The unique combination of natural processes and human activities present in western North America can strongly affect the exposure of fish and birds to methylmercury, the most toxic form of mercury (Hg).
The environmental health risk of Hg is strongly associated with landscape-scale processes that facilitate the conversion of inorganic Hg to methylmercury (MeHg). Inorganic Hg is naturally present in the landscape of western North America due to the geology of the region and its introduction through a combination of historic and contemporary human activities. This combination of distinct patterns in landscape structure, climate, and ecosystems can differentially affect the occurrence, transport, and food web bioaccumulation of Hg and MeHg from the wide variety of sources that exist in western North America.
This synthesis project resulted in the compilation, analysis, and interpretation of spatial and temporal patterns of Hg and MeHg occurrence in air, soil, vegetation, sediments, fish, and wildlife across western North America, which provided the most comprehensive evaluation to date (2016) on the distribution of Hg and MeHg in this region. Scientists evaluated the connections between landscape variables and concentrations of Hg and MeHg. Scientists also conducted time series analyses over several decades and assessed how resource management activities, such as reservoir management, affected Hg cycling. Additionally, Hg concentrations in fish and birds were evaluated relative to a series of toxicity benchmarks to evaluate potential risk to fish, wildlife, and humans. Results of this synthesis are published in a special issue of Science of the Total Environment.
Key Findings
- MeHg contamination in fish and birds is common in many areas throughout western North America, and many areas were found to have Hg concentrations above levels associated with toxicity.
- Patterns of MeHg exposure in fish and wildlife across western North America do not overlap with patterns of inorganic Hg on the landscape, which indicates a disconnect between inorganic Hg distribution and bioaccumulation in fish and wildlife. For example, forest soils contain more Hg than soils from semi-arid lands, yet the highest levels of MeHg in fish and wildlife tended to occur in semi-arid areas.
- Vegetation patterns strongly influence the amount of Hg emitted to the atmosphere from soils due to the effect of shading and plant uptake, thus forested areas retain atmospherically deposited Hg, whereas less-vegetated areas tend to release Hg to the atmosphere.
- Land disturbance, such as urban development, agriculture, and wildfires, are important factors in releasing stored Hg from the landscape, potentially making it available for biological uptake.
- Land and water management activities can strongly influence how inorganic Hg transforms to MeHg and can be transferred to fish, wildlife, and humans. Fish Hg concentrations are 1.5–2.6 times higher in reservoirs than in natural lakes, and the magnitude to water-level fluctuations was strongly correlated with fish Hg concentrations.
These studies highlight that environmental health risks associated with bioaccumulation in fish and birds in western North America are controlled by processes associated with MeHg production rather than the location of inorganic Hg sources or deposition. Developing strategies to mitigate MeHg production in the West may be particularly beneficial for reducing wildlife exposure.
This study was supported by the U.S. Geological Survey's (USGS) Powell Center for Analysis and Synthesis, USGS Ecosystem Mission Area's Environmental Health Program (Contaminant Biology Program and Toxic Substances Hydrology) as well as The National Park Service Air Resources Division, and the U.S. Environmental Protection Agency Region 10 Regional Applied Research Effort (RARE) Program.
More Information
- USGS Featured Story: Comprehensive Study finds Widespread Mercury Contamination Across Western North America
- Mercury Cycling, Bioaccumulation, and Risk across Western North America: A Landscape Scale Synthesis Linking Long-Term Datasets, Biodiversity Research Institute
- Mercury in Western North America—Spatiotemporal Patterns, Biogeochemistry, Bioaccumulation, and Risks, Special Issue of Science of the Total Environment on the Mercury synthesis
Related Featured Science Activities
See below for other science related to this research.
Ecologically-Driven Exposure Pathways Science Team
Mercury in Fish from 21 National Parks in the West
Satellite Tracking of Birds in Alaska Points to Distant Sources of Lead and Mercury Exposure
Mercury cycling, bioaccumulation, and risk across western North America: a landscape scale synthesis linking long-term datasets
Below are publications associated with this project.
Prediction of fish and sediment mercury in streams using landscape variables and historical mining
Comparison of mercury mass loading in streams to atmospheric deposition in watersheds of Western North America: Evidence for non-atmospheric mercury sources
Mercury and methylmercury in aquatic sediment across western North America
Trends in mercury wet deposition and mercury air concentrations across the U.S. and Canada
Estimating mercury emissions resulting from wildfire in forests of the Western United States
A synthesis of terrestrial mercury in the western United States: Spatial distribution defined by land cover and plant productivity
Reservoirs and water management influence fish mercury concentrations in the western United States and Canada
Assessing potential health risks to fish and humans using mercury concentrations in inland fish from across western Canada and the United States
Spatiotemporal patterns of mercury accumulation in lake sediments of western North America
Mercury risk to avian piscivores across western United States and Canada
Mercury in western North America: A synthesis of environmental contamination, fluxes, bioaccumulation, and risk to fish and wildlife
Methylmercury degradation and exposure pathways in streams and wetlands impacted by historical mining
Below are news stories associated with this project.
