Environmental Health - Toxic Substances Hydrology Program
Some stream ecosystems are much more sensitive to the trace amounts of mercury deposited in them from the atmosphere than others. This variation in the sensitivity of streams was discovered by a team of U.S. Geological Survey (USGS) scientists while they were studying the fate of atmospherically deposited mercury in eight watersheds. They reported their discovery in a recent series of articles published in Environmental Science and Technology. The team found that, for a given amount of atmospherically deposited mercury, fish in some watersheds will have high levels of mercury contamination while fish in other watersheds will not. The study's results show that total mercury and methylmercury concentrations in the streams were much more variable than the observed variation in the atmospheric deposition of mercury (nine orders of magnitude variation in concentration for streams and four for atmospheric deposition). The articles document that the characteristics of the watershed, particularly the abundance of wetlands and the amount of dissolved organic carbon in stream water, exert a strong influence on how atmospherically deposited mercury is transformed to methylmercury and subsequently bioaccumulated in stream food webs.
Over two decades of research on mercury contamination in the environment has greatly improved scientists' understanding of the fate of mercury in aquatic ecosystems. However, the vast majority of this research has been conducted on lakes, wetlands, and reservoirs, leaving streams relatively less well understood. These findings can help decision makers better anticipate concentrations of mercury and methylmercury in streams and understand how mercury makes its way into fish in streams in comparable environmental settings. The Toxic Substances Hydrology Program contributed to this large study conducted by the USGS National Water-Quality Assessment (NAWQA) Program.
Brigham, M.E., Wentz, D.A., Aiken, G.R., and Krabbenhoft, D.P., 2009, Mercury cycling in stream ecosystems--1. Water column chemistry and transport: Environmental Science and Technology, v. 43, no. 8, p. 2,720-2,725, doi:10.1021/es802694n. (Free download)
Chasar, L.C., Scudder, B.C., Stewart, A.R., Bell, A.H., and Aiken, G.R., 2009, Mercury cycling in stream ecosystems--3. Trophic dynamics and methylmercury bioaccumulation: Environmental Science and Technology, v. 43, no. 8, p. 2,733-2,739, doi:10.1021/es8027567. (Free download)
Marvin-DiPasquale, M., Lutz, M.A., Brigham, M.E., Krabbenhoft, D.P., Aiken, G.R., Orem, W.H., and Hall, B.D., 2009, Mercury cycling in stream ecosystems--2. Benthic methylmercury production and bed sediment-pore water partitioning: Environmental Science and Technology, v. 43, no. 8, p. 2,726-2,732, doi:10.1021/es802698v. (Free download)
Additional References on the Fate of Mercury in Watersheds
Gorski, P.R., Armstrong, D.E., Hurley, J.P., and Krabbenhoft, D.P., 2008, Influence of natural dissolved organic carbon on the bioavailability of mercury to a freshwater alga: Environmental Pollution, v. 154, no. 1, p. 116-123, doi:10.1016/j.envpol.2007.12.004.
Shanley, J.B., Mast, A.M., Campbell, D.H., Aiken, G.R., Krabbenhoft, D.P., Hunt, R.J., Walker, J.F., Schuster, P.F., Chalmers, A., Aulenbach, B.T., Peters, N.E., Marvin-DiPasquale, M., Clow, D.W., and Shafer, M.M., 2008, Comparison of total mercury and methylmercury cycling at five sites using the small watershed approach: Environmental Pollution, v. 154, no. 1, p. 143-154, doi:10.1016/j.envpol.2007.12.031.
Schuster, P., Shanley, J., Marvin-Dipasquale, M., Reddy, M., Aiken, G., Roth, D., Taylor, H., Krabbenhoft, D., and DeWild, J., 2008, Mercury and organic carbon dynamics during runoff episodes from a northeastern USA watershed: Water, Air, and Soil Pollution, v. 187, no. 1, p. 89-108, doi:10.1007/s11270-007-9500-3.
Nelson, S.J., Johnson, K.B., Weathers, K.C., Loftin, C.S., Fernandez, I.J., Kahl, J.S., and Krabbenhoft, D.P., 2008, A comparison of winter mercury accumulation at forested and no-canopy sites measured with different snow sampling techniques: Applied Geochemistry, v. 23, no. 3, p. 384-398, doi:10.1016/j.apgeochem.2007.12.009.