Reconnaissance Survey of Mercury in Water, Sediment, and Fish from U.S. Streams

A reconnaissance survey of Hg in water, streambed sediment, and fish at over 300 sites across the Nation was conducted from 1998 through 2005. The objectives of the survey were to 1) assess total mercury (THg) and methylmercury (MeHg) in water and streambed sediment, and THg in fish; 2) span regional and national gradients in mercury source strength (deposition, mining) and factors that govern mercury cycling; 3) identify ecosystem characteristics that favor the production and bioaccumulation of MeHg; and 4) explore environmental factors that may drive regional and national variations in fish mercury concentrations.

Site selection targeted several specific settings thought to be important to the source, transport, or speciation of mercury in aquatic ecosystems. Settings included

• urban - thought to have elevated depositional sources and enhanced mercury runoff due to impervious surfaces;
• cultivated agriculture - enhanced runoff of dissolved and colloidal Hg associated with organic matter, and particulate Hg from eroded soils;
• mining - historical gold-mining which used Hg°, and cinnabar mining; and
• reference - relatively low Hg source strength, minimal disturbance of runoff processes.

Land cover in reference settings included forest, rangeland, non-cultivated agriculture (hay, pasture, orchards), and wetland. Each site was sampled once, typically during summertime low-flow conditions, for mercury and related constituents in stream water, streambed sediment, and top predator (piscivorous) fish. Largemouth bass were targeted; at sites where bass were not available in sufficient numbers, alternative top predator fish species were selected.

Results from the 1998 reconnaissance survey are described by Brumbaugh and others (2001) and Krabbenhoft and others (1999).