Revised Methods for Characterizing Stream Habitat in the National Water-Quality Assessment Program

Abstract

Stream habitat is characterized in the U.S. Geological Survey’s National Water-Quality Assessment (NAWQA) 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 that 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 scales. This habitat protocol contains updated methods for evaluating habitat in NAWQA Study Units. Revisions are based on lessons learned after 6 years of applying the original NAWQA habitat protocol to NAWQA Study Unit ecological surveys. Similar to the original protocol, these revised methods for evaluating stream habitat are 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 allowing flexibility in habitat assessment within individual Study Units. Procedures are described for collecting habitat data at basin and segment scales; these procedures include use of geographic information system data bases, topographic maps, and aerial photographs. Data collected at the reach scale include channel, bank, and riparian characteristics. INTRODUCTION 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 (Gilliom and others, 1995) 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. 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. Study Unit investigations in the NAWQA Program are done on a staggered time scale in approximately 59 of the largest and most significant hydrologic systems across the Nation (Gilliom and others, 1995). These investigations, which consist of 4 to 5 years of intensive assessment followed by 5 years of low-intensity assessment, consist of four main components—(1) retrospective analysis; (2) occurrence and distribution assessment; (3) assessment of long-term trends and changes; and (4) case studies of sources, transport, fate, and effects (Gilliom and others, 1995). Occurrence and distribution assessments are done in a nationally consistent and uniform manner for identification of spatial and temporal trends in water quality at a national scale (Gilliom and others, 1995). Characterization of stream habitat is an essential component of many water-quality assessment programs (Osborne and others, 1991) and an important element in the NAWQA Program (Gurtz, 1994).