Mercury Trends in Fish from Streams and Lakes in the United States, 1969 - 2005

Ann Chalmers1, Denise Argue2, David Gay3, Mark Brigham4, Dave Lorenz4 and Christopher Schmitt5

A national compilation of fish-mercury concentration data from state and federal monitoring programs was used to analyze trends in mercury (Hg) concentrations in fish from streams and lakes across the U.S. Trends were analyzed by site and by state on samples of the same fish species and tissue type, using similar fish lengths. Trends were evaluated over 2 time periods, 1969 - 1987, and 1988 - 2005. In addition, the most recent fish data (1995 - 2005) was compared to concurrent wet Hg deposition data from the Mercury Deposition Network (MDN). Downward Hg trends in fish from data collected between 1969-1987 outweighed upward trends by 6:1. Downward Hg trends in fish during the 1970ís and 1980ís are consistent with decreases in atmospheric Hg deposition inferred from many records of sediment, ice, and peat cores. The Southeastern U.S. consistently had more upward trends than other regions of the country both in site trends (1969-1987) and statewide trends (1988-2005). Upward Hg trends in fish from the Southeastern U.S. is supported by MDN wet deposition increases in the region and may be attributed to a greater influence of global atmospheric emissions in the Southeastern U.S. Overall, statewide fish data (1988-2005 and 1996-2005) did not have significant Hg trends (52 and 62 percent respectively). A lack of Hg trends in fish in the more recent data was consistent with the lack of trends in Hg wet deposition at MDN sites and relatively constant global emissions over the same time period. Although few significant trends were observed in the more recent Hg data in fish, it is anticipated that Hg concentrations in fish will decrease with decreases in atmospheric Hg deposition, however, the magnitude and timing of the response is uncertain.

1 U.S. Geological Survey, Montpelier, VT, T: 802-828-4511, E:
2 U.S. Geological Survey, Pembroke, NH
3 Illinois State Water Survey, Champaign, IL
4 U.S. Geological Survey, Mounds View, MN
5 U.S. Geological Survey, Columbia, MO