Geochemistry of phosphorus in a carbonate aquifer affected

by seawater intrusion

René M. Price (FIU) Jeremy C. Stalker (FIU)Jean L. Jolicoeur (FIU)

Naples

Everglades National Park

2003 Salinity contourIn wells < 25 m

A

A’

50

100

300

Hawthorn Group

Floridan Aquifer

met

ers

Sea Level 0 Biscayne AquiferTamiami Sands

Gray Limestone AquiferUnnamed Sands

1000

Hawthorn Group (Aquiclude)

Surficial Aquifer

Seawater IntrusionSeawater Intrusion

A A'

Sites sampled in Sept. 2007 Surface water Porewater (30-60 cm) Wells (2 – 8 m)

Geochemical Parameters P, N, TOC Ca2+, Mg2+, N+, K+, Cl-, SO4

2-, HCO3-

pH, Temp, Sal.

Groundwater Sampling

0

2

4

6

8

10

0 10 20 30 40

salinity (psu)

TP

(m M

)

Surface Water

Groundwater

Gulf of Mexico

0

2

4

6

8

10

0 10 20 30 40

salinity (psu)P

O43-

(m M

)

Surface Water

Groundwater

Gulf of Mexico

(Boyer et al., 1999)

y = 0.12x - 0.49

R2 = 0.59

0

2

4

6

8

10

0 10 20 30 40

salinity (psu)P

O43-

(m M

)

Surface Water

Groundwater

Gulf of Mexico

Linear (Groundwater)

y = 0.1427x

R2 = 0.4061

0

2

4

6

8

10

0 10 20 30 40

salinity (psu)

TP

(m M

)

Surface Water

Groundwater

Gulf of Mexico

Linear (Groundwater)

-2.0

-1.5

-1.0

-0.5

0.0

0.5

1.0

0 25 50 75 100

% seawater

SI a

rag

on

ite

Surface water

Supersaturation (mineral precipitation)

undersaturation (mineral dissolution)

-2.0

-1.5

-1.0

-0.5

0.0

0.5

1.0

0 25 50 75 100

% seawater

SI a

rag

on

ite

Surface water

-2.0

-1.5

-1.0

-0.5

0.0

0.5

1.0

0 25 50 75 100

% seawater

SI a

rag

on

ite

Surface water

groundwater

-2.0

-1.5

-1.0

-0.5

0.0

0.5

1.0

0 25 50 75 100

% seawater

SI c

alci

te

Surface water

groundwater

-10.0

-8.0

-6.0

-4.0

-2.0

0.0

0 25 50 75 100

% seawater

SI a

pat

ite

Surface water

groundwater

Research Question

How much P is incorporated in Biscayne Aquifer limestone?

What are the adsorption/desorption characteristics of P in fresh versus salty

groundwater?

Water-Rock Interactions

Ion Exchange

CaCO3

Dissolution

P Extraction Methods

0.5 g rock Dried and weighed

Sequential Extraction1. MgCl – loosely adsorbed fraction 2. HCl digestion followed by filtration

for total P determinations3. Total P determination on filter

residue for organic fraction

Phosphorus in Biscayne Aquifer Limestone

0

10

20

30

40

50

looselyadsorbed

HCl organic total

P Fraction

g P

/g r

ock

Adsorption/Desorption cube experiments

• Cube 0.2m on a side of Key Largo Limestone. • freshwater (DIW) and seawater matrix

• with PO43- varying from 0 to 20μM

6

2

3 4 5

6

2

3 4 55

0.0

0.1

0.2

0.3

0.4

0.5

0.6

0.7

0.8

0.9

1.01.0

conservative non-conservative

Breakthrough Curves

C/C

o

liters

DIW with 8 and then 20 mM of P

Adsorption

Liters through the cube

0 10 20 30 40 50

Pout / P

in (

%)

0.0

0.2

0.4

0.6

0.8

1.020 mM of P : 60% of P adsorbed 8 mM of P : 80% of P adsorbed

DIW vs. Seawater with 8 mM of PO43-

Adsorption

Liters through the cube

0 10 20 30 40 50

Pout / P

in (

%)

0.0

0.2

0.4

0.6

0.8

1.0

DIW + 8 mM of PO4 : 80% of P Adsorbed SW + 8mM of PO4: 15% of P Adsorbed

Desorption

Liters through the cube

0 20 40 60 80 100

P ou

t (m M

/L)

0

5

10

15

20

Sal

inity

fra

ctio

n

0.0

0.2

0.4

0.6

0.8

1.0

Seawater DIWSalinity

Geochemical Analysis

Cl - (mM)

0 100 200 300 400 500 600

Ca

2+ (

mM

)

0

2

4

6

8

10

12

14

Left - DI, Right - SW

Seawater mixing line

SW + PSW FlushingDI + PDI FlushingSW + DI Mixed

Cl- (mM)

0 100 200 300 400 500 600

HC

O3- (

mM

)

0.0

0.5

1.0

1.5

2.0

2.5

3.0

Left - DI, Right - SW

Seawater mixing line

SW FlushingDI + PDI FlushingSW + DI Mixed

Water Table

Seawater Intrusion

Brackish Zone

OceanP Ion Exchange

CaCO3

Dissolution

Conclusions

Publications• Price, R.M, and P.K. Swart, 2006, Geochemical indicators of

groundwater recharge in the Surficial Aquifer System, Everglades National Park, Florida, USA, in Harmon, R.S., and Wicks, C., eds., Perspectives on karst geomorphology, hydrology, and geochemistry—A tribute volume to Derek C. Ford and William B. White: Geological Society of America Special Paper 404:251-266.

• Price, R.M., P.K. Swart, and J.W. Fourqurean, 2006, Coastal groundwater discharge-an additional source of phosphorus for the oligotrophic wetlands of the Everglades, Hydrobiologia, 569:23-36.

• Price, R.M, J.D. Happell, Z. Top, and P. K. Swart. 2003, Use of tritium and helium to define groundwater flow conditions in Everglades National Park. Water Resources Research, 39(9), doi:10.1029/2002WR001929.

Acknowledgements• Jim Fourqurean –FIU Biology and SERC• Len Scinto-FIU SERC• Tatiana Marquez-FIU Environmental Sciences• Srikumar Roy- IIT Kharagpur, India• Kevin Cunningham-USGS• Chris Reich-USGS• Kevin Cunningham-USGS• Chris Reich-USGS• Thomas Smith III- USGS• Gordon Anderson - USGS• Vic Engel - ENP• Jana M. Newman – SFWMD

Funding Provided by: South Florida Water Management District and the Southeast Environmental Research Center

PHREEQC Results

Chloride (mM)

0 100 200 300 400 500 600

Sat

urat

ion

inde

x

-2

-1

0

1

2SW SIcDI SIcSW SIaDI SIa

Western Coastline of ENPSept. 2007

Gulf of Mexico(Boyer et al. 1999)

y = -0.74x + 103.57

R2 = 0.02

0

50

100

150

200

250

0 5 10 15 20 25 30 35 40

salinity (psu)

To

tal N

(m M

)

Surface Water Groundwater Linear (Groundwater)