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Nutrient Transport in Groundwater Near Isolated Wetlands and Drainage Ditches

Permanent Link: http://ufdc.ufl.edu/UFE0020582/00001

Material Information

Title: Nutrient Transport in Groundwater Near Isolated Wetlands and Drainage Ditches Implications to Best Management Practices
Physical Description: 1 online resource (84 p.)
Language: english
Creator: Bevc, Elizabeth L
Publisher: University of Florida
Place of Publication: Gainesville, Fla.
Publication Date: 2007

Subjects

Subjects / Keywords: ditches, flux, lake, meter, okeechobee, phosphate, transport, watershed
Environmental Engineering Sciences -- Dissertations, Academic -- UF
Genre: Environmental Engineering Sciences thesis, M.E.
bibliography   ( marcgt )
theses   ( marcgt )
government publication (state, provincial, terriorial, dependent)   ( marcgt )
born-digital   ( sobekcm )
Electronic Thesis or Dissertation

Notes

Abstract: Using the Interactive Groundwater (IGW) program, computer modeling of phosphate transport from isolated wetlands into a drainage ditch provides insight into the trends of subsurface phosphate transport around isolated wetlands. The passive nutrient flux meter (PNFM) was utilized to measure groundwater and phosphate flux from isolated wetlands in the Lake Okeechobee basin. The groundwater and phosphate flux measurements were collected to provide baseline values for general phosphate flux estimates from the isolated wetlands. The phosphate flux was measured from isolated wetlands to the subsurface discharging into the drainage ditch. Field measurements from a transect of wells near a drainage ditch were also completed. The phosphate flux measurements and knowledge of the trends related to isolated wetlands and phosphate transport were used to scale up phosphate mass loads from single isolated wetlands and a drainage ditch to basin-wide phosphate mass loads. With an estimate of the area of the wetlands in the basin, the amount of phosphate retained by each wetland was calculated to provide the tons per year of phosphate loads that could be eliminated or delayed from entering Lake Okeechobee by increasing the effectiveness of best management practices (BMPs). If BMPs are focused on drainage ditches the total phosphate load to Lake Okeechobee from overland and subsurface transport through the drainage ditches could be eliminated. Basin- wide estimates of phosphate loads from isolated wetlands and drainage ditches ranged from 2 to 16 metric tons per year. The basin-wide estimates confirm that there is the possibility of reducing at the very least one to two metric tons of phosphorus per year from entering Lake Okeechobee by increasing the effectiveness of BMPs in isolated wetlands and drainage ditches.
General Note: In the series University of Florida Digital Collections.
General Note: Includes vita.
Bibliography: Includes bibliographical references.
Source of Description: Description based on online resource; title from PDF title page.
Source of Description: This bibliographic record is available under the Creative Commons CC0 public domain dedication. The University of Florida Libraries, as creator of this bibliographic record, has waived all rights to it worldwide under copyright law, including all related and neighboring rights, to the extent allowed by law.
Statement of Responsibility: by Elizabeth L Bevc.
Thesis: Thesis (M.E.)--University of Florida, 2007.
Local: Adviser: Annable, Michael D.

Record Information

Source Institution: UFRGP
Rights Management: Applicable rights reserved.
Classification: lcc - LD1780 2007
System ID: UFE0020582:00001

Permanent Link: http://ufdc.ufl.edu/UFE0020582/00001

Material Information

Title: Nutrient Transport in Groundwater Near Isolated Wetlands and Drainage Ditches Implications to Best Management Practices
Physical Description: 1 online resource (84 p.)
Language: english
Creator: Bevc, Elizabeth L
Publisher: University of Florida
Place of Publication: Gainesville, Fla.
Publication Date: 2007

Subjects

Subjects / Keywords: ditches, flux, lake, meter, okeechobee, phosphate, transport, watershed
Environmental Engineering Sciences -- Dissertations, Academic -- UF
Genre: Environmental Engineering Sciences thesis, M.E.
bibliography   ( marcgt )
theses   ( marcgt )
government publication (state, provincial, terriorial, dependent)   ( marcgt )
born-digital   ( sobekcm )
Electronic Thesis or Dissertation

Notes

Abstract: Using the Interactive Groundwater (IGW) program, computer modeling of phosphate transport from isolated wetlands into a drainage ditch provides insight into the trends of subsurface phosphate transport around isolated wetlands. The passive nutrient flux meter (PNFM) was utilized to measure groundwater and phosphate flux from isolated wetlands in the Lake Okeechobee basin. The groundwater and phosphate flux measurements were collected to provide baseline values for general phosphate flux estimates from the isolated wetlands. The phosphate flux was measured from isolated wetlands to the subsurface discharging into the drainage ditch. Field measurements from a transect of wells near a drainage ditch were also completed. The phosphate flux measurements and knowledge of the trends related to isolated wetlands and phosphate transport were used to scale up phosphate mass loads from single isolated wetlands and a drainage ditch to basin-wide phosphate mass loads. With an estimate of the area of the wetlands in the basin, the amount of phosphate retained by each wetland was calculated to provide the tons per year of phosphate loads that could be eliminated or delayed from entering Lake Okeechobee by increasing the effectiveness of best management practices (BMPs). If BMPs are focused on drainage ditches the total phosphate load to Lake Okeechobee from overland and subsurface transport through the drainage ditches could be eliminated. Basin- wide estimates of phosphate loads from isolated wetlands and drainage ditches ranged from 2 to 16 metric tons per year. The basin-wide estimates confirm that there is the possibility of reducing at the very least one to two metric tons of phosphorus per year from entering Lake Okeechobee by increasing the effectiveness of BMPs in isolated wetlands and drainage ditches.
General Note: In the series University of Florida Digital Collections.
General Note: Includes vita.
Bibliography: Includes bibliographical references.
Source of Description: Description based on online resource; title from PDF title page.
Source of Description: This bibliographic record is available under the Creative Commons CC0 public domain dedication. The University of Florida Libraries, as creator of this bibliographic record, has waived all rights to it worldwide under copyright law, including all related and neighboring rights, to the extent allowed by law.
Statement of Responsibility: by Elizabeth L Bevc.
Thesis: Thesis (M.E.)--University of Florida, 2007.
Local: Adviser: Annable, Michael D.

Record Information

Source Institution: UFRGP
Rights Management: Applicable rights reserved.
Classification: lcc - LD1780 2007
System ID: UFE0020582:00001


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NUTRIENT TRANSPORT IN GROUNDWATER NEAR ISOLATED WETLANDS AND
DRAINAGE DITCHES: IMPLICATIONS TO BEST MANAGEMENT PRACTICES


























By

ELIZABETH L. BEVC


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

2007





































2007 Elizabeth L. Bevc









ACKNOWLEDGMENTS

I want to thank my advisor, Michael Annable. Without his guidance and support this

would not have been possible. I also want to thank my parents and sister for their unending

support and encouragement. Finally, I thank Joe for his patience, understanding and support

during the research and writing process.









TABLE OF CONTENTS

page

A CK N O W LED G M EN TS ................................................................. ........... ............. 3

LIST OF TABLES ........................................ ......... ....................

LIST O F FIG U RE S ................................................................. 7

LIST OF ABBREVIATION S ................... ....... ............ ........ ................................ 9

ABSTRAC T ................................................... ............... 10

CHAPTER

1 INTRODUCTION ............... .......................................................... 12

The Lake Okeechobee Watershed Phosphate Problem .................................. ...............12
Isolated W etlands........................... ..................................14
The Basics of Phosphorus in W wetlands .................................... ............. ........ ....... 14
W wetlands P hosphate C ycle ................................................................................... ... 15
Phosphate Transport through Isolated Wetlands to Lake Okeechobee...........................16
Computer Modeling of Isolated Wetlands and Ditches............................ .................... 18

2 INTERACTIVE GROUNDWATER MODEL ........................................... ............... 23

Interactive Groundwater Program and Capabilities .................................... ...............23
IG W M odel D design and D description ......................................................................... ...... 24
IGW M odel M methods and R results ................................................ .............................. 26
H hydraulic Conductivity (K ) .............................................. ........ ......................... 26
Partitioning C efficient (K d).............................................................. ............... 27
H ead D difference (AH )................................................. .... ............. .. ..... 27
W etla n d S iz e .............................................................................................................. 2 8
D instance from W etland ..................................................... .............. .. 28
Interactive Groundwater M odel Conclusions..................................................................... 29

3 PASSIVE NUTRIENT FLUX METER FIELD DATA............... .... ......... ............... 35

S ite D e sc rip tio n ................................................................................................................ 3 5
M methods ......................... .......... ........................... ........ 36
Passive Nutrient Flux M eter Description ............................................. ............... 36
W e ll D e sig n ............................................................................................................... 3 8
PN FM D eploym ent ................. .................................... ................ .. .............39
PN FM R em oval .................................................................... .............. .. 39
A n a ly sis ..........................................................................................................4 0
R e su lts ................... ...................4...................0..........




4









W after F lux M easurem ents.................................................................. .....................4 1
Phosphate Flux Measurements ................. ........... ..... ............... 42
M measured and Calculated Data Comparisons........................................ ....... ............ 43
C onclu sions.......... ..........................................................46

4 BASIN WIDE LOADS BASED ON LOCAL FLUX MEASUREMENTS ..........................70

Basin W ide Phosphorus Calculations for Isolated W wetlands .................................................70
Comparison of Calculated Mass Load to Literature Estimates for Isolated Wetlands...........71
Phosphate Retention by Drainage Ditches .................................................. 72
Basin Wide Phosphorus Calculations for Drainage Ditches ...............................................72
C onclu sions.......... ............................... ................................................73

5 CON CLU SION .......... ................................................................. ............. ... 77

L IST O F R E F E R E N C E S ............................................... ................................... .......................8 1

B IO G R A PH IC A L SK E T C H .............................................................................. .....................84









LIST OF TABLES


Table page

1-1 Land use and net phosphorus imports in the northern Lake Okeechobee watershed........21

2-1 Hydraulic conductivity of soil determined by slug test preformed at Larson Dixie
R a n ch ............................................................................................ 3 0

2-2 Measured porewater total phosphate values for Larson Dixie Ranch ............................31

2-3 IGW m odel w etland and soil param eters................................... ...................... .. .......... 31

2-4 Partitioning coefficient values. ........................................ ............................................32

3-1 Comparison of averages and coefficients of variation between resident tracer mass
remaining on resin for Larson Dixie and Beaty wetlands............................................... 56

3-3 Comparison of averages and coefficients of variation between resident tracer mass
remaining on resin for Pelaez wetlands. ........................................ ........................ 58

3-4 PNFM Darcy flux estimates compared to the Darcy flux...................................... 65

3-5 Mass flux for each section in each PNFM and mass load estimates .............................65

3-6 Summary table of the average phosphate mass load per wetland ...............................68

3-7 Number of days water gradient was into and out of the wetlands and grams of
phosphate measured throughout deployment period. .............................. ................68

3-8 Mass flux measurements estimated from the PNFM and gradient calculations ..............68

3-9 Mass fluxes estimated from the PNFM for the Pelaez transect ..............................69

3-10 Summary table of average and estimated range for phosphate parameters.....................69

4-1 Basin wide estimates of phosphate mass loading and reduction from isolated
w wetlands ......................................................... .................................76

4-2 Basin wide estimates of phosphate mass loading from drainage ditches using a
conservative drainage ditch length.......................................................... ............... 76

4-3 Basin wide estimates of phosphate mass loading from drainage ditches using a
liberal drainage ditch length ...................................................................... ...................76









LIST OF FIGURES


Figure page

1-1 Location and land uses in the Lake Okeechobee watershed...................................20

1-2 Phosphate cycle in w wetlands ........................................... .................. ............... 21

1-3 Groundwater flow system with flow through groundwater between wetlands ...............22

1-4 Groundwater flow system with impermeable layers present. Local flow lines as well
as region al are sh ow n ............ .... ........................................................................... .. ....... .. 22

2-1 A diagram of the basic m odel layout ................................................... ..................29

2-2 The basic m odel layout ..................................................... ........ .. ............. 30

2-3 Hydraulic Conductivity versus break Through Time ................................ ...............31

2-4 Partitioning Coefficient versus Break Through Time..................... .............................. 32

2-6 Size of Wetland versus Break Through Time ...................................... ...............33

2-7 Distance from wetland versus Break Through Time .....................................................33

2-8 Distance of Ditch from Wetlands verse Break Through Time ........................................34

3 -1 L arso n D ix ie R an ch ................................................................................. ................ .. 4 7

3-2 B eaty R an ch ............................................................................... 4 8

3 -3 P e la e z R a n c h ................................................................................................................ 4 9

3-4 Cross section of PN FM installed in w ell .................................. .......................... ......... 50

3-5 Cross section of PNFM installation at Pelaez Ranch ............................. 51

3-6 Water table elevation observations for Larson Dixie Wetland 1......................................52

3-7 Water table elevation observations for Larson Dixie Wetland 2 .....................................53

3-8 Water table elevation observations for Beaty Wetland 1................................... .........54

3-9 Water table elevation observations for Beaty Wetland 2................................................54

3-10 Water table elevation observations for Pelaez Wetland 4. ..............................................55

3-11 Days and sections of PNFM's saturated throughout deployment..................................55









3-12 Water flux verse depth at Larson Dixie Wetland for each well location...........................59

3-13 Water flux verse depth at Beaty wetland for each well location. ......................................60

3-14 Water flux verse depth at Pelaez wetland for each well location. ....................................60

3-15 Water flux verse depth at Pelaez transect for each well location. ....................................61

3-16 Larson Dixie wetland 1 phosphate flux verse depth at each well location......................61

3-17 Larson Dixie wetland 2 phosphate flux verse depth at each well location......................62

3-18 Beaty wetland phosphate flux verse depth at each well location....................................62

3-19 Pelaez wetland 1 phosphate flux verse depth at each well location ................................63

3-20 Pelaez wetland 4 phosphate flux verse depth at each well location. ................................63

4-1 Lake Okeechobee drainage basins. The yellow basins are priority basins.....................75









LIST OF ABBREVIATIONS

BMP Best management practices

BTT Break through time

DWSM Dynamic Watershed Simulation Model

GIS Geographic Information System

AH Head difference

HSPF Hydrological Simulation Program-Fortran

IGW Interactive Ground Water

K Hydraulic conductivity

Kd Partitioning coefficient

m/day Meters per day

NPDS National pollutant discharge system

PFM Passive flux meter

PNFM Passive nutrient flux meter

Ppb Parts per billion

Ppm Parts per million

SFWMD South Florida Water Management District

SWAT Soil and Water Assessment Tool

TMDL Total maximum daily load

TP Total phosphate

WAM Watershed Assessment Model









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

NUTRIENT TRANSPORT IN GROUNDWATER NEAR ISOLATED WETLANDS AND
DRAINAGE DITCHES: IMPLICATIONS TO BEST MANAGEMENT PRACTICES

By

Elizabeth L. Bevc

August 2007

Chair: Michael Annable
Major: Environmental Engineering Sciences

Using the Interactive Groundwater (IGW) program, computer modeling of phosphate

transport from isolated wetlands into a drainage ditch provides insight into the trends of

subsurface phosphate transport around isolated wetlands. The passive nutrient flux meter

(PNFM) was utilized to measure groundwater and phosphate flux from isolated wetlands in the

Lake Okeechobee basin. The groundwater and phosphate flux measurements were collected to

provide baseline values for general phosphate flux estimates from the isolated wetlands. The

phosphate flux was measured from isolated wetlands to the subsurface discharging into the

drainage ditch. Field measurements from a transect of wells near a drainage ditch were also

completed. The phosphate flux measurements and knowledge of the trends related to isolated

wetlands and phosphate transport were used to scale up phosphate mass loads from single

isolated wetlands and a drainage ditch to basin-wide phosphate mass loads. With an estimate of

the area of the wetlands in the basin, the amount of phosphate retained by each wetland was

calculated to provide the tons per year of phosphate loads that could be eliminated or delayed

from entering Lake Okeechobee by increasing the effectiveness of best management practices

(BMPs).









If BMPs are focused on drainage ditches the total phosphate load to Lake Okeechobee

from overland and subsurface transport through the drainage ditches could be eliminated. Basin-

wide estimates of phosphate loads from isolated wetlands and drainage ditches ranged from 2 to

16 metric tons per year. The basin-wide estimates confirm that there is the possibility of

reducing at the very least one to two metric tons of phosphorus per year from entering Lake

Okeechobee by increasing the effectiveness of BMPs in isolated wetlands and drainage ditches.









CHAPTER 1
INTRODUCTION

The Lake Okeechobee Watershed Phosphate Problem

Lake Okeechobee is located in south Florida and has an area of 730 square miles with an

average depth of 8.6 feet (US EPA Region 4, 2006). The Lake Okeechobee watershed covers

3.5 million acres including north to south Orlando and the areas south, east and west surrounding

the lake (Figure 1-1). The lake supplies water for the surrounding agriculture, urban areas, and

environment. Lake Okeechobee provides flood protection for the surrounding community, a

mult-million dollar sport fishing industry, and habitat for wading birds, migratory waterfowl, and

the Everglades Snail Kite, an endangered animal (US EPA Region 4, 2006).

In 1986, one of the largest algae blooms ever documented covered 120 square miles of the

western quarter of the lake. It was determined that the algae bloom could be controlled by

phosphorus regulation (Rechcigl, 1997). In 2001, the Total Maximum Daily Load (TMDL)

proposed an annual load of 140 metric tons of phosphorus in order to reach the in-lake goal of 40

ppb phosphorus (FDEP, 2001). Point sources to Lake Okeechobee are regulated by National

Pollutant Discharge Elimination System (NPDES) permits and do not make up any portion of the

TMDL to Lake Okeechobee. Nonpoint sources of phosphorus to the lake include agriculture,

wildlife, septic systems, and stormwater runoff. Cattle and dairy pasture lands are the primary

agricultural activities north and northwest of the lake, while cropland, sugarcane and vegetables

dominate south and east of the lake. Agricultural activities produce 98% of the phosphorus that

is imported into the watershed (US EPA Region 4, 2006).

Land uses for the Lake Okeechobee basin can be seen in Figure 1-1. Major land uses in

the northern Lake Okeechobee watershed include improved pastures (36%), wetlands/water

bodies (21%), rangeland/unimproved pastures (16%), forested uplands (10%), citrus (5%), urban









(3%), sugarcane field (2%), dairy farm (2%), sod farm (0.9%), ornamentals (0.6%), and row

crops (0.6%) (Hiscock et al., 2003). Best management practices (BMPs) for phosphorus have

been established for all the land uses (FDEP, 2001). This paper will focus on cattle pasture

BMPs. Cattle pasture BMPs include structural improvements such as fencing and water tanks to

deter cattle from waterways, berms and culverts/risers to retain surface water on pastures, herd

and pasture management by rotational grazing, altered feeding and fertilizer regimes, and

chemical amendments (Graham, 2006).

Hiscock, Thourot and Zhang's 2003 phosphorus budget for the northern Lake Okeechobee

watershed indicated that 74% of the phosphorus inputs per year are stored on-site in upland soils

and vegetation, 26% is discharged to runoff. The net phosphate imports from each land use can

be seen in Table 1.1. Of the phosphorus inputs from the runoff 32% is stored in the wetlands and

68% is loaded to Lake Okeechobee (Hiscock et al., 2003). By retaining the runoff on the

pastures or in the isolated wetlands located throughout the watershed phosphorus is stored in the

soil instead of flowing over the pasture lands into ditches draining to Lake Okeechobee

(Gathumbi et al., 2005; Dunne et al., 2006). The isolated wetlands can also provide high quality

forage production, areas for the cattle to cool themselves, wildlife habitats and greater vegetation

productivity (Gathumbi et al., 2005).

The objective of this study was to extend field measurements collected by Hamilton (2005)

of phosphate flux from isolated wetlands in the Lake Okeechobee watershed. Additional

wetland sites were assessed and a drainage ditch instrumented to quantify phosphate flux. The

field measurements of phosphate flux provide a baseline for a general phosphate flux estimate

from the isolated wetlands. Computer modeling of phosphate transport through groundwater

provides insight into subsurface phosphate transport trends between isolated wetlands and the









drainage ditch. With the estimated phosphate flux from isolated wetland and knowledge of the

trends related to isolated wetlands and phosphate transport the phosphate loads were scaled up

from the phosphate retention capacity of a single isolated wetland and drainage ditch to

determine the Lake Okeechobee watershed's retention capacity for phosphate though water

retention in isolated wetlands. With an estimate of the area of the wetlands in the basin, the

amount of phosphate retained by each wetland was calculated to provide the tons per year of

phosphate inflows that could be eliminated or delayed from entering Lake Okeechobee with an

increase in retention time of surface water runoff. The objectives of the research were to:

Model groundwater flow and phosphate transport between an isolated wetland and the
drainage ditch discharging from the wetland under varying conditions

Quantify and compare phosphate flux around five isolated wetlands on ranch lands (two
conducted as part of this study) and a transect of a drainage ditch on ranch lands

Scale up the findings to provide a basin-wide conclusion about the benefits of water
detention in isolated wetlands for reduction of phosphate to Lake Okeechobee and
phosphate loads attributed to groundwater discharge to drainage ditches.

Isolated Wetlands

The Basics of Phosphorus in Wetlands

Phosphate in soil is a key ingredient in productive agricultural lands however natural

topsoil is often phosphate deficient, 0.05-1.1 g phosphate kg-1 soil (Reynolds and Davies, 2001).

The common primary inorganic forms of phosphate in soil are apatite and phosphates of

aluminum and iron. These inorganic forms become bioavailable as soil water soluble reactive

phosphates after weathering and dissolution. Plants readily take up and assimilate the soil water

soluble reactive phosphates. However the plants are competing with the soluble reactive

phosphate's mineral binding affinity. The inorganic phosphate becomes a part of secondary

minerals, not bioavailable to plants, such as hydrous sesquioxides, amorphous iron, aluminum









oxides or hydroxides. Phosphorus in biomass of plants may eventually find its way back to the

soil by leaf-fall, decomposition, consumption or excrement by animals.

Phosphate levels in natural soils are quite stable and low which leads to fertilization for

agriculture and subsequently runoff of phosphates into nearby water bodies. Non-point inputs of

bioavailable phosphate from agricultural lands have been shown in several studies to be a major

contributor to phosphate loading of drainage waters (Reynolds and Davies, 2001).

Wetlands Phosphate Cycle

Naturally occurring inputs of phosphate into wetlands include surface inflows and

atmospheric deposition. Outputs of phosphate include surface runoff and infiltration to

groundwater. Phosphorus is found in wetlands in many different forms and interconversions of

these forms occur.

Figure 1-2 depicts the phosphate cycle in a wetland including the storage and transfers of

phosphate. Soluble reactive phosphate can be converted to tissue phosphate by plants or sorbed

to wetland soils and sediments. Insoluble phosphate precipitates form and may re-dissolve under

certain conditions (Kadlec and Knight, 1996). Wetland vegetation plays a large role in

phosphate assimilation and storage. Because of rapid turnover the phosphate storage is short

term and phosphate is released during plant decomposition. While some vegetation absorbs

phosphate directly from the water column most uptake phosphorus from the soil porewater

creating gradients between the phosphorus in soil porewater and the water column. When the

concentration of phosphate in the water column is higher than in the soil or sediment porewater

the phosphate diffuses into the sediment/soil (Reddy et al., 1999).

The principal phosphate compounds found in wetlands are dissolved phosphate, solid

mineral phosphate, and solid organic phosphate. The principal inorganic species of phosphate

are related by pH-dependent dissolution series:









H3PO4 = H2P04- + H
H2PO4- = HP04-2 + H
HP04-2 = PO4-3 + H

Some important phosphate precipitate cations that are found in wetlands under certain

conditions include: apatite (Ca5(C1,F)(P04)3), hydroxylapatite (Ca5(OH)(PO4)3), variscite

(Al(P04)(2H20)), strengite (Fe(P04)2H20), vivianite (Fe3(P04)28H20), and wavellite

(A13(OH)3(P04)2(5H20)). Phosphate also forms co-precipitates with other minerals such as

ferric oxyhyroxide and carbonate minerals. Overall phosphate mineral chemistry is very

complex (Kadlec and Knight, 1996).

Wetlands can serve as sources or sinks for phosphate depending on the soils sorption

capacities. Fluctuating waterlogged and drained conditions on wetlands can alter the redox

potential and thus retention and release phosphate occurs. The redox potential is influenced by

organic matter input and affects phosphate solubility (Reddy et al., 1998).

Phosphate Transport through Isolated Wetlands to Lake Okeechobee

Phosphate is transported first from the surrounding environment into the ditches and

isolated wetlands that eventually drain to Lake Okeechobee. Isolated wetlands are depressions

that have no permanent connection to the surrounding water bodies. However, intermittent

overland flow, subsurface flow and drainage ditches can hydrologically connect the isolated

wetlands to surrounding water bodies and other wetlands (Dunne et al., 2003). Overland and

subsurface flow transports phosphate both into the isolated wetlands from the surrounding

environments and out of the wetland into the surrounding environment (Reddy et al., 1999).

