The USGS Mercury Research Laboratory conducts assessments on national and regional scales.
National Scale Mercury Assessments
Mercury is truly a global pollutant that can affect landscapes far away from the source. Because of this, we have embarked on several national-scale mercury assessments to help monitor the impact of mercury across the country, including:
Mercury is among the chemical and physical stressors that can affect the ecology of small streams. The RSQA seeks to characterize the relationships between key stressors (i.e.: contaminants, nutrients, sediment, and streamflow alteration) and the overall health of the ecosystem. For each assessment, about 100 wadable streams, are sampled for chemical constituents over a short period in the spring/summer. The sampling culminates with an ecological survey of habitat, algae, benthic invertebrates, and fish, along with the collection of streambed sediment for chemical analysis and toxicity testing. To date, five RSQA campaigns have been completed: the Midwest (2013), the Southeast (2014), the Pacific Northwest (2015), the Northeast (2016), and California (2017). This effort is part of the USGS National Water-Quality Assessment (NAWQA) program.
The long-range atmospheric transport of mercury (Hg) makes anthropogenic emissions a serious concern for even the most remote regions of the United States. The transport and rapid bioaccumulation of Hg have resulted in fish concentrations that impose wildlife and human health concerns across the nation, even in pristine national parks. We partnered with the National Park Service and the USGS Forest and Rangeland Ecosystem Science Center (FRESC) to survey Hg concentrations and Hg stable isotopes across game fish and dragonflies in over 50 national parks. The goal of this work was to understand Hg sources to the food web and cycling differences between parks based on factors such as ecoregion, physical characteristics (e.g. elevation, canopy cover), and water chemistry.
Most of the mercury that enters a lake is typically recycled through the system until it is eventually buried in the bed sediments. The concentration of mercury in the sediments is one indicator of potential impairment to the fishery. We partner with the USEPA to provide concentrations of total and methylmercury in surface sediments for their National Lakes Assessment (NLA) program. The effort uses a statistical survey of lakes, ponds, and reservoirs across the US that is designed to: catalog the condition of lakes that support healthy biological condition and recreation; estimate the breadth of stressors that impact lake quality, and provide information on the long term improvement or degradation of lakes nationwide.
With the 2011 promulgation of the Mercury and Air Toxics Standards by the U.S. Environmental Protection Agency, and the successful negotiation by United Nations Environment Programme of the Minamata Convention, global emissions of mercury (Hg) to the atmosphere from anthropogenic sources are expected to decline. Recent reports suggest regional gaseous Hg declines have already begun well before they were anticipated; however, providing independent evidence for the drivers of such declines is difficult. To address this challenge, the U.S. Geological Survey and the National Atmospheric Deposition program (NADP) have initiated a national-scale effort to establish a baseline of total gaseous mercury (TGM) and Hg stable isotopic compositions using bulk-air sampling at 31 sites distributed across North America over a two-year period (March 2016 – May 2018).
Regional Scale Mercury Assessments
The long-term fate of atmospherically derived mercury deposition is dependent on the local environmental conditions. We have partnered on several regional-scale mercury assessments to better understand the biogeochemical mechanisms controlling the transport and transformation of mercury, including:
The Laurentian Great Lakes are among the largest freshwater lakes in the world and are a highly utilized and valuable North American resource. The Great Lakes have gone through substantial ecosystem-wide changes in the last century and are now home to a multitude of aquatic invasive species, pollutants of concern, and industrially polluted nearshore areas. Even still, mercury concentrations in Great Lakes pelagic water are some of the lowest that we’ve measured, however commonly consumed predator fish are often near mercury consumption advisory levels. Efforts to resolve this paradox began with the Great Lakes Restoration Initiative in 2010 and are still ongoing. The goal of this research was to create a comprehensive data set from various environmental matrices across all five lakes, and to examine how mercury cycles within the lakes and enters the food web.
