Modeling Phosphorus Dynamics in Everglades Wetlands

by

W. W. Walker & R. H. [email protected] [email protected]

Support from U.S. Dept. of the Interior & U.S. Army COEData from South Florida Water Management District

GEER ConferenceJuly 31, 2008

Modeling Phosphorus Dynamics in Everglades Wetlands & Stormwater Treatment Areas

Topics

• Model Concepts & Evolution• STA Modeling• Marsh Modeling• Limitations & Directions• Data & Research Needs

Phosphorus Mass Balance Models• Aggregated Variables & Processes• Limited User Input Data • Calibrated & Tested vs. Regional Datasets• Testing Strategies

– Independent Datasets or Time Periods– Residuals Analysis

• Applicability Limited by Data Boundaries• Uncertainty Evaluated• Excel / Visual Basic Platforms• Details: wwwalker.net/dmsta & …/epgm

Model Applications• Engineering Design

– Design & Optimization of Stormwater Treatment Areas– Evaluation of Regional Water Mgt & P Control Plans– Consideration of BMP’s, STA’s & Reservoirs

• Adaptive Management– Forecasting Marsh Enrichment/Recovery– Benchmark for Interpreting Monitoring Data

• STA Performance• Downstream Marsh Transects

– Optimizing STA Operation (Flows, Depths, Veg.)– Integrating Research & Monitoring Data– Identifying Research Questions & Data Gaps

Al d bi d di

Marsh Phosphorus Gradient

7+

Permanent Storage

~ Biomass P

Soil P

Water ColumnP

Soil P

Water ColumnP

~ Biomass P

Water ColumnP

Water ColumnP

1 3+3Number of Calibration Parameters

Net Fluxes

Model Evolution, 1993 - 2008

Everglades Phos. Gradient Model1993-1995 1996-1997 1999-2002, 2003-2005 Concept

EPGM/DMSTA HybridDynamic Model for STA'sSTA Design Model

> 80 Platforms Used in Calibration & TestingDaily Water & P Balances, .01-150 km2, 1-30yrs

DMSTA2 – 2005Calibrations to Five Community Types

Actual Operation

Full Operation Assumed in Design

STA-2 Simulation, 2001-2007

STA-1W Simulation, 2000-2007

Actual Operation

Full Operation Assumed in Design

Al d bi d di

Marsh Phosphorus Gradient

Inflows

WCA-2A Gradient TP ConcentrationsDMSTA Simulation, 1978-2004

4 km

7 km

10 km

Coupled EPGM & DMSTA

P Storage g / m2

0.005 - 0.1

0.2 - 4?

?1 - 3

tt-1....

t-n

Permanent Storage

Vegetation

Floc

2 - 10 Soil - Layer Cake

Cwater = F ( X , T) Csoil = F ( X , Z , T)

Water

"Biomachine"

Soil P Accretion vs. Water TP

0

200

400

600

800

1000

1200

0 20 40 60 80 100 120

Water-Col. P Conc (ppb)

P A

ccre

tion

Rat

e (m

g/m

2 -yr)

K = 10 m/yrWCA-2A / UFLWCA-2A / Duke

STADM & EPGM CornerstonesDated Soil Cores from WCA-2A, 1991

Reflecting 26 Yrs of P Loading & Peat Accretion

0

200

400

600

800

1000

1200

1400

1600

1800

2000

0 200 400 600 800 1000

P Accretion Rate (mg/m2-yr)

Soil

P C

onte

nt (

mg

/ kg

)

WCA-3AWCA-1WCA-2A / UFLAWCA-2A / Duke

Soil P Content vs. Accretion Rate

EPGM Simulation of WCA-2A - 1991Gradients in Soil P Content & Accretion Rates

0

500

1000

1500

2000

2500

0 2 4 6 8 10 12

Distance South of L-39 (km)

Soi

l P C

onte

nt (m

g/kg

)

0.0

0.2

0.4

0.6

0.8

1.0

1.2

0 2 4 6 8 10 12Distance South of L-39 (km)

Soil

Accr

etio

n R

ate

(cm

/yr)

0.0

0.1

0.2

0.30.4

0.5

0.6

0.70.8

0.9

1.0


Soil

Accr

etio

n R

ate

(kg/

km2-

yr)

0

200

400

600

800

1000

1200


Soil

P A

ccre

tion

Rat

e (m

g/m

2-yr

)

P Accretion P Content

Soil Volume AccretionSoil Mass Accretion

SFWMD Research Transects, 1996-2006Plant Storage Estimated From DMSTA CalibrationTP Conc. Range ~80 to 8 ppb, Water TP Storage ~ 0.004 to 0.04 g/m2

0

5

10

15

20

25

F1 F2 F3 F4 F5

TP g

/m2

WaterPlantsFloc0-2 cm Soil2-10 cm Soil

TP Storage in WCA-2A, 1996-2006

Time Scales of P Storage in Soil & VegetationBased upon DMSTA & EPGM Calibrations

