).

The Histosol soil can be characterized as fibric (peat) or hemic (mucky/peat), and is

typically composed of the remains of dead plants.

Organic soil accretion depends on plant productivity (Day et al., 2004) and

hydrology (Craft and Richardson, 1993), among other things. When plant productivity is

great enough to deposit sufficient recalcitrant litter at a rate faster than soil microbes can

oxidize it, organic soil accretes biologically. Differing rates of soil accretion and

decomposition influence plant colonization and community structure (Bridgham et al.,

1996). Accretion can also be affected by abiotic parameters including hydropattern, fire,

storms, temperature, pH, oxygen, and water chemistry, among others.

Organic soil accretes in locations with a long hydroperiod, because of limited

availability of oxygen when soil is flooded, which consequently limits aerobic microbial

respiration. Lewis (2005) suggested that ridges may accrete soil at a greater rate than

sloughs because ridges have higher plant productivity and a slower litter-decomposition

rate. If the water becomes too deep, emergent plant growth is limited or eliminated. This

can decrease the potential plant productivity of the area and consequently decrease the

soil-accretion rate, as less plant litter accretes as soil. However, if the water table falls

below the soil surface, the soil comes in contact with more oxygen, allowing greater

oxidation of organic matter. Therefore, a delicate balance exists among hydrologic

parameters regulating the soil-accretion rate.

Lewis (2005) suggested that plant-litter decomposition rates differ between ridges

and sloughs. Plants such as C. jamaicense produce more recalcitrant litter, partly because

of their higher C:N:P ratio, which makes them more resistant to decomposition. Higher plant-litter recalcitrance can slow the rate of litter decomposition; and thus can lead to greater rates of soil accretion, especially on ridges where C. jamaicense grows.

Decomposition of organic soil is complex and is regulated by a number of factors including plant/detrital substrate quality and quantity (DeBusk and Reddy, 1998); hydrology (Happell and Chanton, 1993); and supply and type of electron acceptors

(D’Angelo and Reddy, 1994). Consequently, accretion and decomposition are often

influenced by the same abiotic parameters.

Current Condition

Recent hydrologic management of the Everglades has resulted in water tables that

are lower than historic conditions. A water table below the soil surface results in at least

two types of soil loss. Everglades droughts can result in severe burning of organic soil

(Smith et al., 2003), and destabilize the ridge and slough. As the water table drops below

the soil surface, oxygen becomes available for microbes to oxidize organic soil, causing

soil loss to occur at a greater rate than could have occurred historically. Furthermore,

there has been a reduction in plant community integrity, a change and decrease in wildlife

populations, and a change in the historic functioning of the Everglades (Davis and

Ogden, 1994). As a result of lowered water tables, some sloughs and wet prairies have been colonized by C. jamaicense (Loveless, 1959). Sloughs are important because they contain most of the plant and animal diversity in the ridge and slough, and provide

oxygen to the water via periphyton photosynthesis (Craighead, 1968; Gleason, 1974;

Kushlan, 1976; Browder, 1982).

Historical accounts suggest that the topographic difference between a ridge and adjacent slough was 61 to 91 cm (Wright, 1912; Baldwin and Hawker, 1915). Loveless

(1959) found topographic differences between the ridge and slough from a few centimeters up to 61 cm. Current topographic surveys indicate the ridge and slough landscape is in jeopardy because of a decrease in their topographic difference (Science

Coordination Team, 2003). This decrease has been attributed to anthropogenic changes in hydropattern over the past several decades, due to an effort to drain portions of the

Everglades to make it suitable for agriculture and residential development.

Everglades Restoration

Everglades restoration under the Comprehensive Everglades Restoration Plan will depend on scientific studies to provide data for sound hydrology management (Perry,

2004). The Plan seeks to restore many components of the Everglades, including the ridge and slough community. Research is needed to understand how hydrology and other abiotic parameters influence the development and maintenance of the ridge and slough.

It is important to understand the interaction of hydrology with the ridge and slough, since hydrologic management can influence abiotic parameters. Hydrologic management can help restore ridge and slough form and function. However, there is a scarcity of information on hydrologic parameters and their influence on ridge and slough soil. It is also necessary to understand the mechanisms affecting soil accretion since a larger topographic difference between ridge and slough may be necessary to restore the plant community to its pre-drainage condition. The rate of soil oxidation and factors influencing this rate are paramount to our understanding and preservation of this system.

Everglades scientists have proposed several hypotheses that influence the ridge and slough topography:

• The erosive force of water flow induces sediment transport (Science Coordination Team, 2003). This hypothesis states that flowing water physically scours and transports sediment from the slough and sometimes deposits sediment on the ridge, thereby helping to maintain the topographic difference.

• Lewis (2005) suggested that differences in plant litter recalcitrance between ridge and slough plants influence the rate of decomposition between the ridge and slough. This research demonstrated that ridge plants decompose at a slower rate, and therefore accrete more organic matter than sloughs. This research also found that C. jamaicense has greater productivity than slough plants, therefore more biomass is produced in the ridges which also helps ridges accrete soil at a faster rate than sloughs. Both of these factors can reinforce the topographic difference between a ridge and slough.

• An important and historically significant regulator of soil accretion is fire (Kuhry, 1994). Since ridge soils are higher in elevation and more likely to dry out than sloughs, it seems likely that ridges would be more susceptible to the deleterious effects of fire.

• Corrugated bedrock topography could provide higher locations for ridges to form and lower recesses for sloughs to occupy. Although this phenomenon explains the causative formation of some tree islands (islands formed on bedrock outcroppings), no studies have described bedrock topography as a means for ridge and slough formation. However, it is possible that ridges formed on higher bedrock outcroppings, and over time, the organic matter acidity dissolved the limestone to its current flattened topography.

• Hydrologic parameters differ in the ridge and slough, and can influence ridge and slough soil decomposition (which influences topography).

Objective

The objective of this research is to address the last hypothesis. To address this hypothesis, several parameters are measured such as water flow, sediment transport, and

CO2 and CH4 emission from soil. Measuring these parameters helps to better understand

how abiotic parameters can influence soil accretion and decomposition. Furthermore,

this research adds to our understanding of how current hydrologic management affects

the ridge and slough community. Understanding the differences in hydrologic parameters

between high and low integrity ridge and slough landscapes helps explain why some

ridges and sloughs have a greater topographic difference than others. Finally, this

research provides valuable information for hydrologic managers seeking the proper

hydropattern to optimize soil accretion and restore the ridge and slough community.

CHAPTER 2 WATER FLOW AND PARTICULATE TRANSPORT

Introduction

The hydrologic cycle influences the plants and soil of the Everglades. The wet season often begins in early June and ends in November. This six-month span is typically responsible for 82% of the 145 cm average annual rainfall in the Everglades

(Schomer and Drew, 1982). During this time, the ridge and slough experience increased water levels and flows. Higher water levels typically cause greater water velocities, since hydrologic gradient is greater between the upstream Everglades water table and sea level.

The Everglades is normally inundated for most of the year, except during droughts, when

lightning or human caused fires can sweep over the marsh (Loveless, 1959).

The dry season is characterized by cloudless skies, windier days, and more frequent

weather fronts. The drier, moving air, increases evapotranspiration, which can decrease

water tables in the Everglades at a fast rate if no rainfall is available to replenish the

wetland. Recent trends in the Shark River Slough portion of ENP indicate that water

table falls approximately 30 cm each month in the dry season (personal observation).

The few rain events that move through in the dry season do little to raise water table significantly.

In addition to natural hydrologic cycles, anthropogenic control of water levels and

flows can be significant. For example, in southern WCA-3A, the S-12 water control

structures may be closed, causing water to pond, therefore reducing flows and water

8 9 velocity in both WCA-3A by holding water up, and in ENP by preventing water delivery into ENP. This has resulted in sustained deep water in the southern half of WCA-3A.

