Benthic invertebrate communities are evaluated as part of the ecological survey component of the U.S. Geological Survey's National Water-Quality Assessment Program. These biological data are collected along with physical and chemical data to assess water-quality conditions and to develop an understanding of the factors that affect water-quality conditions locally, regionally, and nationally. The objectives of benthic invertebrate community characterizations are to (1) develop for each site a list of tax a within the associated stream reach and (2) determine the structure of benthic invertebrate communities within selected habitats of that reach. A nationally consistent approach is used to achieve these objectives. This approach provides guidance on site, reach, and habitat selection and methods and equipment for qualitative multihabitat sampling and semi-quantitative single habitat sampling. Appropriate quality-assurance and quality-control guidelines are used to maximize the ability to analyze data within and among study units.
The U.S. Geological Survey's (USGS) National Water-Quality Assessment (NAWQA) Program is designed to assess status and trends in the Nation's water quality and to develop an understanding of the major factors that affect observed water-quality conditions and trends (Hirsch and others, 1988; Leahy and others, 1990). This is accomplished by collecting biological, physical, and chemical data at sites that represent major natural and anthropogenic factors thought to control water quality in a river basin. Together these data are used to provide an integrated assessment of water quality within selected environmental settings, to assess trends in water quality, and to investigate major natural and anthropogenic factors, such as ecoregion, land use, stream size, hydrology, and geology, that influence water quality.
The biological components of the NAWQA Program, ecological surveys (Cuffney and others, 1993; Meador, Cuffney, and Gurtz, 1993; Meador, Hupp, and others, 1993; Porter and others, 1993) and tissue contaminants (Crawford and Luoma, 1993) offer a number of advantages over monitoring physical and chemical water-quality constituents (Price, 1978). These include (1) increased sensitivity to a wide variety of natural and anthropogenic