LONG-TERM AND LARGE-SCALE TRENDS IN MERCURY BIOACCUMULATION

SUWANNEE RIVER BASIN, FLORIDA

Lia C. Chasar

Environmental Sciences InstituteFlorida A & M University

United States Geological SurveyNational Water Quality Assessment Program

Florida Integrated Science Center

Ted R. Lange

Florida Freshwater Fish and Conservation Commission

Methylation efficiency

Mercury source strength

Food chain

Hg in fish

After T.E. Mumley and K.E. Abu-Saba, in press.

Primary Study ObjectiveTo investigate the effects of source strength,

cycling, and food web interactions on the bioaccumulation of mercury in stream

ecosystems

USGS National Water Quality Assessment Program (NAWQA)Bioacumulation of Mercury in Stream Ecosystems

Stable isotopes help establishestuarine/marine trophic relationships

13C (o/oo)

-15.0 -14.5 -14.0 -13.5 -13.0

15N

(o/

oo)

4

6

8

10

12

14

Penaeid shrimp

Gray Snapper

Blacktip Shark

Schooner BankFlorida Bay

Atwell, L. et al. 1998. Can. J. Fish. Aquat. Sci. 55:1114-1121

Adapted by Robin Stewart, USGS, Menlo Park

Relationship between Hg and 15N in a marine food web

15N (per mil)

8 10 12 14 16 18 20 22

Hg

(u

g/g

dw

)

0.01

0.1

1

10

15N=5.5

15N9.5

Food web complexity

↑trophic level ≈ ↑15N ≈ ↑Hg burden

Questions

• Stable isotopes useful in establishing trophic relationships in riverine systems? – surface water run-off– tributaries– sharp gradients in water chemistry and productivity

Questions

• Stable isotopes useful in establishing trophic relationships in riverine systems? – surface water run-off– tributaries– sharp gradients in water chemistry and productivity

• Influence of local biogeochemical processes on bioaccumulation of contaminants (sp. Mercury) in riverine systems?– i.e. variability within a river reach vs. entire basin?

Long-term Monitoring of Mercury Body Burden for Largemouth Bass

Fowlers Bluff, Suwannee River

Collection Dates8/

1987

10/1

988

10/1

989

4/19

905/

1991

6/19

926/

1993

3/19

943/

1995

3/19

9612

/199

61/

1998

6/19

981/

1999

3/20

003/

2001

4/20

021/

2003

1/20

04

EH

g3

(g

/g)

0.0

0.2

0.4

0.6

0.8

1.0

1.2

8/19

8710

/198

810

/198

94/

1990

5/19

916/

1992

6/19

933/

1994

3/19

953/

1996

12/1

996

1/19

986/

1998

1/19

993/

2000

3/20

014/

2002

1/20

03

0.0

0.2

0.4

0.6

0.8

1.0

1.2

Drivers for fluctuations? (no apparent change in atm. dep.)

Questions

• Stable isotopes useful in establishing trophic relationships in riverine systems? – surface water run-off– tributaries– sharp gradients in water chemistry and productivity

• Influence of local biogeochemical processes on bioaccumulation of contaminants (sp. Mercury) in riverine systems?– i.e. variability within a river reach vs. entire basin?

• What drives temporal trend in mercury body burden of fish in Suwannee River basin?

The Suwannee River Basin(courtesy of Suwannee River Water Management District)

Gulf of M

exico

Gulf of M

exico

GeorgiaFlorida

Suwannee River

Santa Fe River

Withlacoochee RiverAlapaha River2002

2002

2002

1993, 2002

1993, 2002

1993, 2002

1993, 2002

1993, 2002

1993, 2002

1993

1993

1987-2002

River mile upstream from mouth of Suwannee River

Redbreast Sunfish2002

0 20 40 60 80 100 120 140 160 180

TH

g (

g/g)

0.02

0.04

0.06

0.08

0.10

0.12

0.14

Largemouth Bass2002

0 20 40 60 80 100 120 140 160 180

EH

g 3 (

g/g)

0.1

0.2

0.3

0.4

0.5

0.6

0.7

0.8

r ²=0.83

Suwannee RiverWithlacoochee RiverSanta Fe River

r2=0.89

Crayfish2002

20 40 60 80 100 120 140 160 180

MH

g (

g/g

)

-0.005

0.000

0.005

0.010

0.015

0.020

0.025

0.030

r2=0.68

13C (o/oo) relative to River Mile

20 40 60 80 100 120 140 160 180

13 C

(o

/oo

)

-32

-30

-28

-26

-24

-22

-20

15N (o/oo) relative to River Mile

20 40 60 80 100 120 140 160 180

15 N

(O

/OO

)

4

6

8

10

12

14

16

18

Role of Trophic Complexity?

Difference in stable isotopic signature (C, N) between crayfish and largemouth bass along river course

River miles upstream of Suwannee River mouth

20 40 60 80 100 120 140 160 180

(

13C

, 15N

) (o

/oo)

-12

-10

-8

-6

-4

-2

0

2

4

15N only slight decrease with distance upstreamMean 15N = 5.04 (±1.19)‰

Carbon

Nitrogen

Long-term flowMid- to Upper Suwannee River

Dis

ch

arg

e (

cfs

)

0

2000

4000

6000

8000

10000

12000

14000

16000Branford (76 river miles)White Springs (170 river miles)

pH

(fie

ld)

3

4

5

6

7

8

9

170 mi.

76 mi. 56 mi. 17 mi.

185 mi.

113 mi.135 mi.

Transport/transformation?(pH, DOC vary in both space and time)

Conclusions

• THg body burden in all three consumers has experienced decrease since 1987, however values have peaked repeatedly

• THg increases with increasing distance upstream for crayfish, redbreast sunfish and largemouth bass

• Stable isotopes indicate that local biogeochemical processes and mercury transport/transformation are likely more important than trophic level shifts in mercury bioaccumulation

What’s next?

• importance of water level– natural variability

• seasonal wetting/drying river margins – extreme events

• extended drought• flooding

• forcing factors – pH– DOC– additional Hg loading

• moving further downstream– continue decrease?– estuary as mixing zone?

• pH, quality of DOC, SO4 -

• resource management– temporal trends/advisories

Future Research:

Project SupportFlorida Department of Environmental ProtectionFlorida Fish and Wildlife Conservation CommissionUS Geological SurveyFlorida State UniversityWashington State University

Additional AcknowledgementsFDEPKerry TateTom AtkesonDon Axelrad

FFWCCDoug RichardsBeth Sargent

WSURay Lee

USGSTerry PetroskyLori Lewis

Lookin’ for bugs in all the wrong places…