Sulfate as a Contaminant

in Freshwater Ecosystems:

Sources, Impacts and Mitigation

Speaker:

William H. Orem

U.S. Geological Survey

956 National Center, Reston, VA 20192

703-648-6273; borem@usgs.gov

Acknowledgments

Funding: ●USGS Priority Ecosystems Studies Program for South Florida

(G. Ronnie Best, Coordinator)

●Florida Department of Environmental Protection

(Donald Axelrad)

Co-Authors:William H. Orem1, Cynthia C. Gilmour2, David P. Krabbenhoft3,

and George R. Aiken4

1U.S. Geological Survey, Reston, VA2Smithsonian Environmental Research Center, Edgewater, MD3U.S. Geological Survey, Middleton, WI4U.S. Geological Survey, Boulder, CO

Acid RainDry

Deposition

Sea

SpraySurface

Runoff

Agriculture

Mine drainage

Urban runoff

Industrial runoff

Saltwater Intrusion

Sealevel Rise

Groundwater

Major Sources of Sulfur

to Freshwater Wetlands

Fire and Drought

~10-50 mg/L

~1-10 mg/L

> 50 mg/LEAA

Sulfate Distributions

In Surface Water

Lake

Okeechobee

WCA

2WCA

3

Gulf

of

Mexico

West

Palm

Beach

Miami<1.0 mg/L

Everglades

National

Park

Big

Cypress

National

Preserve

WCA

1

?

Sulfate moves from the EAA

and Lake Okeechobee down

canals and is discharged into

the Everglades through water

control structures and

breaches in levees

precipitation

2.5 mg/l

+5 permil

Sources of Sulfate to Marshes

of the Northern Everglades

canal discharge

58 mg/l

+21 permil

SO4/Cl = 0.5

shallow groundwater (3.8 m)

0.5 mg/l

+25 permil

deep groundwater (9.7 m)

186 mg/l

+12 permil

SO4/Cl = 0.2

diffusion and oxidation

of sulfide

marsh water

55 mg/l

+23 permil

SO4/Cl = 0.5

Water Conservation Area 2A, Site F1

Sulfate from

Lake Okeechobee

and EAA Fields

Uar

= 1.30

Uar

= 0.97

At low sulfate

concentrations

S isotope values span a

broad range, indicating

multiple sources

As sulfate concentrations

increase, a trend line in the

S isotope values emerges,

indicating that a single

source is dominating

The S isotope trend line

converges on a value of

about +16 per mil.

Agricultural sulfur used in

the EAA has a similar S

isotope value.

Everglades – Fire and Drought/Rewet Cycles

Effects on Sulfur and Mercury Biogeochemistry

● Oxidation of organic soil by fire or drought converts reduced

sulfur species (organic sulfur and metalsulfides) to sulfate, and

releases soil bound mercury and DOC

● After rewet, sulfate is remobilized into water, stimulating microbial

sulfate reduction and mercury methylation

● Large amounts of methylmercury may be produced before sulfate

is depleted and/or sulfide levels buildup to levels that inhibit

methylation

● Effect observed in field studies in the Everglades, in STAs

routinely dried down and rewet, and confirmed experimentally in

laboratory microcosm experiments

Background Photo: Fire in Northern WCA 3 – 1999

Experimental Dry/Rewet Setup

Desiccated Peat

Sulfur Impacts

on Freshwater Wetlands

● Sulfate promotes methylation

of mercury to its most toxic

and bioaccumulative form:

methylmercury

● Sulfide is toxic to plants and

animals

● Sulfate promotes release of

nutrients from sediments

(internal eutrophication)

● Sulfide binds metal ions and

sequesters them in soils as

metal sulfides

● Sulfate enhances

biodegradation of organic soils

sulfate

from canals

SOIL

SURFACE

WATER

mercury from

distant sources

Agricultural Fields and Canals

Everglades Agricultural Area

sulfate

sulfide

sulfate-reducing bacteria

Hg2+

methylmercury

bioaccumulation

of methylmercury

rainfall

Hg2+

Hg2+

sulfate in runoff

from agricultural

fields

Linking Sulfate and Methylmercury

in the Florida Everglades

Everglades

Marsh

Sulfate-MeHg Response

Goldilocks Zone

Sulfide

Inhibition

Zone

Sulfate

Limitation

Zone

“Just Right”

High SO4

Low SO4

MeHg

sw sulfate, mg/L

pw sulfide, mg/L

10-20 0> 50

0.2-0.3 0> 5

Relationship Between Sulfate and MeHg

ENR F1 U3 2BS 3A15 TS7 TS9 WCA1

su

rfa

ce

wa

ter

su

lfa

te

or

po

re w

ate

r su

lfid

e,

M

0.1

1

10

100

1000

Km

eth

, d

-1

0.00

0.01

0.02

0.03

0.04

0.05

Sulfate

methylation rate

Sulfide

Distributional data across Everglades’ sites

● MeHg production increases w/ SO4

up to at least 100 µM (10

mg/L)

● Methylation declines at porewater sulfide above ~ 20 µM (0.6

mg/L)

