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Habitat Assessment
A general habitat assessment is crucial in evaluating the ecological integrity of a site. The assessment is done using a visually-based approach to characterizing the physical habitat structure of the stream site. Habitat assessment evaluates the human-induced degradation of the habitat. Parameters are selected to measure various aspects of the habitat structure and to allow for an integrated assessment of the site. Appropriate parameters are selected for the type of stream under study, and may differ widely between high gradient (see example) or low gradient (see example) streams.Each parameter is assessed and rated on a scale from 0-20. All of the ratings are totaled to derive a habitat ranking for the site. The habitat ranking is compared against the reference condition to make an assessment relative to the region. A successful visually-based assessment of the physical habitat structure depends on several factors:
- Relevant, clearly defined parameters;
- A continuum of conditions, from suboptimal to optimal, for each parameter;
- Measurable characteristics or categorical choices to minimize subjectivity in judging the attributes of each parameter;
- Experienced, adequately trained investigators; and
- Sufficient documentation and ongoing training to evaluate and correct errors.
Optimal habitat structure depends on several factors. Structural heterogeneity provides for diverse "niche space" and greater species diversity. An established, healthy habitat is important for colonization stability. Finally, a well-developed energy base is needed to support life and all related biological processes. The quality of the physical habitat restricts the biological potential of a site. Habitat and biological diversity are closely linked, and a degraded habitat structure is one of the primary stressors to aquatic life.
Water quality measurements from the survey site are also pertinent to the assessment of the stream habitat. The RBPs call for direct measurements of temperature, conductivity, dissolved oxygen, pH, and turbidity. Notations on water odors and water surface oils are also taken. Water quality measurements taken at the time of the survey are used in combination with the physical characterization of the habitat to provide a more insightful analysis of the site. Taken together, these data are good indicators of adverse impacts on the stream ecosystem and of the ability of the stream to support a healthy aquatic community. Click below for the RBP document's more detailed account of this topic, or continue with the remainder of this module and visit the full document site later.