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Benthic communities (sampled once annually from 1986 to 1989) at stations impacted by copper and zinc were characterized by reduced species richness, reduced abundance, and a shift in community composition from sensitive to tolerant taxa. Benthic community structure varied annually due to fluctuations in stream discharge and improvements in water quality. Sensitivity of 13 dominant taxa to Cu was measured in outdoor experimental streams by exposing organisms to Cu (25 μg/L) for 10 d. Sensitivities (si), defined as proportioned reduction in abundance in treated streams relative to controls, ranged from 1.00 for several species of Ephemeroptera that were completely eliminated to −0.14 for taxa that increased in treated streams (Chironomidae: Orthocladiini). An index of community sensitivity (ICS) based on si and relative abundance of dominant taxa (pi) was developed for the Clinch River. The ICS was highly sensitive to heavy metals and useful for distinguishing reference and impacted stations. There was good agreement between the ICS and other community-level approaches in identifying impacted stations. We suggest that specific ICS values, based on si estimates of dominant taxa within a region, may be employed to predict the degree of metal impact in other streams within that region.

This research compares effects of heavy metals on macroinvertebrate communities in outdoor experimental streams with those observed at impacted field sites. Natural assemblages of aquatic macroinvertebrates were established on substrate-filled trays which were then transferred to outdoor stream mesocosms. Exposure of these communities to low levels of copper and zinc (target concentration = 12 μg/L) significantly reduced the number of taxa, number of individuals, and abundance of most dominant taxa within 4 d. After 10 d, control streams were dominated by Ephemeroptera and Tanytarsini chironomids, whereas treated streams were dominated by Hydropsychidae and Orthocladiini. Responses of benthic communities to metals observed at the Clinch River (Russell Co., Virginia), a system impacted by copper and zinc, were similar to those in experimental streams. Ephemeroptera and Tanytarsini, which comprised 38–46% of the macroinvertebrate community at upstream reference stations, were significantly reduced at all effluent sites. As in treated experimental streams, impacted stations were dominated by Hydropsychidae and Orthocladiini. The similarity of our experimental results to those obtained from Clinch River field sites suggests that outdoor stream mesocosms may be employed to predict macroinvertebrate community responses to heavy metals.

Selected temperatures increased for 15 fish species in a laboratory gradient when acclimated to 3 °C increments from 12 to 27 °C. Temperature preferences exceeded acclimation temperatures between 12 to 27 °C for all except the telescope shiner (Notropis telescopus), yellow perch (Perca flavescens), rainbow trout (Salmo gairdneri), brown trout (Salmo trutta), and brook trout (Salvelinus fontinalis). At 30, 33, or 36 °C acclimation, preferred temperatures were less than the acclimation temperature. The highest temperature preferences occurred at acclimations of 27, 30, or 33 °C. Bluegill (Lepomis macrochirus), spotted bass (Micropterus punctulatus), rockbass (Ambloplites rupestris), and the spotfin shiner (Notropis spilopterus) consistently selected the highest temperatures while the lowest temperatures were preferred by the salmonids. Final temperature preferences were usually greater than 29 °C for most centrarchids, above 24 °C for most cyprinids, and less than 19 °C for salmonids.Avoidance temperatures increased as acclimation temperature increased. Upper avoidances tested at high acclimation temperatures (30–36 °C) either equalled or exceeded the 7-day upper lethal temperature limit of the species by 1–2 °C, while avoidances were below this upper lethal limit when tested at the acclimation temperature closest to the species' final temperature preference.