10 ppb 50 ppb

0.1

1.0

10.0

100.0

0 10 20 30 40 50 60Water TP Conc ppb

Year

s

0 - 10 cm SoilBD = .10 g/cc

BD = .05 g/cc

30 - 60 yrs

7- 14 yrs

0.7 - 3 yrs

0 - 2 cm SoilBD = .10 g/cc

BD = .05 g/cc

0.2 - 0.6 yrs

3 - 6 yrs

10 - 20 yrs

Submergent

EmergentVegetation

0

500

1000

1500

2000

2500

E1 E2 E3 E4 E5 F1 F2 F3 F4 F5 U1 U2 U3 X1 X2 X3 X4 Y4 Z1 Z2 Z3 Z4

TP m

g / k

g

Floc0-2 cm2-10 cm

WCA-2A --> WCA-1 -->

Soil P Contents vs. Depth IncrementsSFWMD Research Transects, 1996-2006

Effect of Including Floc on 0-10 cm Soil TP SFWMD Research Transects, 1996-2006

0

200

400

600

800

1000

1200

1400

1600

E1 E2 E3 E4 E5 F1 F2 F3 F4 F5 U1 U2 U3 X1 X2 X3 X4 Y4 Z1 Z2 Z3 Z4

TP m

g / k

g

0-10 cm Soil0-10 cm Soil + Floc

WCA-2A --> WCA-1 -->

Coupled DMSTA/EPGM Simulation of Soil TP GradientsSFWMD Research Transects in WCA-2A, 1996-2006

Year =1996

0200400600800

100012001400160018002000

0 5 10 15 20Distance (km)

Soi

l TP

mg/

kg0-10 cm0-10 cm + FlocPredicted

Year =1997

0

200

400

600

800

1000

1200

1400

1600

1800

0 5 10 15 20

Distance (km)

Soi

l TP

mg/

kg

0-10 cm0-10 cm + FlocPredicted

Year =1998

0

200

400

600

800

1000

1200

1400

1600

1800


Soil T

P m

g/kg


Year =1999

0

200

400

600

800

1000

1200

1400

1600

1800


Soi

l TP

mg/

kg


Year =2000

0

200

400

600

800

1000

1200

1400

1600

1800


Soi

l TP

mg/

kg


Year =2001

0

200

400

600

800

1000

1200

1400

1600

1800

2000

0 5 10 15 20

Distance (km)

Soil

TP m

g/kg


Year =2004

0

200

400

600

800

1000

1200

1400

1600

1800

0 5 10 15 20

Distance (km)

Soil

TP m

g/kg


Year =2006

0

200

400

600

800

1000

1200

1400

1600

1800

0 5 10 15 20

Distance (km)

Soil

TP m

g/kg


0 - 10 cm SoilWith & Without Floc

Simulated Historical P Gradients in WCA-2A, 1965-2005

0 - 10 cm Soil TP

0

200

400

600

800

1000

1200

1400

1600

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15

Distance km

mg/

kg20051995198519751965

2005

1965

Increasing then Decreasing

Increasing

WCA-2A Simulation, 1963 - 2007Areas Exceeding Water & Soil P Criteria

Inflow TP Load

020406080

100120

1963 1973 1983 1993 2003

TP L

oad

mt/y

r

Water Column TP Conc

020406080

100120140160180

1963 1973 1983 1993 2003

Area

> 10 ppb> 20 > 50

Vegetation P Storage

020406080

100120140160180

1963 1973 1983 1993 2003

Area

>500 mg/m2>1000>2000

Soil TP, Depth = 0 - 2 cm

020406080

100120140160180

1963 1973 1983 1993 2003

> 500 mg/kg> 700> 1000


020406080

100120140160180

1963 1973 1983 1993 2003Ar

ea

> 500 mg/kg> 700> 1000

Cattail Density

020406080

100120140160180

1963 1973 1983 1993 2003

Area

>10%>50%>90% ?

Decreasing Rainfall & P Load

A

Water Column TP Conc

020406080

100120140160180

1963 1973 1983 1993 2003 2013 2023 2033 2043 2053

Are

a

> 10 ppb> 20 > 50

Vegetation P Storage

020406080

100120140160180

1963 1973 1983 1993 2003 2013 2023 2033 2043 2053

Are

a

>500 mg/m2>1000>2000

Inflow TP Load

0

20

40

60

80

100

120

1963 1973 1983 1993 2003 2013 2023 2033 2043 2053

TP L

oad

mt/y

r

BMP's

STA's

Hypothetical 10 ppb

“Taking Her Out for a Spin”100-Year Simulation of WCA-2A – Restoration Scenario

Areas Exceeding Water & Soil P Criteria


020406080

100120140160180

1963 1973 1983 1993 2003 2013 2023 2033 2043 2053

> 500 mg/kg> 700> 1000


020406080

100120140160180

1963 1973 1983 1993 2003 2013 2023 2033 2043 2053A

rea

> 500 mg/kg> 700> 1000

Cattail Density

020406080

100120140160180

1963 1973 1983 1993 2003 2013 2023 2033 2043 2053

Are

a

>10%>50%>90%

Model Explicit Factors

• Water & Mass Balance• Inflow Volumes & Loads• Rainfall, ET, Seepage• Depths / Hydraulics• Community Types• P Uptake by Vegetation/Floc• P Recycle from Veg/Floc• Net P Accretion in Soils

Implicit FactorsEmbedded in Calibrations

• Phosphorus Speciation• Calcium • Topographic Variations• Non-Ideal Flow • Particle / Floc Transport• STA Startup Transients• Community Transition• Plant Uptake from Soil• P Release from Soil• Vertical Transport of P within Soil

Data & Research Needs to Support Modeling

• Continue / Expand Marsh Transects• Dated Sediment Cores• Consistent Soil Sampling Methods vs. Yrs, Investigators, & Sites• Soil P Criteria for Ecological Impact (Depth Interval, Speciation, Conc.

Levels) to Track Restoration Progress• The 0-10 cm / 400-500 mg/kg Criteria Reflect Historical Conditions,

but are “Ambitious” Goals with Very Long Time Scales. • Floc Characterization & Transport • Soil P Reflux Studies• Impact of Calcium on P Cycling Parameters • Differences in Treatment Efficiency - Lake Okee vs. EAA Runoff• Several others….

Documents

Modeling Phosphorus Dynamics in Everglades Wetlands