Mercury Accumulation in Waterbirds (Black Rails) Related to Sediment Chemistry in San Francisco Bay Wetlands Completed
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.
Methylmercury is a globally pervasive contaminant that is a concern in San Francisco Bay, California, because hydraulic mining during the Gold Rush resulted in mercury-contaminated sediments in the bay. Mercury-contaminated sediments have put several species of waterbirds, including the State-threatened California black rail (Laterallus jamaicensis coturniculus), at risk of exposure and adverse effects from methylmercury.
Black rails are year-round residents of San Francisco Bay, and previous studies demonstrated that a portion of the black rail population had methylmercury concentrations that could result in reproductive toxicity. Black rails from different wetlands had different concentrations of methylmercury; however, little is known about the factors that contribute to spatial differences in bioaccumulation in birds inhabiting the San Francisco Bay watershed. Understanding these drivers could provide clues to potential management strategies to mitigate exposure.
Sediment methylmercury concentrations differed among three tidal wetlands in the Petaluma River watershed in northern San Francisco Bay. Moreover, 3 of 26 measurements were identified that explained differences in sediment chemistry among wetlands: the porewater concentration of ferrous iron, the percent organic matter, and the sediment methylmercury concentration.
Without harm to the birds, the researchers measured stable carbon and nitrogen isotopes in feather samples and invertebrate prey to evaluate methylmercury biomagnification in food webs, and regurgitated material was analyzed to study the black rail diet. Food web structure and biomagnification were similar among wetlands. In addition, regurgitation samples indicated that black rails had similar diets among wetlands. Given the similarities in diet, food web structure, and methylmercury biomagnification among wetlands, the scientists concluded that the variation in sediment chemistry and associated sediment methylmercury production was the primary driver of differences in methylmercury concentrations among black rails from different wetlands.
Determining which regions and species are at risk of methylmercury toxicity remains challenging because methylmercury production and availability are controlled by complex and variable factors in tidal wetlands. Studies, such as this one, that consider the effect of sediment chemistry, food web structure, and diet on methylmercury bioaccumulation, provide the science to support management decisions and mitigation strategies for methylmercury contamination.
This research was supported by the USGS Environmental Health Program (Contaminant Biology and Toxic Substances Hydrology) of the Ecosystems Mission Area, the USGS Western Ecological Research Center, a Calfed Bay-Delta Program grant (ERP02D-P62) to the San Francisco Estuary Institute, the U.S. Fish and Wildlife Service San Francisco Estuary Program, and the University of California Davis John Muir Institute for the Environment.
Below are other related science activities.
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
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
Methylmercury Impacts to Reproduction in the Eastern Mosquitofish (Gambusia holbrooki)
Below are publications associated with this research.
Disentangling the effects of habitat biogeochemistry, food web structure, and diet composition on mercury bioaccumulation in a wetland bird
Potential effects of mercury on threatened California black rails
Home range, habitat selection, and movements of California Black Rails at tidal marshes at San Francisco Bay, California
- Overview
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.
Methylmercury is a globally pervasive contaminant that is a concern in San Francisco Bay, California, because hydraulic mining during the Gold Rush resulted in mercury-contaminated sediments in the bay. Mercury-contaminated sediments have put several species of waterbirds, including the State-threatened California black rail (Laterallus jamaicensis coturniculus), at risk of exposure and adverse effects from methylmercury.
Black rails are year-round residents of San Francisco Bay, and previous studies demonstrated that a portion of the black rail population had methylmercury concentrations that could result in reproductive toxicity. Black rails from different wetlands had different concentrations of methylmercury; however, little is known about the factors that contribute to spatial differences in bioaccumulation in birds inhabiting the San Francisco Bay watershed. Understanding these drivers could provide clues to potential management strategies to mitigate exposure.
Sediment methylmercury concentrations differed among three tidal wetlands in the Petaluma River watershed in northern San Francisco Bay. Moreover, 3 of 26 measurements were identified that explained differences in sediment chemistry among wetlands: the porewater concentration of ferrous iron, the percent organic matter, and the sediment methylmercury concentration.