Campbell et al. documented phosphorus transport by runoff and groundwater during large and

small rainfall events on several experimental pasture sites (Campbell et al., 1995).

Phosphate inputs to the Lake Okeechobee watershed are primarily in the form of pasture

fertilizer and dairy feed (Hiscock et al., 2003). Advective transport is the main transport process









that moves phosphorus from the surrounding environment overland and through the drainage

ditches into the isolated wetlands. Land with lower relief has a tendency to flood and discharge

phosphorus by overland flow to ditches (Campbell et al., 1995).

Subsurface transport of phosphate by advective transport depends on the velocity of

groundwater flow. Land with greater relief, more rapid groundwater flow and little overland

flow generates subsurface discharges of phosphate to ditches and wetlands (Campbell et al.,

1995). Groundwater flow is driven by the water pressure gradient or hydraulic head between the

saturated soil surface and the aquifer. The velocity of groundwater flow is affected by the soils

hydraulic conductivity (Reddy et al., 1999). Winter and LaBaugh illustrated how elevation and

impermeable soil layers effect groundwater flows between isolated wetlands in Figures 1-3 and

1-4 (Winter and LaBaugh, 2003). The spodic layer can simulate the impermeable layers

depicted in Figure 1-5. The spodic layer in the Lake Okeechobee watershed is very tight

however in some locations there are holes or voids in which water can move easily. Horizontal

water movement can occur entirely above or below the spodic layer as well as intersect the

spodic layer and flow above and below the spodic layer (Haan, 1995). The vertical flows of

groundwater are driven by gravity and plant uptake to support transpiration (Reddy et al., 1999).

Once in the isolated wetlands, horizontal flows from diffusion and dispersion processes

move the phosphate through the isolated wetlands (Reddy et al., 1999). Phosphate is mobilized

in the isolated wetlands between sediments and the overlying water column by advection,

dispersion, diffusion, seepage, resuspension, sedimentation and bioturbation (Reddy et al., 1999).

Advective transport through either ditch flow or subsurface flow transports phosphate from

the surrounding environment into ditches and isolated wetlands that drain to Lake Okeechobee.









Computer Modeling of Isolated Wetlands and Ditches

Recently the Watershed Assessment Model (WAM) was applied to evaluate the effects of

water detention in depressions on a beef cattle ranch in the Lake Okeechobee watershed. WAM

is a physically based model that performs watershed-related hydrological and water quality

analyses. Land use, soil, weather, and land management practices were all input into WAM with

the use of Geographic Information System (GIS) functions which overlay the ranch features

(Zhang et al., 2006).

The WAM modeled a 3,295-ha area that included improved, unimproved, semi-improved,

woodland pastures, wetlands, upland forest, and citrus land uses were included. A major

drainage canal surrounds three sides of the modeled area and several rainfall stations are in the

area. Water quality parameters included soluble nitrogen, particulate nitrogen, groundwater

nitrogen, soluble phosphorus, particulate phosphorus, groundwater phosphorus, sediment

phosphorus and biological oxygen demand (Zhang et al., 2006).

WAM used the above input and output parameters to assess the stormwater retention for

three pasture land uses that were suitable to retain water for the ranch. The stormwater storage

was simulated by defining a detention depth or the ratio of detention depth to land use area. The

stormwater storage was assumed to be low lying areas or existing wetlands. Several scenarios

using detention depths of 0.25 and 0.5 inches and the three land uses were evaluated.

Overall, it was found that a 20% reduction in phosphorus load can be accomplished with a

detention range of 0.25 to 0.5 inches over all three land uses. A reduction of 16% of phosphorus

load was found when 0.25 inch detention depth was used on all the land types. While use of 0.25

inch on the beef pastures, 0.5 inch on the woodland and unimproved pastures provided a 19%

reduction in phosphorous levels. A 4% reduction in phosphorus load was found with a detention

depth of 0.25 inch for the unimproved and woodland pastures. With an increase in detention









depth to 0.5 inch over the two land uses the percent reduction in phosphorus moves to 7%

(Zhang et al., 2006).

The applicability of the above study to this research is obvious and the most relevant study

found pertaining to the assessment of BMP's or isolated wetlands through computer modeling.

The use of computer models to simulate water quality including the phosphorus cycle was

evaluated in Borah and Bera's Water-Scale Hydrologic and Nonpoint-Source Pollution Models.

Review of Applications (Borah and Bera, 2004).

Borah and Bera selected three models from an evaluation of eleven to provide a review of

each model's numerous applications. SWAT, or Soil and Water Assessment Tool, is a model for

long-term continuous simulations in predominately agricultural watersheds. SWAT's

applications indicated the primary use for phosphorus modeling is assessing the impacts of dairy

management practices on dairy manure phosphate loading. The third model is DWSM, or

Dynamic Watershed Simulation Model, is a storm event simulation model for agricultural and

suburban watersheds. DWSM provided an application showing the effects to phosphorus loads

during storm events (Borah and Bera, 2004).

Including phosphorus loading applications of models in the three models reviewed

indicates that there is on going work towards more accurate phosphorus loading in groundwater

modeling. Arnold and Fohrer's review of SWAT2000 suggested that future work should

strengthen SWAT2000's phosphorus interactions with soils and different soil types (Arnold and

Fohrer, 2005).
















Lardti


rliyBan
Dai ry 9i 1a
ary
i rm ft iM


allrvmSmd Bpr.Ame





F .^ ;- ,















S0 m. 18 27 lo S -
SCD FIMs


PNWID

































FIgra Land WUa Type In te Lak Okeechobuo Waterhed




Figure 1-1. Location and land uses in the Lake Okeechobee watershed (Guan et al., 2007).
Figure 1-1. Location and land uses in the Lake Okeechobee watershed (Guan et al., 2007).










Table 1-1. Land use and net phosphorus imports in the northern Lake Okeechobee watershed.
Land use Area Phosphate net import
Ha tons/year


Abandoned dairy
Citrus
Commercial forestry
Dairy
Field crop
Forested upland
Golf course
Improved pasture
Ornamentals
Rangeland
Residential
Row crops
Sod farm
Sugarcane
Unimproved pasture
Wetland
Water and other land uses
Total


2,344
25,392
13,299
8,525
2,276
49,887
377
183,778
3,212
46,641
9,740
2,868
4,816
8,755
33,453
95,423
25,215
516,000


-2
458
16
-8
4
558
30
1
151
545
-235
9
0
0
0
1,717


Hiscock, J. G., Thourot, C. S., Zhang, J., 2003. Phosphorus Budget-land use relationships for
the northern Lake Okeechobee watershed, Florida. Eco. Eng., 21: 63-74, Table 2.


Inoaai P \. Oran" P \
.orthophoLph ae) \ -- POnho,' r issok opnho ar'rPdate
Orga. P Fr, li-org_ P
(dissolved,prt.rul-e___ or Ca D C-.-.. -- m Deirs lortp hoasp
Oniho-P Plant ua -----
--- 7--7-


IShort-ten :rm : Lonig-ternm X

:: phohate moifrabi o- : (POt retei-t-in) (pea ) I ::::::::-)::: "::

Figure 1-2. Phosphate cycle in wetlands (IFAS, 1999).




















1 -,

0--


Figure 1-3. Groundwater flow system with flow through groundwater between wetlands (Winter
and LaBaugh, 2003).





CTERSB Lira r Isalh local l e
,,sn: ftmps ec oh ,, rd .I ..e't r f 'l
h e ir*M, nnNr- *cW tow &FO'i -
Ee3'CV~a

3iI.


0 20 4M000 BDa am i.3 12iR000 314AX I
ME TEFS


Figure 1-4. Groundwater flow system with impermeable layers present.
as regional are shown (Winter and LaBaugh, 2003).


Local flow lines as well


W4 k~rfo4


MwTE
METERS


LOM. 12.w 141M, i.Go"









CHAPTER 2
INTERACTIVE GROUNDWATER MODEL

Interactive Groundwater Program and Capabilities

The Interactive Groundwater (IGW) Model is a software package for real time, unified

deterministic and stochastic 2D and 3D groundwater modeling (Li and Liu, 2006). The IGW

Model eliminates the bottlenecks in traditional modeling technologies allowing the full

utilization of today's increased computing power (Li and Liu, 2003). Efficient computational

algorithms allow IGW to simulate complex 2D and 3D flows and transport in saturated aquifers.

These flows and transport mechanisms are subject to systemic and "random" stresses as well as

geological and chemical heterogeneity (Liao et al., 2003). The IGW Model was utilized for this

analysis due to its real-time modeling, visualization and analysis capabilities.

The IGW Model was utilized to model phosphate transport in groundwater from isolated

wetlands towards an outflow ditch. Water budgets preformed for the wetlands indicate

groundwater recharge from the isolated wetland (Perkins and Jawitz, 2007). Transport variables

were identified and assessed as major factors to phosphate transport. The effect of each variable

on phosphate break through time (BTT) was determined. Phosphate BTT was investigated to

evaluate how long phosphate is detained by isolated wetlands due to transport through the

groundwater. The management practice investigated here is the use of structures at the outlet of

wetlands or filling in of ditches to retain water in the wetlands for longer time periods. The

transport variables used in the IGW model include media hydraulic conductivity, phosphate

partitioning coefficient, head difference between wetland and outflow ditch, wetland size and

ditch distance from wetlands. By exploring the effects the variables have on the phosphate BTT

the practices designed for detention of water in isolated wetlands can be evaluated.









IGW Model Design and Description

The basic design of the model was a circular wetland with a single ditch leaving the

wetland. Located along the ditch, several groundwater monitoring wells provided observations

of phosphate concentration over time. These observation points are used to determine BTT. For

the base case the wetland was modeled as approximately 180 meters in diameter and the ditch

was 375 meters in length. The basic layout of the model can be seen in Figure 2-1.

The wetland was created within IGW as one layer with two zones. A zone enables the

modeler to assign physical and chemical properties, sources, sinks, and aquifer elevations. The

whole grid or work space was assigned a zone and given Lake Okeechobee soil characteristics;

this will be referred to as the aquifer zone. The wetland was created by defining a circular zone

and assigning wetland characteristics. The wetland boundary was overlain by a polyline to

enable a constant head to be assigned to the wetland perimeter. The ditch was also represented

as a polyline and begins two grid cells or 24 meters below the wetland edge. The wetland and

ditch are separated to enable accurate flow lines to be depicted, Figure 2-2. Monitoring wells

were placed along the ditch.

The aquifer in the soil and wetland zones was assigned a surface elevation often meters, a

top elevation of ten meters and a bottom elevation of eight meters. This represents an aquifer

that is two meters saturated thickness similar to the wetlands used in this study.

The soil and wetland parameters assigned to the zones include hydraulic conductivity,

partitioning coefficient, effective porosity, phosphate concentration in the wetland and phosphate

concentration in the porewater. A literature search was completed on each parameter to provide

the best values for the Lake Okeechobee basin isolated wetlands. The variables were selected to

facilitate model runs to establish functional relationships. Once established those relationships

were used to assess parameters appropriate to for the sites.









The range applied for hydraulic conductivity was based on slug tests preformed at Larson

Dixie Ranch (Bhadha, 2006). The results of the slug test are shown in Table 2-1; see Figure 3-1

for well locations. The measured hydraulic conductivity from four wells surrounding the

wetland ranged from 0.08 to 0.25 m/day. The average hydraulic conductivity of the wells is 0.15

m/day. The IGW model used a hydraulic conductivity of 100 m/day to facilitate model run

times.

Soil tests for phosphate partitioning coefficient were not available for the Lake

Okeechobee wetland sites. Thus a phosphate partitioning coefficient for a similar wetland was

used 4.94e-3 m3/kg (Reddy et al., 1995).

A study of south Florida found the porosity of the aquifers to be 0.3 (Meyer, 1989). A

porosity of 0.3 was used throughout the IGW model.

The concentration of phosphate in the wetland water found on the Larson Dixie site ranged

from on average 2 to 3 ppm (Bhadha, 2006). This range is based on depth profiles measured for

total phosphate in the wetlands. The total phosphate value was used since the measured

dissolved and soluble reactive phosphate measurements were similar values to the total

phosphate.

Groundwater samples were collected from November 2004 to March 2005 from specific

monitoring wells at Larson Dixie Ranch, see Figure 3-1 for well locations (Perkins, 2006). The

total phosphate concentrations in the groundwater are shown in Table 2-2. Groundwater samples

of total phosphate in LW2MW1, LW2MW2 and LW2MW6 provided a range of values as well

as an average for these monitoring well. LW2MW3, LW2MW4 and LW2MW5 had only one or

two samples providing only an average total phosphate concentration. An overall average of

0.33 ppm and overall range is 0.1 to 1 ppm is calculated. To simplify the IGW model the initial









phosphate concentration in groundwater was assumed to zero. This allows for the model to

determine the net effect of detaining water in the wetlands.

IGW Model Methods and Results

The IGW modeling objective was to assess the effect of system variables on the phosphate

transport time through the aquifer to the drainage ditch. The modeling results provide estimates

on how long holding water is the wetland will delay loads to Lake Okeechobee. The transport

variables evaluated in the IGW model include aquifer hydraulic conductivity, phosphate

partitioning coefficient, head difference between the wetland and ditch, wetland size and ditch

distance from wetland.

The BTT is the time at which ten percent of the original concentration of phosphate in the

wetland is found in the monitoring wells located along the ditch. The wetland phosphate

concentration in all runs was 3 ppm thus the BTT is defined as the year that 0.3 ppm is found in

the monitoring wells located along the ditch.

Each transport variable was evaluated in the model independently, that is no other

parameters were changed in the model during the specific runs. Table 2-3 shows the parameters

used throughout the runs unless otherwise discussed below.

Hydraulic Conductivity (K)

Hydraulic conductivity (K) is a main transport variable effecting the BTT of phosphate.

Model runs were completed with K from 50 to 250 meters per day in 50 unit increments. Two

monitoring wells were placed along the ditch at 100 and 250 meters from the wetlands. The

results of the runs are displayed in Figure 2-3; the best fit lines characterize the inverse

relationship observed.









Partitioning Coefficient (Kd)

The partitioning or distribution coefficient, relates the amount of solute, or phosphorus in

the model, sorbed onto the soil to the amount that is dissolved in water (Liao et al., 2003). This

measure of phosphate partitioning was evaluated to determine how much of a difference one

degree of freedom has with regards to BTT. Seven partitioning coefficients were evaluated and

are shown in Table 2-1. Two monitoring wells were placed along the ditch at 100 and 250

meters from the wetlands. Figure 2-4 shows the general trend of increasing partitioning

coefficient increasing BTT. After regression analysis, R2=0.997 and R2=1, indicating a near

perfect linear relationship between partitioning coefficient and BTT.

Head Difference (AH)

A weir between the outlet of the wetland and the ditch can be manipulated to increase the

amount of water held in the wetland. This forces more water to flow through the aquifer rather

than directly through surface water. This variable was manipulated by changing the head

difference between the wetland and ditch polylines. The wetland constant head boundary was

arbitrarily assigned 100 meters while the ditch constant head boundary changes to enable the

effect of head differences to be observed. The ditch constant head boundary changes from 99.0

to 99.75 meters in 0.25 meter increments.

The monitoring well that observed the BTT was located 100 meters from the wetland.

Figure 2-5 depicts the observations of the phosphorus BTT with changing head difference

including a best fit line depicting the power relationship. Generally as the head difference

between the wetland and the ditch become smaller the longer the time required for the phosphate

to reach 100 meters from the wetland in the ditch.









Wetland Size

Several different size wetlands were modeled to determine the influence of wetland size on

phosphate transport time to the drainage ditch. Wetland sizes of 50, 100, 200 and 400 meters in

diameter were modeled. The BTT was found at four points along the ditch from monitoring

wells placed at 24, 104, 184, and 264 meters from the wetland. Figure 2-6 shows that there is

little effect on BTT with an increase in wetland size until larger wetland sizes are reaches such at

400 meters in diameter.

Distance from Wetland

Four monitoring wells were placed long the ditch at 80 meters a part beginning at 20

meters from the wetland. The model was run and the BTT was found for each well. The BTT

approximately doubled from well to well as it covered the same distance. This can be seen in

Figure 2-7.

An instantaneous BTT for the well at 20 meters from the wetland (Figure 2-7) can be

misleading. Figure 2-8 shows the actual BTT is reached around two months and not

instantaneously. Figure 2-8 is created from the plume mass balance provided by the IGW model.

The ditch's starting point was moved by 25 meters for each run beginning at 25 meters and

ending at 100 meters from the wetland. This enabled the BTT to be found on the plume mass

balance for the four different ditch starting points. The distance from the wetland relates to a

BMP of filling in the drainage ditch which requires the water to flow underground to reach the

drainage ditch. Figure 2-8 clarifies that the phosphate takes time to flow underground to the

ditch. The lines indicate that filling the drainage ditch in by about 20 meters the BTT is near 1.5

years.










Interactive Groundwater Model Conclusions

Inverse relationships were found between the BTT and hydraulic conductivity and head

difference. Linear relationships were found between the BTT and partitioning coefficient and

the distance from the wetland. The wetlands size showed very little effect on BTT unless the

wetland diameter became larger then 400 meters which was larger than the six isolated wetlands

studied in the Lake Okeechobee basin.







'Homogeneous Aquifer


Constant Head'B'oundary

Circular Wetland





Seperation between
S Ditch and Wetland




Monitoring Wells Constant Had B oundry



..





Figure 2-1. Diagram of the basic model layout it shown above with the wetland shown in black
and the ditch in green leaving the wetland below. Two monitoring wells, in yellow,
are shown along the ditch.







































Figure 2-2. Basic model layout is shown above with the wetland shown in black and the ditch in
green leaving the wetland below. The red within the wetland indicates the highest
phosphate concentration. Two monitoring wells, in yellow, are shown along the
I I
I. -





























into the ditch.

Table 2-1. Hydraulic conductivity of soil determined by slug test preformed at Larson Dixie
Ranch


Well ID
LWMW2
LWMW5
LWMW3
LWMW6
LWMW1
soil surrounding wetland:


Measured hydraulic conductivity
cm/hr m/day
1.100
0.520
0.340
0.490
0.130
0.060


Average in


0.25
0.13
0.08
0.12
0.03
0.15


Bhadha, J., 2006. Dixie Larson Ranch: Wetland Measured Phosphate Concentrations and
Hydraulic Conductivity. Unpublished raw data.).










Table 2-2. Measured porewater total phosphate values for Larson Dixie Ranch


Well ID


Range of total phosphate (ppm) Average total phosphate
(ppm)


LW2MW1 0.42 to 0.66 0.51
LW2MW2 0.12 to 1.02 0.36
LW2MW3 -- 0.37
LW2MW4 -- 0.34
LW2MW5 -- 0.12
LW2MW6 0.11 to 0.42 0.25
Perkins, D.B., 2006. Dixie Larson Ranch: Porewater Phosphate Concentrations. Unpublished
raw data.

Table 2-3. IGW model wetland and soil parameters
Model and soil parameters Value used
Hydraulic conductivity (K) 100 m/day
Wetland size 180 meters
Partitioning coefficient (kd) 4.94e-3 m3/kg
Effective porosity 0.3
Head difference (AH) 1 meter
Constant phosphorus concentration in the
wetland 3ppm


1000
900-
800 -
700 -
8 600
S500-
S400
300 -
200 -


0 -
-


50 100


150
K (m/day)


200


Figure 2-3. Hydraulic Conductivity versus Break Through Time


*Well 1 at 100 meters from
wetland
Well 2 at 250 meters from
wetland








*
"; !U









Table 2-4. Partitioning coefficient values.
Partitioning coefficient values liters per
kilogram
4.94e-6
2.00e-6
3.5e-6
4.94e-7
4.94e-8
4.94e-9
0.0


100
90
80
70
S60
s50
S40
30
20
10
0


0.00E+00 1.00E-06 2.00E-06 3.00E-06 4.00E-06 5.00E-06 6.00E-06
Kd (m3/g)


Figure 2-4. Partitioning Coefficient versus Break Through Time


80
70
60 -
50
-40-
-30
20
10
0


y = 17.232X-09971


Figure 2-5. Head Difference versus Break Through Time


0 0.25 0.5 0.75
Changing Head (m)










450
400
350
300
250
200
150
100
50 -
0 -
o


200 300
Wetland Size (m)


Figure 2-6. Size of Wetland versus Break Through Time


140

120 -

400 -

80

60 -

40

20-

0 -


50 100 150 200
Delta X (m from wetland)


Figure 2-7. Distance from wetland versus Break Through Time


x


SWell 1 at 24 meters from wetland
X
Well 2 at 104 meters from wetland
Well 3 at 184 meters from wetland
X X X Well 4 at 264 meters from wetland


* U


400


250


300










4.5
4 U
3.5
3
>2.5
S2
1.5 -

1l-
0.5
0
0 20 40 60 80 100 120

Displaced Ditch Distance from Wetland (m)


Figure 2-8. Distance of Ditch from Wetlands verse Break Through Time









CHAPTER 3
PASSIVE NUTRIENT FLUX METER FIELD DATA

Site Description

Three ranches, Larson Dixie, Beaty and Pelaez Ranch, were used to test the Passive

Nutrient Flux Meter (PNFM). Field data was collect at Larson Dixie and Beaty Ranches in July

2005 by Kelly Hamilton and at Pelaez in September 2006 (Hamilton, 2005). All the ranches are

located within the Lake Okeechobee watershed in Okeechobee County, Florida. The ranches all

support cow-calf operations and allowed access to the sites for continuous research. The three

ranches all have drained, isolated wetlands with connecting ditches that transport water off the

ranch. The wetlands have fluctuating water levels depending on rainfall events. The local water

table and thus the wetland water levels fluctuate from flooded to dry often within a few days to

weeks. All three ranches are dominated by Myakka-Immokalee-basiner soils. These soils are

poorly drained, nearly level, sandy soils that dominate most of Okeechobee County (Lewis et al.,

2001). The ranches are dominated by Bahia grass (Paspalum natatum Fluegge') (Dunne et al.,

2006).

Larson Dixie Ranch is located at N 0270 20.966', W 080056.465', Beaty Ranch is located

at N 0270 24.665', W 0800 56.940' and Pelaez Ranch is located at N 270 16.422', W

080056.453' (Google Earth, 2007). The wetlands, well locations, flumes and general layout of

each of the ranches are shown in Figures 3-1-3-3. The well identification numbers describe the

location and type of well such as LW2MW5 describes a monitoring well located at Larson Dixie

wetland 2 or PTFM5 describes a flux meter well at the Pelaez Ranch transect.









Methods


Passive Nutrient Flux Meter Description

The Passive Flux Meter (PFM) technology is a method of determining contaminant and

groundwater fluxes in the saturated zone of an aquifer (Hatfield et al., 2004). The PFM has been

laboratory and field tested at hazardous waste sites and proven to be a reliable measure of fluxes

(Annable et al., 2005). The PNFM has been designed to measure nutrient fluxes including

phosphorus (Cho et al., 2007). The PNFM may provide a means to decrease the cost and time

necessary in measuring nutrient fluxes in groundwater.

After deployment and recovery, the PFM samples are collected and analyzed for the mass

of tracer remaining and the mass of contaminant intercepted which are used to calculate the local

cumulative water and contaminant fluxes (Annable et al., 2005). If reversible, linear,

instantaneous resident tracer partitioning takes place between the sorbent and water, the specific

discharge (q) through the PFM at a specific well depth can be found by equation 3-1:


[q= 61.6(1-M )]

t (3-1)
where r is the radius of the flux meter cylinder, 0 is the water content of the flux meter sorbent,

Rd is the retardation of the resident tracer on the sorbent, MR is the relative mass of the tracer

remaining within the flux meter, and t is the sampling duration (Annable et al., 2005).

The contaminant mass flux (Jc) can be determined by using equation 3-2:



c acI (3-2)


where q is the specific discharge, Mc is the mass of contaminant sorbed, a is the convergence or

divergence of flow around the flux meter, r is the radius of the flux meter cylinder, L is the









length of the sorbent matrix, MRc is the relative mass of a hypothetical resident tracer retained

after time period t where that tracer has the same retardation as Rdc. Equation 2 assumes

reversible, linear and instantaneous contaminant partitioning between the sorbent and the water

(Annable et al., 2005). For a more in depth discussion on the PFM technology see Annable et

al., 2005, Hatfield et al., 2004, or Cho et al., 2007.

The PNFM and PFM use similar designs including a permeable, sorptive media contained

in a cylindrical casing which fits snugly into wells below the water table. The sorbent in the

PNFM facilitates rapid adsorption and desorption of inorganic and organic substances. The

PNFM uses a strongly basic, macroporous-type, anion exchange resin known as Lewatit S 6328

A (Sybron Chemicals Inc Birmingham, NJ). Lewatit S 6328 has a matrix consisting of cross-

linked polymer made of styrene and divinylbenzene with a relatively uniform charge distribution

of ion-active sites throughout the structure (Cho et al., 2007).