- Overview
The unique combination of natural processes and human activities present in western North America can strongly affect the exposure of fish and birds to methylmercury, the most toxic form of mercury (Hg).
Photo of Foster's Tern (Sterna forsteri) while hunting. Forster's terns are among the most at-risk wildlife species to mercury toxicity in western North America. Photo Credit: Joshua Ackerman, USGS The environmental health risk of Hg is strongly associated with landscape-scale processes that facilitate the conversion of inorganic Hg to methylmercury (MeHg). Inorganic Hg is naturally present in the landscape of western North America due to the geology of the region and its introduction through a combination of historic and contemporary human activities. This combination of distinct patterns in landscape structure, climate, and ecosystems can differentially affect the occurrence, transport, and food web bioaccumulation of Hg and MeHg from the wide variety of sources that exist in western North America.
This synthesis project resulted in the compilation, analysis, and interpretation of spatial and temporal patterns of Hg and MeHg occurrence in air, soil, vegetation, sediments, fish, and wildlife across western North America, which provided the most comprehensive evaluation to date (2016) on the distribution of Hg and MeHg in this region. Scientists evaluated the connections between landscape variables and concentrations of Hg and MeHg. Scientists also conducted time series analyses over several decades and assessed how resource management activities, such as reservoir management, affected Hg cycling. Additionally, Hg concentrations in fish and birds were evaluated relative to a series of toxicity benchmarks to evaluate potential risk to fish, wildlife, and humans. Results of this synthesis are published in a special issue of Science of the Total Environment.
Key Findings
- MeHg contamination in fish and birds is common in many areas throughout western North America, and many areas were found to have Hg concentrations above levels associated with toxicity.
- Patterns of MeHg exposure in fish and wildlife across western North America do not overlap with patterns of inorganic Hg on the landscape, which indicates a disconnect between inorganic Hg distribution and bioaccumulation in fish and wildlife. For example, forest soils contain more Hg than soils from semi-arid lands, yet the highest levels of MeHg in fish and wildlife tended to occur in semi-arid areas.
- Vegetation patterns strongly influence the amount of Hg emitted to the atmosphere from soils due to the effect of shading and plant uptake, thus forested areas retain atmospherically deposited Hg, whereas less-vegetated areas tend to release Hg to the atmosphere.
- Land disturbance, such as urban development, agriculture, and wildfires, are important factors in releasing stored Hg from the landscape, potentially making it available for biological uptake.
- Land and water management activities can strongly influence how inorganic Hg transforms to MeHg and can be transferred to fish, wildlife, and humans. Fish Hg concentrations are 1.5–2.6 times higher in reservoirs than in natural lakes, and the magnitude to water-level fluctuations was strongly correlated with fish Hg concentrations.
These studies highlight that environmental health risks associated with bioaccumulation in fish and birds in western North America are controlled by processes associated with MeHg production rather than the location of inorganic Hg sources or deposition. Developing strategies to mitigate MeHg production in the West may be particularly beneficial for reducing wildlife exposure.
This study was supported by the U.S. Geological Survey's (USGS) Powell Center for Analysis and Synthesis, USGS Ecosystem Mission Area's Environmental Health Program (Contaminant Biology Program and Toxic Substances Hydrology) as well as The National Park Service Air Resources Division, and the U.S. Environmental Protection Agency Region 10 Regional Applied Research Effort (RARE) Program.
More Information
- USGS Featured Story: Comprehensive Study finds Widespread Mercury Contamination Across Western North America
- Mercury Cycling, Bioaccumulation, and Risk across Western North America: A Landscape Scale Synthesis Linking Long-Term Datasets, Biodiversity Research Institute
- Mercury in Western North America—Spatiotemporal Patterns, Biogeochemistry, Bioaccumulation, and Risks, Special Issue of Science of the Total Environment on the Mercury synthesis
Related Featured Science Activities
- Science
See below for other science related to this research.
