Stream habitat is characterized in the U.S. Geological Survey's National Water-Quality Assessment Program as part of an integrated physical, chemical, and biological assessment of the Nation's water quality. The goal of stream habitat characterization is to relate habitat to other physical, chemical, and biological factors to describe water-quality conditions. To accomplish this goal, environmental settings are described at sites selected for water-quality assessment. In addition, spatial and temporal patterns in habitat are examined at local, regional, and national levels. Although habitat characterization is an important component of a number of Federal, State, and local water-quality assessment programs, no current set of habitat evaluation procedures meets the objectives of the habitat assessment component of the National Water-Quality Assessment Program.
Evaluation of stream habitat is based on a spatially hierarchical framework that incorporates habitat data at basin, segment, reach, and microhabitat scales. This framework provides a basis for national consistency in collection techniques while allowin g flexibility in habitat assessment within individual study units. Procedures are described for collecting habitat data at basin and stream segment scales that include use of geographic information system data bases, maps, and aerial photographs. Data collected at the stream reach scale include more than 34 riparian and instream habitat characteristics evaluated during one-time site visits, and surveys of the channel and riparian area during repeated sampling.
The U.S. Geological Survey's (USGS) National Water-Quality Assessment (NAWQA) Program is designed to assess the status of 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 assessment is accomplished by collecting physical, chemical, and biological data at sites that represent major natural and human factors (for example, ecoregion, land use, stream size, hydrology, and geology) that are thought to control water quality in the river basin. These data are used to provide an integrated assessment of water quality within selected environmental settings, assess trends in water quality, and investigate the influence of major natural and human factors on water quality.