The sorptive media was equilibrated with alcohol tracers that desorb as groundwater flows

through the device. The alcohol tracers provide the groundwater flux while the resin allows for

measurement of phosphorus flux. The alcohol tracers suite used at Larson Dixie and Beaty

Ranch included 2,4-dimethyl-3-pentanol, 1-Hexanol, 1-Heptanol, 1-Octanol, 2-Octanol and 2-

ethyl-1-hexanol (Hamilton, 2005). Pelaez Ranch used 1-Hexanol, 1-Heptanol, and 1-Octanol as

the alcohol tracers.

Figure 3-4 shows a cross section of a PNFM installed in a well. The device is made with

an inner PVC rod, clamps at the bottom and top holding in place a nylon mesh sock filled with

the resin. The PNFM was designed to be approximately 91 cm long with a diameter of 3.18 cm.

The length used was based on the well screen intervals ranging from 107 to 201 cm. The PNFM









was divided into four sections to help reduce vertical flow, each about 23 cm containing an

estimated 240 ml of resin.

At the Pelaez Ranch, monitoring wells were constructed with an inside joint protruding

into the well requiring modification of the PNFM deployment method. A nine foot long

expandable protective netting (Cole-Parmer Poly-Net U-09405-30) was used with a second three

foot section of netting located around the bottom end of the nine foot length to assist in inserting

the PNFM through the well joint. The nine foot and three foot sleeves were inserted into the

well so that the three foot section was below the well joint. Then a PNFM with a third layer of

protective netting was inserted into the well through the nine foot section to seat adjacent to the

three foot section at the bottom of the well. This technique allowed the PNFM to slide easily

past the well joint yet still fit snuggly to the well walls due to the three layers of expandable

mesh. See Figure 3-5 for a cross section of the installed PNFM. The diameter of the Pelaez

Ranch PNFM's was 5.08 cm and all other specifications of the PNFM were the same as PNFM

used at Larson Dixie Ranch and Beaty Ranch.

Well Design

At the Larson Dixie and Beaty Ranches the flux wells were installed using a hand auger,

most were located an estimated one meter from a monitoring well. The monitoring wells were

used to obtain water samples for phosphorus measurements and to deploy transducers to monitor

water levels. PVC pipe (3.175 cm diameter) and sections of well screen ranging from 122 to 152

cm long were used to construct the wells. See Figures 3-1 and 3-2 for well locations. The well

casing was terminated at ground level to protect from animal disturbances. The wells were

covered with a 20 cm PVC cap even with the ground surface (Hamilton, 2005).

The Pelaez Ranch wells were installed using a hollow stem auger drill rig with radius of

5.08 cm and depths similar to Larson Dixie and Beaty Ranch. Most of the flux wells were paired









with shallow monitoring wells screened to a depth of one to two feet and were above the spodic

horizon. All of these wells were dry during the PNFM deployments. Pelaez Ranch well

locations are shown in Figure 3-3.

PNFM Deployment

Deployment of the PNFM took place at all sites during wet periods. At the Larson Dixie

Ranch several wells (LW1MW8, LW2MW2, LW2MW4, LW2MW5) were submerged at the

time of deployment. In this case, a PVC coupler with a casing extension was used to insert the

PNFM (Hamilton, 2005). In total, seven PNFM were deployed at Larson Dixie Ranch, five

around one wetland and two around the second wetland. Four PNFMs were deployed at the

Beaty Ranch, two at each wetland. See Figure 3-1 and 3-2 for well locations. Water table values

were recorded throughout the deployment period at Larson Dixie Ranch and Beaty Ranch. The

PNFM's at Larson Dixie and Beaty Ranch were deployed for a period of 34 days.

Eighteen PNFMs were deployed at the Pelaez Ranch, four around each wetland and ten at

the transect crossing the ditch location. See Figure 3-3 for well locations. Water table levels

were recorded for five of the wells. The Pelaez Ranch PNFM's were deployed for a period of 33

days.

PNFM Removal

All the ranches used the same removal technique. The PNFMs were extracted from the

wells fully intact. Then the resin was carefully removed in sections from the sock. In a clean

bowl, each 20 cm section of the PNFM was mixed to homogenize the sample. Two samples of

the resin were taken from the homogenized mixture and added to vials with extraction solution.

The first vial contained 60 ml of 2M KC1 in a 125 ml sample bottle with approximately 25 g of

resin added. The second sample was approximately 10 g placed into 30 ml isopropyl alcohol in a

40 ml sample vial. Each of the 4 sections per PNFM were sampled in this manner. All vials









were pre-weighed then weighed after the samples were collected to determine the mass of

sample added. All the samples were rotated and equilibrated for 24 hours.

Analysis

The amount of residual alcohol tracer was determined by subsampling the isopropyl

alcohol vial after it had settled for 24 hours. This sample was analyzed using a gas

chromatograph to obtain the concentration of each tracer.

A 5 ml sample was obtained from the top of the 2M KC1 vial after settling for 24 hours and

used for the Total Phosphorus (TP) (Hach Method 8190, 2003). The TP method was used since

many of the samples had an organic color that would interfere with the Orthophosphate Method

8178 (Hach Method 8178, 2003). The TP method, while still using colorimetric comparison,

was based on the change in color intensity once the reagents were added as opposed to the

Orthophosphate Method that compared the color change intensity in the vial to a single

calibration measurement at the beginning of sampling.

Sources of error within the PNFM application can be significant. Error can be potentially

generated at any step in the process. Water table fluctuations can interfere with the sorption and

cause volatilization of the resident tracers. Not obtaining a homogenous mixture of resin during

the retrieval process can introduce error. The analysis stage may introduce error when fine

particles stay suspended within the solution after extraction. Care must be taken to ensure

settling of the particulates.

Results

The water table elevations during the deployment periods for each of the wetlands are

shown in Figures 3-6 to 3-10. Water table elevation data was not obtained for Pelaez wetland 1.

The water table observations were used to obtain gradient calculations and

exposure/submergence durations for the PNFMs in each well, see Figure 3-11. From these









observations it is clear that some of the PNFMs had a greater volume of resin within the

saturated zone then others. The desaturated zones of the PNFMs may result in volatilization of

the alcohol tracers and inaccurate flux estimates.

Washers were installed in the PNFMs to prevent vertical flow however several storm

events at each of the sites may have created periods of desaturation and saturation. Figure 3-11

shows that the Beaty and Pelaez sites remained saturated throughout the deployment. Pelaez

water table elevations were based on wetland water levels as opposed to well water levels thus

the saturation times have been interpolated for all of Pelaez wetland 4 wells. Wells LW2MW6

and LW2MW5 were not paired with transducers and the water table elevations were interpolated

for these locations. At the Larson Dixie sites, the rapid water table fluctuations interfered with

phosphorus and water flux measurements to a depth of 90 cm. The locations of the PNFM in the

Larson wells dictated whether the water table fluctuations interfered with the flux measurements.

Water Flux Measurements

Since the groundwater flux was unknown at each of the wetlands a suite of several resident

tracers were applied to the resin in the PNFMs. The average mass remaining and the coefficients

of variation for each tracer used at Larson Dixie and Beaty Ranches are shown in Table 3-1. For

the Larson Dixie and Beaty Ranch deployment it was determined that 1-Heptanol would provide

the most reliable water flux data. The coefficients of variation are compared among the mass

remaining in each PNFM. For Larson Dixie and Beaty sites 1-Heptonal and 2-Octanol had the

smallest variations. However, 2-Octanol had more mass remaining than the initial concentration

thus the data is considered unreliable. The 1-Octanol had similar results to 1-Heptanol with

more variation between fluxes and provided a similar flux pattern but within a larger range (0.01

to 0.06 m/day) (Hamilton, 2005).









The average mass remaining and the coefficients of variation for each tracer used at Pelaez

Ranch are shown in Table 3-2. The largest quantity of mass remaining for the alcohol tracers at

the Pelaez site was 1-Octanol. However for the PNFMs used in wells PW1FM21, PW1FM25

and PW4FM11 1-heptanol had the most mass remaining thus 1-heptanol was used to determine

the water flux at those locations. The water flux was determined to be higher at the Pelaez site

thus in the future a shorter deployment time should be used in order to ensure that more tracer

mass remains to improve accuracy of the water flux measurements.

The water flux profile with depth based on the PNFM deployment for each of the wetlands

is relatively constant around 3 cm/day at the Larson Dixie and Beaty wetlands as shown in

Figures 3-12, and 3-13. More variation in water flux is seen at the Pelaez Ranch with a range

from 0 to 7.5 cm/day, Figure 3-14. While a constant water flux with depth is expected the

Larson Dixie sites were unexpectedly similar. Either the water flux was as constant as reported

or all the wells were exposed to similar biological activity that reduced all the 1-Heptanol to the

same level of remaining mass within the PNFMs. Additional deployments would be helpful to

validate the results.

Pelaez wells PTFM1-10 provide phosphate flux along a transect of the ditch which drains

the wetland and surrounding areas, see Figure 3-3 for well locations. The water flux along the

transect is shown in Figure 3-15 and has a similar range to Pelaez Ranch wetlands.

Phosphate Flux Measurements

Phosphate mass flux found for each well, grouped by wetland, can be seen in Figure 3-16

through 3-20. Larson Dixie and Beaty Ranch's phosphate flux shows a very distinguished trend

where the phosphate flux increases closer to the ground surface and the remains at a constant low

value at deeper depths. No trend can be seen from Pelaez wetland 1 phosphate flux which may

be due to the distance between wells and the wetland. The Pelaez wetland 4 indicates a trend of









increasing phosphate flux as depth increases. The difference in trends between Pelaez wetland 4,

Larson Dixie and Beaty wetlands maybe due to land practices or differing water flux between

sites.

The phosphate flux along the Pelaez ditch site transect is shown in Figure 3-21. Figure 3-

21 indicates there that there are higher phosphate fluxes on the east side of the ditch then the

west side and on average the phosphate flux is higher along the ditch then in the flux observed at

the wetlands. The east side also shows a similar trend to Larson Dixie and Beaty wetlands in

that the phosphate flux is higher at the surface and remains a constant low value at deeper depths.

The west side of the transect shows a trend of similar to Pelaez wetland 4 where the phosphate

flux increased with depth. This variation in phosphate flux maybe due to land use practices or

different water flux on each side of the ditch, shown in Figure 3-15. In future deployments along

the transect transducers should be used to observe the surrounding water table to determine the

direction of groundwater flow into or out of the drainage ditch.

Measured and Calculated Data Comparisons

The Darcy Flux was measured directly from the PNFM were compared to values

calculated using Darcy's Law (equation 3-3), Table 3-3.

dh
q -K dl (3-3)


Where q is Darcy flux (cm/day), K is the hydraulic conductivity (cm/day) and dh

represents the change in head over a distance dl (cm). The gradients, or dh/dl, were determined

using the average change in head difference during the time of deployment from the water table

data (Figures 3-6 to 3-10) and dividing by average radius of the wetland. The radius of each

wetland was estimated using aerial imagery from Google Earth. While slug tests preformed at









Larson Dixie Ranch provided an average hydraulic conductivity of 0.15 m/day, 3 m/day was

used to calculate Darcy flux. The larger hydraulic conductivity of 3 m/day provided comparable

estimates to the measured Darcy flux values (Bhadha, 2006).

The Darcy flux averages presented in Table 3-3 indicate that the calculated Darcy fluxes

are less than those measured using the PNFM. The measured Darcy flux is very consistent at all

the sites with the Pelaez sites having a slightly higher Darcy flux. The calculated Darcy flux has

a wider range of values possibly due to the difference in size of the wetlands or the variability in

the quality and quantity of water table data. Recall that Pelaez wetland 4 does not have any

water table observations thus the gradient could not be calculated for the wetland.

Mass load (mg/day) was calculated from the local contaminant mass flux (Jc) values

presented in Tables 3-1 and 3-2. Jc was calculated using equation 3-2. The mass load, Mo, was

calculated by multiplying J, by the vertical cross sectional area of flow from the wetland,

equations 3-4.


Mo = J, x 2r x depth (3-4)

Where r is the radius from the center of the wetland to the PFM wells and depth is the

length of the PFM, 3 feet or 0.91 meters for all the PNFMs. The J, and Mo for each section of

NPFM for each well, average mass load per well and average mass load for each wetland is

provided in Table 3-4. Table 3-5 provides a summary of the average mass load from the wetland

to the aquifer for each wetland in g/day.

The range of mass loads per wetland is from 0.82 to 3.23 g/day. Pelaez wetland 1 is by far

the largest wetland thus has the largest mass load. Beaty wetland 2 has the lowest mass load

which maybe due to the well placement being north of the wetland and the wetland draining

south.









The water table plots were used to determine the flow into and out of the wetlands, Figures

3-6 to 3-10. When the water table is above the ground surface the water is flowing into the

wetland. When the water table is below ground level, which is the majority of the time, the flow

is out of the wetland, Table 3-7. The grams of phosphate transported into and out of the wetland

are calculated from the average wetland mass loads determined in Table 3-5 and can be found in

Table 3-6. The cumulative mass phosphate leaving the wetlands range from 25 to 95 grams

during the deployments, 33 to 34 days ,and it is assumed that the majority of phosphate is

leaving the wetlands through groundwater flow. During future deployments surface water

phosphate samples taken during the deployment period would enable verification of phosphate

transport mechanisms.

Table 3-8 shows the mass flux measured by the PNFM and the mass flux found from

calculated Darcy velocity using total phosphate measurements at each well. The mass of

phosphorus that left the wetland through groundwater was estimated through an initial total

phosphate sample at the surface of the wetland during the deployment of the PNFMs. The

concentration was then multiplied by the volume of water in the wetland resulting in a mass.

The calculated mass flux on average is higher than the measured mass flux. The calculated mass

flux could be better estimated with more samples of total phosphate since this is based on only

one measurement. The Larson Dixie wetland 1 and Beaty wetland 1 both had total phosphate

levels greater than one milligram per liter which explains their larger values. The mass flux

estimated at Pelaez transect is on average much larger than the mass flux the wetlands, Table 3-

9. Wells PTFM3, PTFM4, PTFM5, PTFM6, PTFM7 and PTFM8 are within a meter of the

drainage ditch with PTFM7 and PTFM8 having larger mass flux than any of the average wetland

values.









Conclusions

The data provided above allow a range of estimated phosphate parameters, including

Darcy flux, mass loads and mass flux per wetland and mass flux per ditch, to be established for

wetlands and ditches, Table 3-10. Water flux for Larson Dixie and Beaty Ranches were

consistently around 3 cm/day while Pelaez Ranch had a larger range of water flux, from 0 to 7.5

cm/day. The Pelaez Ranch transect shows a similar range in water flux to the Pelaez wetlands.

Phosphate flux was found to increase closer to the ground surface at Larson Dixie and Beaty

Ranches while Pelaez Ranch showed the inverse trend at one wetland and not distinct trend at the

other wetland. The Pelaez Ranch transect had higher phosphate flux then the wetlands and

higher phosphate flux on the east side of the drainage ditch.

The measured Darcy flux is very consistent at all the sites with the Pelaez sites having a

slightly higher Darcy flux. The calculated Darcy flux had a wider range of values then the

measured Darcy flux. The mass loads per wetland range from 0.82 to 3.23 g/day. Pelaez

wetland 1 has the largest mass load. The cumulative mass phosphate leaving the wetlands during

the deployment ranges from 25 to 95 grams. The calculated mass flux on average is higher than

the measured mass flux. The mass flux estimated at the Pelaez transect is on average much

higher than the mass flux in the wetlands.

Additional deployments are needed to validate the results presented here. Further

deployments should include a more comprehensive set of surface water samples and water table

measurement.




















Fence

L-W1-FI 1 L-W1-FL2


L-W1-MW6 \ L-W2-MW3
X. L-W1-MW5 T *L-W2-FM3
.* \' L-W2-MW5
L-W1- 4 0 L-W2-MW6
L-W- 7 T L-W2-FM5
T *W L L-W2-M V1 L-W2-FM6
S\
L-W1-FM7 L-W1-FM
L-W1-MW8 L-W2-MW2 T L-2-MW4
\* L-W2-FM2
L-W1-MWOO X L-W2-FM4
L-W1-MW2 L-baroe 1 L-W2-FL1
L-Weather
Highway L-W2-FL2

Retention
pond 0.6 miles



Figure 3-1. Larson Dixie Ranch The highlighted wells contained PNFM and the red T indicates
a transducer in the monitoring well.
















B-W2-FM

T
B-W1-MW5 B-W1-MW2
B-W2-FM5 B-Wl-MW1
T

B-W2-FM B-W1-MW3
*


B-W1-MWOO
*


T B-W2-MW2
a B-W2-FM2


SAccess Road
*


D.
(D
ft .
*,
*.


Ditc' B-W1-FL

Ditch" B-W1-FL2


B-W2-MW5
*B-W2-FM5


B-baro
B-W2-FL1
< *B-Weather

Ditch' B-W2-FL2


SB-W2-FM


0.8 miles


Figure 3-2. Beaty Ranch The highlighted wells contained PNFM and the red T indicates a
transducer in the monitoring well.






































PTFM2 PTFM4 N T

PTFM1 PTFM5 0.28 miles
Figure 3-3. Pelaez Ranch All the flux meter (FM) wells contained PNFM and only wetland 4
contained a transducer in the wetland.






















WT


.- &BDrirng


Screened Interval


Figure 3-4. Cross section of PNFM installed in well (Hamilton, 2005).


_____j

















Water Table







2nd Mesh Layer
3' Long ___


~II~
.x.


_-----st Mesh Layer
9' Long




Well
Joints


3-3rd Mesh Layer
Attached to NPFM


Screened

Interval


Figure 3-5. Cross section of PNFM installation at Pelaez Ranch.














0.5
0.4 W
.4 --LW1MW4
0.3 _____
0.2 --- LW1MW7
0.1 "W. -"


0.1
-0.5
-01.1 ---
-0.2 "
-0.3
: -0o.4
o -0.5
-0.6
-0.7 __ _
-0.8 _
-0.9 U, ,
1 -- -- -- --_ -_
-1.1 ----
-1.2
-1.3
-1.4
-1.5
7/17 7/19 7/21 7/23 7/25 7/27 7/29 7/31 8/2 8/4 8/6 8/8 8/10 8/12 8/14 8/16 8/18 8/20 8/22 8/24

Date 2005

Figure 3-6. Water table elevation observations for Larson Dixie Wetland 1.












0.1


-0.1


-0.3

-0.4




~. -0.7
-0.8 _

-0.9 ____ _

-1 -- LW2MW1-

-1.1 --- LW2MW3-

-1.2 --LW2MW4

-1.3 L W2MW2

-1.4 -
7/17 7/19 7/21 7/23 7/25 7/27 7/29 7/31 8/2 8/4 8/6 8/8 8/10 8/12 8/14 8/16 8/18 8/20 8/22 8/24


Date 2005

Figure 3-7. Water table elevation observations for Larson Dixie Wetland 2.













































7/17 7/19 7/21 7/23 7/25 7/27 7/29 7/31 8/2 8/4 8/6 8/8 8/10 8/12 8/14 8/16 8/18 8/20 8/22 8/24

Date 2005


Figure 3-8. Water table elevation observations for Beaty Wetland 1.


-0.1
-0.2
-0.3
-0.4
-0.5
-0.6
-0.7
-0.8
-0.9
-1


7/17 7/19 7/21 7/23 7/25 7/27 7/29 7/31 8/2 8/4 8/6 8/8 8/10 8/12 8/14 8/16 8/18 8/20 8/22 8/24

Date 2005

Figure 3-9. Water table elevation observations for Beaty Wetland 2.


-BW2MW2

--BW2MW2
-- BW2MW 1















-0.6


-0.7


-0.8


Q -0.9


-1 -


-1.1


-1.2
9/7 9/11 9/15


9/19 9/23 9/27 10/1 10/5 10/9
Date 2005


Figure 3-10. Water table elevation observations for Pelaez Wetland 4.





40
U days saturated

35


30 -


25 -_
i-

S20
U,

15 -


10 -



5-
0



10- N 1`-- I
5 -) --- In



hi hi hi hi hi hi -i m m g
20 cm sections of each PNFM (top-bottom) saturated

Figure 3-11. Days and sections of PNFM's saturated throughout deployment.











Table 3-1. Comparison of averages and coefficients of variation between resident tracer mass
remaining on resin for Larson Dixie and Beaty wetlands.


Well ID


LW2MW4 avg

std
cv
LW2MW6 avg
std
cv
LW2MW3 avg
std
cv
LW2MW5 avg
std
cv
LW2MW2 avg
std
cv
LW1MW8 avg
std
cv
LW1MW7 avg
std
cv
BW1MW5 avg
std
cv
BW1MW2 avg
std
cv
BW2MW2 avg
std
cv
BW2MW5 avg
std
cv


Mass
remaining
2,4 DMP

0.334
0.142
0.424
0.065
0.014
0.222
0.371
0.168
0.453
0.400
0.142
0.354
0.243
0.213
0.876
0.105
0.065
0.616
0.276
0.054
0.198
0.003
0.001
0.194
0.077
0.016
0.210
0.073
0.016
0.213
0.020
0.003
0.164


Mass
remaining
1-heptanol

0.179
0.007
0.038
0.163
0.027
0.167
0.160
0.019
0.116
0.151
0.017
0.113
0.166
0.016
0.097
0.149
0.016
0.111
0.159
0.019
0.117
0.128
0.014
0.107
0.153
0.006
0.038
0.180
0.041
0.229
0.123
0.020
0.166


Mass
remaining
2-octanol

1.099
0.048
0.044
0.892
0.074
0.083
1.131
0.080
0.070
1.181
0.136
0.115
0.990
0.201
0.203
0.936
0.131
0.139
0.915
0.157
0.171
0.663
0.073
0.110
0.889
0.023
0.026
0.651
0.088
0.136
0.750
0.127
0.169


Mass
remaining
2E1H

0.979
0.034
0.035
0.940
0.175
0.186
0.837
0.355
0.424
1.131
0.356
0.315
0.556
0.417
0.749
0.826
0.297
0.360
0.396
0.078
0.196
0.122
0.121
0.993
0.592
0.200
0.338
0.941
0.120
0.127
0.313
0.067
0.215


Mass
remaining
1-Octanol

0.571
0.159
0.278
0.462
0.047
0.102
0.318
0.060
0.188
0.273
0.093
0.340
0.326
0.076
0.234
0.338
0.031
0.090
0.365
0.036
0.099
0.403
0.093
0.232
0.328
0.015
0.045
0.345
0.080
0.232
0.182
0.031
0.168











Table 3-1. (continued)


Well ID


All Wells avg
std


Mass
remaining
2,4 DMP

0.179
0.148
0.829


Mass
remaining
2-octanol


Mass
remaining
1-heptanol

0.155
0.018
0.116


Mass
remaining
2E1H-


0.918
0.178
0.194


Mass
remaining
1-Octanol

0.356
0.100
0.282


0.694
0.320
0.461











Table 3-2. Comparison of averages and coefficients of variation between resident tracer mass
remaining on resin for Pelaez wetlands.
Well ID Mass remaining Mass remaining Mass remaining
1-hexanol 1-heptanol 1-Octanol


P


P


P


PTFM1 avg
std
cv
PTFM2 avg
std
cv
PTFM3 avg
std
cv
PTFM4 avg
std
cv
PTFM5 avg
std
cv
PTFM10 avg
std
cv
PTFM9 avg
std
cv
PTFM8 avg
std
cv
PTFM7 avg
std
cv
PTFM6 avg
std
cv
W4FM19 avg
std
cv
W4FM17 avg
std
cv
W4FM15 avg


0.013
0.008
0.585
0.024
0.004
0.151
0.004
0.005
1.236
0.006
0.008
1.325
0.010
0.010
0.986
0.000
0.000
NA
0.000
0.000
NA
0.000
0.000
NA
0.002
0.003
1.732
0.003
0.005
2.000
0.011
0.019
1.732
0.075
0.102
1.352
0.060


0.189
0.034
0.181
0.220
0.020
0.089
0.174
0.096
0.550
0.074
0.072
0.975
0.175
0.042
0.242
0.118
0.019
0.162
0.023
0.028
1.197
0.039
0.024
0.609
0.066
0.032
0.490
0.106
0.063
0.593
0.116
0.109
0.938
0.278
0.174
0.626
0.302


0.525
0.041
0.077
0.566
0.049
0.086
0.559
0.120
0.215
0.222
0.149
0.674
0.445
0.050
0.111
0.452
0.020
0.044
0.269
0.137
0.509
0.189
0.023
0.121
0.231
0.039
0.169
0.493
0.065
0.133
0.340
0.126
0.369
0.485
0.218
0.450
0.636










Table 3-3. (continued)
Well ID


std
cv
PW4FM13 avg
std
cv
PW4FM11 avg
std
cv
PW1FM25 avg
std
cv
PW1FM23 avg
std
cv
PW1FM21 avg
std
cv
All Wells avg
std
cv


Mass remaining
1-hexanol
0.066
1.103
0.042
0.013
0.305
0.454
0.212
0.467
0.111
0.101
0.908
0.018
0.007
0.411
0.253
0.018
0.070
0.062
0.121
1.958


Mass remaining
1-heptanol
0.119
0.395
0.325
0.035
0.108
0.714
0.245
0.343
0.379
0.216
0.570
0.152
0.031
0.204
0.440
0.062
0.141
0.221
0.186
0.843


Mass remaining
1-Octanol


0.162
0.255
0.674
0.029
0.043
0.807
0.155
0.193
0.667
0.242
0.362
0.348
0.060
0.173
0.528
0.087
0.164
0.474
0.198
0.418


- LW2MW4
-- LW2MW6
LW2MW3
LW2MW5
-- LW2MW2
-*-LW1MW8
- LW1MW7


1 2 3
Water Flux (cm/day)


Figure 3-12. Water flux verse depth at Larson Dixie Wetland for each well location.


