More than 50 years of existing mercury and selenium concentrations in native and nonnative fish species residing in streams within the Upper Colorado River Basin were compiled and analyzed to provide an understanding of concentrations among different species, sampling years, and locations to determine potential health risks. Concentrations of mercury and selenium were above health benchmarks in 13 percent and 48 percent of individual fish, respectively, suggesting the health of some fishes may be impaired by these contaminants.
Native fish within the Upper Colorado River Basin encounter a suite of stressors including invasive species, habitat degradation, and flow alterations. Less attention has been given to contaminants as possible stressors, except for mercury and selenium, which are included in population recovery plans for some managed fish species of the Upper Colorado River Basin. Although these contaminants are known to be elevated in some fish species of the Upper Colorado River Basin, a broader spatial and temporal assessment was needed to understand the potential threats that these contaminants may have on the long-term viability of managed fish populations.
To meet this need, U.S. Geological Survey (USGS) scientists compiled 50 years (1962–2011) of mercury and selenium tissue concentrations for native and nonnative fish (2,324 individuals) collected during previous studies within the Upper Colorado River Basin. These studies were done to provide an understanding of concentrations among different species, sampling years, and locations in context with fish health benchmarks to determine potential health risks. The scientists used a statistical technique (linear mixed effects models) to estimate the average total mercury and selenium for each fish species while accounting for fish size, location, and year sampled. This technique allowed for comparison of contaminant concentrations among different studies.
Mercury and selenium concentrations varied by species and by location within the watershed. Concentrations of mercury and selenium were above health benchmarks in 13 and 48 percent of individual fish, respectively, and some species of management concern, such as the federally endangered Colorado pikeminnow (Ptychocheilus lucius) and the candidate roundtail chub (Gila robusta), accumulated mercury above health benchmarks. The Colorado pikeminnow and the razorback sucker (Xyrauchen texanus) had selenium concentrations that exceeded the selenium benchmarks. Most mercury exceedances were in White-Yampa River fish, whereas most selenium exceedances were in the Gunnison tributary fish.
The study identified data and knowledge gaps that can be used to guide research and monitoring to address the effects of mercury and selenium on species populations and recovery. For example, there is still a lack of mercury and selenium accumulation data for many native species in the Upper Colorado River Basin, including the razorback sucker, as well as for many nonnative fish. As such, a subsequent study on the razorback sucker and Colorado pikeminnow investigated selenium mobilization, partitioning, and trophic transfer along approximately 60 river miles of the selenium-impaired segment of the Lower Gunnison River. Results indicated that periods of selenium mobilization to surface waters have a larger-than-expected effect on selenium concentrations in food webs, that dissolved selenium concentrations are insufficient for predicting selenium concentrations in riverine food webs, and that ecosystem managers may underestimate risks by modeling selenium exposure based on those metrics.
This research demonstrates how a critical review of existing data can identify gaps and guide more targeted research. The retrospective assessment can inform future fish collection strategies to reveal if these contaminants pose additional risks to fish health today.
Funding for this study was provided by the Bureau of Land Management, Trapper Mine Corporation, Colorado River Round Table, Colorado Species Trust Fund, and the USGS Environmental Health Program (Toxic Substances Hydrology and Contaminant Biology), which is part of the Ecosystems Mission Area.
See below for other science related to this research.
Long-Term Monitoring Reveals How Water and Biota in Remote Lakes Respond Differently to Changes in Atmospheric Deposition of Mercury
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
Flood Redistributes Mercury in Grand Canyon Aquatic Food Webs
Wetland Management Technique Designed to Reduce Mercury in Water and Fish Tested During a Short-Term Field Study
Mercury Accumulation in Waterbirds (Black Rails) Related to Sediment Chemistry in San Francisco Bay Wetlands
- Overview
More than 50 years of existing mercury and selenium concentrations in native and nonnative fish species residing in streams within the Upper Colorado River Basin were compiled and analyzed to provide an understanding of concentrations among different species, sampling years, and locations to determine potential health risks. Concentrations of mercury and selenium were above health benchmarks in 13 percent and 48 percent of individual fish, respectively, suggesting the health of some fishes may be impaired by these contaminants.
