Cooperators: USGS: National Water Quality Assessment (NAWQA) Program, USGS Toxic Substances Hydrology Program, USGS National Research Program, Wisconsin Department of Natural Resources, Menominee Indian Tribe of Wisconsin
Project Chief: Barbara C. Scudder
Location: Nationwide, including 3 sites in Wisconsin: Oak Creek in Milwaukee, Evergreen River in the Menominee Indian Reservation, and Pike River near Amberg
Project Number: 9BI81
Period of Project: October 2001–September 2006
Problem
Mercury is a widespread contaminant affecting aquatic ecosystems. Methylmercury is the most toxic form and it is readily accumulated in aquatic life. It magnifies in concentration in aquatic food chains. Most mercury studies have focused on lakes, reservoirs, and wetlands. Much less is known about mercury in water, sediment, and biota of streams and rivers.
Objective
The objectives of the study are to determine the effects of source strength, cycling, and food-web interactions on bioaccumulation of mercury in fish. The study also aims to quantify the source and seasonality of mercury and methylmercury as well as biogeochemical species and transformation rates related to the aquatic mercury cycle.
Approach
Stream sampling sites were selected based on the availability of target predator fish and mercury-source landscapes including urban and reference or non-cultivated. Three streams in the Western Lake Michigan Drainages (WMIC) NAWQA unit are being sampled as part of this study and data collection for this unit will be complete by September 2004. Total and methylmercury in water are sampled monthly plus during selected storm events over two years. Potential net methylation rates in sediment and mercury in porewater and sediment are measured seasonally. Total mercury and stable carbon and nitrogen isotopes are being determined in predator fish; total and methylmercury and stable isotopes will be determined in food chain organisms (forage fish and invertebrates). Data from the Mercury Deposition Network will be used to determine loading rates so that the amount of mercury entering the stream ecosystems can be assessed in relation to the amount of mercury accumulating in the water, sediment, and fish. The Wisconsin District Mercury Laboratory will analyze surface water, porewater, streambed sediment, and invertebrates for mercury and methylmercury.
Progress (July 2003–June 2004)
Surface water was sampled monthly plus several storm events. Sediment and porewater were collected in June, August, December 2003, and March 2004. Collections of biota were completed in June and August 2003. We provided input and assistance to the Wisconsin Department of Natural Resources (WDNR) toward a new atmospheric MDN site in Milwaukee. The WDNR supplied and installed MDN equipment in fall 2002 and collected samples; the USGS is funding laboratory analyses of the samples through September 2004. The Menominee Indian Tribe provided field assistance at the Evergreen River site in the Menominee Reservation.
Plans (July 2004–June 2005)
Water sampling and analysis of atmospheric deposition samples will continue through September 2004 for the WMIC unit. An intensive streambed sediment sampling is planned at all Wisconsin sites in July 2004 for total and methylmercury, sulfide, and microbial methylation; porewater will be collected concurrently from one site. We will continue to review and process results for a USGS Fact Sheet and national scope journal articles. Additional NAWQA study units across the nation are scheduled to begin mercury sampling in 2005. |