0
-

I-30
-


S-60
C-

-90
E
5

.-120

150


















-30


-60


-90


-120


-13U iI
0 1 2 3 4

Water Flux (cm/day)

Figure 3-13. Water flux verse depth at Beaty wetland for each well location.


-100


1 2 3 4 5

Water Flux (cm/day)


Figure 3-14. Water flux verse depth at Pelaez wetland for each well location.


-- BW1MW5
-- BW1MW2
BW2MW2
BW2MW5


I














-10


-40






t -70
--PTFM1 ---PTFM4

PTFM2 PTFM9

--PTFM7 ---PTFM10

-100
0 1 2 3 4 5 6 7 8 9 10

Water Flux (cm/day)

Figure 3-15. Water flux verse depth at Pelaez transect for each well location.


LW1MW7 LW1MW8


0 0


-30 -30


S-60 --60


-90 -90


-120 -120


-150 -150
0 5 10 0 5 10
P Flux (mg/m2/day)


Figure 3-16. Larson Dixie wetland 1 phosphate flux verse depth at each well location.












LW2MW2


0



-30



-60



S-90



e- -120


0 10
0 5 10


LW2MW3


-Yu



-120


-150
0 5 10


LW2MW4


0 5 10


P Flux (mg/m2/day)


LW2MW5


0



-30



-60


-90



-120



-150
0 5 10


LW2MW6


0 1


-90



-120


-150
0 5 10


Figure 3-17. Larson Dixie wetland 2 phosphate flux verse depth at each well location.


BW1MW2


BW1MWS


BW2MW2


-90


-120


-I- -150
5 10 0

P Flux (mg/m2/day)


S 10
5 10


0 0



-30 --30



-60 -60



-90 -90


] -120
S-120


150 -150
-150
0 5 0
P Flux (mg/m2/day)


Figure 3-18. Beaty wetland phosphate flux verse depth at each well location.


BW2MW5


0


j-30
C,

I-60

1
-90

i
1120


-150
0












PW1FM23








/)


-100 i I
0 2 4 6


-100 I I
0 2 4 6
0246P Flux (mg/mday)
P Flux (mg/m2/day)


0 2 4 6
0 2 46


Figure 3-19. Pelaez wetland 1 phosphate flux verse depth at each well location

PW4FM11 PW4FM13 PW4FM15 PW4FM17


-10


-lO-100 I -100 1 0I
-100 2 4 6 0 2 4 6 -1
0 2 4 6 P Flux (mg/m2/day) 0 2 4 6
Figure 3-20. Pelaez wetland 4 phosphate flux verse depth at each well location.


10



-40



-70



-100
0 2 4 6


PW4FM19


PW1FM25


PW1FM21


I






PTFM9 PTFM10


I


-0 -1I -100 0 I 5 1 -100 -1i 0 -
0 5 10 0 5 10 0 5 10
0 2 10 0 5 10
0 5 P Flux (mg/m2/day) P Flux (mg/m2/day)
Figure 3.21. Pelaez transect phosphate flux verse depth at each well location. Note: The axis
for phosphate flux on well PTFM9.


















64


PTFM1 PTFM2


PTFM7


PTFM4


I










Table 3-4. PNFM Darcy flux estimates compared to the Darcy flux estimated by the calculated
gradient (K=3 m/day).
Wetland Darcy flux estimated by the PNFM Darcy flux estimated by calculated gradients
cm/day cm/day


LW1
LW2
BW1
BW2
PW1
PW4
Average


3.10
3.06
3.14
3.06
4.60
4.08
3.51


3.98
3.29
1.36
2.19

1.70
2.50


Table 3-5. Mass flux for each section in each PNFM and mass load estimates using the areas of
the wetland.


Wetland ID
LW1MW7
LW1MW7
LW1MW7
LW1MW7
LW1MW8
LW1MW8
LW1MW8
LW1MW8
LW2MW2
LW2MW2
LW2MW2
LW2MW2
LW2MW3
LW2MW3
LW2MW3
LW2MW3
LW2MW4
LW2MW4
LW2MW4
LW2MW4
LW2MW5
LW2MW5
LW2MW5


mg/m2/day


6.4
8.5
4.8
5.5
4.7
6.6
9.3
11.9
2.2
3.3
5.3
8.7
0.6
0.8
0.5
1.0
1.5
0.9
0.4
1.1
1.6
1.2
1.6


Mass load
mg/day
2425.0
3213.2
1816.9
2089.7
1781.5
2516.5
3543.6
4521.5
1009.5
1537.6
2422.0
4010.1
260.1
360.0
250.7
452.3
700.0
426.3
193.6
486.0
714.9
553.0
746.6










Table 3-5. (continued)
Jc*
Wetland ID mg/m2/day
LW2MW5
LW2MW6
LW2MW6
LW2MW6
LW2MW6
BW1MW2
BW1MW2
BW1MW2
BW1MW2
BW1MW5
BW1MW5
BW1MW5
BW1MW5
BW2MW2
BW2MW2
BW2MW2
BW2MW2
BW2MW5
BW2MW5
BW2MW5
BW2MW5
PW1FM25
PW1FM25
PW1FM25
PW1FM25
PW1FM25
PW1FM23
PW1FM23
PW1FM23
PW1FM23
PW1FM21
PW1FM21
PW1FM21
PW1FM21
PW1FM21
PW4FM19


Mass load
mg/day
2368.2
2175.2
1969.3
1212.0
2905.2
995.3
1359.8
1438.2
3699.4
72.5
639.1
973.7
931.7
55.5
45.8
52.3
71.6
2246.0
2096.1
735.6
1243.8
3921.9
2100.3
4041.6
3247.3
3129.7
5112.5
9296.0
4439.8
6282.8
0.0
0.0
66.6
323.6
130.1
593.3









Table 3-5. (continued)
Jc*
Wetland ID mg/m2/day
PW4FM19
PW4FM19
PW4FM19
PW4FM17
PW4FM17
PW4FM17
PW4FM17
PW4FM17
PW4FM15
PW4FM15
PW4FM15
PW4FM15
PW4FM13
PW4FM13
PW4FM13
PW4FM13
PW4FM13
PW4FM11
PW4FM11
PW4FM11
PW4FM11


Mass load
mg/day
1148.7
3565.6
1769.2
172.2
0.0
0.0
1897.0
632.3
466.3
193.7
2976.2
1212.0
38.1
35.1
73.4
2319.3
809.3
3644.9
4472.2
5410.2
4509.1










Table 3-6. Summary table of the average phosphate mass load per wetland.
Average phosphate
Wetland mass load
g/day
LW1 2.74
LW2 1.24
BW1 1.26
BW2 0.82
PW1 3.23
PW4 1.45

Table 3-7. Number of days water gradient was into and out of the wetlands and grams of
phosphate measured throughout deployment period.


Wetland Gradient in Gradient out


days


days


LW1
LW2
BW1
BW2
PW4


Cumulative
Phosphate in Phosphate out at
phosphate


grams


30.0
32.5
30.0
33.0
33.0


grams


11.0
1.9
5.1
0.8
0.0


grams


82.2
40.2
37.9
27.0
47.8


93.1
42.1
43.0
27.8
47.8


Table 3-8. Mass flux measurements estimated from the PNFM and gradient calculations.


Wetl s PNFM measurement
Wetlands
mass flux

mg/m2/day


LW1
LW2
BW1
BW2
PW1
PW4
Average


7.46
2.09
2.83
1.83
1.75
1.74
2.71


Mass flux found from Darcy
velocity and TP concentration

mg/m2/day
64.060
8.020
14.820
7.220

0.120
5.898









Table 3-9. Mass fluxes estimated from the PNFM for the Pelaez transect.
Pelaez transect wells PNFM measurement mass flux
mg/m2/day
PTFM1
PTFM2
PTFM3
PTFM4
PTFM5
PTFM6
PTFM7
PTFM8
PTFM9
PTFM10
Average


0.67
5.33
7.23
1.36
4.00
5.48
10.93
8.93
20.62
10.11
7.47


Table 3-10. Summary table of average and estimated range for phosphate parameters.
Average Estimated Range
Darcy Flux (cm/day) 3.51 2.00 4.75
Mass Load per wetland (g/day) 1.79 1.00 3.50
Mass Flux per wetland (mg/m2/day) 2.71 1.50 8.00
Mass Flux per ditch (mg/m2/day) 7.47 0.75 14.00









CHAPTER 4
BASIN WIDE LOADS BASED ON LOCAL FLUX MEASUREMENTS

The field data collected from the six wetlands were used to create a basin-wide estimate of

the total amount of phosphorus exchange between groundwater and isolated wetlands in the

basin. The amount of phosphorus that could be reduced to Lake Okeechobee by detaining more

water in the wetlands for a longer period of time was estimated to be similar to the measured

fluxes. To estimate the amount of phosphate that could be stopped from reaching Lake

Okeechobee the phosphate parameter numbers from Table 3-10 were applied to the priority

basins of the Lake Okeechobee watershed.

The priority basins, S-65E, S-65D, S-154 and S-191 have consistently produced the

highest levels of phosphorus concentrations of all the tributary basins to Lake Okeechobee

(SFWMD and USEPA, 1999). The priority basins have abundant cow calf operations. The

priority basins account for 12% of the land area in the Lake Okeechobee watershed, see Figure

4-1, and 35% of the phosphorus entering the lake (Dunne et al., 2006). The Lake Okeechobee

Action Plan of 1999 states that if the priority basins met their target loads the phosphorus loading

into Lake Okeechobee could be reduced by over 100 tons per year (SFWMD and USEPA, 1999).

Basin Wide Phosphorus Calculations for Isolated Wetlands

By using the characteristics of the six wetlands studied, an estimate of the amount of

phosphorus produced by the all the wetlands located within the priority basins was calculated.

Seven percent of the land surface in the priority basins is reported as isolated wetlands (Dunne et

al., 2006). The priority basin's total area is 974 square miles (SFWMD and USEPA, 1999).

Thus there are an estimated 68 square miles of isolated wetlands within the priority basins. The

average area of the Larson Dixie and Beaty ranch's four wetlands was determined by area

measurements taken over a month's time at the wetlands on Larson Dixie and Beaty Ranches









(Perkins, 2005). The average area of the four wetlands was 7,900 square meters. Thus there is

an approximate 22,400 individual isolated wetlands in the priority basins.

By taking the average and range of phosphate mass flux shown in Table 3-9 and

multiplying them by the number of individual isolated wetlands estimated for the basin, the

estimated mass load average and range is calculated, Table 4-1. The phosphate mass load

estimated represents the priority basin's total phosphate mass load between isolated wetlands and

groundwater. This calculation produces phosphorus mass load range for the priority basins of

2.6 to 14 metric tons per year with an average of 4.69 metric tons per year, Table 4-1.

Comparison of Calculated Mass Load to Literature Estimates for Isolated Wetlands

Based on other studies, if the detention of water in the isolated wetlands is capable of

decreasing the mass load approximately 4 to 20 percent then between 0.10 to 2.77 metric tons

per year will not reach Lake Okeechobee, see Table 4-1 (Zhang et al., 2006). South Florida

Water Management District studies indicate that small on-site wetlands can potentially remove

between 25 to 80% of the phosphorus they receive which would increase the anticipated

phosphorus removal seen in Table 4-1 (SFWMD and USEPA, 1999). The Lake Okeechobee

Annual Report for 2005 indicated that retaining water on a 410 acre wetland reduces phosphorus

by 1.2 metric tons per year, a 71% reduction (Grey et al., 2005).

Literature estimates for phosphate reduction from water detention in isolated wetlands

range from 4 to 80% of the wetlands phosphorus stored in the wetland. With such a broad range

it is obvious that more studies are needed to confirm the effectiveness of water detention in

isolated wetlands to reduce phosphate loads. However, the reduction of 100 metric tons per year

of phosphate that the Lake Okeechobee Action Plan of 1999 discusses is out of the range of the

above estimates (SFWMD and USEPA, 1999). SFWMD and USEPA may also have taken into

consideration other phosphate BMPs.









Phosphate Retention by Drainage Ditches

Similar to isolated wetlands, drainage ditches can serve as a source or sink for phosphorus.

As a temporary phosphorus sink, erosion and overland flow can transport inorganic, organic and

dissolved phosphorus into drainage ditches. The reducing conditions that occur with the

accumulation of standing water in the ditches may enhance solubilization of sediment bound

phosphate into drainage ditches (Sallade and Sims, 1997). Phosphorus rich sediments, newly

soluble phosphorus and organic matter can accumulate in drainage ditches until storm events

transport the materials out of the ditch system.

The phosphate flux measurements obtained from the ditch transect at Pelaez Ranch were

used as a representative measurement of phosphate flux along drainage ditches in the Lake

Okeechobee priority basins. By using an estimate of the length of ditches in the priority basins

and multiplying by the phosphate discharge flux the mass load of phosphate from drainage

ditches in the priority basins was estimated. The mass load of phosphate from the drainage ditch

was compared with the mass load of phosphate from the wetlands to determine if best

management practices should be applied to the ditches or if focus should remain on the isolated

wetlands.

Basin Wide Phosphorus Calculations for Drainage Ditches

Table 4-2 depicts the average and the range of phosphate mass flux from wells PTFM3 to

PTFM8, which run parallel to the drainage ditch. To determine the phosphate mass load in the

priority basin the total length of drainage ditches was required. Estimates of the total length of

drainage ditches were sparse. The greatest ditching density found for unimproved pastures,

improve pasture, intensively managed pastures and citrus and row crops was 18 km/km2 (Haan,

1995). To determine the maximum amount of phosphorus from the drainage ditches it was

assumed that all of the area in the priority basins has the greatest ditching density for land uses.









By multiplying the ditching density by the area of the priority basins a drainage ditch length of

45,000 km was determined. Steinman and Rosen describe the total linear meters of canals in the

watershed north of Lake Okeechobee to be 4,000 km (Steinman and Rosen, 2000). Calculating

the mass loads with each estimate of ditch length results in very different numbers. Both

estimates of drainage ditch length were used in order to create a range of possible phosphate

mass loads from drainage ditches into Lake Okeechobee.

To obtain a mass load, the discharge area the drainage ditches was required. The discharge

area was found by using the one meter depth that the PNFM measured and multiplying it twice

to represent each side of the drainage ditch. This provides a phosphate mass load of 4 and 31

metric tons per year with an average of 18 metric tons per year, Table 4-2.

Using the larger drainage ditch length of 45,000 km, the phosphate mass load range

increased to 22 to 362 metric tons per year, see Table 4-3. From the estimates of phosphate

loads from drainage ditches in Lake Okeechobee is shown that there was a greater opportunity in

reducing the phosphate from drainage ditches than from isolated wetlands.

Conclusions

Using the phosphate flux from the six isolated wetlands studied basin wide estimates for

phosphate mass loads from wetlands and drainage ditches were calculated. Using literature as a

guide the reduction of phosphate mass loads to Lake Okeechobee from isolated wetlands was

calculated. From these calculations it was shown that the drainage ditches and isolated wetlands

may contribute the same range of phosphate mass loads to Lake Okeechobee. However

depending on the drainage ditch length used the drainage ditches may play a substantially larger

part in phosphate mass loads than previously thought. The phosphate mass load from isolated

wetlands was calculated to range from 2.6 to 14 metric tons per year while the drainage ditches

contributed 2 to 360 metric tons per year. To help reduce the range of phosphate mass load for









drainage ditch and provide a more accurate estimate an up to date drainage ditch total length in

the priority basins should be established. Also the isolated wetlands and ditches are inundated

about 3 months out of the year (SFWMD, 2007). These seasonal variations may decrease the

phosphate mass load from both the isolated wetlands and drainage ditch.

By reducing the tributaries with the highest phosphorus loads the most progress will be

seen in restoring Lake Okeechobee's water quality. Hiscock reported a change in phosphorus

retention in wetlands from 61% in 1991 to 31% in 2003 and blamed decreased phosphate

assimilation potential for the reduction (Hiscock et al., 2003). Thus the wetland soils phosphate

assimilation capacity may need to be taken into consideration during further studies. Rapid,

inexpensive soil tests, such as tests for phosphate and organic matter testing for bioavailable

phosphate in top sediments, could be used on drainage ditch sediments to identify the areas with

greater potential to release or retain phosphate (Sallade and Sims, 1997). Further field studies

involving the PNFM can help to narrow the range of phosphate mass loading and reduction. The

use of PNFM before and after a detention structure is erected at an isolated wetland can provide

a more accurate picture of the effects an isolated wetland has on phosphorus loading.










































































Priority Basins:
S-191
S-154
S-65D
S-65E


SL Lucie


Pamn Beach


Figure 4-1. Lake Okeechobee drainage basins. The yellow basins are priority basins (SFWMD,
2007).


NCH









Table 4-1. Basin wide estimates of phosphate mass loading and reduction from isolated
wetlands.


Phosphate mass Phosphate mass load
flux range range


(metric tons/year)
2.59
4.69
13.84


Phosphate mass load
reduction by 4%
(metric tons/year)


0.10
0.19
0.55


Phosphate mass load
reduction by 20%
(metric tons/year)
0.52
0.94
2.77


Table 4-2. Basin wide estimates of phosphate mass loading from drainage ditches using a
conservative drainage ditch length.
Phosphate mass flux range Phosphate mass load range


mg/m2/day


(metric tons/year)


1.36
6.32
10.93


3.97
18.46
31.91


Table 4-3. Basin wide estimates of phosphate mass loading from drainage ditches using a liberal
drainage ditch length.


Mass flux range Mass load range


mg/m2/day


1.36
6.32
10.93


Mass load range


(metric tons/year) (metric tons/year)
22.55 45.10
104.77 209.54
181.11 362.22


mg/m2/day
1.50
2.71
8.00









CHAPTER 5
CONCLUSION

Several aspects of Lake Okeechobee's phosphate problem were explored through this

research. The IGW model was used to model groundwater and phosphate flow between an

isolated wetland and the drainage ditch discharging water from the wetland. Field measurements

of phosphate flux were conducted using the PNFM. The field data collected from the six

isolated wetlands, four under a previous study (Hamilton, 2005), and drainage ditch transect

were analyzed to create general parameters for phosphate levels in the Lake Okeechobee

watershed. These general phosphate parameters were used to create a basin wide estimate of the

total phosphate mass load in isolated wetlands and drainage ditches. Estimates of how much

phosphate could be retained in the wetlands and drainage ditches provide guidelines on which

BMPs will be the most effective in reducing the phosphate load to Lake Okeechobee.

The IGW model was chosen to analyze phosphate flow and transport mechanisms

throughout the isolated wetlands and drainage ditch system. The IGW was utilized for its real-

time modeling, visualization and analysis capabilities. The effects of hydraulic conductivity,

partitioning coefficient, head difference between the wetland and outflow ditch, wetland size and

distance from wetlands on BTT, the time it takes for phosphate to reach a specific point down

stream, were analyzed. The BTT given realistic conditions ranged from 15 years to 300 years.

Hydraulic conductivity and head difference both showed inverse relationships to BTT. Linear

relationships were seen with BTT verse partitioning coefficient and BTT verse distance from the

wetland. Little effect was seen on the BTT with varying the size of the wetland. The above

variables effect on BTT provides insight into which BMP will be most effective for phosphate

reduction.









Three ranches used for cow calf operations in the Lake Okeechobee watershed provided an

opportunity to identify general trends of phosphate in isolated wetlands and drainage ditches.

The PNFM provide an accurate and inexpensive means of measuring phosphate flux in at each of

the six isolated wetlands. The field data obtained from the PNFMs included water flux,

phosphate flux, and provided values for comparison with calculated Darcy flux, phosphate mass

loads and fluxes.

Larson Dixie and Beaty ranches exhibited similar trends in water and phosphate flux.

Water flux for both ranches were consistently around 3 cm/day and phosphate flux trends

increased from deepest depth to the ground surface. Pelaez ranch had a larger range of water

fluxes from 0 to 7.5 cm/day and the phosphate flux increased as the depth increased. Water flux

at the Pelaez transect resembles the Pelaez wetland trend in water flux. The Pelaez ranch

transect indicated higher phosphate flux then the wetland and higher phosphate flux on the

eastern side of the drainage ditch than the western side.

Darcy flux for each of the wetland sites was measured and also calculated using estimated

wetland gradients. Darcy flux ranged from 2.0 to 4.8 cm/day. The measured Darcy flux was

consistent at all the sites with the Pelaez sites having a slightly higher Darcy flux. The calculated

Darcy flux had a slightly larger range of values than the measured flux. Phosphate mass loads

were calculated for each of the wetlands and ranged from 0.82 to 3.2 g/day. Pelaez wetland 1 had

the largest mass load. The calculated phosphate mass flux on average is higher than the

measured mass flux. The mass flux estimated at the Pelaez transect is on average much higher

than the mass flux in the wetlands.

Basin wide estimates of phosphate mass load for the priority basins in the Lake

Okeechobee watershed were created from the field data collected. The average area of the









isolated wetlands were calculated and scaled up to estimate the number and area of the isolated

wetlands in the priority basins. The range and average of the phosphate mass flux from the

isolated wetlands was used to estimate the total mass load from isolated wetland in the priority

basins. The same types of calculations were applied to drainage ditches of the priority basin.

Basin wide isolated wetland and drainage ditch phosphate mass loads were similar in

range, starting at 2.6 and 2.0 metric tons per year, respectively. The upper range from 32 to 362

metric tons per year for the drainage ditches depending on the estimate for total length of

drainage ditches in the priority basins of the Lake Okeechobee watershed. With a more accurate

and descriptive estimate of drainage ditches in the Lake Okeechobee priority basins a smaller

range of phosphate mass load may be possible. Other studies indicate that detaining water in

isolated wetlands for a longer time period, between 4 to 80% of the phosphorus stored in

wetlands can be retained in the wetland (Zhang et al., 2006; SFWMD and USEPA, 1999; Grey et

al., 2005).

The basin wide estimates confirm that there is potential to reduce one to two metric tons of

phosphorus per year from entering Lake Okeechobee by increasing the effectiveness of BMPs in

isolated wetlands and drainage ditches.

Future deployments of the PNFM at the isolated wetlands and drainage ditch transect

should be completed to provide a comprehensive data set for analysis. A more comprehensive

set of surface water samples should be taken during future deployments to compare with the

concentration of phosphate in the groundwater. More data should be collected at the drainage

ditch including water table elevations during the deployment.









To create a more accurate total basin mass load a survey of size and number of isolated

wetland in the Lake Okeechobee basin could be completed. A more accurate total length of

drainage ditches in the Lake Okeechobee priority basins is also needed.

The reduction of phosphorus mass load can be determined by deploying PNFMs before a

weir is placed in an isolated wetland to obtain baseline measurement of groundwater and

phosphate flux. PNFMs can be used after the weir is built and a comparison of phosphate

changes due to the retention of water in the isolated wetland can be completed. The phosphate

assimilation capacity of the soil can be observed over time to see if the reduction in phosphate

decreases the longer water is retained in the wetland.

BMPs have been applied throughout the Lake Okeechobee watershed reducing the

phosphate loads to the lake by tons per year (SWFMD and USEPA, 1999). With continued

research on the most effective BMPs, cooperation from the land owners and efforts from the

SFWMD, FDEP, and USEPA the TMDL of 140 metric tons per year of phosphorus to Lake

Okeechobee can potentially be met.









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BIOGRAPHICAL SKETCH

Elizabeth Bevc studied at the University of Florida receiving both her Bachelor of Science

and Master of Engineering degrees in environmental engineering sciences. Her master's class

work focused on groundwater hydrology including contaminate transport. Elizabeth hopes to

apply the knowledge gained at the University of Florida to remediate contaminated sites.





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1 NUTRIENT TRANSPORT IN GROUNDWATE R NEAR ISOLATED WETLANDS AND DRAINAGE DITCHES: IMPLICATIONS TO BEST MANAGEMENT PRACTICES By ELIZABETH L. BEVC A THESIS PRESENTED TO THE GRADUATE SCHOOL OF THE UNIVERSITY OF FLOR IDA IN PARTIAL FULFILLMENT OF THE REQUIREMENTS FOR THE DEGREE OF MASTER OF ENGINEERING UNIVERSITY OF FLORIDA 2007

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2 2007 Elizabeth L. Bevc

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3 ACKNOWLEDGMENTS I want to thank my advisor, Michael Anna ble. Without his guidance and support this would not have been possible. I also want to thank my parent s and sister for their unending support and encouragement. Finally, I thank Joe for his patience, understanding and support during the research a nd writing process.