Elevated mercury levels in the aquatic food web of the Florida Everglades has been a public concern since the late 1980’s and remains a persistent issue confronting ecosystem restoration. Several factors that indicate sensitivity to mercury contamination are characteristic of the Everglades, including: elevated atmospheric Hg deposition; the presence of wetlands; abundant natural organic carbon in surface water and sediments; ample supply of anaerobic substrate; plentiful sources of sulfate; and common occurrences of environmental disturbances that are known to promote methylation (e.g., fire and droughts).
The USGS MRL assembled a multidisciplinary team that addressed seasonal distributions of aqueous mercury species in the Water Conservation Areas of the northern Everglades and examined key biogeochemical processes in more detail (i.e.: diel cycling, sedimentary methylation, and biotic transfer). Outcomes from this research identified in-situ production of MeHg by sulfate-reducing bacteria as the main factor controlling the spatial and temporal distribution of MeHg across the Greater Everglades. In addition, this production of MeHg was strongly influenced by sulfate and DOC concentrations.
In collaboration with the National Park Service, we are examining the drivers of spatial and temporal variability of total mercury and methylmercury across the Everglades National Park. We sample surface water and forage fish at 76 sites across the park on an annual basis at the conclusion of the wet season. Of interest are the isotopic signatures of mercury in the forage fish which indicate in-situ methylation of atmospheric mercury in areas flooded with canal water that drains the Water Conservation Areas to the north.
The controls on methylmercury production in the Hells Canyon Reservoir Complex are fundamentally changing the way we think about the microbiology of mercury methylation. While investigating the sources and transformations of mercury that influence downstream fisheries, we noticed ecosystem conditions that were not traditionally thought to be conducive to methylmercury production. In particular, the appearance of water-column methylation under redox conditions that do not favor sulfate reduction. In conjunction with the Idaho Department of Environmental Quality and the Idaho Power Company, we are collaborating with Trina McMahon at the University of Wisconsin to investigate the unusual microbial ecology that drives methylmercury production in the system – a three reservoir chain along a 100-mile stretch of the Snake River on the border between Oregon and Idaho.
Work on mercury in Alaska falls into three broad categories:
Mercury trends in the Yukon River. Long-term monitoring (about 20 years) of mercury and methylmercury concentrations and loading in the Yukon River is done monthly during the ice-free season and once under ice at Pilot Station. The Arctic region is among the most areas on Earth by climate change, but it is uncertain how warming will affect mercury cycling at high latitudes.
Mercury evasion from thermokarst soils in the high Arctic. Thermokarsting is the melting of permafrost and widespread collapse of the surface of the high Arctic. The resulting landscape has numerous small depressions that are much wetter than the surrounding intact permafrost and where active layer (depth of soil that thaws each spring) is substantially deeper and warmer. The increase in the active layer depth and temperature has been a cause for concern for mercury researchers, given high-latitude peatland soils are among the largest mercury reservoirs on Earth and the increased mobility of this pool through evasion and runoff.
Effects of trophic status on mercury methylation. Our understanding of mercury methylation has undergone a renaissance in the past decade due to the availability of new research tools. An important new finding is that the genetic coding for methylation is present over a much wider range of microbial clades that previously thought. This project sought to measure methylation rates in wetlands exhibiting a wide range of trophic conditions and relate those results to the dominant microbial processes occurring at the various sites.
Source Identification to Inform Restoration
Numerous sites across the country and around the globe are subject to severe impairment due to Hg contamination. Sites with historic Hg releases tend to be orders of magnitude higher in concentration than background regions, only receiving atmospheric deposition of Hg. It can be extremely complex to determine the contribution of legacy contaminant Hg to the food web, due to potential mixing with contemporary sources (e.g. deposition). For these sites we apply natural abundance Hg stable isotope measurements to assess source contribution with the goal to provide information to support remedial and restoration processes.
