Results from a 3-year study indicate there was support for the use of open- and deep-water treatment pools at the downstream end of seasonal wetlands to reduce methylmercury concentrations in water exported from the wetlands, but the treatment had no measurable effect on wetland fish. Questions remain about the long-term potential for mercury removal using this wetland management strategy.
Wetlands are productive habitats for fish and wildlife and provide ecological and economic benefits; however, the biogeochemical conditions common in wetlands, particularly seasonal wetlands, have been shown to facilitate methylmercury production, making methylmercury available to wetland animals and to downstream habitats.
Land managers are seeking methods to reduce methylmercury export from seasonal wetlands because methylmercury is a highly toxic form of mercury that affects the nervous system. Moreover, methylmercury can accumulate in fish, potentially affecting their health and the health of fish-consuming humans and wildlife.
The U.S. Geological Survey’s Ecologically-Driven Exposure Pathways Science Team tested the efficacy of a wetland management strategy designed to address the dual goals of reducing the amount of methylmercury exported from wetlands to downstream habitats and reducing methylmercury bioaccumulation in fish within the wetlands themselves.
The team’s approach was to modify the physical structure of existing seasonal wetlands to enhance the naturally occurring processes that have been shown to reduce methylmercury in other surface waters. These naturally occurring processes include particle settling, microbial degradation, and photo-demethylation. The team established four treatment and four control wetlands at the Cosumnes River Preserve in California. The control wetlands received traditional wetland management. In contrast, treatment wetlands had open- and deep-water pools constructed at the downstream end in an attempt to remove methylmercury from surface waters.
During 2015–17, 3,000 (1,000 per year) western mosquitofish were tagged, weighed, and then caged for 30 days each season at specific locations within the control and treatment wetlands to determine changes in methylmercury concentrations. Water was sampled within 1 week of fish deployment and again within 1 week of fish retrieval.
Methylmercury concentrations in water were successfully decreased within treatment wetlands only during the third year of study, but treatment cells were not effective for reducing mercury concentrations in wetland fish. The scientists concluded there was limited support for the use of open- and deep-water treatment pools at the downstream end of seasonal wetlands to reduce methylmercury concentrations in water. Scientists suggest it may take more than 3 years to see decreases in fish mercury concentrations because wetland construction activities likely resulted in a short-term increase in methylmercury concentrations in fish. Therefore, it may take longer term studies to fully observe reductions in methylmercury concentrations in fish and water.
This research was funded by the U.S. Geological Survey Environmental Health Program (Contaminants Biology and Toxic Substances Hydrology) of the U.S. Geological Survey Ecosystems Mission Area, U.S. Environmental Protection Agency, California Department of Fish and Wildlife, and U.S. Geological Survey's San Francisco Bay-Delta Priority Ecosystems Science Program.
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Bioaccumulation of Mercury in Fish Varied by Species and Location in the Chesapeake Bay Watershed—Summary of Existing Data and a Roadmap for Integrated Monitoring
Mercury Accumulation in Waterbirds (Black Rails) Related to Sediment Chemistry in San Francisco Bay Wetlands
Dragonfly Larvae are Effective Bioindicators of Mercury Exposure in Fish and Amphibians—Results of Citizen Science in 100 National Parks and Protected Places
Food Web Changes Dampen Expected Reductions in Lake Trout Mercury Levels in Lake Michigan—Invasive Species Play Major Role
Mercury Isotope Ratios used to Determine Sources of Mercury to Fish in Northeast U.S. Streams
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- Overview
Results from a 3-year study indicate there was support for the use of open- and deep-water treatment pools at the downstream end of seasonal wetlands to reduce methylmercury concentrations in water exported from the wetlands, but the treatment had no measurable effect on wetland fish. Questions remain about the long-term potential for mercury removal using this wetland management strategy.
Sources/Usage: Public Domain. Visit Media to see details.The Cosumnes River Preserve, California. Wetlands are productive habitats for fish and wildlife and provide ecological and economic benefits; however, the biogeochemical conditions common in wetlands, particularly seasonal wetlands, have been shown to facilitate methylmercury production, making methylmercury available to wetland animals and to downstream habitats.
Land managers are seeking methods to reduce methylmercury export from seasonal wetlands because methylmercury is a highly toxic form of mercury that affects the nervous system. Moreover, methylmercury can accumulate in fish, potentially affecting their health and the health of fish-consuming humans and wildlife.
