Complex Response to Decline in Atmospheric Deposition of Mercury
Studies at Voyageurs National Park Revealed Trends in Mercury
U.S. Geological Survey (USGS) scientists found that mercury concentrations in shallow waters and methylmercury (MeHg) concentrations in fish in four lakes in Voyageurs National Park, Minnesota, were not consistent with decreases in the wet atmospheric deposition of mercury recorded at nearby monitoring stations for over a decade. Methylmercury is a toxic form of mercury (Hg) that accumulates and biomagnifies in aquatic food webs. Some of the Hg entering aquatic ecosystems is converted to MeHg. Among other things, sulfate levels have been related to the conversion of Hg to MeHg.
Records indicate decreases in the annual wet deposition of mercury and sulfate at two adjacent precipitation monitoring sites from 1998 to 2012 (mean decreases of 32 and 48 percent, respectively). While two of the four lakes studied showed consistent decreases in Hg in water and in MeHg in small yellow perch between 2001 and 2012 (mean decreases of 46.5 and 34.5 percent, respectively), a third lake showed significant increases in both Hg in water and MeHg in fish, and a fourth lake showed no consistent trend during the same period. The fourth lake, however, was known to be disturbed by forest fire and changes in shoreline due to beaver activity, both of which could affect Hgmethylation.
An increasing number of monitoring sites around the Nation have documented declining trends in mercury deposition over the past decade. This study, however, demonstrates that ecosystem responses can be complex, local factors within the watershed may be important, and responses in ecosystem mercury levels may require longer time periods than those observed in this study.
Other reports from this collaborative, long-term effort (Weiner and others, 2006, and Woodruff and others, 2009) are listed below. This study was supported by the USGS Toxic Substances Hydrology Program, Minnesota Pollution Control Agency, National Park Service, U.S. Environmental Protection Agency, National Park Service/USGS Water Quality Partnership Program, and University of Wisconsin-La Crosse.
Related science listed below.
North American and European Atmospheric Mercury Declines Explained by Local and Regional Emission Reductions
New Tool to Track Sources and Exposure Pathways of Mercury in the Environment — Application for Predatory Fish in the Great Lakes
Comprehensive Assessment of Mercury in Streams Explains Major Sources, Cycling, and Effects
U.S. Geological Survey (USGS) scientists found that mercury concentrations in shallow waters and methylmercury (MeHg) concentrations in fish in four lakes in Voyageurs National Park, Minnesota, were not consistent with decreases in the wet atmospheric deposition of mercury recorded at nearby monitoring stations for over a decade. Methylmercury is a toxic form of mercury (Hg) that accumulates and biomagnifies in aquatic food webs. Some of the Hg entering aquatic ecosystems is converted to MeHg. Among other things, sulfate levels have been related to the conversion of Hg to MeHg.
Records indicate decreases in the annual wet deposition of mercury and sulfate at two adjacent precipitation monitoring sites from 1998 to 2012 (mean decreases of 32 and 48 percent, respectively). While two of the four lakes studied showed consistent decreases in Hg in water and in MeHg in small yellow perch between 2001 and 2012 (mean decreases of 46.5 and 34.5 percent, respectively), a third lake showed significant increases in both Hg in water and MeHg in fish, and a fourth lake showed no consistent trend during the same period. The fourth lake, however, was known to be disturbed by forest fire and changes in shoreline due to beaver activity, both of which could affect Hgmethylation.
An increasing number of monitoring sites around the Nation have documented declining trends in mercury deposition over the past decade. This study, however, demonstrates that ecosystem responses can be complex, local factors within the watershed may be important, and responses in ecosystem mercury levels may require longer time periods than those observed in this study.
Other reports from this collaborative, long-term effort (Weiner and others, 2006, and Woodruff and others, 2009) are listed below. This study was supported by the USGS Toxic Substances Hydrology Program, Minnesota Pollution Control Agency, National Park Service, U.S. Environmental Protection Agency, National Park Service/USGS Water Quality Partnership Program, and University of Wisconsin-La Crosse.
Related science listed below.