Atmospheric Deposition Contributions to Mercury Yields in Select Watersheds in the Western United States and Canada
The atmosphere plays an important role in the delivery to and cycling of mercury (Hg) in the environment and it can be a major source of Hg contamination to surface waters. Globally, atmospheric deposition of Hg is the primary source of Hg related concerns for human and ecosystem health (Fitzgerald and others, 1998). In California and other areas in the United States, Hg use in gold and silver mining in the 1800s resulted in thousands of tons of Hg lost into the environment (Alpers and Hunerlach, 2000; Conaway and others, 2004; Gray and others, 2014).
These Hg deposits continue to affect the ecosystems downstream from these historic mining operations. It is unknown what the emissions (gas and particle) from abandoned mine sites are contributing to the elevated regional atmospheric Hg levels, but atmospheric deposition (wet and dry) is the dominant source of Hg over much of the nation (Wentz and others, 2014;). Mercury is a problem in sensitive habitats across the United States, including California's Sierra-Nevada lakes and the Sacramento-San Joaquin Delta. The contribution of Hg atmospheric deposition to upstream riverine loads is unknown but may be significant. Current estimates of atmospheric deposition have a high degree of uncertainty, and given the potential importance of this pathway to Hg loadings, improvement in atmospheric deposition estimates is warranted.
The Mercury Deposition Network (MDN) has many sampling sites across the United States and Canada, but only wet deposition is collected and the sampling site density falls off dramatically west of the Mississippi River. Current assessments suggest that dry deposition can be an important, and in some cases dominant, means of Hg removal from the atmosphere (Landis and Keeler, 2002; Sakata and Marumoto, 2005, Lyman and others, 2007, Caldwell and others, 2007, Van Metre, 2012). There is a need for Hg monitoring in watersheds, especially in western North America because of this paucity of dry deposition data. Quantifying atmospheric Hg deposition will support resource managers and regulatory agencies in identifying pollution sources and aid in how best to regulate emissions.
Current monitoring methods are not able to provide spatially comprehensive information on the wet and dry deposition of Hg, and modeling has become an important tool to estimate the atmospheric deposition of Hg over wide areas (Gbor and others, 2007; Ryaboshapko and others, 2007; Lin and others, 2006). Model estimates of Hg dry deposition range from <1 to 3 times the rate of wet deposition (St. Louis and others, 2001; Evers, 2005; Seigneur and others, 2004). These results suggest that atmospheric dry deposition of Hg can be more significant than previously thought.
Streamflow generally transports considerably less mercury from the watershed than is deposited by wet and dry depositional processes (Shanley and others, 2008; Brigham and others, 2009; Journey and others, 2012). Runoff contributions of atmospherically deposited Hg to river loads, however, are variable and difficult to quantify. The amount of Hg transported into streams and rivers by runoff has been estimated to range from 10% to 95% of total atmospheric deposition and is dependent upon the annual rainfall amount, the amount of Hg retained by the soil and vegetation, and the density of impervious surfaces within the watershed (Shanley and others, 2008; Brigham and others, 2009; Journey and others, 2012; Hoff and others, 1996; Tsai and Hoenicke, 2001).
It is logical that the amount of Hg transported in streams and rivers should be higher relative to atmospheric inputs in watersheds with non-atmospheric sources, such as Hg-contaminated runoff from abandoned mines and urban areas. To date, there has been no comprehensive compilation of Hg load data from streams and rivers in western North America. By compiling published Hg load data for streams and rivers from previous peer-reviewed studies and supplementing that data with new load calculations where sufficient, reliable data are available for Hg concentration and streamflow, it will be possible to compare stream and river Hg loads in watersheds with and without non-atmospheric contributions. By normalizing the stream and river loads to atmospheric Hg loads (both wet and dry, based on available modeling results), this should provide the first quantitative demonstration of the importance of non-atmospheric Hg sources to surface water Hg transport in western North America.
The overall goals of this work are: 1) to demonstrate the importance of non-atmospheric Hg sources to surface water Hg transport in western North America, and 2) to document data gaps and limitations so that future studies can be designed to address the issue more comprehensively.
The time periods for this analysis will be between the late 1990s and 2011. The effort will be focused in those areas where long-term Hg water concentration data and streamflow data have been collected.
This study addresses the following USGS Science Strategies (USGS, 2007): Understanding Ecosystems and Predicting Ecosystem Change; Ensuring the Nation's Economic and Environmental Future – By investigating the contribution of an important environmental component, the atmosphere, in the distribution of Hg within select watersheds and its contribution to Hg loads and yields in rivers throughout western North America. The comparison of select rivers/watersheds within the western US, Canada, and Alaska with respect to landscapes, habitat types, climates, and Hg sources will elucidate the impact each of these attributes has in the cycling of Hg in the environment.
The Role of Environment and Wildlife in Human Health: A System that Identifies Environmental Risk to Public Health in America; The results of this study will build our understand on how the atmospheric deposition of Hg, as well as land use and land cover, and climate changes water quality and aquatic ecosystem health. The results can also be used as a base-line to monitor changes in the aerial deposition of Hg as the climate changes over time, especially in California during drought years .