Without harm to the birds, the researchers measured stable carbon and nitrogen isotopes in feather samples and invertebrate prey to evaluate methylmercury biomagnification in food webs, and regurgitated material was analyzed to study the black rail diet. Food web structure and biomagnification were similar among wetlands. In addition, regurgitation samples indicated that black rails had similar diets among wetlands. Given the similarities in diet, food web structure, and methylmercury biomagnification among wetlands, the scientists concluded that the variation in sediment chemistry and associated sediment methylmercury production was the primary driver of differences in methylmercury concentrations among black rails from different wetlands.
Determining which regions and species are at risk of methylmercury toxicity remains challenging because methylmercury production and availability are controlled by complex and variable factors in tidal wetlands. Studies, such as this one, that consider the effect of sediment chemistry, food web structure, and diet on methylmercury bioaccumulation, provide the science to support management decisions and mitigation strategies for methylmercury contamination.
This research was supported by the USGS Environmental Health Program (Contaminant Biology and Toxic Substances Hydrology) of the Ecosystems Mission Area, the USGS Western Ecological Research Center, a Calfed Bay-Delta Program grant (ERP02D-P62) to the San Francisco Estuary Institute, the U.S. Fish and Wildlife Service San Francisco Estuary Program, and the University of California Davis John Muir Institute for the Environment.
- Science
Below are other related science activities.
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...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
Combined analyses of mercury, nitrogen, and carbon isotopes in archived lake trout ( Salvelinus namaycush ) tissues and sediment cores in Lake Michigan from 1978 to 2012 indicated that lake trout mercury concentrations mirrored declines in mercury sources prior to the arrival of invasive species that changed mercury transfer through the food and dampened the expected decreases in mercury...Mercury Isotope Ratios used to Determine Sources of Mercury to Fish in Northeast U.S. Streams
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...Methylmercury Impacts to Reproduction in the Eastern Mosquitofish (Gambusia holbrooki)
USGS researchers investigate the effects of methylmercury contamination on reproduction of the Eastern mosquitofish, a common fish in South Florida. - Publications
Below are publications associated with this research.
Disentangling the effects of habitat biogeochemistry, food web structure, and diet composition on mercury bioaccumulation in a wetland bird
Methylmercury (MeHg) is a globally pervasive contaminant with known toxicity to humans and wildlife. Several sources of variation can lead to spatial differences in MeHg bioaccumulation within a species including: biogeochemical processes that influence MeHg production and availability within an organism’s home range; trophic positions of consumers and MeHg biomagnification efficiency in food websAuthorsLaurie Anne Hall, Isa Woo, Mark C. Marvin-DiPasquale, Danika C Tsao, David P. Krabbenhoft, John Y. Takekawa, Susan E. W. De La CruzPotential effects of mercury on threatened California black rails
San Francisco Bay (SFB) estuary sediments contain high levels of mercury (Hg), and tidal marsh resident species may be vulnerable to Hg contamination. We examined Hg concentrations in California black rails, a threatened waterbird species that inhabits SFB tidal salt marshes. We captured 127 black rails during the prebreeding and postbreeding seasons and examined the influence of site, sex, and yeAuthorsDanika C. Tsao, A. Keith Miles, John Y. Takekawa, Isa WooHome range, habitat selection, and movements of California Black Rails at tidal marshes at San Francisco Bay, California
Little is known about the movements and habitat selection of California Black Rails (Laterallus jamaicensis coturniculus) in coastal California. We captured 130 Black Rails, of which we radio-marked 48, in tidal marshes in San Francisco Bay during 2005 and 2006. Our objective was to examine their home ranges, movements, and habitat selection to improve the species' conservation. The mean fixed-kerAuthorsDanika C. Tsao, John Y. Takekawa, Isa Woo, Julie L. Yee, Jules G. Evens