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4 TABLE OF CONTENTS page ACKNOWLEDGMENTS...............................................................................................................3 LIST OF TABLES................................................................................................................. ..........6 LIST OF FIGURES................................................................................................................ .........7 LIST OF ABBREVIATIONS..........................................................................................................9 ABSTRACT....................................................................................................................... ............10 CHAPTER 1 INTRODUCTION..................................................................................................................12 The Lake Okeechobee Watershed Phosphate Problem..........................................................12 Isolated Wetlands.............................................................................................................. ......14 The Basics of Phosphorus in Wetlands...........................................................................14 Wetlands Phosphate Cycle..............................................................................................15 Phosphate Transport through Isolated Wetlands to Lake Okeechobee...........................16 Computer Modeling of Isolat ed Wetlands and Ditches..........................................................18 2 INTERACTIVE GROUNDWATER MODEL......................................................................23 Interactive Groundwater Pr ogram and Capabilities...............................................................23 IGW Model Design and Description......................................................................................24 IGW Model Methods and Results..........................................................................................26 Hydraulic Conductivity (K).............................................................................................26 Partitioning Coefficient (Kd)...........................................................................................27 Head Difference ( H)......................................................................................................27 Wetland Size................................................................................................................... .28 Distance from Wetland....................................................................................................28 Interactive Groundwater Model Conclusions.........................................................................29 3 PASSIVE NUTRIENT FLUX METER FIELD DATA.........................................................35 Site Description............................................................................................................... .......35 Methods........................................................................................................................ ..........36 Passive Nutrient Flux Meter Description........................................................................36 Well Design.................................................................................................................... .38 PNFM Deployment.........................................................................................................39 PNFM Removal...............................................................................................................39 Analysis....................................................................................................................... ....40 Results........................................................................................................................ .............40

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5 Water Flux Measurements...............................................................................................41 Phosphate Flux Measurements........................................................................................42 Measured and Calculated Data Comparisons..................................................................43 Conclusions.................................................................................................................... .........46 4 BASIN WIDE LOADS BASED ON LOCAL FLUX MEASUREMENTS..........................70 Basin Wide Phosphorus Calcula tions for Isolated Wetlands.................................................70 Comparison of Calculated Mass Load to L iterature Estimates for Isolated Wetlands...........71 Phosphate Retention by Drainage Ditches.............................................................................72 Basin Wide Phosphorus Calcula tions for Drainage Ditches..................................................72 Conclusions.................................................................................................................... .........73 5 CONCLUSION..................................................................................................................... ..77 LIST OF REFERENCES............................................................................................................. ..81 BIOGRAPHICAL SKETCH.........................................................................................................84

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6 LIST OF TABLES Table page 1-1 Land use and net phosphorus imports in the northern Lake Okeechobee watershed........21 2-1 Hydraulic conductivity of soil determined by slug test preformed at Larson Dixie Ranch.......................................................................................................................... .......30 2-2 Measured porewater total phosphate values for Larson Dixie Ranch...............................31 2-3 IGW model wetland and soil parameters...........................................................................31 2-4 Partitioning coefficient values...........................................................................................32 3-1 Comparison of averages and coefficients of variation between resident tracer mass remaining on resin for Larson Dixie and Beaty wetlands..................................................56 3-3 Comparison of averages and coefficients of variation between resident tracer mass remaining on resin for Pelaez wetlands.............................................................................58 3-4 PNFM Darcy flux estimates compared to the Darcy flux..................................................65 3-5 Mass flux for each section in each PNFM and mass load estimates.................................65 3-6 Summary table of the average phosphate mass load per wetland......................................68 3-7 Number of days water gradient was in to and out of the wetlands and grams of phosphate measured throughout deployment period.........................................................68 3-8 Mass flux measurements estimated from the PNFM and gradient calculations................68 3-9 Mass fluxes estimated from the PNFM for the Pelaez transect.........................................69 3-10 Summary table of average and esti mated range for phosphate parameters.......................69 4-1 Basin wide estimates of phosphate ma ss loading and reductio n from isolated wetlands....................................................................................................................... ......76 4-2 Basin wide estimates of phosphate mass loading from drainage ditches using a conservative drainage ditch length.....................................................................................76 4-3 Basin wide estimates of phosphate mass loading from drainage ditches using a liberal drainage ditch length...............................................................................................76

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7 LIST OF FIGURES Figure page 1-1 Location and land uses in the Lake Okeechobee watershed..............................................20 1-2 Phosphate cycle in wetlands..............................................................................................21 1-3 Groundwater flow system with flow through groundwater between wetlands.................22 1-4 Groundwater flow system with impermeable la yers present. Local flow lines as well as regional are shown.........................................................................................................22 2-1 A diagram of the basic model layout.................................................................................29 2-2 The basic model layout..................................................................................................... .30 2-3 Hydraulic Conductivity ve rsus break Through Time........................................................31 2-4 Partitioning Coefficient versus Break Through Time........................................................32 2-6 Size of Wetland versus Break Through Time....................................................................33 2-7 Distance from wetland ve rsus Break Through Time.........................................................33 2-8 Distance of Ditch from We tlands verse Break Through Time..........................................34 3-1 Larson Dixie Ranch......................................................................................................... ..47 3-2 Beaty Ranch................................................................................................................ .......48 3-3 Pelaez Ranch............................................................................................................... .......49 3-4 Cross section of PNFM installed in well...........................................................................50 3-5 Cross section of PNFM installation at Pelaez Ranch.........................................................51 3-6 Water table elevation observat ions for Larson Dixie Wetland 1.......................................52 3-7 Water table elevation observat ions for Larson Dixie Wetland 2.......................................53 3-8 Water table elevation obse rvations for Beaty Wetland 1...................................................54 3-9 Water table elevation obse rvations for Beaty Wetland 2...................................................54 3-10 Water table elevation observ ations for Pelaez Wetland 4.................................................55 3-11 Days and sections of PNFM's saturated throughout deployment......................................55

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8 3-12 Water flux verse depth at Larson Dixie Wetland for each well location...........................59 3-13 Water flux verse depth at Beaty wetland for each well location.......................................60 3-14 Water flux verse depth at Pelaez wetland for each well location......................................60 3-15 Water flux verse depth at Pel aez transect for each well location......................................61 3-16 Larson Dixie wetland 1 phosphate flux verse depth at each well location........................61 3-17 Larson Dixie wetland 2 phosphate flux verse depth at each well location........................62 3-18 Beaty wetland phosphate flux vers e depth at each well location.......................................62 3-19 Pelaez wetland 1 phosphate flux verse depth at each well location..................................63 3-20 Pelaez wetland 4 phosphate flux ve rse depth at each well location..................................63 4-1 Lake Okeechobee drainage basins. Th e yellow basins are priority basins.......................75

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9 LIST OF ABBREVIATIONS BMP Best management practices BTT Break through time DWSM Dynamic Watershed Simulation Model GIS Geographic Information System H Head difference HSPF Hydrological Simulation Program-Fortran IGW Interactive Ground Water K Hydraulic conductivity Kd Partitioning coefficient m/day Meters per day NPDS National pollutant discharge system PFM Passive flux meter PNFM Passive nutrient flux meter Ppb Parts per billion Ppm Parts per million SFWMD South Florida Wate r Management District SWAT Soil and Water Assessment Tool TMDL Total maximum daily load TP Total phosphate WAM Watershed Assessment Model

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10 Abstract of Thesis Presen ted to the Graduate School of the University of Florida in Partial Fulfillment of the Requirements for the Master of Engineering NUTRIENT TRANSPORT IN GROUNDWATE R NEAR ISOLATED WETLANDS AND DRAINAGE DITCHES: IMPLICATIONS TO BEST MANAGEMENT PRACTICES By Elizabeth L. Bevc August 2007 Chair: Michael Annable Major: Environmental Engineering Sciences Using the Interactive Groundw ater (IGW) program, computer modeling of phosphate transport from isolated wetlands into a draina ge ditch provides insigh t into the trends of subsurface phosphate transport around isolated wetlands. The passive nutrient flux meter (PNFM) was utilized to measure groundwater an d phosphate flux from isolated wetlands in the Lake Okeechobee basin. The groundwater and phos phate flux measurements were collected to provide baseline values for general phosphate flux estimates from the isolated wetlands. The phosphate flux was measured from isolated wetla nds to the subsurface discharging into the drainage ditch. Field measurements from a trans ect of wells near a drai nage ditch were also completed. The phosphate flux measurements and know ledge of the trends related to isolated wetlands and phosphate transport were used to scale up phosphate mass loads from single isolated wetlands and a drainage ditch to basin-wide phosphate mass loads. With an estimate of the area of the wetlands in the basin, the amount of phosphate retained by each wetland was calculated to provide the tons pe r year of phosphate loads that c ould be eliminated or delayed from entering Lake Okeechobee by increasing the effectiveness of best management practices (BMPs).

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11 If BMPs are focused on drainage ditches th e total phosphate load to Lake Okeechobee from overland and subsurface trans port through the drainage ditches could be eliminated. Basinwide estimates of phosphate loads from isolated wetlands and drainage ditc hes ranged from 2 to 16 metric tons per year. The ba sin-wide estimates confirm that there is the possibility of reducing at the very least one to two metric t ons of phosphorus per year from entering Lake Okeechobee by increasing the effectiveness of BMPs in isolated wetlands and drainage ditches.

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12 CHAPTER 1 INTRODUCTION The Lake Okeechobee Watershed Phosphate Problem Lake Okeechobee is located in south Florida and has an area of 730 square miles with an average depth of 8.6 feet (US EPA Region 4, 2006). The Lake Okeechobee watershed covers 3.5 million acres including north to south Orland o and the areas south, east and west surrounding the lake (Figure 1-1). The lake supplies water for the surroundi ng agriculture, urban areas, and environment. Lake Okeechobee provides fl ood protection for the surrounding community, a mult-million dollar sport fishing industry, and habitat for wading birds, migratory waterfowl, and the Everglades Snail Kite, an endange red animal (US EPA Region 4, 2006). In 1986, one of the largest algae blooms ever documented covered 120 square miles of the western quarter of the lake. It was determin ed that the algae bloom could be controlled by phosphorus regulation (Rechcigl, 1997). In 2001, the Total Ma ximum Daily Load (TMDL) proposed an annual load of 140 metr ic tons of phosphorus in order to reach the in-lake goal of 40 ppb phosphorus (FDEP, 2001). Point sources to Lake Okeechobee are regulated by National Pollutant Discharge Elimination System (NPDES) permits and do not make up any portion of the TMDL to Lake Okeechobee. Nonpoint sources of phosphorus to the lake include agriculture, wildlife, septic systems, and stormwater runoff. Cattle and dairy pasture lands are the primary agricultural activ ities north and northwest of the lake, while cropland, sugarcane and vegetables dominate south and east of the lake. Agricultural activities produce 98% of the phosphorus that is imported into the watershed (US EPA Region 4, 2006). Land uses for the Lake Okeechobee basin can be seen in Figure 1-1. Major land uses in the northern Lake Okeechobee watershed include improved pastures (36%), wetlands/water bodies (21%), rangeland/unimproved pastures (16%), forested uplands (10 %), citrus (5%), urban

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13 (3%), sugarcane field (2%), dairy farm (2%), sod farm (0.9%), ornamentals (0.6%), and row crops (0.6%) (Hiscock et al., 2003). Best management practi ces (BMPs) for phosphorus have been established for all the land uses (FDEP, 200 1). This paper will focus on cattle pasture BMPs. Cattle pasture BMPs include structural imp rovements such as fencing and water tanks to deter cattle from waterways, berms and culverts/r isers to retain surface water on pastures, herd and pasture management by rota tional grazing, altered feeding and fertilizer regimes, and chemical amendments (Graham, 2006). Hiscock, Thourot and Zhangs 2003 phosphorus budget for the northern Lake Okeechobee watershed indicated that 74% of the phosphorus inputs per year are stored on-site in upland soils and vegetation, 26% is discharged to runoff. The net phosphate imports from each land use can be seen in Table 1.1. Of the phosphorus inputs from the runoff 32% is stored in the wetlands and 68% is loaded to Lake Okeechobee (Hiscock et al., 2003). By reta ining the runoff on the pastures or in the isolated we tlands located throughout the waters hed phosphorus is stored in the soil instead of flowing over the pasture la nds into ditches drai ning to Lake Okeechobee (Gathumbi et al., 2005; Dunne et al ., 2006). The isolated wetlands can also provide high quality forage production, areas for the cat tle to cool themselves, wildlife habitats and greater vegetation productivity (Gathumbi et al., 2005). The objective of this study wa s to extend field measurements collected by Hamilton (2005) of phosphate flux from isolated wetlands in the Lake Okeechobee watershed. Additional wetland sites were assessed and a drainage d itch instrumented to quantify phosphate flux. The field measurements of phosphate flux provide a baseline for a general phosphate flux estimate from the isolated wetlands. Computer m odeling of phosphate transport through groundwater provides insight into subsurface phosphate transp ort trends between isolated wetlands and the

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14 drainage ditch. With the estimated phosphate fl ux from isolated wetland and knowledge of the trends related to isolated we tlands and phosphate transport the phosphate loads were scaled up from the phosphate retention capacity of a si ngle isolated wetland and drainage ditch to determine the Lake Okeechobee watersheds retention capacity for phosphate though water retention in isolated wetlands. With an estimate of the area of the wetlands in the basin, the amount of phosphate retained by each wetland was calculated to provide th e tons per year of phosphate inflows that could be eliminated or delayed from entering Lake Okeechobee with an increase in retention time of surface water r unoff. The objectives of the research were to: Model groundwater flow and phosphate transp ort between an isolated wetland and the drainage ditch discharging from the wetland under varying conditions Quantify and compare phosphate flux around five isolated wetlands on ranch lands (two conducted as part of this study) and a tran sect of a drainage ditch on ranch lands Scale up the findings to provide a basin-wide conclusion ab out the benefits of water detention in isolated wetlands for reduc tion of phosphate to Lake Okeechobee and phosphate loads attributed to groundwate r discharge to drainage ditches. Isolated Wetlands The Basics of Phosphorus in Wetlands Phosphate in soil is a key ingredient in productive agricu ltural lands however natural topsoil is often phosphate de ficient, 0.05-1.1 g phosphate kg-1 soil (Reynolds and Davies, 2001). The common primary inorganic forms of phosph ate in soil are apa tite and phosphates of aluminum and iron. These inorganic forms become bioavailable as soil water soluble reactive phosphates after weathering and dissolution. Plants readily take up and assimilate the soil water soluble reactive phosphates. However the plan ts are competing with the soluble reactive phosphates mineral binding affi nity. The inorganic phosphate becomes a part of secondary minerals, not bioavailable to plants, such as hydrous sesquioxides, amorphous iron, aluminum

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15 oxides or hydroxides. Phosphorus in biomass of plants may eventually find its way back to the soil by leaf-fall, decomp osition, consumption or excrement by animals. Phosphate levels in natural soils are quite stable and low which leads to fertilization for agriculture and subsequently runoff of phosphates into nearby water bodies. Non-point inputs of bioavailable phosphate from agricu ltural lands have been shown in several studies to be a major contributor to phosphate load ing of drainage waters (R eynolds and Davies, 2001). Wetlands Phosphate Cycle Naturally occurring inputs of phosphate in to wetlands include surface inflows and atmospheric deposition. Outputs of phosphate include surface runoff and infiltration to groundwater. Phosphorus is found in wetlands in many different forms and interconversions of these forms occur. Figure 1-2 depicts the phosphate cycle in a wetl and including the storag es and transfers of phosphate. Soluble reactive phosphat e can be converted to tissue phosphate by plants or sorbed to wetland soils and sediments. Insoluble phosph ate precipitates form and may re-dissolve under certain conditions (Kadlec and Knight, 1996). Wetland vegetation play s a large role in phosphate assimilation and storage. Because of rapid turnover the phosphate storage is short term and phosphate is released during plant decomposition. While some vegetation absorbs phosphate directly from the water column mo st uptake phosphorus from the soil porewater creating gradients between the phosphorus in soil porewater and the water column. When the concentration of phosphate in the water column is higher than in the soil or sediment porewater the phosphate diffuses into the sedi ment/soil (Reddy et al., 1999). The principal phosphate compounds found in wetlands are dissolved phosphate, solid mineral phosphate, and solid organic phosphate. The principal inorganic species of phosphate are related by pH-dependent dissolution series:

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16 H3PO4 = H2PO4 + H+ H2PO4 = HPO4 -2 + H+ HPO4 -2 = PO4 -3 + H+ Some important phosphate precipitate cations that are found in wetlands under certain conditions include: apatite (Ca5(Cl,F)(PO4)3), hydroxylapatite (Ca5(OH)(PO4)3), variscite (Al(PO4)(2H2O)), strengite (Fe(PO4)2H2O), vivianite (Fe3(PO4)28H2O), and wavellite (Al3(OH)3(PO4)2(5H2O)). Phosphate also forms co-precipi tates with other minerals such as ferric oxyhyroxide and carbonate minerals. Overall phosphate mineral chemistry is very complex (Kadlec and Knight, 1996). Wetlands can serve as sources or sinks for phosphate depending on the soils sorption capacities. Fluctuating waterl ogged and drained conditions on wetlands can alter the redox potential and thus retention a nd release phosphate occurs. The redox potential is influenced by organic matter input and affects phosphate solubility (Reddy et al., 1998). Phosphate Transport through Isolated Wetlands to Lake Okeechobee Phosphate is transported first from the su rrounding environment into the ditches and isolated wetlands that eventually drain to Lake Okeechobee. Isolated wetlands are depressions that have no permanent connection to the su rrounding water bodies. However, intermittent overland flow, subsurface flow and drainage di tches can hydrologically connect the isolated wetlands to surrounding water bodies and other wetlands (Dunne et al., 2003). Overland and subsurface flow transports phosphate both into the isolated wetlands from the surrounding environments and out of the wetland into the surrounding environment (Reddy et al., 1999). Campbell et al. documented phosphorus transpor t by runoff and groundwater during large and small rainfall events on several experiment al pasture sites (Campbell et al., 1995). Phosphate inputs to the Lake Okeechobee waters hed are primarily in the form of pasture fertilizer and dairy feed (Hiscock et al., 2003). Advective transpor t is the main transport process

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17 that moves phosphorus from the surrounding envi ronment overland and through the drainage ditches into the isolated wetlands. Land with lo wer relief has a tendency to flood and discharge phosphorus by overland flow to ditc hes (Campbell et al., 1995). Subsurface transport of phosphate by advectiv e transport depends on the velocity of groundwater flow. Land with greater relief, mo re rapid groundwater fl ow and little overland flow generates subsurface discharges of phos phate to ditches and wetlands (Campbell et al., 1995). Groundwater flow is driven by the water pressure gradient or hydraulic head between the saturated soil surface and the aquifer. The veloc ity of groundwater flow is affected by the soils hydraulic conductivity (Reddy et al., 1999). Wint er and LaBaugh illustrated how elevation and impermeable soil layers effect groundwater flows between isolated wetlands in Figures 1-3 and 1-4 (Winter and LaBaugh, 2003). The spodic laye r can simulate the impermeable layers depicted in Figure 1-5. The spodic layer in the Lake Okeechobee watershed is very tight however in some locations there are holes or voids in which wate r can move easily. Horizontal water movement can occur entirely above or be low the spodic layer as well as intersect the spodic layer and flow above and below the spodi c layer (Haan, 1995). The vertical flows of groundwater are driven by gravit y and plant uptake to support tr anspiration (Reddy et al., 1999). Once in the isolated wetlands, horizontal flow s from diffusion and dispersion processes move the phosphate through the isolated wetlands (Reddy et al., 1999). Phosphate is mobilized in the isolated wetlands between sediments and the overlying water column by advection, dispersion, diffusion, seepage, resuspension, sedime ntation and bioturbation (Reddy et al., 1999). Advective transport through either ditch flow or subsurface fl ow transports phosphate from the surrounding environment into ditches and isolated wetlands that drain to Lake Okeechobee.

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18 Computer Modeling of Isolate d Wetlands and Ditches Recently the Watershed Assessment Model (WAM) was applied to evaluate the effects of water detention in depressions on a beef cattl e ranch in the Lake Okeechobee watershed. WAM is a physically based model that performs wa tershed-related hydrological and water quality analyses. Land use, soil, weather, and land mana gement practices were al l input into WAM with the use of Geographic Information System (GIS ) functions which overlay the ranch features (Zhang et al., 2006). The WAM modeled a 3,295-ha area that included improve d, unimproved, semi-improved, woodland pastures, wetlands, upland forest, a nd citrus land uses were included. A major drainage canal surrounds three sides of the modele d area and several rainfa ll stations are in the area. Water quality parameters included sol uble nitrogen, particulat e nitrogen, groundwater nitrogen, soluble phosphorus, particulate pho sphorus, groundwater phosphorus, sediment phosphorus and biological oxygen demand (Zhang et al., 2006). WAM used the above input and output paramete rs to assess the stormwater retention for three pasture land uses that were suitable to re tain water for the ranch. The stormwater storage was simulated by defining a detenti on depth or the ratio of detenti on depth to land use area. The stormwater storage was assumed to be low lying areas or existing wetlands. Several scenarios using detention depths of 0.25 and 0.5 inches and the three land uses were evaluated. Overall, it was found that a 20% reduction in phosphorus load can be accomplished with a detention range of 0.25 to 0.5 inch es over all three land uses. A reduction of 16% of phosphorus load was found when 0.25 inch detention depth was used on all the land type s. While use of 0.25 inch on the beef pastures, 0.5 inch on the w oodland and unimproved pastures provided a 19% reduction in phosphorous levels. A 4% reduction in phosphorus load was found with a detention depth of 0.25 inch for the unimproved and woodla nd pastures. With an increase in detention

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19 depth to 0.5 inch over the two land uses the percent reduction in phosphorus moves to 7% (Zhang et al., 2006). The applicability of the above study to this re search is obvious and the most relevant study found pertaining to the assessment of BMPs or isolated wetlands thr ough computer modeling. The use of computer models to simulate wa ter quality including th e phosphorus cycle was evaluated in Borah and Beras Water-Scale Hydrologic and Nonpoi nt-Source Pollu tion Models: Review of Applications (Borah and Bera, 2004). Borah and Bera selected three models from an evaluation of eleven to provide a review of each models numerous applications. SWAT, or Soil and Water Assessment Tool, is a model for long-term continuous simulations in predomin ately agricultural watersheds. SWATs applications indicated the primary use for phosphor us modeling is assessing the impacts of dairy management practices on dairy manure phosphate loading. The third model is DWSM, or Dynamic Watershed Simulation Model, is a storm event simulation model for agricultural and suburban watersheds. DWSM provided an appli cation showing the eff ects to phosphorus loads during storm events (Borah and Bera, 2004). Including phosphorus loading applications of models in the three models reviewed indicates that there is on going work towards more accurate phosphorus loading in groundwater modeling. Arnold and Fohrers review of SWAT2000 suggested that future work should strengthen SWAT2000s phosphorus in teractions with soils and di fferent soil types (Arnold and Fohrer, 2005).

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20 Figure 1-1. Location and land uses in the La ke Okeechobee watershe d (Guan et al., 2007).

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21 Table 1-1. Land use and net phosphorus imports in the northern Lake Okeechobee watershed. Land use Area Phosphate net import Ha tons/year Abandoned dairy 2,3447 Citrus 25,392184 Commercial forestry 13,299-2 Dairy 8,525458 Field crop 2,27616 Forested upland 49,887-8 Golf course 3774 Improved pasture 183,778558 Ornamentals 3,21230 Rangeland 46,6411 Residential 9,740151 Row crops 2,868545 Sod farm 4,816-235 Sugarcane 8,7559 Unimproved pasture 33,4530 Wetland 95,4230 Water and other land uses 25,2150 Total 516,0001,717 Hiscock, J. G., Thourot, C. S., Zhang, J., 2003. Phosphorus Budget-land use relationships for the northern Lake Okeechobee watershed, Florida. Eco. Eng., 21: 63-74, Table 2. Figure 1-2. Phosphate cycle in wetlands (IFAS, 1999).

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22 Figure 1-3. Groundwater flow syst em with flow through groundwat er between wetlands (Winter and LaBaugh, 2003). Figure 1-4. Groundwater flow system with impermeable layers present. Local flow lines as well as regional are shown (Winter and LaBaugh, 2003).