The atmosphere plays an important role in the delivery to and cycling of mercury (Hg) in the environment and it can be a major source of Hg contamination to surface waters. Globally, atmospheric deposition of Hg is the primary source of Hg related concerns for human and ecosystem health (Fitzgerald and others, 1998). In California and other areas in the United States, Hg use in gold and silver mining in the 1800s resulted in thousands of tons of Hg lost into the environment (Alpers and Hunerlach, 2000; Conaway and others, 2004; Gray and others, 2014).
These Hg deposits continue to affect the ecosystems downstream from these historic mining operations. It is unknown what the emissions (gas and particle) from abandoned mine sites are contributing to the elevated regional atmospheric Hg levels, but atmospheric deposition (wet and dry) is the dominant source of Hg over much of the nation (Wentz and others, 2014;). Mercury is a problem in sensitive habitats across the United States, including California's Sierra-Nevada lakes and the Sacramento-San Joaquin Delta. The contribution of Hg atmospheric deposition to upstream riverine loads is unknown but may be significant. Current estimates of atmospheric deposition have a high degree of uncertainty, and given the potential importance of this pathway to Hg loadings, improvement in atmospheric deposition estimates is warranted.
The Mercury Deposition Network (MDN) has many sampling sites across the United States and Canada, but only wet deposition is collected and the sampling site density falls off dramatically west of the Mississippi River. Current assessments suggest that dry deposition can be an important, and in some cases dominant, means of Hg removal from the atmosphere (Landis and Keeler, 2002; Sakata and Marumoto, 2005, Lyman and others, 2007, Caldwell and others, 2007, Van Metre, 2012). There is a need for Hg monitoring in watersheds, especially in western North America because of this paucity of dry deposition data. Quantifying atmospheric Hg deposition will support resource managers and regulatory agencies in identifying pollution sources and aid in how best to regulate emissions.
Current monitoring methods are not able to provide spatially comprehensive information on the wet and dry deposition of Hg, and modeling has become an important tool to estimate the atmospheric deposition of Hg over wide areas (Gbor and others, 2007; Ryaboshapko and others, 2007; Lin and others, 2006). Model estimates of Hg dry deposition range from <1 to 3 times the rate of wet deposition (St. Louis and others, 2001; Evers, 2005; Seigneur and others, 2004). These results suggest that atmospheric dry deposition of Hg can be more significant than previously thought.
Streamflow generally transports considerably less mercury from the watershed than is deposited by wet and dry depositional processes (Shanley and others, 2008; Brigham and others, 2009; Journey and others, 2012). Runoff contributions of atmospherically deposited Hg to river loads, however, are variable and difficult to quantify. The amount of Hg transported into streams and rivers by runoff has been estimated to range from 10% to 95% of total atmospheric deposition and is dependent upon the annual rainfall amount, the amount of Hg retained by the soil and vegetation, and the density of impervious surfaces within the watershed (Shanley and others, 2008; Brigham and others, 2009; Journey and others, 2012; Hoff and others, 1996; Tsai and Hoenicke, 2001).
It is logical that the amount of Hg transported in streams and rivers should be higher relative to atmospheric inputs in watersheds with non-atmospheric sources, such as Hg-contaminated runoff from abandoned mines and urban areas. To date, there has been no comprehensive compilation of Hg load data from streams and rivers in western North America. By compiling published Hg load data for streams and rivers from previous peer-reviewed studies and supplementing that data with new load calculations where sufficient, reliable data are available for Hg concentration and streamflow, it will be possible to compare stream and river Hg loads in watersheds with and without non-atmospheric contributions. By normalizing the stream and river loads to atmospheric Hg loads (both wet and dry, based on available modeling results), this should provide the first quantitative demonstration of the importance of non-atmospheric Hg sources to surface water Hg transport in western North America.
The overall goals of this work are: 1) to demonstrate the importance of non-atmospheric Hg sources to surface water Hg transport in western North America, and 2) to document data gaps and limitations so that future studies can be designed to address the issue more comprehensively.
The time periods for this analysis will be between the late 1990s and 2011. The effort will be focused in those areas where long-term Hg water concentration data and streamflow data have been collected.
This study addresses the following USGS Science Strategies (USGS, 2007): Understanding Ecosystems and Predicting Ecosystem Change; Ensuring the Nation's Economic and Environmental Future – By investigating the contribution of an important environmental component, the atmosphere, in the distribution of Hg within select watersheds and its contribution to Hg loads and yields in rivers throughout western North America. The comparison of select rivers/watersheds within the western US, Canada, and Alaska with respect to landscapes, habitat types, climates, and Hg sources will elucidate the impact each of these attributes has in the cycling of Hg in the environment.
The Role of Environment and Wildlife in Human Health: A System that Identifies Environmental Risk to Public Health in America; The results of this study will build our understand on how the atmospheric deposition of Hg, as well as land use and land cover, and climate changes water quality and aquatic ecosystem health. The results can also be used as a base-line to monitor changes in the aerial deposition of Hg as the climate changes over time, especially in California during drought years .