The U.S. Geological Survey’s Ecologically-Driven Exposure Pathways Science Team tested the efficacy of a wetland management strategy designed to address the dual goals of reducing the amount of methylmercury exported from wetlands to downstream habitats and reducing methylmercury bioaccumulation in fish within the wetlands themselves.
The team’s approach was to modify the physical structure of existing seasonal wetlands to enhance the naturally occurring processes that have been shown to reduce methylmercury in other surface waters. These naturally occurring processes include particle settling, microbial degradation, and photo-demethylation. The team established four treatment and four control wetlands at the Cosumnes River Preserve in California. The control wetlands received traditional wetland management. In contrast, treatment wetlands had open- and deep-water pools constructed at the downstream end in an attempt to remove methylmercury from surface waters.
During 2015–17, 3,000 (1,000 per year) western mosquitofish were tagged, weighed, and then caged for 30 days each season at specific locations within the control and treatment wetlands to determine changes in methylmercury concentrations. Water was sampled within 1 week of fish deployment and again within 1 week of fish retrieval.
Methylmercury concentrations in water were successfully decreased within treatment wetlands only during the third year of study, but treatment cells were not effective for reducing mercury concentrations in wetland fish. The scientists concluded there was limited support for the use of open- and deep-water treatment pools at the downstream end of seasonal wetlands to reduce methylmercury concentrations in water. Scientists suggest it may take more than 3 years to see decreases in fish mercury concentrations because wetland construction activities likely resulted in a short-term increase in methylmercury concentrations in fish. Therefore, it may take longer term studies to fully observe reductions in methylmercury concentrations in fish and water.
This research was funded by the U.S. Geological Survey Environmental Health Program (Contaminants Biology and Toxic Substances Hydrology) of the U.S. Geological Survey Ecosystems Mission Area, U.S. Environmental Protection Agency, California Department of Fish and Wildlife, and U.S. Geological Survey's San Francisco Bay-Delta Priority Ecosystems Science Program.
Sources/Usage: Public Domain.Graphical depiction of a seasonal wetland engineered to have a deeper pool and more open water on the downstream side of the wetland. This management strategy was tested during a 3-year period to determine if it resulted in a reduction of methylmercury in caged fish and surface water. - Science
Below are other science features associated with this research.
Bioaccumulation of Mercury in Fish Varied by Species and Location in the Chesapeake Bay Watershed—Summary of Existing Data and a Roadmap for Integrated Monitoring
Fish mercury data from State monitoring programs and research studies within the Chesapeake Bay were compiled and summarized to provide a comprehensive overview of the variation in fish mercury concentrations among species and habitats within the watershed. These data are put into context with existing health benchmarks for humans, birds, and fish. Scientists also provide a roadmap for an...Mercury Accumulation in Waterbirds (Black Rails) Related to Sediment Chemistry in San Francisco Bay Wetlands
The U.S. Geological Survey (USGS) assessed the effect of sediment chemistry, food web structure, and diet on mercury bioaccumulation in black rails in the San Francisco Bay watershed. Differences in mercury accumulation in the birds were related to differences in sediment chemistry in the wetlands.Dragonfly Larvae are Effective Bioindicators of Mercury Exposure in Fish and Amphibians—Results of Citizen Science in 100 National Parks and Protected Places
Mercury concentrations were measured in dragonfly larvae across more than 450 sites in 100 national parks and protected places as part of a partnership among Federal agencies, academic researchers, and more than 4,000 citizen scientists. Mercury concentrations in dragonfly larvae were positively correlated with mercury concentrations in fish and amphibians living in the same aquatic environments...Food Web Changes Dampen Expected Reductions in Lake Trout Mercury Levels in Lake Michigan—Invasive Species Play Major Role
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Mercury isotope analyses were used to distinguish different sources of mercury to fish in 23 streams along a forested-rural to urban-industrial land-use gradient in the Northeastern United States. The use of mercury isotope measurements in fish tissue allow for distinguishing different sources of mercury that are bioaccumulating into the food web. Mercury isotope signatures in fish in forested...Science to Help Understand Exposure and Toxicological Effects of Environmental Mercury to Representative Birds
Exposure and toxicity of environmental mercury to birds can be enhanced or lessened due to the available sources and forms of mercury and other species dependent factors such as life stage, migratory patterns, foraging and nesting behaviors, transfer of mercury from mothers to eggs, and sex. For example, mercury exposure can lead to sublethal toxicological effects that can influence parental... - Publications