Day 57

y = 0.023x + 0.0572

R2 = 0.5854

0.0

0.1

0.2

0.3

0.4

0.5

0.6

0 5 10 15 20

SO4, mg/L

Me

20

2H

g, n

g/g

dw

Relationship Between Sulfate and MeHg – Mesocosm Studies

-Add sulfate to Everglades soil and MeHg

production increases (confirmed at 5

different sites)

-Linear relationship between sulfate and

MeHg production through 20 mg/L

-Sulfide inhibition above 20 mg/L sulfate

-Results confirmed by field, laboratory,

and mesocosm data

OUT CONT D10 D20 S4 S8 S12 S16 S20S12/D10

Me

Hg

F,

ng/L

0.0

0.2

0.4

0.6

0.8

1.0

1.2

1.4

1.6

1.8

sw

su

lfa

te,

mg

/L

0

2

4

6

8

10

12

14

16

pw

su

lfid

e,

ug/L

0

10

20

30

40

50

6/23/03

8/13/03

11/17/03

11/18/04

Sulfate

Sulfide

Data from: Gilmour, Krabbenhoft, Orem, Aiken

Data from: Gilmour, Krabbenhoft, Orem, Aiken

Pn

(µ

mo

l CO

2 m

-2 s

-1)

0

2

4

6

8

10

12

14

ab

a

abb

c

c

Cladium

Sulfide Concentration (mM)

Aerated 0 0.25 0.5 0.75 1

Pn

(µ

mo

l CO

2 m

-2 s

-1)

0

5

10

15

20

25

ab

aab

a

ab

b

Typha

Pn

(µm

ol C

O2

m-2

s-1

)

reduced (no halo)

1cm

1cm

reduced

(no halo)

Oxidized

(halo)

A B

Development of oxidized haloes around roots of Typha (A) and

Cladium (B) immersed in a reduced methylene blue-agar medium.

(Chabbi , McKee, Mendelssohn 2000)

● Cladium oxidized zone only

at root tips;Typha oxidized

zone all along root axis.

Sulfide Toxicity and

Macrophyte Growth

● Sawgrass (Cladium) more

sensitiveto to sulfide

toxicity than cattail (Typha)

sulfide levels >9 ppm Li, Mendelssohn, Chen, and Orem

Freshwater Biology, 2010

Copper-Nickel Sulfide Mining in Minnesota and

Sulfide Toxicity to Wild Rice

In Freshwater Wetlands

Mining of Sulfide Ores

oxidation

to sulfate

discharge of sulfate

to natural waters

Effects on Wild Rice:

healthy roots (left) and roots

with sulfidic black

discoloration (right)

Symptons of Sulfide Toxicity in Macrophytes

-interveinal chlorosis of emerging leaves

-black, poorly developed root system

-increased occurrence of diseases

1

FePO4(s)

H2S

FeS2(s)

+

PO4

3-

SO4

2-

SO4

2-

H2S

microbial

sulfate reduction

stimulation of

anaerobic microbial activity

organic soil

biodegradation

DOC

NH4

+

SURFACE WATER

SOIL Porewater

Internal Eutrophication from

Sulfate Contamination of Freshwater Wetlands

syntrophy

Sulfate Stimulation of Internal Eutrophication

-degradation of organic matter in soils

-enhanced release of nutrients into surface and

pore water

-enhanced release of disolved organic matter

(DOC and DON) into surface and pore water

Everglades Mesocosm

Study

● Reduce sulfur loading at source

-BMPs for agricultural sources

-Emission regulations for acid rain

-Reduce or mitigate mine drainage at source

-Avoid wet/dry cycles leading to internal sulfate sources

● Sulfate Mitigation

-Redeisgn existing Stormwater Treatment Areas (STAs) to

improve sulfate removal

-Pass contaminated water through limestone and feldspar as

an initial removal process

-Consider use of large anaerobic bioreactors

-Use of permeable reactive barriers for sulfate removal

-Reverse osmosis desalination

● Avoid direct discharges of contaminated water to sensitive wetland

areas

-use buffer wetlands to protect more sensitive areas

Sulfate Contamination of Freshwater Wetlands:

Mitigation Strategies

0

1

2

3

4

5

6

3/15

/1995

13-D

ec-9

5

27-M

ar-9

6

7-Ju

n-96

4-Dec

-96

21-A

pr-97

11-J

ul-97

14-J

an-9

8

29-J

un-98

19-J

ul-99

10-M

ay-0

0

10-J

ul-00

25-S

ep-0

0

1-Aug-0

1

29-N

ov-01

4-Dec

-01

9-Ja

n-02

6-Feb

-02

6/10

/2003

08/1

8/03

9/15

/2003

11/1

7/03

12/1

5/200

3

Su

lfate

(m

g/L

), H

gT

(n

g/L

)

0

0.1

0.2

0.3

0.4

0.5

0.6

0.7

0.8

0.9

1

MeH

g (

ng

/L)

Sulfate

HgT

MeHg

Central Everglades

Site 3A15

Decreasing sulfate loading in central Everglades resulted in rapid decline

in methylmercury production and levels of methylmercury in fish in <3

years

Response of Wetlands to Reduction in Sulfate Loading

can be Rapid

Questions?