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23 CHAPTER 2 INTERACTIVE GROUNDWATER MODEL Interactive Groundwater Program and Capabilities The Interactive Groundwater (IGW ) Model is a software package for real time, unified deterministic and stochastic 2D and 3D gr oundwater modeling (Li and Liu, 2006). The IGW Model eliminates the bottlenecks in tradi tional modeling technologies allowing the full utilization of todays increased computing pow er (Li and Liu, 2003). Efficient computational algorithms allow IGW to simulate complex 2D and 3D flows and transport in saturated aquifers. These flows and transport mechanisms are subject to systemic and random stresses as well as geological and chemical heterogeneity (Liao et al., 2003). The IGW Model was utilized for this analysis due to its real-time modeling, vi sualization and analysis capabilities. The IGW Model was utilized to model phosphate transport in groundwater from isolated wetlands towards an outflow ditch. Water budg ets preformed for the wetlands indicate groundwater recharge from the isolated wetland (P erkins and Jawitz, 2007). Transport variables were identified and assessed as major factors to p hosphate transport. The effect of each variable on phosphate break through time (BTT) was determin ed. Phosphate BTT was investigated to evaluate how long phosphate is detained by isol ated wetlands due to transport through the groundwater. The management practi ce investigated here is the use of structures at the outlet of wetlands or filling in of ditches to retain water in the wetlands for longer time periods. The transport variables used in the IGW model include media hydraulic conductivity, phosphate partitioning coefficient, head difference betw een wetland and outflow ditch, wetland size and ditch distance from wetlands. By exploring th e effects the variables have on the phosphate BTT the practices designed for detention of wate r in isolated wetlands can be evaluated.

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24 IGW Model Design and Description The basic design of the model was a circular wetland with a singl e ditch leaving the wetland. Located along the ditch, several groundwa ter monitoring wells provided observations of phosphate concentration over time. These observation points are used to determine BTT. For the base case the wetland was modeled as approx imately 180 meters in diameter and the ditch was 375 meters in length. The basic layout of the model can be seen in Figure 2-1. The wetland was created within IGW as one la yer with two zones. A zone enables the modeler to assign physical and chemical properti es, sources, sinks, and aquifer elevations. The whole grid or work space was assigned a zone and given Lake Okeechobee soil characteristics; this will be referred to as th e aquifer zone. The wetland was cr eated by defining a circular zone and assigning wetland characteri stics. The wetland boundary was overlain by a polyline to enable a constant head to be assigned to the we tland perimeter. The ditch was also represented as a polyline and begins two grid cells or 24 meters below the wetland edge. The wetland and ditch are separated to enable accurate flow lines to be depicted, Figure 2-2. Monitoring wells were placed along the ditch. The aquifer in the soil and wetland zones was assigned a surface elevation of ten meters, a top elevation of ten meters and a bottom elevatio n of eight meters. This represents an aquifer that is two meters saturate d thickness similar to the wetl ands used in this study. The soil and wetland parameters assigned to the zones include hydraulic conductivity, partitioning coefficient, effective porosity, phosph ate concentration in the wetland and phosphate concentration in the porewater. A literature se arch was completed on each parameter to provide the best values for the Lake Okeechobee basin isol ated wetlands. The variables were selected to facilitate model runs to establish functional rela tionships. Once established those relationships were used to assess parameters appropriate to for the sites.

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25 The range applied for hydrauli c conductivity was based on sl ug tests preformed at Larson Dixie Ranch (Bhadha, 2006). The results of the sl ug test are shown in Ta ble 2-1; see Figure 3-1 for well locations. The measured hydraulic c onductivity from four wells surrounding the wetland ranged from 0.08 to 0.25 m/day. The aver age hydraulic conductivity of the wells is 0.15 m/day. The IGW model used a hydraulic conduct ivity of 100 m/day to facilitate model run times. Soil tests for phosphate partitioning coeffici ent were not available for the Lake Okeechobee wetland sites. Thus a phosphate part itioning coefficient for a similar wetland was used 4.94e-3 m3/kg (Reddy et al., 1995). A study of south Florida found the porosity of the aquifers to be 0.3 (Meyer, 1989). A porosity of 0.3 was used throughout the IGW model. The concentration of phosphate in the wetland water found on the Larson Dixie site ranged from on average 2 to 3 ppm (Bhadha, 2006). This range is based on depth profiles measured for total phosphate in the wetlands. The total phosphate value wa s used since the measured dissolved and soluble reactive phosphate measurements were similar values to the total phosphate. Groundwater samples were collected from November 2004 to March 2005 from specific monitoring wells at Larson Dixie Ranch, see Figure 3-1 for well locations (Perkins, 2006). The total phosphate concentra tions in the groundwater are shown in Table 2-2. Groundwater samples of total phosphate in LW2MW1, LW2MW2 and LW 2MW6 provided a range of values as well as an average for these monitoring well. LW2MW3, LW2MW4 and LW2MW5 had only one or two samples providing only an average total phos phate concentration. An overall average of 0.33 ppm and overall range is 0.1 to 1 ppm is calcu lated. To simplify the IGW model the initial

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26 phosphate concentration in groundwater was assume d to zero. This allows for the model to determine the net effect of detaining water in the wetlands. IGW Model Methods and Results The IGW modeling objective was to assess the effect of syst em variables on the phosphate transport time through the aquifer to the drainage ditch. The modeling results provide estimates on how long holding water is the wetland will delay loads to Lake Okeechobee. The transport variables evaluated in the IGW model include aquifer hydr aulic conductivity, phosphate partitioning coefficient, head difference between the wetland and ditch, wetland size and ditch distance from wetland. The BTT is the time at which ten percent of the original concentra tion of phosphate in the wetland is found in the monito ring wells located along the d itch. The wetland phosphate concentration in all runs was 3 ppm thus the BTT is defined as the year that 0.3 ppm is found in the monitoring wells located along the ditch. Each transport variable was evaluated in the model independently, that is no other parameters were changed in the model during the specific runs. Table 2-3 shows the parameters used throughout the runs unless otherwise discussed below. Hydraulic Conductivity (K) Hydraulic conductivity (K) is a main transport variable eff ecting the BTT of phosphate. Model runs were completed with K from 50 to 250 meters per day in 50 unit increments. Two monitoring wells were placed along the ditch at 100 and 250 meters from the wetlands. The results of the runs are displa yed in Figure 2-3; the best f it lines characterize the inverse relationship observed.

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27 Partitioning Coefficient (Kd) The partitioning or distribution coefficient, re lates the amount of solute, or phosphorus in the model, sorbed onto the soil to the amount that is dissolved in water (Liao et al., 2003). This measure of phosphate partitioning was evaluated to determine how much of a difference one degree of freedom has with regards to BTT. Seven partitioning coefficients were evaluated and are shown in Table 2-1. Two monitoring we lls were placed along the ditch at 100 and 250 meters from the wetlands. Figure 2-4 shows the general trend of increasing partitioning coefficient increasing BTT. After regression analysis, R2=0.997 and R2=1, indicating a near perfect linear relationship between partitioning coefficient and BTT. Head Difference ( H) A weir between the outlet of the wetland and the ditch can be manipulated to increase the amount of water held in the wetland. This forces more water to flow through the aquifer rather than directly through surface water. This va riable was manipulated by changing the head difference between the wetland and ditch polylin es. The wetland constant head boundary was arbitrarily assigned 100 meters while the ditch constant head boundary ch anges to enable the effect of head differences to be observed. The ditch constant head boundary changes from 99.0 to 99.75 meters in 0.25 meter increments. The monitoring well that observed the BTT wa s located 100 meters from the wetland. Figure 2-5 depicts the observations of the phosphorus BTT with changing head difference including a best fit line depict ing the power relationship. Gene rally as the head difference between the wetland and the ditch become smalle r the longer the time required for the phosphate to reach 100 meters from the wetland in the ditch.

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28 Wetland Size Several different size wetlands were modeled to determine the influence of wetland size on phosphate transport time to the drainage ditc h. Wetland sizes of 50, 100, 200 and 400 meters in diameter were modeled. The BTT was found at four points along the ditch from monitoring wells placed at 24, 104, 184, and 264 meters from the wetland. Figure 2-6 shows that there is little effect on BTT with an incr ease in wetland size until larger wetland sizes are reaches such at 400 meters in diameter. Distance from Wetland Four monitoring wells were placed long the di tch at 80 meters a part beginning at 20 meters from the wetland. The model was r un and the BTT was found for each well. The BTT approximately doubled from well to well as it covere d the same distance. This can be seen in Figure 2-7. An instantaneous BTT for the well at 20 meters from the we tland (Figure 2-7) can be misleading. Figure 2-8 shows the actual B TT is reached around two months and not instantaneously. Figure 2-8 is created from the plume mass bala nce provided by the IGW model. The ditchs starting point was moved by 25 meters for each run beginning at 25 meters and ending at 100 meters from the wetland. This enabled the BTT to be found on the plume mass balance for the four different d itch starting points. The distan ce from the wetland relates to a BMP of filling in the drainage ditch which requi res the water to flow underground to reach the drainage ditch. Figure 2-8 clarif ies that the phosphate takes ti me to flow underground to the ditch. The lines indicate that fi lling the drainage ditch in by a bout 20 meters the BTT is near 1.5 years.

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29 Interactive Groundwater Model Conclusions Inverse relationships were found between th e BTT and hydraulic conductivity and head difference. Linear relationshi ps were found between the BTT and partitioning coefficient and the distance from the wetland. The wetlands size showed very little e ffect on BTT unless the wetland diameter became larger then 400 meters whic h was larger than the six isolated wetlands studied in the Lake Okeechobee basin. Figure 2-1. Diagram of the basic model layout it shown above with the wetland shown in black and the ditch in green leavi ng the wetland below. Two monitoring wells, in yellow, are shown along the ditch.

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30 Figure 2-2. Basic model layout is shown above with the wetland s hown in black and the ditch in green leaving the wetland below. The red within the wetland indicates the highest phosphate concentration. Two monitoring wells, in yellow, are shown along the ditch. Flow lines are also de picted showing phosphate tran sport path from the wetland into the ditch. Table 2-1. Hydraulic conductivity of soil determined by slug test preformed at Larson Dixie Ranch Measured hydraulic conductivity Well ID cm/hr m/day LWMW2 1.1000.25 LWMW5 0.5200.13 LWMW3 0.3400.08 LWMW6 0.4900.12 LWMW1 0.1300.03 Average in soil surrounding wetland= 0.0600.15 Bhadha, J., 2006. Dixie Larson Ranch: Wetland Measured Phosphate Concentrations and Hydraulic Conductivity. Unpublished raw data.).

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31 Table 2-2. Measured porewater total phos phate values for Larson Dixie Ranch Well ID Range of total phosphate (ppm)Average total phosphate (ppm) LW2MW1 0.42 to 0.660.51 LW2MW2 0.12 to 1.020.36 LW2MW3 --0.37 LW2MW4 --0.34 LW2MW5 --0.12 LW2MW6 0.11 to 0.420.25 Perkins, D.B., 2006. Dixie Larson Ranch: Pore water Phosphate Concentrations. Unpublished raw data. Table 2-3. IGW model wetland and soil parameters Model and soil parameters Value used Hydraulic conductivity (K) 100 m/day Wetland size 180 meters Partitioning coefficient (kd) 4.94e-3 m3/kg Effective porosity 0.3 Head difference ( H) 1 meter Constant phosphorus co ncentration in the wetland 3ppm 0 100 200 300 400 500 600 700 800 900 1000 050100150200250300 K (m/day)BTT (years) Well 1 at 100 meters from wetland Well 2 at 250 meters from wetland Figure 2-3. Hydraulic Conductivity versus Break Through Time

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32 Table 2-4. Partitioning coefficient values. Partitioning coefficient values liters per kilogram 4.94e-6 2.00e-6 3.5e-6 4.94e-7 4.94e-8 4.94e-9 0.0 0 10 20 30 40 50 60 70 80 90 100 0.00E+001.00E-062.00E-063.00E-064.00E-065.00E-066.00E-06 Kd (m3/g)BTT (years) Well 1 at 100 meters from wetland Well 2 at 250 meters from wetland Figure 2-4. Partitioning Coeffici ent versus Break Through Time y = 17.232x-0.99710 10 20 30 40 50 60 70 80 00.250.50.751 Changing Head (m)BTT (years) Figure 2-5. Head Difference ve rsus Break Through Time

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33 0 50 100 150 200 250 300 350 400 450 0100200300400500 Wetland Size (m)BTT (years) Well 1 at 24 meters from wetland Well 2 at 104 meters from wetland Well 3 at 184 meters from wetland Well 4 at 264 meters from wetland Figure 2-6. Size of Wetland ve rsus Break Through Time 0 20 40 60 80 100 120 140 050100150200250300 Delta X (m from wetland)BTT (years) Figure 2-7. Distance from wetla nd versus Break Through Time

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34 Figure 2-8. Distance of Ditch from Wetlands verse Break Through Time 0 0.5 1 1.5 2 2.5 3 3.5 4 4.5 020406080100120 Displaced Ditch Distance from Wetland (m)BTT (years)

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35 CHAPTER 3 PASSIVE NUTRIENT FLUX METER FIELD DATA Site Description Three ranches, Larson Dixie, Beaty and Pel aez Ranch, were used to test the Passive Nutrient Flux Meter (PNFM). Fi eld data was collect at Larson Dixie and Beaty Ranches in July 2005 by Kelly Hamilton and at Pelaez in September 2006 (Hamilton, 2005). All the ranches are located within the Lake Okeechobee watershed in Okeechobee County, Florida. The ranches all support cow-calf operations and allowed access to th e sites for continuous research. The three ranches all have drained, isolat ed wetlands with connecting ditc hes that transport water off the ranch. The wetlands have fluctuat ing water levels depending on rainfall events. The local water table and thus the wetland water levels fluctuate from flooded to dry often within a few days to weeks. All three ranches are dominated by My akka-Immokalee-basiner so ils. These soils are poorly drained, nearly level, sandy soils that domi nate most of Okeechobee County (Lewis et al., 2001). The ranches are domi nated by Bahia grass ( Paspalum natatum Fluegge`) (Dunne et al., 2006). Larson Dixie Ranch is located at N 027 20.966, W 080.465, Beaty Ranch is located at N 027 24.665, W 080 56.940 and Pelaez Ranch is located at N 27 16.422, W 080.453 (Google Earth, 2007). The wetlands, well locations, flumes a nd general layout of each of the ranches are shown in Figures 3-1-3-3. The well identification numbers describe the location and type of well such as LW2MW5 de scribes a monitoring well located at Larson Dixie wetland 2 or PTFM5 describes a flux meter well at the Pelaez Ranch transect.

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36 Methods Passive Nutrient Flux Meter Description The Passive Flux Meter (PFM) technology is a method of determining contaminant and groundwater fluxes in the saturated zone of an aquifer (Hatfield et al., 2004). The PFM has been laboratory and field tested at ha zardous waste sites and proven to be a reliable measure of fluxes (Annable et al., 2005). The PNFM has been designed to measure nutrient fluxes including phosphorus (Cho et al., 2007). The PNFM may provide a means to decrease the cost and time necessary in measuring nutrien t fluxes in groundwater. After deployment and recovery, the PFM samp les are collected and analyzed for the mass of tracer remaining and the mass of contaminant intercepted which ar e used to calculate the local cumulative water and contaminant fluxes (Annabl e et al., 2005). If reversible, linear, instantaneous resident tracer pa rtitioning takes place between the sorbent and water, the specific discharge (q) through the PFM at a specific well depth can be found by equation 3-1: t M R r qR d)] 1 ( 67 1 [ (3-1) where r is the radius of the flux meter cylinder, is the water content of the flux meter sorbent, Rd is the retardation of the resident tracer on the sorbent, MR is the relative mass of the tracer remaining within the flux meter, and t is the sampling duration (Annable et al., 2005). The contaminant mass flux ( Jc ) can be determined by using equation 3-2: dc RC c cR M L r qM J ) 1 ( .2 (3-2) where q is the specific discharge, Mc is the mass of contaminant sorbed, is the convergence or divergence of flow around the flux meter, r is the radius of the flux meter cylinder, L is the

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37 length of the sorbent matrix, MRC is the relative mass of a hypotheti cal resident tracer retained after time period t where that tracer has the same retardation as Rdc. Equation 2 assumes reversible, linear and instantaneous contaminan t partitioning between the sorbent and the water (Annable et al., 2005). For a more in depth di scussion on the PFM tec hnology see Annable et al., 2005, Hatfield et al., 2004, or Cho et al., 2007. The PNFM and PFM use similar designs incl uding a permeable, sorptive media contained in a cylindrical casing which fits snugly into we lls below the water table. The sorbent in the PNFM facilitates rapid adsorption and desorption of inorganic and organic substances. The PNFM uses a strongly basic, macroporous-type, anion exchange resin known as Lewatit S 6328 A (Sybron Chemicals Inc Birmingham, NJ). Le watit S 6328 has a matrix consisting of crosslinked polymer made of styrene a nd divinylbenzene with a relative ly uniform charge distribution of ion-active sites throughout the structure (Cho et al., 2007). The sorptive media was equilibrated with alc ohol tracers that desorb as groundwater flows through the device. The alcohol tracers provide the groundwater fl ux while the resin allows for measurement of phosphorus flux. The alcohol tra cers suite used at Larson Dixie and Beaty Ranch included 2,4-dimethyl-3-pentanol, 1-Hexa nol, 1-Heptanol, 1-Octanol, 2-Octanol and 2ethyl-1-hexanol (Hamilton, 2005). Pelaez Ranch us ed 1-Hexanol, 1-Hepta nol, and 1-Octanol as the alcohol tracers. Figure 3-4 shows a cross section of a PNFM inst alled in a well. The device is made with an inner PVC rod, clamps at the bottom and t op holding in place a nylon mesh sock filled with the resin. The PNFM was designed to be approx imately 91 cm long with a diameter of 3.18 cm. The length used was based on the well screen in tervals ranging from 107 to 201 cm. The PNFM

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38 was divided into four sections to help reduce vertical flow, each about 23 cm containing an estimated 240 ml of resin. At the Pelaez Ranch, monitoring wells were c onstructed with an inside joint protruding into the well requiring modification of the PNFM deployment method. A nine foot long expandable protective netting (Cole-Parmer Poly -Net U-09405-30) was used with a second three foot section of netting located aroun d the bottom end of the nine foot length to assist in inserting the PNFM through the well joint. The nine foot and three foot sl eeves were inserted into the well so that the three foot section was below the well joint. Then a PNFM with a third layer of protective netting was inserted in to the well through the ni ne foot section to seat adjacent to the three foot section at the bottom of the well. This technique allowed the PNFM to slide easily past the well joint yet still fit snuggly to the well walls due to the three layers of expandable mesh. See Figure 3-5 for a cross section of the installed PNFM. The diameter of the Pelaez Ranch PNFMs was 5.08 cm and all other specifi cations of the PNFM were the same as PNFM used at Larson Dixie Ranch and Beaty Ranch. Well Design At the Larson Dixie and Beaty Ranches the fl ux wells were installed using a hand auger, most were located an estimated one meter from a monitoring well. The monitoring wells were used to obtain water samples for phosphorus measur ements and to deploy transducers to monitor water levels. PVC pipe (3.175 cm diameter) and sections of well screen ranging from 122 to 152 cm long were used to construct the wells. See Figures 3-1 and 3-2 for well locations. The well casing was terminated at ground level to protect from animal disturbances. The wells were covered with a 20 cm PVC cap even with the ground surface (Hamilton, 2005). The Pelaez Ranch wells were installed using a hollow stem auger drill rig with radius of 5.08 cm and depths similar to Larson Dixie and Beat y Ranch. Most of the flux wells were paired

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39 with shallow monitoring wells screened to a dept h of one to two feet an d were above the spodic horizon. All of these wells were dry during the PNFM deployments. Pelaez Ranch well locations are shown in Figure 3-3. PNFM Deployment Deployment of the PNFM took place at all s ites during wet periods. At the Larson Dixie Ranch several wells (LW1MW8, LW2MW2, LW 2MW4, LW2MW5) were submerged at the time of deployment. In this case, a PVC coupler with a casing extension wa s used to insert the PNFM (Hamilton, 2005). In total, seven PNFM we re deployed at Larson Dixie Ranch, five around one wetland and two around the second wetla nd. Four PNFMs were deployed at the Beaty Ranch, two at each wetland. See Figure 3-1 a nd 3-2 for well locations. Water table values were recorded throughout the de ployment period at Larson Dixie Ranch a nd Beaty Ranch. The PNFMs at Larson Dixie and Beaty Ranch were deployed fo r a period of 34 days. Eighteen PNFMs were deployed at the Pel aez Ranch, four around each wetland and ten at the transect crossing the ditch location. See Fi gure 3-3 for well locations. Water table levels were recorded for five of the wells. The Pel aez Ranch PNFMs were deployed for a period of 33 days. PNFM Removal All the ranches used the same removal technique. The PNFMs were extracted from the wells fully intact. Then the resi n was carefully removed in sections from the sock. In a clean bowl, each 20 cm section of the PNFM was mixed to homogenize the sample. Two samples of the resin were taken from the homogenized mixtur e and added to vials with extraction solution. The first vial contained 60 ml of 2M KCl in a 125 ml sample bottle with approximately 25 g of resin added. The second sample was approximately 10 g placed into 30 ml isopropyl alcohol in a 40 ml sample vial. Each of th e 4 sections per PNFM were sampled in this manner. All vials

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40 were pre-weighed then weighed after the samp les were collected to determine the mass of sample added. All the samples were ro tated and equilibrated for 24 hours. Analysis The amount of residual alcohol tracer was determined by subsampling the isopropyl alcohol vial after it had sett led for 24 hours. This sample was analyzed using a gas chromatograph to obtain the con centration of each tracer. A 5 ml sample was obtained from the top of the 2M KCl vial after settling for 24 hours and used for the Total Phosphorus (TP) (Hach Method 8190, 2003). The TP method was used since many of the samples had an organic color that would interfere with the Orthophosphate Method 8178 (Hach Method 8178, 2003). The TP method, wh ile still using colorimetric comparison, was based on the change in color intensity onc e the reagents were a dded as opposed to the Orthophosphate Method that compared the color change intensity in the vial to a single calibration measurement at the beginning of sampling. Sources of error within the PNFM application can be significant. Error can be potentially generated at any step in the pro cess. Water table fluctuations ca n interfere with the sorption and cause volatilization of the resident tracers. No t obtaining a homogenous mixture of resin during the retrieval process can introduce error. The analysis stage may introduce error when fine particles stay suspended within the solution after extraction. Ca re must be taken to ensure settling of the particulates. Results The water table elevations dur ing the deployment periods for each of the wetlands are shown in Figures 3-6 to 3-10. Water table elevation data was not obtained for Pelaez wetland 1. The water table observations were used to obtain gradient calculations and exposure/submergence durations for the PNFMs in each well, see Figure 3-11. From these

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41 observations it is clear that some of the PN FMs had a greater volume of resin within the saturated zone then others. Th e desaturated zones of the PNFMs may result in volatilization of the alcohol tracers and inaccurate flux estimates. Washers were installed in the PNFMs to pr event vertical flow however several storm events at each of the sites may have created pe riods of desaturation and saturation. Figure 3-11 shows that the Beaty and Pelaez sites remained saturated throughout the deployment. Pelaez water table elevations were based on wetland wate r levels as opposed to well water levels thus the saturation times have been interpolated fo r all of Pelaez wetland 4 wells. Wells LW2MW6 and LW2MW5 were not paired with transducers a nd the water table elevations were interpolated for these locations. At the Larson Dixie sites, the rapid water table fluctuations interfered with phosphorus and water flux measurements to a depth of 90 cm. The locations of the PNFM in the Larson wells dictated whether the water table fluctu ations interfered with the flux measurements. Water Flux Measurements Since the groundwater flux was unknown at each of the wetlands a suite of several resident tracers were applied to the resin in the PNFMs. The average mass remaining and the coefficients of variation for each tracer used at Larson Dixi e and Beaty Ranches are shown in Table 3-1. For the Larson Dixie and Beaty Ranch deployment it wa s determined that 1-Heptanol would provide the most reliable water flux data. The coeffi cients of variation are compared among the mass remaining in each PNFM. For Larson Dixie a nd Beaty sites 1-Heptonal and 2-Octanol had the smallest variations. However, 2-Octanol had mo re mass remaining than the initial concentration thus the data is considered unreliable. The 1Octanol had similar result s to 1-Heptanol with more variation between fluxes a nd provided a similar flux pattern but within a larger range (0.01 to 0.06 m/day) (Hamilton, 2005).

