Bioaccumulation
of Mercury by Fish and Fish-Forage Organisms in Camp Far West Reservoir,
Yuba and Placer Counties, California
The Problem
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Sorting
aquatic macroinvetebrates at the Bear River arm of Camp Far
West Reservoir. |
Mercury contamination from historic gold mining operations is widespread
in many rivers, lakes, and reservoirs on the western slopes of the
Sierra Nevada. Miners used mercury (quicksilver) to recover gold
from placer (alluvial) mines, which used hydraulic, drift, and dredging
methods, and from hardrock (lode) mines. At hydraulic mining operations,
placer ores were eroded with monitors (water cannons) and the resulting
slurry was directed through sluices and drainage tunnels where the
gold particles were combined with liquid mercury to form gold-mercury
amalgam. About 10-30% of the mercury used in this process was lost
each season, resulting in highly contaminated sediments downstream
from the mines. The annual loss of mercury from a typical sluice
was likely several hundred pounds during the operating season or
roughly 3-8 million pounds statewide. Although mercury was also
used in drift mining operations, in dredging operations, and at
hardrock mines, the amounts lost to the environment by these sources
have not been estimated. The northwestern Sierra Nevada region has
been mined extensively for both hardrock and placer deposits of
gold. In this region, the highest average concentrations of mercury
measured in fish tissues occur in the Bear River and South Yuba
River watersheds. Other investigators reported that mercury concentrations
were highest in upper-trophic-level predators (largemouth bass Micropterus
salmoides, smallmouth bass M. dolomieui, and spotted
bass M. punctatus) from Camp Far West Reservoir and Lake
Combie on the Bear River and Lake Englebright on the South Yuba
River, with lower concentrations occurring in benthic omnivores
(channel catfish, Ictalurus punctatus) and intermediate-trophic-level
predators (bluegill, Lepomis macrochirus; green sunfish,
L. cyanellus; and black crappie, Pomoxis nigromaculatus).
Moreover, 14% (8 of 57) of the basses had mercury concentrations
that exceeded 1.0 mg/kg (wet weight basis), the
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Electrofishing
boat being used as a work platform to sort aquatic macroinvertebrates
at the Rock Creek arm of Camp Far West Reservoir. |
FDA action level
for regulating mercury concentrations in commercial fish. A multidisciplinary
investigation by USGS is attempting to better understand mercury
dynamics and to identify hot spots within Camp Far West Reservoir
in order to determine if remediation efforts can reduce risks to
aquatic biota and humans (USGS 2001). The present study, which is
part of the multidisciplinary investigation, will examine several
ecological variables that could influence or control the amount
of mercury bioaccumulated by fish.
Objectives
Specific objectives are as follows: (i) to determine if mercury body burdens vary temporally and spatially in selected fishes and fish-forage macroinvertebrates; (ii) to determine how mercury body burdens vary according to chronological ages of fishes; (iii) to determine how mercury body burdens vary according to the trophic status of fishes; and (iv) to determine if methylmercury:total mercury ratios differ among fishes and fish-forage macroinvertebrates.
Methodology
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Close-up
view of spotted bass. |
Fish and macroinvertebrates will be sampled from Camp Far West Reservoir at three general locations as follows: the Bear River arm, the Rock Creek arm, and the lower reservoir adjacent to the dam. Fish will be sampled at bimonthly intervals from March 2002 to August 2003 whereas macroinvertebrates will be sampled only during July 2002 and July 2003.
Fish will be measured for total length and weight, and scale samples will be taken from a standard "scale sample area." The fish will then be preserved for analysis of gut contents. Excess fish and all non-target species will be counted and released alive.
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Melissa
Farinha (left) with a spotted bass captured while electrofishing
at Camp Far West Reservoir. Amy Story is on the right. |
During August 2002 and August 2003, the first 10 fish of selected species and size categories from each of three sampling sites will be identified with unique codes, measured for total length and weight, sampled for scales, then individually wrapped and bagged in plastic and placed on wet ice. Within 12 hr after returning to the field station, the gastrointestinal tracts (anterior end of esophagus to pyloric sphincter) of all sampled fish will be opened by dissection to remove gut contents. During August 2002, fish will be processed further by dissecting skinless and boneless fillets from both sides of each individual. After weighing, the fillets will be wrapped and bagged in plastic, then frozen. The remaining carcass (including dissected organs) of each fish will be weighed, then wrapped and bagged in plastic and frozen.
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Fracine
Mejia (left) removing scale samples from a spotted bass. Amy
Story (right) is holding a scale (coin) envelope. |
Bottom sediments and associated vegetation collected during July 2002 and July 2003 will be sorted for macroinvertebrates (crayfish, mayfly nymphs, and midge larvae). After sorting, the macroinvertebrates will be composited according to taxa and sampling site, then stored frozen. During each sampling date (July 2002 or July 2003), an attempt will be made to collect three composite samples of each macroinvertebrate taxon from each of the three sampling sites. Each composite sample should weigh at least 2.0 g (wet weight).
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Melissa
Farinha viewing magnified scale images with a microprojector. |
A maximum of 509 samples or subsamples of fish and macroinvertebrates will be analyzed for moisture content and total mercury concentration, whereas a maximum of 79 subsamples will be analyzed for methylmercury concentration. Frozen samples packaged at the Field Station will be shipped overnight to the Columbia Environmental Research Center (CERC), Columbia, Missouri, or USGS-approved laboratories for all mercury measurements.
Standard techniques will be used to determine fish ages from scale samples and food habits from gut samples.
Highlights and Key Findings
Results are not yet available for this recently initiated study.
Where Are We Headed In 2003
We will sample fish at bi-monthly intervals throughout FY-03 for determinations of age and gut contents. In addition, fish and macroinvertebrates will be sampled in July-August 2003 for mercury analysis.
Project Contact
Michael Saiki
U.S. Geological Survey
Western Fisheries Research Center
Dixon Duty Station
6924 Tremont Road
Dixon, CA 95620-9648
Email: michael_saiki@usgs.gov
Phone: 707-678-0682 x617
Fax: 707-678-5039
Publications
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