National Priority List (Superfund) applications
We are working with cooperators at FWS and NOAA to determine if legacy Hg contamination from two historic chlor alkali facilities influence sediment and fish concentrations in the main stems of the Mobile and Tombigbee Rivers.
The drainage of Black Butte Mine is a major concern for biota Hg concentrations in the downstream the Willamette River and Cottage Grove reservoir. Our team, with collaboration with EPA Region 10, have examined soils, waters, suspended particulate matter, and biota from this region to assess the source signature and transport of Hg from Black Butte Mine.
Hannibal Pool is a stretch of the Ohio River that is heavily industrialized and still receives Hg industrial effluents from coal power generation plants, an operating chlor alkali facility, and a historic superfund site. We are collaborating with EPA region 3 to determine the contribution of Hg in industrial effluents to Hg burdens in biota in the region including mussels and fish.
Berry’s Creek within the NJ Meadowlands is a heavily industrialized site and contributes Hg to the Hackensack River (Reinfelder and Janssen, 2019). We are currently working with FWS to assess the contribution of legacy Hg to avian species within the region.
Contaminated mining waste from the Sulphur Bank Mercury Mine was released into wetland regions of Clear Lake, causing bioaccumulation concerns within the region. In collaboration with the USGS California Water Science Center and USGS Forest and Rangeland Ecosystem Science Center (FRESC) we are examining the fate and transport of mining waste Hg as well as its influence on the food web of Clear Lake.
GLRI Areas of Concern Application
The St. Louis River estuary (SLRE) is the largest tributary to Lake Superior and is impacted by fish consumption advisories for Hg related to historic industrialization of the region. In collaboration with EPA, Minnesota Pollution Control Agency (MPCA), Wisconsin Department of Natural Resources (WI DNR) and other local and tribal partners we are examining the contribution of legacy Hg to the food web. The SLRE project is the largest Hg isotope project designed to date. The analyses include water column, sediments, and the food web measurements as well as a comparison to an analogous geomorphic reference site, the Bad River in WI. The goal for the SLRE project is to apply Hg isotopes to assess source contribution but, also use these isotope tracers as tools for assessing post-restorations success.
The Fox River, WI is a major contributor of Hg to Lake Michigan due to historic paper mill activity in the lower stretch of the river. Given the ubiquitous nature of Hg contamination within sediments of the system novel species-specific measurements were made within the system to assess the direct link between legacy contamination in sediments and the lower food web.
To better understand the global cycle of mercury we have collaborated internationally to examine important ecosystems that are sensitive to mercury deposition.
- Mercury Cycling in Gabon
- Mercury Cycling and Bioaccumulation in Global Oceans
- Arctic Great Rivers Observatory (ArcticGRO)
Spurred by a concerning set of preliminary data showing that exploited Gabonese sustenance fisheries were severely contaminated with MeHg, the USGS MRL teamed up with Parcs Gabon, Cornell University and University of Wisconsin Madison to perform a nationwide assessment of freshwater and estuarian fisheries. This expedition paves the way for understanding the mercury transport in the global tropics through two dominant disturbances, artisanal scale gold mining and deforestation.
Mercury stable isotopes have provided insight on the sources of mercury and nuances in bioaccumulation (e.g. feeding depth) within ocean food webs. Despite these promising observations, these measurements have only been performed within limited ocean basins. The USGS MRL and Dan Madigan (University of Windsor) are working with researchers around the globe to assess mercury concentrations and stable isotope values in different food webs across the Atlantic, Pacific, and Indian oceans.
ArcticGRO is an international collaboration investigating the effects of climate and watershed disturbances that impact the biology, chemistry and circulation of the Arctic Ocean. We collaborate with Woods Hole Research Center to measure mercury concentrations in waters from some of the Earth’s largest rivers: the Yukon and Mackenzie in Canada and the Ob’, Yenisey, Lena, and Koylma in Russia. Together these rivers transport vast quantities of water and waterborne constituents into the Arctic Ocean and surrounding seas.