Sources/Usage: Public Domain.U.S. Geological Survey scientists holding a Colorado pikeminnow during a sampling trip in the Upper Colorado River Basin. Native fish within the Upper Colorado River Basin encounter a suite of stressors including invasive species, habitat degradation, and flow alterations. Less attention has been given to contaminants as possible stressors, except for mercury and selenium, which are included in population recovery plans for some managed fish species of the Upper Colorado River Basin. Although these contaminants are known to be elevated in some fish species of the Upper Colorado River Basin, a broader spatial and temporal assessment was needed to understand the potential threats that these contaminants may have on the long-term viability of managed fish populations.
To meet this need, U.S. Geological Survey (USGS) scientists compiled 50 years (1962–2011) of mercury and selenium tissue concentrations for native and nonnative fish (2,324 individuals) collected during previous studies within the Upper Colorado River Basin. These studies were done to provide an understanding of concentrations among different species, sampling years, and locations in context with fish health benchmarks to determine potential health risks. The scientists used a statistical technique (linear mixed effects models) to estimate the average total mercury and selenium for each fish species while accounting for fish size, location, and year sampled. This technique allowed for comparison of contaminant concentrations among different studies.
Mercury and selenium concentrations varied by species and by location within the watershed. Concentrations of mercury and selenium were above health benchmarks in 13 and 48 percent of individual fish, respectively, and some species of management concern, such as the federally endangered Colorado pikeminnow (Ptychocheilus lucius) and the candidate roundtail chub (Gila robusta), accumulated mercury above health benchmarks. The Colorado pikeminnow and the razorback sucker (Xyrauchen texanus) had selenium concentrations that exceeded the selenium benchmarks. Most mercury exceedances were in White-Yampa River fish, whereas most selenium exceedances were in the Gunnison tributary fish.
The referenced media source is missing and needs to be re-embedded.White River in the Upper Colorado River Basin. The study identified data and knowledge gaps that can be used to guide research and monitoring to address the effects of mercury and selenium on species populations and recovery. For example, there is still a lack of mercury and selenium accumulation data for many native species in the Upper Colorado River Basin, including the razorback sucker, as well as for many nonnative fish. As such, a subsequent study on the razorback sucker and Colorado pikeminnow investigated selenium mobilization, partitioning, and trophic transfer along approximately 60 river miles of the selenium-impaired segment of the Lower Gunnison River. Results indicated that periods of selenium mobilization to surface waters have a larger-than-expected effect on selenium concentrations in food webs, that dissolved selenium concentrations are insufficient for predicting selenium concentrations in riverine food webs, and that ecosystem managers may underestimate risks by modeling selenium exposure based on those metrics.
This research demonstrates how a critical review of existing data can identify gaps and guide more targeted research. The retrospective assessment can inform future fish collection strategies to reveal if these contaminants pose additional risks to fish health today.
Funding for this study was provided by the Bureau of Land Management, Trapper Mine Corporation, Colorado River Round Table, Colorado Species Trust Fund, and the USGS Environmental Health Program (Toxic Substances Hydrology and Contaminant Biology), which is part of the Ecosystems Mission Area.
- Science
See below for other science related to this research.
Long-Term Monitoring Reveals How Water and Biota in Remote Lakes Respond Differently to Changes in Atmospheric Deposition of Mercury
A comparison of regional mercury atmospheric deposition data with water, yellow perch, and dragonfly larvae samples from lakes in Voyageurs National Park indicates that decreases in mercury emissions resulted in mercury reduction in water from these remote lakes, but mercury declines in biota were significant in only one of three lakes, likely because resident biota integrate exposure over much...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...Flood Redistributes Mercury in Grand Canyon Aquatic Food Webs
Scientists coupled the concepts of energy flow through food webs with measurements of mercury in organic matter and animals to estimate mercury fluxes and fate during an experimental flood in the Colorado River. The flood redistributed mercury in simple, upstream food webs but not in more complex, downstream food webs.Wetland Management Technique Designed to Reduce Mercury in Water and Fish Tested During a Short-Term Field Study
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.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. - Publications