Hydrology plays a large role influencing plants, soil, and topography in the ridge and slough. It is therefore important to understand hydrologic parameters such as hydroperiod, water depth, and flow. Hydrologic management of the Everglades can manipulate each of these parameters and potentially utilize them to reinforce the ridge and slough topographic difference.

Hydroperiod

Wetland hydroperiod is defined as the number of days per year that surface water is present. Ridges experience a shorter hydroperiod than sloughs since they have a higher soil elevation. Hydroperiod varies considerably on a temporal and spatial basis.

Temporally, ridges and sloughs can experience long hydroperiods some years due to tropical storm activity. Drought years can significantly reduce hydroperiod. Spatially, southern WCA-3A tends to have a longer hydroperiod than ENP, since it is managed as a reservoir. Due to the higher soil elevation, central WCA-3A just south of Alligator Alley

(Interstate-75) experiences a shorter hydroperiod compared to southern WCA-3A.

Water Depth

Water depth varies considerably depending on location in the Everglades.

Southern WCA-3A becomes progressively shallower as one heads north, due to the damming effect of the S-12 gate closures and Tamiami trail (U.S. route 41). Since water is held back in southern WCA-3A, it results in deeper than normal water conditions

(David, 1996). Everglades National Park receives water flow from WCA-3A, which along with rainfall, can sustain surface water in ENP for most of the year except during the end of the dry season.

Water is often deepest toward the end of the wet season, and shallowest at the end of the dry season. Rainfall primarily dictates this trend. From 1967-1979, Shark River

Slough occasionally experienced water depths over 1 meter (Olmsted and Armentano,

1997). The water table can often fall below the soil surface in drought years, depending

on location in the Everglades. Water depth recedes slowly due to the shallow soil slope

and great water flow drag due to the wetland plants in the water column impeding water

flow.

Fluctuating water levels play a large role in temperature and pH (Vaithiyanathan

and Richardson, 1998), dissolved oxygen (Kushlan, 1979), and soil redox (Seybold et al.,

2002). Typically, if one abiotic parameter changes, it affects another parameter.

Variations in water column TP and TN in sloughs were inversely related to water depth

fluctuations, suggesting a strong link with hydrology (Vaithiyanathan and Richardson,

1998). Specific water depths are important for survival of wetland plants. Several

animals such as the Everglades Snail Kite are influenced by changes in water depths

(Bennetts et al., 2002). Current water management practices result in ENP water depths

being too shallow in the dry season and too deep in the wet season, relative to historic

conditions.

Water Flow

Water flow is defined as the volume of water moving per unit time. This

calculation takes into account water velocity (distance/time) and the cross-sectional area

of flow, which includes water depth and channel width. Water flow has the potential to

deliver nutrients from upstream habitats to downstream locations. Sklar and van der Valk

(2003) proposed that Everglades tree island tail formation is in part due to nutrient

delivery flowing from the upstream head of the island, and stimulating primary

productivity downstream. Flow influences processes such as nutrient transport, soil

accretion and soil loss (Brandt et al., 2000). Brandt et al. also noted that interruption in water flow altered the shapes of tree islands in WCA-1 from a directional to a generally amorphous shape. The loss of linearity in some ridge and slough locations has been partially attributed to the reduction in water flow (Science Coordination Team, 2003).

The role of water flow has received a lot of attention recently in the Everglades scientific community, possibly being an important driver in ridge and slough maintenance

(Science Coordination Team, 2003). Many flowing systems experience a translocation of sediment as it is removed from one location and deposited in another. In the Everglades, there has been speculation on the role of flocculant transport and its influence on soil accretion. If flocculant material is repeatedly translocated from one location to another, this may reinforce a topographic difference between the ridge and slough.

Water velocity in ENP is often less than 1 cm s-1, with velocities in the southeast

portion averaging 0.8 and 0.5 cm s-1 in 1997 and 1999 respectively (Schaffranek and Ball,

2001). Historic velocities are believed to have been greater since much of the Everglades

freshwater is currently diverted to the Atlantic Ocean, instead of its historic flow path

into the Gulf of Mexico.

Water flow can significantly influence physical and chemical parameters within the

water column. Various mires in Ontario, Canada, demonstrated increased oxygen

concentration as water velocity increased, approaching saturation at velocities above

1 cm s-1 (Sparling, 1966). Sparling also noted that percent saturation of oxygen doubled

when water velocity tripled from less than 1 cm s-1 to over 3 cm s –1, both at night and

during the day. If water flow shifts from laminar to turbulent flow, oxygen entry into the

water column is greatly increased and is no longer limiting. It is unknown if the

Everglades experiences significant turbulent flows. These conditions might be reached

during hurricane activity.

Hypotheses

There is minimal information on water flow in the ridge and slough even though this physical process has been proposed as a possible determinant in shaping the landscape. Water flow may affect redox, temperature, dissolved oxygen, and pH. The first and most fundamental question is whether there is a difference in flow between a ridge and slough.

Hypothesis: Flow will be greater in a slough than in an adjacent ridge.

There is minimal information on particulate transport in the ridge and slough. An abiotic parameter such as water flow may provide a mechanism for transporting particulates, which can then settle out and add to soil accretion (counterbalancing the impacts of oxidative soil loss). High water velocities in sloughs may flush out sediment and maintain the topographic difference between the ridge and slough (Science

Coordination Team, 2003).

Hypothesis: Particulate transport will be greater in sloughs versus ridges.

Site Selection

Four sites were selected based upon a reconnaissance of WCA-3A and ENP, which indicated that each site experiences a different hydropattern. Sites were chosen in interior portions of the Everglades, relatively far from anthropogenic impacts such as canals and nutrient inflows (Figure 2-1). A baseline vegetation, soil, and hydrologic study was conducted to characterize each site.

Site 3A1 is located roughly 6 km south of Alligator Alley in WCA-3A. Site 3A1 is

in an area with elongated ridges with a relatively diverse plant assemblage in the sloughs.

Ridges here have a dense stand of C. jamaicense. Of the four sites, 3A1 is located in an area that is considered by the Science Coordination Team (2003) to be some of the best- preserved ridge and slough. Based upon an initial survey, this site has an average

topographic difference of 16 cm between the ridge and slough.

Site 3A2 (Figure 2-2) is located in central southern WCA-3A. Spatially, this region appears to contain more slough habitat than ridge habitat. This site has the longest hydroperiod and deepest water of the four sites. As a result, Nymphaea odorata is the

most common slough plant. The thickest flocculant layer occurs here, averaging 15 cm in the slough. This site has the largest topographic difference between ridge and slough

(25 cm).

Site ENP1 (Figure 2-3) is located in Northeast Shark Slough, which was historically the deepest portion of the Everglades, and is now shallower due to water

diversion to the western Everglades (Light and Dineen, 1994). Site ENP1 is unique

among the four sites due to the predominance of marl soil. This region resembles a

sawgrass plain with small pockets of slough, which can also be characterized as wet

prairie. This site has a topographic difference between ridge and slough of 9 cm.

Site ENP2 (Figure 2-4) is located in central southern Shark River Slough in ENP,

where the width of the ridge and slough landscape narrows as it nears the Gulf of

Mexico, and joins the Shark River tributaries. The region surrounding ENP2 has ridges

and sloughs that exhibit some linearity, and are susceptible to a low water table due to

lack of upstream freshwater delivery in times of drought. On May 12, 2002, a water table

19 cm below the soil surface was measured in the slough. A water table this low would seem unlikely in the pre-drainage era, except during an extreme drought. This site has a topographic difference of 18 cm between its ridge and slough.

Coordinates of the middle of each transect are listed in Table 2-1.

Materials and Methods

A baseline survey was conducted once at each of the 4 study sites to characterize the plants, along with the soil and bedrock topography (Figure 2-5). Sites were visited approximately once every 12 weeks from November 2002 to November 2004. Site visits tended to occur more often during the end of the wet season and beginning of the dry season, while wet-season visits were scarce because of field logistics. During each visit, the following measurements were conducted in the ridge and slough: water velocity, water depth, and total suspended solids (TSS).

