environmental influences, such as chemical contaminants, hydrologic modifications, sedimentation, and thermal pollution; (2) greater ability to measure biological effects directly without the need to extrapolate from chemical measurements and laboratory effect studies; (3) increased analytical sensitivity as a result of bioconcentration of certain contaminants [For example, bioconcentration by a factor greater than 10,000 is possible (Phillips, 1980).]; (4) greater integration of exposure 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 (5) a high degree of public interest and concern, particularly regarding the consumption of contaminated fish and mollusks as well as the protection of threatened and endangered species. These characteristics make biological investigations an important supplement to the basin-wide physical and chemical water-quality investigations of the NAWQA Program.
The objective of the ecological survey component of the NAWQA
Program is to characterize benthic invertebrate, fish (Meador, Cuffney,
and Gurtz, 1993) and algal communities (Porter and others, 1993), as well
as associated instream and riparian habitats (Meador, Hupp, and others,
1993). Benthic invertebrates (insects, mollusks, crustaceans, and worms)
are important elements of ecological surveys because they tend to (1) live
in, on, or near streambed sediments; (2) have, with the exception of most
mollusks, life cycles (months to a few years) that are intermediate to
fish (years to decades) and algae (days to weeks); and (3) be relatively
sessile compared to larger organisms, such as fish. This combination of
characteristics ensures that benthic invertebrates (1) respond to natural
and anthropogenic environmental conditions that physically or chemically
alter streambed sediments (for example, sedimentation, xenobiotics,
eutrophication, or hydrologic modifications),
(2) integrate effects
over an approximately annual time period, and (3) characterize effects
over a relatively small spatial area in contrast with fish, which may
travel over long distances. These factors make benthic invertebrates well
suited for use in assessing site-specific water quality and comparing spatial patterns of
water quality at multiple sites, and for integrating effects that
represent 6 months to a year of exposure at a site. Benthic invertebrates
also are particularly useful for monitoring cumulative effects imparted
to a site by conditions in the entire upstream landscape (Hynes, 1975).
Consequently, these organisms are used increasingly by State and Federal
agencies as a cost-effective method (Tesmer and Wefring, 1981) of
assessing water-quality conditions in a regulatory context (Lenat, 1988;
Ohio Environmental Protection Agency, 1988; Shackleford, 1988; Plafkin and
others, 1989; U. S. Environmental Protection Agency, 1990).
Community analysis offers a number of 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 from natural substrates (1) directly relate to actual ambient conditions, (2) take into account a large range of species representing a variety of exposure pathways, (3) eliminate the need to culture and maintain test organisms, and (4) incorporate secondary effects that arise from the interactions of populations through competitive and predator-prey interactions. Community surveys remain the only means of