The biological components of NAWQA consist of ecological surveys (characterizations of fish, benthic invertebrate, and algal communities) and tissue contaminant studies. Biological components are important to an integrated assessment of water quality because of factors such as (1) sensitivity to a wide variety of natural and human environmental influences (for example, chemical constituents, hydrologic modifications, sedimentation, and thermal enhancement); (2) increased analytical sensitivity due to bioconcentration of certain contaminants; (3) integration of exposure to environmental influences over multiple temporal and spatial scales (for example, algae integrate exposure over several millimeters and for periods of several weeks, whereas fish may integrate exposure over many kilometers and for a decade or more); and (4) a high degree of public interest and concern, particularly for endangered species.
Ecological surveys as part of NAWQA are designed to characterize fish, benthic invertebrate, and algal communities and associated instream and riparian habitats. Community analysis offers several advantages for large-scale water-quality assessments when compared with toxicity testing (American Society for Testing of Materials, 1988), biochemical characterization (Day and Scott, 1990; Hontela and others, 1991; Monod and Vindimian, 1991; Schoor and others, 1991), or direct measurement of ecological processes. For example, community surveys directly relate to actual ambient conditions, take into account a large range of species representing a variety of environmental exposure pathways, eliminate the need to culture and maintain test organisms, and incorporate secondary effects that arise from the interactions of populations through competitive and predator-prey interactions. Community surveys remain the only means of directly assessing the biological integrity of a site and the only approach that is sensitive to toxicological influences and habitat degradation resulting from changes in land use.
A fish community is a group of fishes belonging to a number of different species that occur in the same area and interact with each other. The structure of a fish community is determined by the species present, their relative abundances, life-stages and size distributions, and their distributions in space and time. Changes in fish community structure occur with natural or human changes in the physical and chemical characteristics of their environment. The ability to detect changes in fish community structure can be gained by developing an increased understanding of the factors that determine the distribution and abundance of fish species and identifying relations among patterns in fish community structure, physical habitat, and water chemistry conditions (Tonn and others, 1983).
The study of fish communities is an essential component of many water-quality assessment programs (Hendricks and others, 1980; Karr and others, 1986; Ohio Environmental Protection Agency, 1987; Plafkin and others, 1989) because fish are particularly sensitive indicators of water-quality conditions (Smith, 1971; Fausch and others, 1990). Human influences, such as changes in water chemistry or physical habitat modifications, can alter fish communities by disrupting their structures. Changes in fish community structure can be detected through changes in size components of the community, functional groups, species diversity, and relative abundance (Wootton, 1990).