Flow Measurements

At each study site, three locations in a ridge and three in the adjacent slough were randomly located along the site transect which spanned from a ridge, crossing a slough, and into the adjacent ridge. To measure water velocity, approximately 1 µL of fluorescein dye (visual tracer) was injected into the middle of the water column using an eye-dropper (Figure 2-6). After one minute, the distance traveled by the leading edge of the dye plume and direction of plume movement was noted. Three consecutive tracer trials were conducted at each sample site along the transect.

Water depth was measured with a measuring tape at several locations along the same transect in each ridge and slough. At each sample location, the measuring tape was inserted vertically into the water until resistance was felt as it contacted the soil surface.

Therefore, the water depth reading was not solely water, since the measurement in some

instances included the flocculant layer above the soil (which varied from 1 to 15 cm).

Surface water flow was calculated by multiplying water depth by water velocity

during each site visit. Since each ridge and slough had a different width, flow was

normalized so that data were presented as flow across a 1 meter span perpendicular to the

direction of water movement:

Flow (m3 s-1) = width (1 m) X water depth (m) X water velocity (m s-1).

Total Suspended Solids (Particulate) Transport Measurements

Three locations were randomly located in a ridge and slough, although each sample

location had to be relatively clear of plants and periphyton. This would assure that only

water column particulates were filtered, and no particulate matter from plants or

periphyton would be sampled, resulting in skewed data. To measure total suspended solids, an electric peristaltic pump (ISCO brand) extracted surface water, which was pushed through a 47 mm diameter, 0.45 µm pore size, glass fiber filter (Figure 2-7).

Filters were pre-treated in the laboratory by passing 30 mL of distilled-deionized water through them to remove any lose glass fibers which could have sloughed off in the field and resulted in erroneous data. In the field, four liters of water were typically filtered at a rate of 2 L min-1 at each sample location. Filters were individually stored in plastic petri

dishes on ice until they were dried at 104oC for 1.5 hours. Filters where then placed on a

balance to determine mass of solids per liter of water filtered. Particulate transport was

calculated by multiplying surface water flow by TSS.

Data were analyzed using JMP, a statistical software program (SAS Institute,

2001). If data were not normally distributed, which was often the case, they were log

transformed to fit the criteria for a statistical test. All tests of significance were made at

α=0.05.

Results

Water Velocity

Of all four study sites, ENP2 was found to have the greatest average water velocity in both the ridge and slough, while 3A2 velocity was the lowest. Only ENP1 had significantly greater velocities in the slough compared to the ridge, while 3A1 and ENP2 had significantly greater velocities in the ridge (Figure 2-8). Velocities appeared to be more influenced by site location and not ridge versus slough.

When averaging among all sites and sampling times, there was no significant difference in water velocity between ridges and sloughs. However, there was a considerable seasonal variation in velocities between sites and between ridges and sloughs primarily in response to water levels (Figure 2-9). When water level dropped below the soil surface, leaving pockets of water, there was no measurable water velocity.

Water Depth

3A2 had the greatest average water depth of all sites (Figure 2-10). Water depths were variable among sites, with water table sometimes below the ridge soil surface at

3A1, ENP1, and ENP2 in the dry season.

Water Flow

At site 3A2 and ENP1, flow was significantly greater in sloughs than ridges (Figure

2-11). The greater flows in sloughs were often due to the deeper water in sloughs and not due to greater velocities. A water depth difference of only a few centimeters can make a large difference in the flow rate.

ENP2 had significantly greater flows in the ridge and slough than the other 3 sites.

This was due more to faster velocity than water depth. Flows were very seasonal and

influenced by both water velocity and depth. Although water velocity was greater at 3A1

compared to 3A2, flow was similar at both sites because water depth was greater at 3A2.

Total Suspended Solids

Total suspended solids generally increased moving from the northern to the

southern sites (Figure 2-12). Sloughs often had higher average total suspended solids,

although not significantly so.

Total Suspended Solids (Particulate) Transport

Sloughs typically had significantly greater TSS transport than ridges. Sloughs also

had greater variability in TSS transport (Figure 2-13).

Discussion

Increased water velocity coincided with the wet season, as expected. However,

during one site visit in the dry season, only pockets of water were present on the 3A1

ridge. As a result, there was no flow. As long as an area was flooded, water was

flowing. Once water table falls to the point where only pockets of water are present, then

water flow ceases, or is at least not measurable by the dye tracer technique. Water

velocity was often slowest at 3A2 due most likely to the effect of the S-12 gate closures,

which caused surface water to pond and slow its movement southward. The one

exception to this observation was after the hurricanes of 2004 when velocities were much

greater, most likely due to the opening of the S-12 gates. This data was not included in

the main dataset, and is instead located separately in Table 2-2 because these velocities

are outliers and are considered to be more characteristic of a peak event, than a base flow.

It is likely that water velocity was much greater in the 3A2 slough versus the ridge

because the slough has little plant biomass in the water column to impede flow.

Water velocity was generally greatest at ENP2. This may occur partly because at

this site, the ridge and slough landscape narrows, and water flow is more channelized as

it makes its way towards the Shark River. Additionally, the ENP2 ridge had many open

pockets of water, which were sparsely populated with plants, thereby minimizing friction

between the plants and water movement. Water velocity appeared to be greatest in

locations with the least plant biomass in the water column, a trend consistent with a study

conducted by Bazante et al. (2004). Wetland plants create an impediment to water flow,

and can redirect water movement (Sand-Jensen et al., 1989). In measurement locations

with few plants, the dye used to measure water velocity traveled in more of a compact

plume, while a plume moving through many plants experienced more dispersion. In

these locations, determining the leading edge of the plume became somewhat difficult.

The centroid of the plume would perhaps be a better estimate of velocity, but would have

been more difficult to characterize. If the centroid was used to determine velocity, values

would be roughly 25% lower than they are reported here. Therefore, water velocities

reported in this study can be considered to be on the higher end of the spectrum of ridge

and slough velocities.

Bazante et al. (2004) measured water velocities in northwest ENP using a handheld

velocity meter, reporting 0.8 cm s–1 in the ridge, and 0.9 cm s–1 in the slough. They

reported sufficient velocity corroboration between their velocity meter and their dye

tracer technique. Troxler-Gann et al. (2005) measured water velocity in the southeast

portion of the Everglades, containing mostly C. jamaicense. They reported an average

velocity of 0.8 cm s-1, although this data includes an experiment where water flow was

restricted in some areas, and therefore this velocity value most likely underestimates the

true velocity of that area.

Water was deepest at 3A2, due to the construction of the Tamiami Trail along with

the ponding of water due to hydrologic management of the S-12 structures. Slough soil

appeared very loosely consolidated, indicating the infrequent recession of water table

below the soil surface. Water was shallower at 3A1, which may partly explain the

greater plant diversity noted in its ridge and slough. The relatively high topographic

difference (16 cm) here was surprising since this site may experience a shorter ridge

hydroperiod, compared to the other ridge sites, which would indicate higher rates of soil

oxidation, leading to a narrowing of the topographic difference. If ridge plant

productivity and recalcitrance is high, this may help offset any soil oxidation.

Water depths appeared to be consistently shallow at ENP1, which may partly

explain the marl soils at this site. Soil had an abundance of shells, indicating a high pH

throughout the soil profile, and a possibility that some of the TSS measured here had a calcitic component. Water was never deep at ENP1, yet the site contained surface water during each visit. This hydrologic condition most likely explains the predominance of the marl soil. Shallow water sustained for long periods is optimal for marl accretion.

Of the four ridges, water flow was greatest at ENP2, due mostly to relatively higher velocity and not deep water. Whereas in the 3A2 ridge and slough, water was deep, but since velocity was minimal, flow was minimal. Flow is naturally regulated by rainfall amount, and anthropogenically regulated by water control structure operation.

