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Documentation of stream habitat is an essential component of many water-quality assessment programs (Osborne and others, 1991). Environmental assessments are sometimes made to determine consequences of alteration of stream habitat as a result of proposed impoundment, channelization, or land use. Habitat assessment provides baseline information on environmental settings so that changes resulting from human or natural causes can be identified, estimated, or predicted. In addition, habitat assessment can assist in identification of limiting physical and(or) chemical factors critical to biological communities.

Physical, chemical, and biological attributes of a stream, when combined with the environmental requirements of aquatic organisms, influence the presence or absence of a given organism in a stream. Habitat characteristics influence species distributions at different spatial scales. For example, fish species distribution is affected by climate (Tonn, 1990), stream gradient (Sheldon, 1968), and particle size of substrate within a specific section of stream (Hynes, 1975).

Although habitat evaluation is an essential component of water-resource investigations, little uniformity in concept or methodology exists (Osborne and others, 1991). Despite this fact, many State and regional assessment programs incorporate habitat data (Osborne and others, 1991). However, manuals that provide guidelines for conducting habitat evaluations (for example, Bovee, 1982; Platts and others, 1983; Hamilton and Bergersen, 1984; Platts and others, 1987) often have a regional or single-purpose focus. Therefore, no current set of habitat evaluation procedures meets the objectives of water-resource investigations conducted as part of the NAWQA Program.

The goal of stream habitat characterization as part of NAWQA is to relate habitat to other physical, chemical, and biological factors to interpret 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. An integrated data base provides information to generate additional hypotheses and address specific questions at local, regional, and national levels. No single document can encompass all stream habitat variables that are encountered across the Nation. Therefore, the methods described in this document must be continuously tested and refined, and new methods evaluated.

Purpose and Scope

This document provides detailed procedures for characterizing stream habitat as part of the USGS's NAWQA Program. These procedures allow for appropriate habitat descriptions and standardization of measurement techniques to facilitate unbiased evaluations of habitat influences on water-resource conditions at local, regional, and national levels.

A conceptual framework for evaluating stream habitat is provided that establishes a basis for consistency in collection techniques and allows for flexibility in the assessment of habitat at individual sites. Procedures are described for collecting habitat data at basin and stream segment scales using geographic information system (GIS) data bases, maps, and aerial photographs. Data collected at the stream reach scale include riparian and instream