by electrofishing, seining, or gill netting, or are observed directly by snorkeling or scuba diving (Meador et al., 1993b). Selection of methods is best made based on experience and reference to reputable published sources (e.g., APHA, 1989; MacDonald et al., 1991; Meador et al., 1993a, in addition to those cited above). In addition, important aspects of statistical design and data analysis must be incorporated into the study plan, but these are beyond the scope of this paper (e.g., Green, 1979; MacDonald et al., 1991; Norris and Georges, 1993; Resh and McElravy, 1993).
Bioassessment of pollution in inland waters has been going on for a long time (e.g., Hynes, 1960; Karr, 1991; Cairns and Pratt, 1993), and a number of different measures and indices have been proposed. However, the recent renewed interest in biological integrity and its assessment has resulted in a reevaluation of those metrics that seem most effective, in an attempt to come up with standardized protocols (e.g., Karr et al., 1986; Plafkin et al., 1989; Karr, 1991; Resh and Jackson, 1993; Kerans and Karr, 1994). After representative samples of the biota are obtained, the organisms are identified and enumerated, their biomass and condition are determined, and relevant metrics are calculated. A biological "metric" is an absolute or derived measure that is sensitive to ecological conditions. The number of species present in a community is one of the simplest and most reliable metrics. A variety of other metrics have been examined for use in bioassessment, although additional testing and refinement still are needed. Some are sensitive to certain types of pollution, such as organic matter or inorganic sediments, whereas others are more general in their response. Some of the most popular metrics for periphyton, macroinvertebrates, and fish are listed in Table 1. Adjustments in the list are necessary to accommodate regional differences in distribution and assemblage structure and function (e.g., Miller et al., 1988).
Richness is the number of different kinds of individuals (usually species or genera) in the total community or a specified assemblage. The Pinkham and Pearson community similarity index incorporates abundance and species composition (Plafkin et al., 1989). The quantitative similarity index for taxa compares two communities in terms of presence or absence of taxa and relative abundance (Shackleford, 1988). The Hilsenhoff biotic index summarizes the tolerances of macroinvertebrates to organic pollution (Hilsenhoff, 1987, 1988; Plafkin et al., 1989). Dominance measures assume that a highly skewed species-abundance distribution reflects an impaired community. The Hydropsychidae: Trichoptera ratio includes the mildly pollution-tolerant hydropsychids but excludes the pollution-intolerant arctopsychids from the family total. Functional feeding group designations are based on the manner in which food is obtained (see Merritt and Cummins, 1984, for details). Scrapers rasp or chew food growing attached to a surface such as rock, wood, or living aquatic vascular plants. Filterers employ self-constructed nets or specialized anatomical