Water flow direction was often in line with (parallel to) the linearity of the ridge

and slough community, except at ENP1. At this site, water was flowing from the west, instead of from the north, as it is believed to have historically flowed. Water flow

direction at ENP1 is greatly altered due most likely to lack of water flow into Northeast

Shark Slough. Water enters ENP through the S-12 gates and flows southeast towards

Northeast Shark Slough.

Since water flow was assumed to be sheet flow, it was assumed that water in the

whole column was moving at the same velocity. This included water in the flocculant

layer, although flocculant material was not observed to be moving. Therefore, flow

values could be overestimated in locations such as the 3A2 slough where the flocculant

layer was about 15 cm thick. Water may have been flowing through the flocculant layer,

although no measurements in the layer were made, since the dye tracer technique would

not work here due to poor visibility within the layer.

Flow was lower towards the end of the wet season, on into the dry season when

water levels receded, and often periphyton and plant matter would partially clog the

sloughs. It seems reasonable that water velocities would be more consistent in the ridge

where the lack of light penetration into the water column impedes growth of submerged

plants. During these times, the physical effects of velocity may play less of a role in

shaping soil topography, and instead vegetative growth may play a greater role when

litter is deposited and becomes new soil.

Total suspended solids measured in this study were relatively low, compared to

other water bodies (Table 2-3). Bazante et al. (2004) measured TSS in the ridge and

slough surrounding tree islands in the northwest portion of ENP and reported TSS values

21 typically between 0.5 to 1.5 mg L-1. Low TSS values help to explain why water in the ridge and slough is so clear, allowing light entry throughout the slough water column, even in water over 1 m deep. Total suspended solids values are also low due to the general absence of denser, inorganic matter in the water column (Bazante et al., 2004).

The filter paper used for this TSS study often had a tan color from slough water, and a dark brown color from the ridges. A study conducted by Sutula et al. (2003), reported

TSS from creeks that discharge from the Everglades into eastern Florida Bay with values ranging from 5 to over 100 mg L-1 with an average around 10 mg L-1. Their analyses suggest that TSS was correlated with physical parameters such as direction of water flow and wind velocity in one creek, while biological activity such as chlorophyll a, influenced

TSS in two other creeks.

The higher TSS transport and larger variability of TSS in the slough may be due to the greater presence of calcitic periphyton in the sloughs. When this periphyton senesces, it may release calcium into the water and increase TSS transport values, as calcium is filtered from the water column. During one sample visit, the water column appeared white and a bit murky at ENP1 and ENP2, possibly due to calcium in the water column.

Instances like this may have been the cause for higher than expected TSS transport, especially at ENP1 with its calcitic soil.

Over time, TSS transport could play a significant role in soil loss and accretion, although this study did not derive the origin or fate of the TSS. Therefore, it is unknown if TSS travels far downstream or how long solids have been suspended in the water column, and if the TSS moves from sloughs and deposits on ridges. Total suspended

solids may not settle at all if they become oxidized in the water column. Further study

could elucidate the origin and fate of TSS.

Total suspended-solids transport as measured in this study is somewhat different

than the sediment transport hypothesis proposed by the Science Coordination Team

(2003), in that TSS transport is occurring in the water column, whereas sediment

transport may occur in the water column and/or as bed flow. This study did not measure

bed flow, since it was not observed and was therefore considered immeasurable at least

during the routine weather events experienced during each site visit.

Given that soil cores taken from ridges appeared to have soil that was composed of

ridge plants, while the slough cores appeared to have soil that was composed of slough plants, one would assume that if sediment transport did occur, sediment that originates from the slough is deposited downstream in the slough, while sediment in a ridge is

deposited downstream in a ridge. If water velocity was significantly increased, it is

possible for sediment to be carried out of the Everglades, into the Gulf of Mexico. This

scenario is unfavorable since soil would be unable to accrete in the Everglades with each

sediment transport event.

Flow may serve other important services such as alligator hole formation and

maintenance. If an alligator is wallowing in a hole while water is flowing, flow might

carry away suspended sediment and allow gator holes to become deeper, instead of

sediment settling back into the gator hole.

Conclusions

The velocities measured during this study did not appear to be great enough to

physically transport sediment, which in most cases would have been flocculant material.

Judging by the low TSS values obtained from this study, particulate transport appears to

be minimal, at least during routine weather events. It is possible that only very large rain

events due to hurricanes or tropical storms would be able to provide enough water to

create the velocity necessary to physically scour and transport sediment.

Figure 2-1. The four study sites in the southern Everglades. Reprinted with permission from Lewis, C. L. 2005. Linkages among vegetative substrate quality, biomass production, and decomposition in maintaining Everglades ridge and slough vegetative communities. Master’s thesis. University of Florida, Gainesville, Florida. Figure 1-1, p. 2.

Figure 2-2. Photograph of site 3A2 at the ridge and slough interface looking south into the length of the slough.

Figure 2-3. Aerial photograph of site ENP1 showing the transect used to survey this site.

Figure 2-4. Photograph of site ENP2 showing the ridge and slough interface.

Table 2-1. Study site coordinates. Site Coordinates (NAD 1983) 3A1 N 26o05.448, W 80o43.596 3A2 N 25o53.939, W 80o43.974 ENP1 N 25o42.317, W 80o36.203 ENP2 N 25o33.584, W 80o46.895

Figure 2-5. Cross section of the transect at each site. A) Site 3A1. B) Site 3A2. C) Site ENP1. D) Site ENP2. Vertical measurements taken at 5 m intervals along the transect. Five nested measurements every 10 m along transect are summarized as standard deviation along soil and bedrock contours. Water depth is based on date of measure. Ridge or slough designation based on prominent vegetation along transect.

Figure 2-5. Continued.

Figure 2-6. Measuring water velocity using fluorescein tracer (green) in slough at ENP2.

Figure 2-7. TSS were filtered in the slough at 3A1.

Figure 2-8. Average water velocity +1 SD at each of the four study sites from November 2002 to February 2004. Asterisk indicates significant difference between ridge and slough (pairwise t-test for each site visit).

Figure 2-9. Seasonal water velocity +1 SD at each of the four study sites. A) Site 3A1. B) Site 3A2. C) Site ENP1. D) Site ENP2.

Figure 2-10. Average water depth +1 SD at each of the four study sites from November 2002 to February 2004. A) Ridges. B) Sloughs.

Figure 2-11. Average water flow per meter width +1 SD at the four study sites from November 2002 to February 2004. Asterisk indicates significant difference between ridge and slough (pairwise t-test for each site visit).

Figure 2-12. Average TSS +1 SD at the four study sites from November 2002 to February 2004. Asterisk indicates significant difference between ridge and slough (pairwise t-test for each site visit).

Figure 2-13. Average TSS transport per meter width +1 SD at the four study sites from November 2002 to February 2004. Asterisk indicates significant difference between ridge and slough (pairwise t-test for each site visit).

Table 2-2. Water velocity in mid-November, 2004. Site Velocity (cm s–1) + 1 SD 3A1 - ridge 0.37 + 0.18 3A1 - slough 0.48 + 0.20 3A2 - ridge 0.43 + 0.12 3A2 - slough 1.53 + 0.57 ENP1 - ridge 0.31 + 0.08 ENP1 - slough 0.37 + 0.10 ENP2 - ridge 1.23 + 0.25 ENP2 - slough 1.27 + 0.24

Table 2-3. Total suspended solids values from various locations. Location TSS range (mg L-1) Source Everglades ridge and slough 0.1 to 2.2 This study Everglades ridge and slough 0.5 to 1.5 Bazante et al., 2004 creeks draining the Everglades 5 to 100+ Sutula et al., 2003 Mississippi River-upper ~40 to 50 James and Barko, 2004 Alaskan rivers 0 to 610 Rember and Trefry, 2004 Yellow River, China 0.13 to 565 Yang et al., 1996

CHAPTER 3 INFLUENCE OF WATER TABLE ON RIDGE AND SLOUGH CO2 AND CH4 PRODUCTION

Introduction

The hydrologic cycle plays a large role in Everglades soil organic matter (Craft and

Richardson, 1993). This soil organic matter comes from the plants that grow in the ridge

and slough. Water depths and hydroperiod influence the type of plants that grow

(Loveless, 1959; Newman et al., 1996). Water depths and hydroperiod can also influence

the rate at which soil decomposes. It is therefore important to understand how hydrology

influences the rate of soil decomposition, as this is an important mechanism in

maintaining the ridge and slough soil topographic difference. In addition to the natural

hydrologic cycle, hydrologic management of the Everglades also influences the rate of soil organic matter decomposition, since both processes can cause water table to fall below soil surface, increasing soil oxidation rate.