Ecologically-Driven Exposure Pathways Science Team
The Ecologically-Driven Exposure Pathways Integrated Science Team identifies how ecological pathways and physiological processes within a single organism can alter exposure and toxicity of contaminants and pathogens and seek to understand outcomes at different scales from individuals to populations and ecosystems.Mercury in Fish from 21 National Parks in the West
U.S. Geological Survey (USGS) and National Park Service (NPS) scientists collaborated in the first study to measure mercury in fish from remote places in 21 National Parks spanning 10 Western States, including Alaska. Mercury levels in fish generally were low, but were elevated in some local areas, including two parks in Utah and Alaska where samples taken from sport fish exceeded the U.S...Satellite Tracking of Birds in Alaska Points to Distant Sources of Lead and Mercury Exposure
U.S. Geological Survey (USGS) scientists measured lead in blood from tundra swans that nest in Alaska and then followed the migration of these birds using satellite telemetry. Levels of lead in blood were higher in adults than young swans,suggesting exposure to lead occurs on wintering areas and/or during migration, rather than on the summer breeding grounds in Alaska. The lowest blood levels were...Mercury cycling, bioaccumulation, and risk across western North America: a landscape scale synthesis linking long-term datasets
Mercury (Hg) is a serious environmental problem that is impacting ecological and human health on a global scale. However, local and regional processes are largely responsible for producing methylmercury, which drives ecological risk. This is particularly true in western North America where the combination of diverse landscapes, habitat types, climates, and Hg sources may disproportionally impact t - Publications
Below are publications associated with this project.
Filter Total Items: 17Prediction of fish and sediment mercury in streams using landscape variables and historical mining
Widespread mercury (Hg) contamination of aquatic systems in the Sierra Nevada of California, U.S., is associated with historical use to enhance gold (Au) recovery by amalgamation. In areas affected by historical Au mining operations, including the western slope of the Sierra Nevada and downstream areas in northern California, such as San Francisco Bay and the Sacramento River–San Joaquin River DelAuthorsCharles N. Alpers, Julie L. Yee, Joshua T. Ackerman, James L. Orlando, Darrell G. Slotton, Mark C. Marvin-DiPasqualeComparison of mercury mass loading in streams to atmospheric deposition in watersheds of Western North America: Evidence for non-atmospheric mercury sources
Annual stream loads of mercury (Hg) and inputs of wet and dry atmospheric Hg deposition to the landscape were investigated in watersheds of the Western United States and the Canadian-Alaskan Arctic. Mercury concentration and discharge data from flow gauging stations were used to compute annual mass loads with regression models. Measured wet and modeled dry deposition were compared to annual streamAuthorsJoseph L. Domagalski, Michael S. Majewski, Charles N. Alpers, Chris S. Eckley, Collin A. Eagles-Smith, Liam N. Schenk, Susan WherryMercury and methylmercury in aquatic sediment across western North America
Large-scale assessments are valuable in identifying primary factors controlling total mercury (THg) and monomethyl mercury (MeHg) concentrations, and distribution in aquatic ecosystems. Bed sediment THg and MeHg concentrations were compiled for > 16,000 samples collected from aquatic habitats throughout the West between 1965 and 2013. The influence of aquatic feature type (canals, estuaries, lakesAuthorsJacob Fleck, Mark C. Marvin-DiPasquale, Collin A. Eagles-Smith, Joshua T. Ackerman, Michelle A. Lutz, Michael T. Tate, Charles N. Alpers, Britt D. Hall, David P. Krabbenhoft, Chris S. EckleyByEcosystems Mission Area, Water Resources Mission Area, Environmental Health Program, Toxic Substances Hydrology, California Water Science Center, Forest and Rangeland Ecosystem Science Center, John Wesley Powell Center for Analysis and Synthesis, Upper Midwest Water Science Center, Mercury Research LaboratoryTrends in mercury wet deposition and mercury air concentrations across the U.S. and Canada
This study examined the spatial and temporal trends of mercury (Hg) in wet deposition and air concentrations in the United States (U.S.) and Canada between 1997 and 2013. Data were obtained from the National Atmospheric Deposition Program (NADP) and Environment Canada monitoring networks, and other sources. Of the 19 sites with data records from 1997–2013, 53% had significant negative trends in HgAuthorsPeter S. Weiss-Penzias, David A. Gay, Mark E. Brigham, Matthew T. Parsons, Mae S. Gustin, Arnout ter ShureEstimating mercury emissions resulting from wildfire in forests of the Western United States
Understanding the emissions of mercury (Hg) from wildfires is important for quantifying the global atmospheric Hg sources. Emissions of Hg from soils resulting from wildfires in the Western United States was estimated for the 2000 to 2013 period, and the potential emission of Hg from forest soils was assessed as a function of forest type and soil-heating. Wildfire released an annual average of 310AuthorsJackson Webster, Tyler J. Kane, Daniel Obrist, Joseph N. Ryan, George R. AikenA synthesis of terrestrial mercury in the western United States: Spatial distribution defined by land cover and plant productivity
