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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…