Decomposition of organic matter is regulated by its physical and chemical composition (Moran et al., 1989; Lewis, 2005), nutrient availability (Qualls and

Richardson, 2000), microbial activity (Hackney et al., 2000), and environmental factors

(Brinson et al., 1981). Some of these environmental factors include moisture, temperature, and the availability of electron acceptors (Reddy and D’Angelo, 1994).

Decomposition in wetland soils typically occurs at a very slow rate since the most efficient electron acceptor, oxygen, is often in limited supply (Vaithiyanathan and

Richardson, 1998).

34 35

Plant litter recalcitrance and nutrient availability (C:N:P ratio) both play a major role in the rate of decomposition. An experiment conducted by Lewis (2005), noted that slough plant litter contains more labile (readily decomposable) carbon since the C:N:P ratio was more favorable for microbes to utilize the organic matter in the plant litter as an electron donor. Conversely, ridges contain mostly C. jamaicense, which has a higher

C:N:P ratio and therefore a more recalcitrant form of organic matter which therefore decomposes at a slower rate. Lewis’ study determined that a slough species, E. cellulosa, decayed at a rate over twice that of C. jamaicense. Additionally, C. jamaicense decomposed at a slower rate since it had a higher percentage of lignin (which is a recalcitrant form of organic matter) as compared to slough species. Since the sites in this study are in relatively low nutrient (N and P) locations, substrate quality and electron acceptor availability are believed to be the primary determinants regulating decomposition.

One possible reason that ridges have higher soil topography is because

C. jamaicense produces a greater quantity of lignin as compared to slough plants (Lewis,

2005). Lignin is the most recalcitrant type of organic matter, and is present in many wetland soils to some degree. Conditions favorable for lignin decomposition include warm temperatures and high litter moisture, oxygen availability, and palatability of litter to microorganisms (Hammel, 1997). Therefore, lignin can decompose in ridge soils if these conditions are met, which often occurs when water table falls below the soil surface.

To sustain the topographic difference between the ridge and slough, it is better for ridges to accrete soil instead of losing it to decomposition. The net difference between

36 plant organic matter production and litter decomposition determines the rate of organic soil accretion. Organic soil accumulates in wetlands as a result of physical, chemical, and biological interactions with plant material (Chen and Twilley, 1999). Senesced plant material can accrete and become organic soil if decomposition rate is reduced during flooded conditions. Therefore, hydroperiod is a major determinant in organic soil accretion, since flooded soils tend to remain hypoxic and minimize aerobic soil respiration rate.

Dissolved oxygen concentration and soil moisture play a large role in regulating organic matter decomposition rate. Dissolved oxygen concentration is affected by the rate of diffusion of oxygen from air into the soil surface, and the oxygen demand created by microbial respiration within the soil (Howeler and Bouldin, 1971). Oxygen is the most efficient electron acceptor in microbially mediated soil respiration, and is often the limiting factor for soil oxidation rate. Organic matter serves as the electron donor during respiration, and is not limiting in the ridge and slough, due to the high abundance of organic matter in the soil.

Aerobic Respiration

Aerobic soil respiration can occur when oxygen is available for heterotrophic microbes. As water table drops below soil surface, aerobic respiration (which is more metabolically efficient than anaerobic respiration) increases, since oxygen becomes much more available (DeBusk, 1996). As a result, CO2 is produced in greater amounts, and a loss of organic matter occurs according to the following reaction:

C6H12O6 + 6O2 Æ 6CO2 + 6H2O.

Aerobic respiration is metabolically favored since it yields a greater amount of energy for microbes. Higher levels of ridge respiration in times of low water table may

have been responsible for large losses of ridge soil and possibly a narrowing of the topographic difference between a ridge and slough. For example, if water table drops to the point where ridge soil becomes exposed to air, while slough soils are still flooded, ridge soils may oxidize at a greater rate, which results in a lower ridge elevation and an unfavorable narrowing of the ridge and slough topographic difference.

Water table drops below soil surface yearly in parts of the ridge and slough such as

WCA-3A near Alligator Alley, WCA-3B, Taylor Slough in ENP, and the eastern and western edges of Shark River Slough in ENP (personal observation) most likely resulting in high rates of aerobic soil respiration. If water table drops too low, soil can dry out and become vulnerable to extreme oxidation, due to wildfires. Both of these scenarios are unfavorable, since these events can reduce the topographic difference between the ridge and slough.

Anaerobic Respiration

Anaerobic respiration is common in wetlands such as the Everglades (Bachoon and

Jones, 1992). Wetlands typically contain anoxic soils, therefore, anaerobic metabolism

of organic matter is more common than in upland environments (Reddy and D’Angelo,

1994). As a result of anoxic conditions and the absence of other electron acceptors,

methanogenesis is the principal pathway for organic matter decomposition in freshwater

wetlands. Methane production is regulated primarily by oxygen availability and other

electron acceptor availabilities, pH, temperature, salinity, organic substrates, nutrient availability, plant physiology, community composition, and hydrology (Megonigal et al.,

2004). In the complete absence of electron acceptors, methanogenesis becomes the dominant metabolic pathway in soil respiration, although it is not as metabolically

efficient as aerobic respiration. Methanogenesis cannot occur in the presence of oxygen

since it is toxic to methanogens.

Once CH4 is produced, it diffuses upward along a concentration gradient toward the sediment water interface. Methane can be oxidized to CO2 by methanotrophic bacteria

when it diffuses up through the soil if it comes in contact with aerobic soil before

escaping into the atmosphere via the following reaction (King, 1992):

CH4 + 2O2 Æ CO2 + 2H2O

In some instances, mass flux of CH4 can occur when CH4 builds up and bubbles

into the atmosphere (ebullition) (Chanton and Martens, 1988). Methane can escape

directly into the atmosphere when plants pass CH4 from their roots and then though their

stems and into the atmosphere (Bosse and Frenzel, 1998).

Aerobic metabolism dominates the surface of sediments, while methanogenesis is common at deeper depths, with little overlap between these zones (Megonigal et al.,

2004). Methanogens are strict anaerobes that produce CH4 as a waste product of energy

metabolism, by often utilizing electron donors such as acetate or more frequently H2

(Megonigal et al., 2004) in the following equation:

4H2 + CO2 Æ CH4 + 2H2O

Objective and Hypotheses

Lewis (2005) demonstrated that sloughs contain more readily decomposable plant

litter than ridges. This indicates that slough soil may release more CO2 and CH4 during litter and soil decomposition. The main objective of this experiment was to determine the difference in soil decomposition rate between ridge and slough soils as measured by CO2 and CH4 emission in relation to water table.

Water table has been shown to affect Everglades soil production rates of CO2 and

CH4 (DeBusk and Reddy, 2003). Determining these rates will help quantify carbon loss in the ridge versus slough. It will also help determine if the ridge or slough is more susceptible to soil loss during drought conditions. It is important to understand the quantity of carbon lost in relation to water table, since Everglades restoration seeks to implement the proper hydrologic regime to sustain the ridge and slough landscape. This can be accomplished by reestablishing and maintaining the topographic difference between the ridge and slough.