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42 The average mass remaining and the coefficients of variation for each tracer used at Pelaez Ranch are shown in Table 3-2. The largest quantity of mass remaining for the alcohol tracers at the Pelaez site was 1-Octanol. However for the PNFMs used in wells PW1FM21, PW1FM25 and PW4FM11 1-heptanol had the most mass remain ing thus 1-heptanol was used to determine the water flux at those locations. The water flux was determined to be higher at the Pelaez site thus in the future a shorter deployment time should be used in order to en sure that more tracer mass remains to improve accuracy of the water flux measurements. The water flux profile with depth based on th e PNFM deployment for each of the wetlands is relatively constant around 3 cm/day at th e Larson Dixie and Beaty wetlands as shown in Figures 3-12, and 3-13. More variation in water flux is seen at the Pelaez Ranch with a range from 0 to 7.5 cm/day, Figure 3-14. While a cons tant water flux with depth is expected the Larson Dixie sites were unexpectedly similar. E ither the water flux was as constant as reported or all the wells were exposed to similar biologica l activity that reduced all the 1-Heptanol to the same level of remaining mass within the PNFMs. Additional deployments would be helpful to validate the results. Pelaez wells PTFM1-10 provide pho sphate flux along a transect of the ditch which drains the wetland and surrounding areas, see Figure 3-3 for well locations. The water flux along the transect is shown in Figure 3-15 and has a similar range to Pelaez Ranch wetlands. Phosphate Flux Measurements Phosphate mass flux found for each well, grouped by wetland, can be seen in Figure 3-16 through 3-20. Larson Dixie and Beaty Ranchs phos phate flux shows a very distinguished trend where the phosphate flux increases closer to th e ground surface and the rema ins at a constant low value at deeper depths. No trend can be s een from Pelaez wetland 1 phosphate flux which may be due to the distance between wells and the we tland. The Pelaez wetland 4 indicates a trend of

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43 increasing phosphate flux as dept h increases. The difference in trends between Pelaez wetland 4, Larson Dixie and Beaty wetlands maybe due to la nd practices or differing water flux between sites. The phosphate flux along the Pelaez ditch site transect is shown in Figure 3-21. Figure 321 indicates there that there ar e higher phosphate fluxes on the eas t side of the ditch then the west side and on average the phosphate flux is high er along the ditch then in the flux observed at the wetlands. The east side also shows a simila r trend to Larson Dixie and Beaty wetlands in that the phosphate flux is higher at the surface and re mains a constant low value at deeper depths. The west side of the transect shows a trend of similar to Pelaez wetland 4 where the phosphate flux increased with depth. This variation in pho sphate flux maybe due to land use practices or different water flux on each side of the ditch, sh own in Figure 3-15. In future deployments along the transect transducers should be used to obser ve the surrounding water table to determine the direction of groundwater flow into or out of the drainage ditch. Measured and Calculated Data Comparisons The Darcy Flux was measured directly from the PNFM were compared to values calculated using Darcys Law (equation 3-3), Table 3-3. dl dh K q (3-3) Where q is Darcy flux (cm/day), K is the hydraulic conductivity (cm/day) and dh represents the change in head over a distance dl (cm). The gradients, or dh/dl were determined using the average change in head difference duri ng the time of deployment from the water table data (Figures 3-6 to 3-10) and dividing by av erage radius of the wetland. The radius of each wetland was estimated using aerial imagery from Google Earth. While slug tests preformed at

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44 Larson Dixie Ranch provided an average hydr aulic conductivity of 0.15 m/day, 3 m/day was used to calculate Darcy flux. The larger hydraulic conductivity of 3 m/day provided comparable estimates to the measured Darcy flux values (Bhadha, 2006). The Darcy flux averages presented in Table 3-3 indicate that the calculated Darcy fluxes are less than those measured using the PNFM. The measured Darcy flux is very consistent at all the sites with the Pelaez sites having a slightly higher Darcy flux. The calculated Darcy flux has a wider range of values possibly due to the differe nce in size of the wetlands or the variability in the quality and quantity of water table data. Recall that Pelaez wetland 4 does not have any water table observations thus the gradient could not be calculated for the wetland. Mass load (mg/day) was calculated fr om the local contaminant mass flux ( Jc) values presented in Tables 3-1 and 3-2. Jc was calculated using equation 3-2. The mass load, M0, was calculated by multiplying Jc by the vertical cross sectional area of flow from the wetland, equations 3-4. depth r J Mc 20 (3-4) Where r is the radius from the center of the wetland to the PFM wells and depth is the length of the PFM, 3 feet or 0.91 meters for all the PNFMs. The Jc and M0 for each section of NPFM for each well, average mass load per we ll and average mass load for each wetland is provided in Table 3-4. Table 35 provides a summary of the aver age mass load from the wetland to the aquifer for each wetland in g/day. The range of mass loads per wetland is from 0.82 to 3.23 g/day. Pelaez wetland 1 is by far the largest wetland thus has the largest mass lo ad. Beaty wetland 2 has the lowest mass load which maybe due to the well placement being north of the wetland a nd the wetland draining south.

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45 The water table plots were used to determine th e flow into and out of the wetlands, Figures 3-6 to 3-10. When the water table is above the ground surface the water is flowing into the wetland. When the water table is below ground level, which is the majority of the time, the flow is out of the wetland, Table 3-7. The grams of ph osphate transported into and out of the wetland are calculated from the average wetland mass load s determined in Table 3-5 and can be found in Table 3-6. The cumulative mass phosphate leavi ng the wetlands range from 25 to 95 grams during the deployments, 33 to 34 days ,and it is assumed that the majority of phosphate is leaving the wetlands through groundwater flow. During future deployments surface water phosphate samples taken during the deployment pe riod would enable verification of phosphate transport mechanisms. Table 3-8 shows the mass flux measured by the PNFM and the mass flux found from calculated Darcy velocity using total phosphate measurements at each well. The mass of phosphorus that left the wetla nd through groundwater was estimat ed through an initial total phosphate sample at the surface of the wetland during the deployment of the PNFMs. The concentration was then multiplied by the volume of water in the wetland resulting in a mass. The calculated mass flux on average is higher than the measured mass flux. The calculated mass flux could be better estimated with more sample s of total phosphate since this is based on only one measurement. The Larson Dixie wetland 1 and Beaty wetland 1 both had total phosphate levels greater than one milligram per liter whic h explains their larger values. The mass flux estimated at Pelaez transect is on average much larger than the mass flux the wetlands, Table 39. Wells PTFM3, PTFM4, PTFM5, PTFM6, PTFM7 and PTFM8 are within a meter of the drainage ditch with PTFM7 and PTFM8 having la rger mass flux than any of the average wetland values.

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46 Conclusions The data provided above allow a range of estimated phosphate parameters, including Darcy flux, mass loads and mass flux per wetland a nd mass flux per ditch, to be established for wetlands and ditches, Table 3-10. Water fl ux for Larson Dixie and Beaty Ranches were consistently around 3 cm/day while Pelaez Ranch ha d a larger range of water flux, from 0 to 7.5 cm/day. The Pelaez Ranch transect shows a sim ilar range in water flux to the Pelaez wetlands. Phosphate flux was found to increase closer to the ground surface at Larson Dixie and Beaty Ranches while Pelaez Ranch showed the inverse tre nd at one wetland and not distinct trend at the other wetland. The Pelaez Ranch transect ha d higher phosphate flux then the wetlands and higher phosphate flux on the east side of the drainage ditch. The measured Darcy flux is very consistent at all the sites with the Pelaez sites having a slightly higher Darcy flux. The calculated Da rcy flux had a wider range of values then the measured Darcy flux. The mass loads per wetland range from 0.82 to 3.23 g/day. Pelaez wetland 1 has the largest mass load. The cumu lative mass phosphate leaving the wetlands during the deployment ranges from 25 to 95 grams. The calculated mass flux on average is higher than the measured mass flux. The mass flux estimated at the Pelaez transect is on average much higher than the mass flux in the wetlands. Additional deployments are needed to valid ate the results presented here. Further deployments should include a more comprehensive set of surface water samples and water table measurement.

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47 Figure 3-1. Larson Dixie Ranch The highlighted wells contained PNFM and the red T indicates a transducer in the monitoring well. N Fence L-W2-MW3 L-W2-MW6 L-W2-MW4 L-W2-MW1 L-W2-MW5 L-W2-MW2 L-W1-MW4 L-W1-MW00 L-W1-MW6 L-W1-MW5 L-W1-MW8 L-W1-MW7 L-W1-MW2 L-W1-FL1 L-W1-FL2 L-W1-FM7 L-W1-FM8 L-W2-FM5 L-W2-FM2 L-W2-FM4 L-W2-FM6 L-W2-FM3 L-W2-FL1 L-W2-FL2 L-baro L-Weather Retention pond Highway Ditch 0.6 miles T T T T T T

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48 Figure 3-2. Beaty Ranch The highlighted well s contained PNFM and the red T indicates a transducer in the monitoring well. N B-W1-MW1 Access Road Ditch B-W1-MW2 B-W2-MW1 Ditch B-W1-MW00 B-W2-MW5 B-W2-MW4 B-W1-MW3 B-W1-MW5 B-baro B-W2-FL1 B-W2-FL2 B-W1-FL1 B-W1-FL2 B-Weather B-W2-MW2 B-W2-FM2 B-W2-FM5 B-W2-FM B-W2-FM B-W2-FM5 B-W2-FM Fence T T T T 0.8 miles

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49 Figure 3-3. Pelaez Ranch All the flux meter (F M) wells contained PNFM and only wetland 4 contained a transducer in the wetland. P-W4-FM P-W5-FM P-W3-FM P-W1-FM P-W2-FM ( ( ( ( ( ( ( ( ( ^ Flume 1 Flume 4 Flume 3 P-Weather Flume 2 Flume 5 6 10 9 ( ( ( ( ( ( ( ( ( ( 3 1 2 4 7 5 8 Ditch 24 25 21/22 23 19/20 17/18 15/16 13/14 11/12Palaez Ranch N Railroad Tracks Access Roads Access Roads P-W11-FM P-W12-MW P-W23-FM P-W25-FM P-W24-MW P-W21-FM P-W22-MW P-W17-FM P-W18-MW P-W19-FM P-W20-MW P-W15-FM P-W16-MW P-W13-FM P-W14-MW P-W6-FM P-W10-FM P-W8-FM P-W9-FM P-W7-FM ^ PW1FM23 PW1FM21 PW1MW22 PW1MW24 PTFM10 PW4FM15 PW4MW16 PW4FM17 PW4MW18 PW4FM13 PW4MW14 PW4FM11 PW4MW12 PW4FM19 PW4MW20 PTFM7 PTFM9 PTFM6 PTFM8 PTFM5 PTFM4 PTFM1 PTFM2 PTFM3 PW1FM25 0.28 miles

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50 Figure 3-4. Cross section of PNFM installed in well (Hamilton, 2005).

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51 Figure 3-5. Cross section of PNFM installation at Pelaez Ranch.

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52 -1.5 -1.4 -1.3 -1.2 -1.1 -1 -0.9 -0.8 -0.7 -0.6 -0.5 -0.4 -0.3 -0.2 -0.1 0 0.1 0.2 0.3 0.4 0.5 7/177/197/217/237/257/277/297/318/28/48/68/88/108/128/148/168/188/208/228/24Date 2005Depth (m) LW1MW4 LW1MW7 Figure 3-6. Water table elevation obse rvations for Larson Dixie Wetland 1.

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53 -1.4 -1.3 -1.2 -1.1 -1 -0.9 -0.8 -0.7 -0.6 -0.5 -0.4 -0.3 -0.2 -0.1 0 0.1 7/177/197/217/237/257/277/297/318/28/48/68/88/108/128/148/168/188/208/228/24Date 2005Depth (m) LW2MW1 LW2MW3 LW2MW4 LW2MW2 Figure 3-7. Water table elevation obse rvations for Larson Dixie Wetland 2.

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54 -1.4 -1.3 -1.2 -1.1 -1 -0.9 -0.8 -0.7 -0.6 -0.5 -0.4 -0.3 -0.2 -0.1 0 0.1 0.2 0.3 0.4 0.5 0.6 0.7 0.8 0.9 1 7/177/197/217/237/257/277/297/318/28/4 8/68/88/108/128/148/168/188/208/228/24 Date 2005Depth (m) BW1MW1 BW1MW2 BW1MW5 Figure 3-8. Water table elevation observations for Beaty Wetland 1. -1 -0.9 -0.8 -0.7 -0.6 -0.5 -0.4 -0.3 -0.2 -0.1 0 0.1 0.2 0.3 0.4 0.5 0.6 0.7 0.8 7/177/197/217/237/257/277/297/318/28/48/68/88/108/128/148/168/188/208/228/24 Date 2005Depth (m) BW2MW2 BW2MW1 Figure 3-9. Water table elevation observations for Beaty Wetland 2.

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55 -1.2 -1.1 -1 -0.9 -0.8 -0.7 -0.6 -0.5 9/79/119/159/199/239/2710/110/510/9Date 2005Depth (m) Figure 3-10. Water table elevation observations for Pelaez Wetland 4. 0 5 10 15 20 25 30 35 40LW2MW4 LW2MW6 LW2MW3 LW2MW5 LW2MW2 LW1MW7 LW1MW8 BW1MW2 BW1MW5 BW2MW2 BW2MW5 PW4FM11 PW4FM13 PW4FM15 PW4FM17 PW4FM1920 cm sections of each PNFM (top-bottom) saturated Days Saturated days saturated Figure 3-11. Days and sections of PN FM's saturated throughout deployment.

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56 Table 3-1. Comparison of averages and coefficien ts of variation between resident tracer mass remaining on resin for Larson Dixie and Beaty wetlands. Well ID Mass remaining Mass remaining Mass remaining Mass remaining Mass remaining 2,4 DMP 1-heptanol 2-octanol 2E1H 1-Octanol LW2MW4 avg 0.334 0.179 1.099 0.979 0.571 std 0.142 0.007 0.048 0.034 0.159 cv 0.424 0.038 0.044 0.035 0.278 LW2MW6 avg 0.065 0.163 0.892 0.940 0.462 std 0.014 0.027 0.074 0.175 0.047 cv 0.222 0.167 0.083 0.186 0.102 LW2MW3 avg 0.371 0.160 1.131 0.837 0.318 std 0.168 0.019 0.080 0.355 0.060 cv 0.453 0.116 0.070 0.424 0.188 LW2MW5 avg 0.400 0.151 1.181 1.131 0.273 std 0.142 0.017 0.136 0.356 0.093 cv 0.354 0.113 0.115 0.315 0.340 LW2MW2 avg 0.243 0.166 0.990 0.556 0.326 std 0.213 0.016 0.201 0.417 0.076 cv 0.876 0.097 0.203 0.749 0.234 LW1MW8 avg 0.105 0.149 0.936 0.826 0.338 std 0.065 0.016 0.131 0.297 0.031 cv 0.616 0.111 0.139 0.360 0.090 LW1MW7 avg 0.276 0.159 0.915 0.396 0.365 std 0.054 0.019 0.157 0.078 0.036 cv 0.198 0.117 0.171 0.196 0.099 BW1MW5 avg 0.003 0.128 0.663 0.122 0.403 std 0.001 0.014 0.073 0.121 0.093 cv 0.194 0.107 0.110 0.993 0.232 BW1MW2 avg 0.077 0.153 0.889 0.592 0.328 std 0.016 0.006 0.023 0.200 0.015 cv 0.210 0.038 0.026 0.338 0.045 BW2MW2 avg 0.073 0.180 0.651 0.941 0.345 std 0.016 0.041 0.088 0.120 0.080 cv 0.213 0.229 0.136 0.127 0.232 BW2MW5 avg 0.020 0.123 0.750 0.313 0.182 std 0.003 0.020 0.127 0.067 0.031 cv 0.164 0.166 0.169 0.215 0.168

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57 Table 3-1. (continued) Well ID Mass remaining Mass remaining Mass remaining Mass remaining Mass remaining 2,4 DMP 1-heptanol 2-octanol 2E1H 1-Octanol All Wells avg 0.179 0.155 0.918 0.694 0.356 std 0.148 0.018 0.178 0.320 0.100 cv 0.829 0.116 0.194 0.461 0.282

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58 Table 3-2. Comparison of averages and coefficien ts of variation between resident tracer mass remaining on resin for Pelaez wetlands. Well ID Mass remaining Mass remaining Mass remaining 1-hexanol 1-heptanol 1-Octanol PTFM1 avg 0.0130.1890.525 std 0.0080.0340.041 cv 0.5850.1810.077 PTFM2 avg 0.0240.2200.566 std 0.0040.0200.049 cv 0.1510.0890.086 PTFM3 avg 0.0040.1740.559 std 0.0050.0960.120 cv 1.2360.5500.215 PTFM4 avg 0.0060.0740.222 std 0.0080.0720.149 cv 1.3250.9750.674 PTFM5 avg 0.0100.1750.445 std 0.0100.0420.050 cv 0.9860.2420.111 PTFM10 avg 0.0000.1180.452 std 0.0000.0190.020 cv NA0.1620.044 PTFM9 avg 0.0000.0230.269 std 0.0000.0280.137 cv NA1.1970.509 PTFM8 avg 0.0000.0390.189 std 0.0000.0240.023 cv NA0.6090.121 PTFM7 avg 0.0020.0660.231 std 0.0030.0320.039 cv 1.7320.4900.169 PTFM6 avg 0.0030.1060.493 std 0.0050.0630.065 cv 2.0000.5930.133 PW4FM19 avg 0.0110.1160.340 std 0.0190.1090.126 cv 1.7320.9380.369 PW4FM17 avg 0.0750.2780.485 std 0.1020.1740.218 cv 1.3520.6260.450 PW4FM15 avg 0.0600.3020.636

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59 Table 3-3. (continued) Well ID Mass remaining Mass remaining Mass remaining 1-hexanol 1-heptanol 1-Octanol std 0.0660.1190.162 cv 1.1030.3950.255 PW4FM13 avg 0.0420.3250.674 std 0.0130.0350.029 cv 0.3050.1080.043 PW4FM11 avg 0.4540.7140.807 std 0.2120.2450.155 cv 0.4670.3430.193 PW1FM25 avg 0.1110.3790.667 std 0.1010.2160.242 cv 0.9080.5700.362 PW1FM23 avg 0.0180.1520.348 std 0.0070.0310.060 cv 0.4110.2040.173 PW1FM21 avg 0.2530.4400.528 std 0.0180.0620.087 cv 0.0700.1410.164 All Wells avg 0.0620.2210.474 std 0.1210.1860.198 cv 1.9580.8430.418 -150 -120 -90 -60 -30 0 012345 Water Flux (cm/day)Depth from Ground Surface (cm) LW2MW4 LW2MW6 LW2MW3 LW2MW5 LW2MW2 LW1MW8 LW1MW7 Figure 3-12. Water flux verse depth at La rson Dixie Wetland for each well location.

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60 -150 -120 -90 -60 -30 0 012345 Water Flux (cm/day)Depth from Ground Surface (cm) BW1MW5 BW1MW2 BW2MW2 BW2MW5 Figure 3-13. Water flux verse depth at Beaty wetland for each well location. -100 -70 -40 -10 012345678Water Flux (cm/day)Depth from Ground Surface (cm) PW4FM17 PW4FM15 PW4FM13 PW4FM11 PW4FM19 PW1FM21 PW1FM23 PW1FM25 Figure 3-14. Water flux verse depth at Pelaez wetland for each well location.

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61 -100 -70 -40 -10 012345678910Water Flux (cm/day)Depth from Ground Surface (cm) PTFM1 PTFM4 PTFM2 PTFM9 PTFM7 PTFM10 Figure 3-15. Water flux verse depth at Pelaez transect for each well location. Figure 3-16. Larson Dixie wetland 1 phosphate flux verse depth at each well location. LW1MW8 -150 -120 -90 -60 -30 0 0510 LW1MW7 -150 -120 -90 -60 -30 0 0510Depth from Ground Surface (cm)P Flux (mg/m2/day)

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62 Figure 3-17. Larson Dixie wetland 2 phosphate flux verse depth at each well location. Figure 3-18. Beaty wetland phosphate fl ux verse depth at each well location.

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63 Figure 3-19. Pelaez wetland 1 phosphate fl ux verse depth at each well location Figure 3-20. Pelaez wetland 4 phosphate fl ux verse depth at each well location. PW1FM23 -100 -70 -40 -100246Depth from Ground Surface (cm) PW1FM25-100 -70 -40 -10 0246 PW1FM21 -100 -70 -40 -10 0246P Flux (mg/m2/day) PW1FM23 -100 -70 -40 -100246Depth from Ground Surface (cm) PW1FM25-100 -70 -40 -10 0246 PW1FM21 -100 -70 -40 -10 0246 PW4FM11 -100 -70 -40 -10 0246Depth from Ground Surface (cm) PW4FM17 -100 -70 -40 -10 0246 PW4FM15 -100 -70 -40 -10 0246 PW4FM13 -100 -70 -40 -10 0246 PW4FM19 -100 -70 -40 -10 0246P Flux (mg/m2/day)

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64 PTFM7-100 -70 -40 -10 0510 PTFM9-100 -70 -40 -10 0510 PTFM4-100 -70 -40 -10 0510 PTFM2-100 -70 -40 -10 0510 PTFM1-100 -70 -40 -10 0510Depth from Ground Surface (cm) PTFM10-100 -70 -40 -10 0510P Flux (mg/m2/day) Ditch P Flux (mg/m2/day) Figure 3.21. Pelaez transect phosphate flux verse depth at each well location. Note: The axis for phosphate flux on well PTFM9.

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65 Table 3-4. PNFM Darcy flux estimates compared to the Darcy flux estimated by the calculated gradient (K=3 m/day). Wetland Darcy flux estimated by the PNFMDarc y flux estimated by calculated gradients cm/day cm/day LW1 3.10 3.98 LW2 3.063.29 BW1 3.141.36 BW2 3.062.19 PW1 4.60 -PW4 4.081.70 Average 3.512.50 Table 3-5. Mass flux for each section in each PNFM and mass load estimates using the areas of the wetland. Jc* Mass load Wetland ID mg/m2/day mg/day LW1MW7 6.4 2425.0 LW1MW7 8.5 3213.2 LW1MW7 4.8 1816.9 LW1MW7 5.5 2089.7 LW1MW8 4.7 1781.5 LW1MW8 6.6 2516.5 LW1MW8 9.3 3543.6 LW1MW8 11.9 4521.5 LW2MW2 2.2 1009.5 LW2MW2 3.3 1537.6 LW2MW2 5.3 2422.0 LW2MW2 8.7 4010.1 LW2MW3 0.6 260.1 LW2MW3 0.8 360.0 LW2MW3 0.5 250.7 LW2MW3 1.0 452.3 LW2MW4 1.5 700.0 LW2MW4 0.9 426.3 LW2MW4 0.4 193.6 LW2MW4 1.1 486.0 LW2MW5 1.6 714.9 LW2MW5 1.2 553.0 LW2MW5 1.6 746.6

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66 Table 3-5. (continued) Jc* Mass load Wetland ID mg/m2/day mg/day LW2MW5 5.1 2368.2 LW2MW6 4.7 2175.2 LW2MW6 4.3 1969.3 LW2MW6 2.6 1212.0 LW2MW6 6.3 2905.2 BW1MW2 2.1 995.3 BW1MW2 2.9 1359.8 BW1MW2 3.0 1438.2 BW1MW2 7.8 3699.4 BW1MW5 0.2 72.5 BW1MW5 1.4 639.1 BW1MW5 2.1 973.7 BW1MW5 2.0 931.7 BW2MW2 0.1 55.5 BW2MW2 0.1 45.8 BW2MW2 0.1 52.3 BW2MW2 0.2 71.6 BW2MW5 5.1 2246.0 BW2MW5 4.8 2096.1 BW2MW5 1.7 735.6 BW2MW5 2.8 1243.8 PW1FM25 2.1 3921.9 PW1FM25 1.1 2100.3 PW1FM25 2.2 4041.6 PW1FM25 1.8 3247.3 PW1FM25 1.7 3129.7 PW1FM23 2.8 5112.5 PW1FM23 5.1 9296.0 PW1FM23 2.4 4439.8 PW1FM23 3.4 6282.8 PW1FM21 0.0 0.0 PW1FM21 0.0 0.0 PW1FM21 0.0 66.6 PW1FM21 0.2 323.6 PW1FM21 0.1 130.1 PW4FM19 0.6 593.3

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67 Table 3-5. (continued) Jc* Mass load Wetland ID mg/m2/day mg/day PW4FM19 1.2 1148.7 PW4FM19 3.7 3565.6 PW4FM19 1.8 1769.2 PW4FM17 0.2 172.2 PW4FM17 0.0 0.0 PW4FM17 0.0 0.0 PW4FM17 1.9 1897.0 PW4FM17 0.6 632.3 PW4FM15 0.5 466.3 PW4FM15 0.2 193.7 PW4FM15 3.1 2976.2 PW4FM15 1.2 1212.0 PW4FM13 0.0 38.1 PW4FM13 0.0 35.1 PW4FM13 0.1 73.4 PW4FM13 2.4 2319.3 PW4FM13 0.8 809.3 PW4FM11 3.7 3644.9 PW4FM11 4.6 4472.2 PW4FM11 5.5 5410.2 PW4FM11 4.6 4509.1