A synthesis of published vegetation mercury (Hg) data across 11 contiguous states in the western United States showed that aboveground biomass concentrations followed the order: leaves (26 μg kg− 1) ~ branches (26 μg kg− 1) > bark (16 μg kg− 1) > bole wood (1 μg kg− 1). No spatial trends of Hg in aboveground biomass distribution were detected, which likely is due to very sparse data coverage and dAuthorsDaniel Obrist, Christopher Pearson, Jackson Webster, Tyler J. Kane, Che-Jen Lin, George R. Aiken, Charles N. AlpersReservoirs and water management influence fish mercury concentrations in the western United States and Canada
Anthropogenic manipulation of aquatic habitats can profoundly alter mercury (Hg) cycling and bioaccumulation. The impoundment of fluvial systems is among the most common habitat manipulations and is known to increase fish Hg concentrations immediately following impoundment. However, it is not well understood how Hg concentrations differ between reservoirs and lakes at large spatial and temporal scAuthorsJames J. Willacker, Collin A. Eagles-Smith, Michelle A. Lutz, Michael T. Tate, Jesse M. Lepak, Joshua T. AckermanAssessing potential health risks to fish and humans using mercury concentrations in inland fish from across western Canada and the United States
Fish represent high quality protein and nutrient sources, but Hg contamination is ubiquitous in aquatic ecosystems and can pose health risks to fish and their consumers. Potential health risks posed to fish and humans by Hg contamination in fish were assessed in western Canada and the United States. A large compilation of inland fish Hg concentrations was evaluated in terms of potential health risAuthorsJesse M. Lepak, Mevin Hooten, Collin A. Eagles-Smith, Michael T. Tate, Michelle A. Lutz, Joshua T. Ackerman, James J. Willacker, Allyson K. Jackson, David C. Evers, James G. Wiener, Colleen Flanagan Pritz, Jay DavisSpatiotemporal patterns of mercury accumulation in lake sediments of western North America
For the Western North America Mercury Synthesis, we compiled mercury records from 165 dated sediment cores from 138 natural lakes across western North America. Lake sediments are accepted as faithful recorders of historical mercury accumulation rates, and regional and sub-regional temporal and spatial trends were analyzed with descriptive and inferential statistics. Mercury accumulation rates in sAuthorsPaul Drevnick, Colin A. Cooke, Daniella Barraza, Jules M. Blais, Kenneth Coale, Brian F. Cumming, Chris Curtis, Biplob Das, William F. Donahue, Collin A. Eagles-Smith, Daniel R. Engstrom, William F. Fitzgerald, Chad V. Furl, John R. Gray, Roland I. Hall, Togwell A. Jackson, Kathleen R. Laird, W. Lyle Lockhart, Robie W. Macdonald, Alisa Mast, Callie Mathieu, Derek C.G. Muir, Peter Outridge, Scott Reinemann, Sarah E. Rothenberg, Ana Carolina Ruiz-Fernandex, V.L. St. Louis, Rhea Sanders, Hamed Sanei, Elliott Skierszkan, Peter C. Van Metre, Timothy Veverica, Johan A. Wiklund, Brent B. WolfeMercury risk to avian piscivores across western United States and Canada
The widespread distribution of mercury (Hg) threatens wildlife health, particularly piscivorous birds. Western North America is a diverse region that provides critical habitat to many piscivorous bird species, and also has a well-documented history of mercury contamination from legacy mining and atmospheric deposition. The diversity of landscapes in the west limits the distribution of avian piscivAuthorsAllyson K. Jackson, David C. Evers, Collin A. Eagles-Smith, Joshua T. Ackerman, James J. Willacker, John E. Elliott, Jesse M. Lepak, Stacy S. Vander Pol, Colleen E. BryanMercury in western North America: A synthesis of environmental contamination, fluxes, bioaccumulation, and risk to fish and wildlife
Western North America is a region defined by extreme gradients in geomorphology and climate, which support a diverse array of ecological communities and natural resources. The region also has extreme gradients in mercury (Hg) contamination due to a broad distribution of inorganic Hg sources. These diverse Hg sources and a varied landscape create a unique and complex mosaic of ecological risk fromAuthorsCollin A. Eagles-Smith, James G. Wiener, Chris S. Eckley, James J. Willacker, David C. Evers, Mark C. Marvin-DiPasquale, Daniel Obrist, Jacob Fleck, George R. Aiken, Jesse M. Lepak, Allyson K. Jackson, Jackson Webster, Robin Stewart, Jay Davis, Charles N. Alpers, Joshua T. AckermanMethylmercury degradation and exposure pathways in streams and wetlands impacted by historical mining
Monomethyl mercury (MMHg) and total mercury (THg) concentrations and Hg stable isotope ratios (δ202Hg and Δ199Hg) were measured in sediment and aquatic organisms from Cache Creek (California Coast Range) and Yolo Bypass (Sacramento Valley). Cache Creek sediment had a large range in THg (87 to 3870 ng/g) and δ202Hg (−1.69 to −0.20‰) reflecting the heterogeneity of Hg mining sources in sediment. TheAuthorsPatrick M. Donovan, Joel D. Blum, Michael B. Singer, Mark C. Marvin-DiPasquale, Martin T.K. Tsui - News
Below are news stories associated with this project.