The objective of this experiment is to determine whether water table elevation influences CO2 and CH4 production differentially in ridge versus slough soils. Several

hypotheses have been proposed:

• A water table above the soil surface will produce more CH4 emission in a

slough soil versus a ridge soil.

• A water table at and below the soil surface will produce more CO2 emission in

a slough soil versus a ridge soil.

• Carbon dioxide emission will increase as water table decreases from flooded to

drained conditions in both ridge and slough soils.

Materials and Methods

Field Collection

In the center of each ridge and slough habitat at sites 3A2 and ENP2, 12 intact soil

cores were collected in November, 2004. All cores were collected from sites that were

flooded at the time of collection. The core cylinders were 27.4 cm long, with an inside

diameter of 9.6 cm. Cores were composed of 0.32 cm thick clear polycarbonate.

Cylinders were hand pressed into the soil to a depth of 20 cm. To provide some

understanding of sites 3A1 and ENP1, three cores were also collected from the ridge and the slough habitat at both of these sites. Most of the cores were collected at 3A2 and

ENP2 because our observation and other investigations suggested these areas have experienced very dissimilar hydropatterns during the past two decades. Therefore,

measuring CO2 and CH4 emission from cores at these sites might help indicate how past

hydrologic management may influence current soil decomposition rate.

Cores were collected randomly within a 10 m2 area in each ridge and slough. No live plants were present in any of the cores collected. Plant litter and flocculant material

present on the core soil surface was left undisturbed and included in the core. Cores were

flooded with site water, capped at both ends, and transported upright back to the

laboratory in coolers at ambient temperature. Cores were stored at room temperature

until the experiment began 4 days after cores were collected.

Laboratory Experiment

In order to simulate drought conditions, a third of all ridge and slough cores from

each site were drained to a water table 15 cm below the soil surface. To simulate a mild

drought, another third of the cores were drained to bring the water table to the soil

surface. This left the flocculant material and litter, if any, somewhat exposed to air,

while the soil was still saturated. To simulate flooded water conditions, the remaining

third of the cores were kept at a water table 5 cm above the soil surface (Figure 3-1).

This allowed the flocculant layer and litter to be in a flooded state. All water tables were

maintained at these treatments for the 48 day duration of the experiment.

Figure 3-1. The three water-table regimes used during the soil core experiment.

Since the cores were capped on both ends, they were airtight and watertight. Cores were submerged in a random arrangement in an ambient-temperature water bath, which varied from 19.5 to 21oC over the course of the experiment. Core bath temperature was recorded before each day when measurements were taken. The only light penetration into the cores was by fluorescent day-lighting, which was assumed to have a minimal impact on CO2 and CH4 emissions since no living plants were present in the cores.

A polyethylene tube was connected from an air compressor, through the top cap on

each core (Figure 3-2). This allowed for ambient air to flow into the headspace of each

core at all times, and minimize the buildup of any gasses. The top cap on each core had a

septum with an outlet valve to allow core headspace air to bubble out into the water bath.

The volume of air that passed through each core headspace was adjusted to allow for measurable amounts of CO2 to accumulate in the headspace, but not to the point of

influencing water chemistry in the core.

Figure 3-2. Cores submerged in ambient water bath with continuous air-flow through the headspace of each core.

Each core headspace was sampled in the afternoon, typically 3 days in a row each week for 48 days. Using 1000 µL insulin syringes (Beckton Dickinson, Franklin Lakes,

NJ), 500 µL of gas from the headspace was extracted through each outlet septum and analyzed on a thermal conductivity detector gas chromatograph (Shimadzu, Model GC-

8A, Kyoto, Japan) to determine CO2 concentration (Figure 3-3).

Methane was sampled using the same technique on the same day, and immediately following the CO2 sampling. For CH4 analyses, 100 µL of gas was extracted from the headspace and analyzed on a flame ionization detector gas chromatograph (Shimadzu,

Model GC-8A, Kyoto, Japan).

Carbon dioxide concentration of ambient air was measured to assure core headspace concentration of CO2 was greater than ambient air CO2 concentration.

Distilled water was added to cores if water evaporated from them, in order to maintain a

constant and intended water table.

The flow rate of air leaving each core headspace was measured by inverting a

10 mL volumetric flask filled with water and measuring the time it takes for bubbles

leaving the outlet septum to fill up the flask.

Mass flux of CO2 and CH4 from each core was calculated as:

flux = ((outflow concentration – inflow concentration) X (air outflow rate) X density of CO2) / area

Results

Although the flooded slough cores (+5 cm) emitted more CH4 than the ridge cores,

it was not a significant difference (Table 3-1).

-2 -1 Table 3-1. Methane flux (µg CH4 cm h ) out of soil cores (mean + SD, n = 8 for each value). Habitat Water table +5 cm 0 cm -15 cm Ridge 0.19 + 0.33 0.13 + 0.24 0.24 + 0.31 slough 0.59 + 1.17 0.52 + 1.67 0.36 + 0.51

The 0 cm water table treatment exhibited no significant difference in CO2 emission

between ridge and slough cores (Table 3-2).

-2 -1 Table 3-2. Carbon dioxide flux (µg CO2 cm h ) out of soil cores (mean + SD, n = 8 for each value). Habitat Water table +5 cm 0 cm -15 cm Ridge 3.6 + 4.6 5.6 + 7.5 14.6 + 10.3 slough 5.3 + 5.5 5.6 + 4.6 14.4 + 7.6

The –15 cm drained cores exhibited no significant difference in CO2 emissions

between ridge and slough cores (Table 3-2).

When averaging all cores, CO2 emission was significantly greater in the –15 cm

drained cores, while the 0 cm and +5 cm cores exhibited no significant difference (Figure

3-4).

No general trend was observed in CO2 emission with any of the water table

treatments (Figure 3-5). No general trend was observed in CH4 emission in any of the

water table treatments (Figure 3-6).

Discussion

Since CO2 flux out of ridge and slough soils exhibited no significant difference between them, the organic matter in the ridge and slough may have the same recalcitrance. This is surprising since Lewis (2005) demonstrated that slough litter is more decomposable than ridges. It is possible that although slough litter is more decomposable, slough soil is not, since the most readily decomposable material is decomposed before litter becomes soil. This distinction is important because Lewis studied plant litter decomposition, whereas this study looked at soil decomposition.

Readily decomposable slough litter may decompose rapidly and leave behind a similar amount of recalcitrant matter as does ridge soil. It is also possible that any readily decomposable slough litter decomposed in the 4 days between time of soil core collection and when CO2 measurements were made.

As hypothesized, the –15 cm water table cores exhibited significantly more CO2 emission than the +5 or 0 cm water table cores; roughly three times the amount. This trend indicates that ridge and slough soil should be kept flooded, or at least saturated, to minimize soil oxidation. Locations such as the Everglades Agricultural Area is a prime example of severe soil oxidation as water table is drastically lowered.

DeBusk and Reddy (2003) noted CO2 flux from Everglades WCA-2A flooded

cores ranged from 1.7 to 3.8 µg C cm-2 h-1, while –15 cm water table cores ranged from

3.8 to 6.5 µg C cm-2 h-1. Methane emission from their –15 cm water table cores ranged

from 0.016 to 0.078 µg C cm-2 h-1. Their study produced similar results to this study in that CH4 flux exhibited much greater variability than CO2 flux measurements. Their

reasoning for this was that ebullition was the primary mechanism for CH4 flux, and since

ebullition is an intermittent process, measurements of CH4 will naturally be more

variable. Ebullition was not observed during this study since soil cores were capped,

therefore it was not possible to observe the water column in any of the cores.

In this experiment, CH4 flux was approximately one-fifth the amount of CO2 flux, and therefore was a relatively minor contributor to total gaseous flux of C out of the soil.