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68 Table 3-6. Summary table of the average phosphate mass load per wetland. Wetland Average phosphate mass load g/day LW1 2.74 LW2 1.24 BW1 1.26 BW2 0.82 PW1 3.23 PW4 1.45 Table 3-7. Number of days water gradient was into and out of the wetlands and grams of phosphate measured throughout deployment period. Wetland Gradient in Gradient ou t Phosphate in Phosphate out Cumulative phosphate days days grams grams grams LW1 4.0 30.0 11.082.2 93.1 LW2 1.5 32.5 1.940.2 42.1 BW1 4.0 30.0 5.137.9 43.0 BW2 1.0 33.0 0.827.0 27.8 PW4 0.0 33.0 0.047.8 47.8 Table 3-8. Mass flux measurements estimated fr om the PNFM and gradient calculations. Wetlands PNFM measurement mass flux Mass flux found from Darcy velocity and TP concentration mg/m2/day mg/m2/day LW1 7.46 64.060 LW2 2.09 8.020 BW1 2.83 14.820 BW2 1.83 7.220 PW1 1.75 -PW4 1.74 0.120 Average 2.71 5.898

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69 Table 3-9. Mass fluxes estimated from the PNFM for the Pelaez transect. Pelaez transect wells PNFM measurement mass flux mg/m2/day PTFM1 0.67 PTFM2 5.33 PTFM3 7.23 PTFM4 1.36 PTFM5 4.00 PTFM6 5.48 PTFM7 10.93 PTFM8 8.93 PTFM9 20.62 PTFM10 10.11 Average 7.47 Table 3-10. Summary table of average and estimated range for phosphate parameters. Average Estimated Range Darcy Flux (cm/day) 3.512.00 4.75 Mass Load per wetland (g/day) 1.791.00 3.50 Mass Flux per wetland (mg/m2/day) 2.711.50 8.00 Mass Flux per ditch (mg/m2/day) 7.470.75 14.00

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70 CHAPTER 4 BASIN WIDE LOADS BASED ON LOCAL FLUX MEASUREMENTS The field data collected from the six wetlands we re used to create a basin-wide estimate of the total amount of phosphorus exchange betwee n groundwater and isolated wetlands in the basin. The amount of phosphorus that could be reduced to Lake Okeechobee by detaining more water in the wetlands for a longer period of time was estimated to be similar to the measured fluxes. To estimate the amount of phosphate that could be stopped from reaching Lake Okeechobee the phosphate parameter numbers from Table 3-10 were applied to the priority basins of the Lake Okeechobee watershed. The priority basins, S-65E, S-65D, S-154 a nd S-191 have consistently produced the highest levels of phosphorus concentrations of all the tributary basins to Lake Okeechobee (SFWMD and USEPA, 1999). The pr iority basins have abundant cow calf operations. The priority basins account for 12% of the land ar ea in the Lake Okeechobee watershed, see Figure 4-1, and 35% of the phosphorus entering the la ke (Dunne et al., 2006). The Lake Okeechobee Action Plan of 1999 states that if the priority ba sins met their target lo ads the phosphorus loading into Lake Okeechobee could be reduced by over 100 tons per year (SFWMD and USEPA, 1999). Basin Wide Phosphorus Calculations for Isolated Wetlands By using the characteristics of the six wetla nds studied, an estimate of the amount of phosphorus produced by the all the wetlands located within the priority basins was calculated. Seven percent of the land surface in the priority basins is reported as isolated wetlands (Dunne et al., 2006). The priority basins total area is 974 square miles (SFWMD and USEPA, 1999). Thus there are an estimated 68 squa re miles of isolated wetlands within the priority basins. The average area of the Larson Dixie and Beaty ranchs four wetlands was determined by area measurements taken over a months time at the wetlands on Larson Dixie and Beaty Ranches

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71 (Perkins, 2005). The average area of the four wetlands was 7,900 square me ters. Thus there is an approximate 22,400 individual isolated wetlands in the priority basins. By taking the average and range of phos phate mass flux shown in Table 3-9 and multiplying them by the number of individual isolated wetlands estimated for the basin, the estimated mass load average and range is ca lculated, Table 4-1. The phosphate mass load estimated represents the priority basins total phosphate mass load between isolated wetlands and groundwater. This calculation pr oduces phosphorus mass load range for the priority basins of 2.6 to 14 metric tons per year with an average of 4.69 metric tons per year, Table 4-1. Comparison of Calculated Mass Load to Li terature Estimates for Isolated Wetlands Based on other studies, if the detention of wa ter in the isolated wetlands is capable of decreasing the mass load approximately 4 to 20 percent then between 0.10 to 2.77 metric tons per year will not reach Lake Okeechobee, see Table 4-1 (Zhang et al., 2006). South Florida Water Management District studies indicate that small on-site wetlands can potentially remove between 25 to 80% of the phosphorus they re ceive which would increase the anticipated phosphorus removal seen in Table 4-1 (SFWMD and USEPA, 1999). The Lake Okeechobee Annual Report for 2005 indicated that retaining water on a 4 10 acre wetland reduces phosphorus by 1.2 metric tons per year, a 71% reduction (Grey et al., 2005). Literature estimates for phosphate reduction from water detention in isolated wetlands range from 4 to 80% of the wetlands phosphorus st ored in the wetland. With such a broad range it is obvious that more studies are needed to confirm the effec tiveness of water detention in isolated wetlands to reduce phosphate loads. Howe ver, the reduction of 100 metric tons per year of phosphate that the Lake Okeechobee Action Plan of 1999 discusses is out of the range of the above estimates (SFWMD and USEPA, 1999). SF WMD and USEPA may also have taken into consideration other phosphate BMPs.

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72 Phosphate Retention by Drainage Ditches Similar to isolated wetlands, drainage ditches can serve as a source or sink for phosphorus. As a temporary phosphorus sink, erosion and overla nd flow can transport i norganic, organic and dissolved phosphorus into drainage ditches. The reducing conditions that occur with the accumulation of standing water in the ditches may enhance solubilization of sediment bound phosphate into drainage ditches (Sallade and Sims, 1997). Phos phorus rich sediments, newly soluble phosphorus and organic matt er can accumulate in drainage ditches until storm events transport the materials out of the ditch system. The phosphate flux measurements obtained from the ditch transect at Pelaez Ranch were used as a representative measurement of phospha te flux along drainage ditches in the Lake Okeechobee priority basins. By using an estimate of the length of ditches in the priority basins and multiplying by the phosphate discharge flux the mass load of phosphate from drainage ditches in the priority basins was estimated. The mass load of phosphate from the drainage ditch was compared with the mass load of phosphate from the wetlands to determine if best management practices should be applied to the d itches or if focus should remain on the isolated wetlands. Basin Wide Phosphorus Calculat ions for Drainage Ditches Table 4-2 depicts the average and the range of phosphate mass flux from wells PTFM3 to PTFM8, which run parallel to the drainage ditc h. To determine the phosphate mass load in the priority basin the total length of drainage ditches was required. Estimates of the total length of drainage ditches were sparse. The greatest ditching density found for unimproved pastures, improve pasture, intensively managed pastur es and citrus and row crops was 18 km/km2 (Haan, 1995). To determine the maximum amount of ph osphorus from the drai nage ditches it was assumed that all of the area in the priority basi ns has the greatest ditchi ng density for land uses.

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73 By multiplying the ditching density by the area of the priority basins a drainage ditch length of 45,000 km was determined. Steinman and Rosen descri be the total linear mete rs of canals in the watershed north of Lake Okeechobee to be 4,00 0 km (Steinman and Rosen, 2000). Calculating the mass loads with each estimate of ditch length results in very different numbers. Both estimates of drainage ditch length were used in order to create a range of possible phosphate mass loads from drainage ditches into Lake Okeechobee. To obtain a mass load, the discharge area the dr ainage ditches was required. The discharge area was found by using the one meter depth that the PNFM measured and multiplying it twice to represent each side of the drainage ditch. This provides a phosphate mass load of 4 and 31 metric tons per year with an average of 18 metric tons per year, Table 4-2. Using the larger drainage ditch length of 45,000 km, the phosphate mass load range increased to 22 to 362 metric tons per year, s ee Table 4-3. From the estimates of phosphate loads from drainage ditches in Lake Okeechobee is shown that there was a greater opportunity in reducing the phosphate from drainage ditche s than from isolated wetlands. Conclusions Using the phosphate flux from the six isolated wetlands studied basin wide estimates for phosphate mass loads from wetlands and drainage ditc hes were calculated. Using literature as a guide the reduction of phosphate mass loads to Lake Okeechobee from isolated wetlands was calculated. From these calculations it was shown th at the drainage ditches and isolated wetlands may contribute the same range of phosphate mass loads to Lake Okeechobee. However depending on the drainage ditch length used the dr ainage ditches may play a substantially larger part in phosphate mass loads than previously th ought. The phosphate mass load from isolated wetlands was calculated to range from 2.6 to 14 metr ic tons per year whil e the drainage ditches contributed 2 to 360 metric tons per year. To help reduce the range of phosphate mass load for

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74 drainage ditch and provide a more accurate estimate an up to date drainage ditch total length in the priority basins should be established. Also the isolated wetlands and ditches are inundated about 3 months out of the year (SFWMD, 2007). These seasonal variations may decrease the phosphate mass load from both the isolated wetlands and drainage ditch. By reducing the tributaries with the highest phosphorus loads the most progress will be seen in restoring Lake Okeechobees water qua lity. Hiscock reported a change in phosphorus retention in wetlands from 61% in 1991 to 31% in 2003 and blamed decreased phosphate assimilation potential for the reduction (Hiscock et al., 2003). Thus th e wetland soils phosphate assimilation capacity may need to be taken into consideration during fu rther studies. Rapid, inexpensive soil tests, such as tests for phospha te and organic matter testing for bioavailable phosphate in top sediments, could be used on drainage ditch sedime nts to identify the areas with greater potential to release or retain phosphate (Sallade and Si ms, 1997). Further field studies involving the PNFM can help to narrow the range of phosphate ma ss loading and reduction. The use of PNFM before and after a detention structur e is erected at an isolated wetland can provide a more accurate picture of the effects an isolated wetland has on phosphorus loading.

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75 Figure 4-1. Lake Okeechobee drainage basins. The yellow basins are priority basins (SFWMD, 2007).

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76 Table 4-1. Basin wide estimates of phosphate mass loading and reduction from isolated wetlands. Phosphate mass flux range Phosphate mass load range Phosphate mass load reduction by 4% Phosphate mass load reduction by 20% mg/m2/day (metric tons/year) (metric tons/year) (metric tons/year) 1.50 2.590.100.52 2.71 4.690.190.94 8.00 13.840.552.77 Table 4-2. Basin wide estimates of phosphate mass loading from drainage ditches using a conservative drainage ditch length. Phosphate mass flux range Phosphate mass load range mg/m2/day (metric tons/year) 1.36 3.97 6.32 18.46 10.93 31.91 Table 4-3. Basin wide estimates of phosphate mass loading from drainage ditches using a liberal drainage ditch length. Mass flux range Mass load range Mass load range mg/m2/day (metric tons/year) (metric tons/year) 1.36 22.55 45.10 6.32 104.77 209.54 10.93 181.11 362.22

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77 CHAPTER 5 CONCLUSION Several aspects of Lake Okeechobees phospha te problem were explored through this research. The IGW model was used to mode l groundwater and phosphate flow between an isolated wetland and the drainage ditch discharging water from the wetland. Field measurements of phosphate flux were conducted using the PNFM The field data collected from the six isolated wetlands, four under a previous study (Hamilton, 2005), and drainage ditch transect were analyzed to create general parameters for phosphate levels in the Lake Okeechobee watershed. These general phosphate parameters were used to create a basin wide estimate of the total phosphate mass load in isolated wetlands an d drainage ditches. Estimates of how much phosphate could be retained in the wetlands and drainage ditches provide guidelines on which BMPs will be the most effective in reduci ng the phosphate load to Lake Okeechobee. The IGW model was chosen to analyze phos phate flow and transport mechanisms throughout the isolated wetlands an d drainage ditch system. The IGW was utilized for its realtime modeling, visualization and analysis capab ilities. The effects of hydraulic conductivity, partitioning coefficient, head difference between the wetland and outflow ditch, wetland size and distance from wetlands on BTT, the time it takes for phosphate to reach a specific point down stream, were analyzed. The BTT given realistic conditions ranged from 15 years to 300 years. Hydraulic conductivity and head difference both show ed inverse relationships to BTT. Linear relationships were seen with B TT verse partitioning coefficient and BTT verse distance from the wetland. Little effect was seen on the BTT w ith varying the size of the wetland. The above variables effect on BTT provides insight into which BMP will be most effective for phosphate reduction.

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78 Three ranches used for cow calf operations in the Lake Okeechobee watershed provided an opportunity to identify gene ral trends of phosphate in isolated wetlands and drainage ditches. The PNFM provide an accurate and inexpensive means of measuring phospha te flux in at each of the six isolated wetlands. The field data obtained from the PNFMs included water flux, phosphate flux, and provided values for compar ison with calculated Darcy flux, phosphate mass loads and fluxes. Larson Dixie and Beaty ranches exhibited si milar trends in water and phosphate flux. Water flux for both ranches were consisten tly around 3 cm/day and phosphate flux trends increased from deepest depth to the ground surface. Pelaez ranc h had a larger range of water fluxes from 0 to 7.5 cm/day and the phosphate flux increased as the depth increased. Water flux at the Pelaez transect resembles the Pelaez wetland trend in water flux. The Pelaez ranch transect indicated higher phosphate flux then the wetland and higher phosphate flux on the eastern side of the drainage ditch than the western side. Darcy flux for each of the wetland sites was meas ured and also calculated using estimated wetland gradients. Darcy flux ranged from 2.0 to 4.8 cm/day. The measured Darcy flux was consistent at all the sites with the Pelaez sites having a slightly higher Darcy flux. The calculated Darcy flux had a slightly larger range of values than the measured flux. Phosphate mass loads were calculated for each of the wetlands and ranged from 0.82 to 3.2 g/day. Pelaez wetland 1 had the largest mass load. The calculated phosphate mass flux on average is higher than the measured mass flux. The mass flux estimated at the Pelaez transect is on average much higher than the mass flux in the wetlands. Basin wide estimates of phosphate mass load for the priority basins in the Lake Okeechobee watershed were created from the fiel d data collected. The average area of the

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79 isolated wetlands were calculated and scaled up to estimate the number and area of the isolated wetlands in the priority basins. The range and average of the phosphate mass flux from the isolated wetlands was used to estimate the total mass load from isolated wetland in the priority basins. The same types of calculations were appl ied to drainage ditches of the priority basin. Basin wide isolated wetland and drainage ditch phosphate mass loads were similar in range, starting at 2.6 and 2.0 metric tons per year respectively. The upper range from 32 to 362 metric tons per year for the drainage ditche s depending on the estimate for total length of drainage ditches in the priority basins of the Lake Okeechobee watershed. With a more accurate and descriptive estimate of draina ge ditches in the Lake Okeec hobee priority basins a smaller range of phosphate mass load may be possible. Ot her studies indicate that detaining water in isolated wetlands for a longer time period, be tween 4 to 80% of the phosphorus stored in wetlands can be retained in the wetland (Zhang et al., 2006; SFWMD and US EPA, 1999; Grey et al., 2005). The basin wide estimates confirm that there is potential to reduce one to two metric tons of phosphorus per year from entering Lake Okeechobee by increasing the effectiveness of BMPs in isolated wetlands and drainage ditches. Future deployments of the PNFM at the isol ated wetlands and drai nage ditch transect should be completed to provide a comprehensive data set for analysis. A more comprehensive set of surface water samples should be taken du ring future deployments to compare with the concentration of phosphate in th e groundwater. More data should be collected at the drainage ditch including water table elevat ions during the deployment.

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80 To create a more accurate tota l basin mass load a survey of size and number of isolated wetland in the Lake Okeechobee basin could be co mpleted. A more accurate total length of drainage ditches in the Lake Okeechobee priority basins is also needed. The reduction of phosphorus mass load can be determined by deploying PNFMs before a weir is placed in an isolated wetland to obtain baseline measurement of groundwater and phosphate flux. PNFMs can be used after the weir is built and a comparison of phosphate changes due to the retention of water in the isolated wetland can be completed. The phosphate assimilation capacity of the soil can be observed ov er time to see if the reduction in phosphate decreases the longer water is retained in the wetland. BMPs have been applied throughout the Lake Okeechobee watershed reducing the phosphate loads to the lake by tons per year (SWFMD and USEPA, 1999). With continued research on the most effective BMPs, cooperatio n from the land owners and efforts from the SFWMD, FDEP, and USEPA the TMDL of 140 me tric tons per year of phosphorus to Lake Okeechobee can potentially be met.

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81 LIST OF REFERENCES Annable, M.D., Hatfield, K., Cho, J., Klammer, H., Parker, B.L., Cherry, J.A., Rao, P.S.C., 2005. Field-scale Evaluation of the pa ssive flux meter for simultaneous measurement of groundwater and contaminant fluxes. Envi ron. Sci. Technol., 39: 7194-7201. Arnold, J. G., and Fohrer, N., 2005. SWAT2000: curre nt capacities and res earch opportunities in applied watershed modeling. Hydr ological Process, 19: 563-573. Bhadha, J., 2006. Dixie Larson Ranch: Wetland Measured Phosphate Concentrations and Hydraulic Conductivity. Unpublished raw data. Borah, D.K. and Bera, M., 2004. Watershed-Scale Hydrologic and Nonpoint-Source Pollution Models: Review of Applications. Tr ansactions of the ASAE, 47.3: 789-803. Campbell, K. L., Capece, J. C., Tremwe l, T. K., 1995. Surface/subsurface hydrology and phosphorus transport in the Kissimmee Ri ver Basin, Florida. Eco. Eng., 5: 301-330. Cho. J., Annable, M.D., Jawitz, J.W., Hatfie ld, K., 2007. Passive flux meter measurement of water and nutrient flux in porous media. S ubmitted to J. Environ. Quality (in press). Dunne, E.J., Reddy, K.R., Clark, M.W., 2006. Phos phorus release and retention by soils of natural isolated wetlands. Int. J. Env. and Pollution, 28: 496-516. Gathumbi, S. M., Bohen, P. J., Graetz, D. A., 2005. Nutrient Enrichment of Wetland Vegetation and Sediment in Subtropical Pastures Soil Sci. Soc. Am. J., 69: 539-548. Google Earth Version 4.0.2737. 2007. Computer soft ware, Mountain View, California. Accessed June 30, 2007. http://earth.google.com/index.html Graham, W. Demonstration of Water Quality Best Management Practices for Beef Cattle Ranching in the Lake Okeechobee Basin. Quar terly Grant report April 2006-June 2006. Gray, S., Colburn, E., ODell, K, Whalen, B. Chapter 3: Lake Okeechobee Annual Report. 2005, 2005 South Florida Environmental Report, SFWMD, West Palm Beach, Florida. Guan, W., Zhang, J., Muszick, D. Integrating Mu ltiple Databases and Computing Platforms with GIS in Support of Water Resource Modeling. SF WMD, West Palm Beach, Florida. Accessed February 28, 2007. http://gis.esri.com/library/userconf /proc99/proceed/papers/pap180/p180.htm Haan, C. T., 1995. Fate and transport of phosphorus in the Lake Okeechobee Basin, Florida. Eco. Eng., 5: 331-339. Hamilton, M., K., 2005. Passive Nutr ient Flux Meters for Determin ation of Phosphorus Flux in Groundwater: Application in Lake Okeechobee Ba sin, Florida. Unpublished Masters Project. University of Florida, Gainesville.

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82 Hatfield, K., Annable, M.D., Cho, J., Klammer, H., 2004. A direct passive method for measuring water and contaminant fluxes in porous media. J. Contam. Hydrol, 75: 155-181. Hiscock, J. G., Thourot, C. S., Zhang, J., 2003. P hosphorus Budget-land use relationships for the northern Lake Okeechobee watershed, Florida. Eco. Eng., 21: 63-74. Hogan, D. M., Jordan, T. E., Walbridge, M. R., 2004. Phosphorus retention and soil organic carbon in restored and natural fr eshwater wetlands. Society of Wetland Science, 24: 573-585. Institute of Food and Agricultural Sciences (IF AS), Soil and Water Science Department and Florida Cooperative Extension Service, 1999. F act Sheet SL170. University of Florida, Gainesville, Florida. http://edis.ifas.ufl.edu/AE148 Kadlec, R.H and Knight, R.L. 1996. Treatme nt Wetlands. CRC Press LLC, Boca Raton, Fl. Lewis, D.L., Liudahl, K.J., Noble, C.V., Ca rter, L.J., 2001. Soil Survey of Okeechobee County, Florida. USDA/NRCS in corporation with the Un iversity of Florida, Institute of Food and Agricultural Sciences, Agricultural Experime ntal Station and the Soil and Water Science Department and Florida Department of Agricultural and Consumer Services. Li, S.G. and Liu, Q., 2006. Interactive Ground Water (IGW). Environmental Modeling and Software, 21; 417-418. Li, S.G. and Liu, Q., 2003. Interactive Ground Wate r (IGW): An Innovative Digital Library for Groundwater Education and Resear ch. Computer Applications in Engineering Education, 11: 179-202. Liao, H.S., Paulson, K.J., Li, S.G., Ni, C. F ., 2003. IGW 3 Reference Ma nual. Department of Civil and Engineering, Mich igan State University. Meyer, F.W., 1989. Hydrogeology, Ground-Water M ovement and Subsurface Storage in the Floridian Aquifer System in Southern Fl orida. USGS Professional Paper 1403-G. McKee, K. A., 2005. Predicting Soil Phosphorus Storage in Historically Isolated Wetlands within the Lake Okeechobee Priority Basins. Unpub lished Masters Thesis. University of Florida, Gainesville. Perkins, D. B. and Jawitz, J.W., 2007. We tland-Groundwater Interactions in Managed Seasonally-Inundated Depre ssional Wetlands. J. of Hydro. (in press). Perkins, D.B., 2006. Dixie Larson Ranch: Pore water Phosphate Concentrations. Unpublished raw data. Perkins, D.B., 2005. Larson Dixie and Beaty Ranch: Water Budgets. Unpublished raw data. Rechcigl, J. E., 1997. Phosphorus Natural vers us Pollution Levels: Lake Okeechobee Case Study. Florida Beef Cattle Short Course.

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83 Reddy, K.R., Diaz, O.A., Scinto, L.J., Agami, M., 1995. Phosphorus dynamics in selected wetlands and streams of the Lake Okeechobee Basin. Eco. Eng., 5: 183-207. Reddy, K. R., Kadlec, R.H., Flaig, E., Gale, P. M., 1999. Phosphorus Retention in Streams and Wetlands: A Review. Critical Reviews of E nvironmental Science and Technology, 29: 82-146. Reddy, K. R., O Connor, G. A., Gale, P.M., 1998. Phosphorus Sorption Capacities of Wetland Soils and Stream Sediments Impacted by Dair y Effluent. J. Envir on. Quality, 27: 438-447. Reynolds, C. S. and Davies, P. S., 2001. Sources and bioavailability of phosphorus fractions in freshwaters: a British perspective. Biol. Rev., 76: 27-64. Sallade, Y. E. and Sims, J.T., 1997. Phosphorus Tran sformations in the Sediments of Delaware's Agricultural Drainage Ways: I. Phosphorus Fo rms and Sorption. J. Environ. Quality, 26: 15711579. South Florida Water Management District ( SFWMD). Lake Okeechobee Priority Basin Map. SFWMD, West Palm Beach, Fl. Accessed April 27, 2007. https://my.sfwmd.gov/pls/portal/docs/PAGE /PG_GRP_SFWMD_WA TERSHED/PORTLET%2 0-%20OKEECHOBEE/TAB179808 5/PRIORITY_BASINS.PDF South Florida Water Management District (SFWMD). DBHYRO: Meteorological Data for Station L001 Weather Station. SFWMD, West Palm Beach, Florida. Accessed June 13, 2007. http://glades.sfwmd.gov/pls/dbhydro _pro_plsql/show_dbkey_info.main_page South Florida Water Management District (SFWMD) and United States Environmental Protection Department (USEPA), 1999. Lake Okeechobee Action Plan. SFWMD, West Palm Beach Florida. Sperry, C. M., 2004. Soil Phosphorus in Isolated Wetlands of Subtropical Beef Cattle Pastures. Unpublished Masters Thesis. University of Florida, Gainesville. Steinman, A. D. and Rosen, B. H., 2000. Lotic -Lentic Linkages Associated with Lake Okeechobee, Florida. Journal of the Nort h American Benthological Society, 19: 733-741. US EPA Region 4, 2006. Proposed Total Maximu m daily Load for Biochemical Oxygen Demand, Dissolved Oxygen, Nutrients and Unionized Ammonia in the Lake Okeechobee Tributaries. September 2006. Vaughan, R.E., 2005. Agricultural Drainage Ditche s: Soils and Implications for Nutrient Transport. Unpublished masters thesis. University of Maryland, College Park. Winter, T. C. and LaBaugh, J. W., 2003. Hydrol ogic Considerations in Defining Isolated Wetlands. Wetlands, 23.3:532-540.

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84 BIOGRAPHICAL SKETCH Elizabeth Bevc studied at the University of Florida receiving both her Bachelor of Science and Master of Engineering degr ees in environmental engineeri ng sciences. Her master's class work focused on groundwater hydrology including c ontaminate transport. Elizabeth hopes to apply the knowledge gained at the University of Florida to remediat e contaminated sites.


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