One possible explanation for this low presence of CH4 is the oxidation of CH4 to CO2 as it moves up through the soil and reaches the anaerobic/aerobic interface (King et al.,

1990; DeBusk and Reddy, 2003). Low CH4 emission may also be due to the lack of emergent plants in the soil cores, which are a key mechanism for transporting CH4 into the atmosphere (Schutz et al., 1991). Some wetland plants allow CH4 to pass through

them, thereby avoiding aerobic soil microbes. Therefore, this experiment may

substantially underestimate the amount of CH4 production in the soil.

Since CH4 has the potential to become oxidized to CO2, CO2 flux measurements

may be overestimated while CH4 flux may be underestimated. Happell and Chanton

(1993), estimated that an average of 46% of CH4 produced in a north Florida swamp soil

was oxidized to CO2 near the soil surface. They also suggested that as wetland soil was drained, CH4 flux decreased. This study along with DeBusk (1996) did not notice a

significant decrease in CH4 flux out of soil as water table decreased.

Since CH4 production is suppressed in the presence of O2, it was expected that the

–15 cm water table would have inhibited CH4 production, although this was not the case.

A falling water table generally causes a decrease in CH4 emissions, due to lower CH4 production, greater CH4 oxidation, or both (Nykanen et al., 1998). A study conducted by

Bachoon and Jones (1992), determined that the majority of CH4 from Everglades peat

and marl soils is produced in the upper 4 cm. Freeman et al. (2002) concluded that

reduced CH4 emissions following a simulated drought in a peatland were due mainly to

its effect on methanogenesis. They proposed that CH4 diffusion through the unsaturated

soil surface was too rapid to permit an increase in CH4 oxidation efficiency due to the

low bulk density of the peat soils. The soils at ENP2 and 3A1 also have low bulk

density, therefore CH4 oxidation may be minimal.

DeBusk and Reddy (2003), considered the O2 production via algal photosynthesis

in the litter layer to be a factor in contributing to oxidation of the litter layer, and

therefore increased decomposition rate. Their experiment was conducted outdoors in

partial sunlight, whereas this experiment was conducted indoors with insufficient light to

support photosynthesis. Therefore, it is unlikely that O2 was produced in the soil cores used in this experiment. The O2 production in DeBusk’s study would explain the lower

rate of CH4 production seen in their experiment compared to this one.

During some sample dates, up to 20% of the cores had water tables that deviated

from their intended level by up to 5 cm, which may have influenced the CO2 and CH4

concentrations measured. This can be attributed to some cores either leaking water out,

or water seeping into the core, if the caps on the core did not remain airtight or watertight

for the duration of the experiment.

The use of soil microcosms devoid of living plants and environmental changes

resulted in an over simplified representation of ridge and slough soil conditions, but

provided the controlled environment necessary for measuring influence of water table on ridge and slough soil respiration rate. Future studies may want to look at in-situ soil

respiration rates, with living plants included in the mesocosm.

Conclusions

Water table plays a role in soil respiration rate of ridge and slough soils. Soil cores

respired more CO2 in the drained cores while CH4 emission was roughly the same

whether cores were flooded or drained. Given this information, it is important to manage

Everglades hydrology in a manner that is cognizant of the effects of water table on soil

respiration. Ridge and slough soil should be kept wet to minimize the loss of soil due to

oxidation. Minimizing soil oxidation is important if ridge and slough soil topography is

to be restored.

Figure 3-3. Extracting gas from core headspace.

All Cores

25 b ) -1 h -2 20 cm 2

15 a a 10

5 flux out of soil (ug CO 2 CO 0 +5cm 0cm -15cm

Figure 3-4. Mean CO2 emission based on water table +1 SD (n=16,16,16). Means with the same letter are not significantly different.

40 ) -1

h 35 -2 cm

2 30

flux out of soil (ug CO 5 2

CO 0 0 5 10 15 20 25 30 35 40 45 50 A

40 ) -1

h 35 -2 cm

2 30

flux out of soil (ug CO 5 2

CO 0 0 1020304050 B

40 )

-1 35 h -2 30 cm 2

10 flux out of soil (ug CO 2 5 CO

0 0 5 10 15 20 25 30 35 40 45 50 days since water table treatment started C Figure 3-5. Carbon dioxide emission based on water table treatment over time +1 SD. A) Water table +5 cm (n=16). B) Water table 0 cm (n=16). C) Water table -15 cm (n=16).

4 ) -1 h -2

cm 3 4

1 flux out of soil (ug CH 4 CH 0 0 5 10 15 20 25 30 35 40 45 50 A

4 ) -1 h -2

cm 3 4

1 flux out of soil (ug CH 4 CH 0 0 1020304050 B

4 ) -1 h -2 cm

4 3

1 flux out of soil (ug CH 4

CH 0 0 1020304050 days since water table treatment started C Figure 3-6. Methane emission based on water table treatment over time +1 SD. A) Water table +5 cm (n=16). B) Water table 0 cm (n=16). C) Water table -15 cm (n=16).

CHAPTER 4 SYNTHESIS OF HYDROLOGY EFFECTS ON RIDGE AND SLOUGH SOIL DEVELOPMENT

In the Everglades, hydrology is the primary physical parameter that humans can

manage to influence soil development. This cannot be overstated, and was the main

reason why this topic was addressed. It is important to understand the influence of hydrology on ridge and slough soil processes, since the Comprehensive Everglades

Restoration Plan seeks to manage hydrology in a manor that could restore the ridge and slough topographic difference. However, the best hydropattern to benefit the ridge and

slough is not currently known. Hydrology can influence several abiotic and biotic

parameters in the ridge and slough that may be a detriment or benefit to soil topography.

Hydrologic parameters differ depending upon which part of the Everglades the

ridge and slough are located. For example, the ridge and slough in the southern portion

of Shark River Slough in ENP, experiences a faster water velocity compared to northeast

Shark Slough. Average water velocity at the ENP1 and ENP2 ridge was 0.35 and

0.9 cm s-1 respectively. Average water velocity at the ENP1 and ENP2 slough was

0.5 and 0.72 cm s-1 respectively. The faster velocities exhibited at ENP2 may promote more linearity of ridges and sloughs. It is important to understand how hydropattern can

dictate the magnitude of abiotic parameters, since these parameters can help to promote

the development and maintenance of the ridge and slough.

Plants may also affect hydropattern in that they help to mix water as water flows

past them. Since the plants act as a barrier to flow, downstream eddies were noticed

51 52

when observing the dye tracer movement. This mixing of the water column may help to

deliver oxygen to the soil surface and increase soil oxidation rate. Therefore, plants can also play a role in breaking up any temperature stratification that may develop.

It is important to maintain a continuous growth of plants, especially on ridges, so that they can maintain their higher topography, and reinforce the ridge and slough

topographic difference. Soil can accrete faster in ridges, given the right hydrologic and

biologic scenario. Proper water depths and hydroperiod would favor high density and

growth rates of C. jamaicense, which provides greater litter deposition rates, leading to a

faster rate of soil accretion.

Hydrology also plays a large role in its influence on plant type that can grow in the

ridge and slough. Since some plants produce more recalcitrant litter than others (Lewis,

2005), hydrology is important to select for certain types of plants, with C. jamaicense

being favorable on ridges. Not only because it is what historically populated the ridges,

but because its high litter recalcitrance helps to accrete new soil. The difference between litter production and decomposition most likely plays a large role in soil accretion rate in

the ridge and slough. Studies are required to measure growth rates of C. jamaicense

under different hydropattern regimes, to better understand which hydropattern results in

the greatest plant growth rate, and accretion of soil. This along with keeping soils wet

enough to minimize soil oxidation can help optimize soil accretion.

Water depths, hydroperiod, and water velocity may have played greater or lesser

roles in soil topography regulation than their current influence. If physical forcing

functions such as hydrology are reduced, biological functions may play a larger role in

shaping Everglades soil topography. For example, a very strong water current (physical

forcing function) in a slough may tend to prevent plants from growing in the slough due

to high turbidity and plants not being able to root in the soil. If flow is reduced, then water clarity may increase, and plants can take root without water flow washing a plant

away. Everglades restoration objectives should take into account the proper recipe for

hydrologic management to allow the biotic factors to work in concert with hydrology to

optimize soil elevation differences between ridges and sloughs.

Water flow can play a vital role in decomposition, since flowing water is the

medium that moves nutrients and oxygen to the microbes that decompose soil organic matter. Since the Everglades is flooded most of the year, and this floodwater is flowing,

the role of flow is important in this aspect. Therefore, flow can at least be seen as a

nutrient transport medium (Sklar and van der Valk, 2003). This research aids in our

understanding of Everglades hydrology, in that any location with standing water that has

hydrologically interconnecting ridges and sloughs will have flowing water. This water

may be moving at a very slow rate (<1 cm s-1), but may still be important to the function

of the ridge and slough.

The hydrologic study in Chapter 2 helps us better understand the range of water

velocities that exist in the ridge and slough. One observation is that any surface water

has some flow to it, unless water table drops so low, that only pockets of water exist.

Water velocity was greatest in locations with the least plants in the water column. This

would suggest that the ridge and slough may best be served by a greater quantity of

submerged aquatic plants to slow the flow of water and therefore minimize the chance of water table falling below soil surface; in effect, maximizing the hydroperiod. If emergent plant density increases, this may increase evapotranspiration and therefore increase the

amount of water lost from the ridge and slough, unless this evaporated water falls back down as rain.

The greatest flows occurred at ENP2, which had the second largest topographic difference between ridge and slough (18 cm). Site 3A2 had the largest topographic difference of 25 cm, although flow was roughly half that of site ENP2. This suggests that other factors besides flow can play a role in maintaining the soil topographic difference.

Site 3A2 may experience a greater velocity and flow if the damning effect of the

Tamiami Trail was reduced.

Total suspended-solids transport aids in the translocation of organic matter, which may influence biological oxygen demand in the water column. Total suspended-solids transport may slow the soil decomposition rate if TSS are great enough to impede sunlight entry into the water column, with the resulting decrease in water column photosynthesis, which would decrease oxygen production available for aerobic microbes to rapidly decompose soil organic matter. If this event occurs, it may only be during peak flows, since the water clarity was high at all times during the TSS study. Additionally, flowing water has the potential to disrupt any thermoclines, and therefore allow oxygen rich water to reach the soil surface, where it could aid in soil decomposition.

Total suspended-solids transport was greatest at ENP2, which may partly be due to the great water velocity, which keeps particles suspended in the water column instead of settling on the soil surface. Site 3A2 exhibited a low TSS transport, and flocculant material in the slough was very easily suspended when walking about the slough. This particulate transport may become an important mechanism in peak events that may pulse a great deal of organic matter out of the ridge and slough and send it downstream.

The soil respiration study in Chapter 3 helps with our understanding of the

Everglades, in that it suggests a beneficial water table that should be maintained to

prevent excess loss of soil from the Everglades. A water table near the soil surface can

be beneficial to allow a greater rate of C. jamaicense seedling germination (Johnson,

2004). Historic water depths on the ridge may not have been too great, which would

stress C. jamaicense and reduce its ability to produce biomass. A hydrology management

regime taking into account these factors may help reestablish the soil topography that characterized the historic ridge and slough.

Hydroperiod plays a critical role in soil decomposition, since a water table decline

below soil surface greatly increases the soil oxidation rate. The soil respiration study

suggests the importance of water table management in the ridge and slough. There is a

correlation between water table and CO2 production. Under saturated soils, CO2

-2 -1 emission was 5.6 µg cm h in both the ridge and slough. Under drained soils, CO2

emission was 14.6 and 14.4 µg cm-2 h-1 in the ridge and slough respectively. Neither of

these results supported my hypothesis stating CO2 flux would be greater from slough

soils. The large increase of CO2 flux in drained soil suggests that ridge and slough soils should at least be kept saturated, since any decrease of water level below soil surface can significantly affect soil oxidation rate, especially since ridge and slough soils are almost entirely organic matter. The ridge and slough in southern WCA-3A probably releases less CO2 than the ridge and slough immediately south of Alligator Alley, where hydroperiod is reduced. Ridge and slough topography is jeopardized in this location, and may see a narrowing of topographic difference if its current hydropattern remains the same.

-2 -1 The flooded soil cores produced 0.19 and 0.59 µg CH4 cm h in the ridge and

slough respectively. Although the slough soil produced more CH4, it was not a

significant difference, therefore not supporting my hypothesis. The contribution of CH4 towards carbon loss is not as great as CO2. Therefore, flooded soils result in less loss of carbon from the ridge and slough versus drained soil. If CH4 is oxidized when moving up through the soil and water column, then CH4 may become a more significant

component of carbon loss, and deserves further study.

Everglades hydrology can be managed to provide the proper hydropattern to

optimize soil accretion with the hopes of regaining portions of the ridge and slough community that have been lost over the past several decades. This soil accretion is important not only to maintain the ridge and slough topography, but to also ward off the effects of increasing sea level, which has resulted in invasion of red mangrove

(Rhizophora mangle) into portions of Shark River Slough and Taylor Slough that have historically been populated by freshwater marsh species (Gleason, 1974). An increased amount of flow into ENP may prevent mangrove seeds from floating into ENP.

Several decades have elapsed since the Everglades was in a natural hydrologic and ecologic state. However, this natural condition is not well known. Historical accounts of the Everglades can do a fair job of recreating its historical hydrology. Several aerial photographs have been taken of the ridge and slough, and if plant species can be depicted from these, a general water depth can be discerned. It is possible that other components of hydropattern can be discerned from historical photographs of the ridge and slough.

With this data, the proper hydropattern can be implemented for the ridge and slough, which can mimic historical hydrologic conditions that the ridge and slough experienced

57 over 100 years ago. It is important to have some sense of historical Everglades hydrology, since this will also give some indication of the historical degree of soil oxidation that occurred. Restoration becomes possible once the managed hydropattern closely mimics the historical hydropattern.

Ridge and slough soil topography would perhaps develop best if Everglades hydrology is returned to its historic state. This would involve the removal of some levees, in order to recreate historic hydroperiod, water depths, flow, timing, and distribution of water. A hydrologic study of well-preserved ridges and sloughs that contain high topographic differences and representative plants could indicate what hydropattern is necessary to restore and maintain the more impaired ridges and sloughs.

This research provides insight into relationships between hydrology and the potential role it plays influencing soil accretion and decomposition. Once several key components and their interactions are understood, Everglades restoration becomes possible. Current studies of Everglades hydrology and soil should seek to understand the ramifications of a change in any one parameter and its influence on another. With this knowledge, the Comprehensive Everglades Restoration Plan can utilize hydrologic management to attempt to recreate historical forcing functions that provide the abiotic parameters which allow for biotic parameters to respond in a fashion similar to the historic Everglades. Everglades hydropattern restoration can promote the development and maintenance of ridge and slough topography. Ridge and slough topographic restoration may lead to the restoration of the ecological components that popularized the

Everglades and the impetus for creating the Everglades National Park.

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BIOGRAPHICAL SKETCH

Eric Jorczak was born sometime in the 20th century, somewhere in the northeastern

U.S. He grew fond of nature rambles at an early age. Historical accounts tell of his unabashed catching of local fauna. This led to university studies in ecology, resulting in a B.S. in biology from the State University of New York at Binghamton. He then perused the country, involved in various field-oriented jobs, and decided that the

Everglades was the place to be. After a stint with hydrology monitoring at Everglades

National Park, the professors at the University of Florida Soil and Water Science

Department graciously hosted him during his tenure as a master’s student.

A self-made man, Eric enjoys many hobbies including chainsaw juggling, hopscotch, and charades with his pet rock, “Rocky.” If you believe this, he has some swampland to sell you in the Everglades.