Trace element bioaccumulation was studied in immature benthic insects from two contaminated river systems to develop these animals as bioindicators. In one river, Cu, Cd, Pb, and Zn were analysed in insects and in fine bed sediments over a 381-km reach downstream of a large copper mining complex. In the other river, As contamination from a gold mine was assessed in insects and bed sediments over a 40-km reach. All insect taxa collected in contaminated river reaches had elevated whole-body trace element concentrations. However, direct comparisons of contamination using a single, common species among stations were limited because few species were distributed throughout the study reaches. Comparisons of contamination at taxomic levels higher than species were complicated by element-specific differences in bioaccumulation among taxa. These differences appeared to be governed by biological and hydrogeochemical factors. The variation in element concentrations among species of the caddisfly Hydropsyche was slightly greater than within individual species. If this genus is representative of others, comparisons of contamination within genera may be a practical alternative for biomonitoring studies when single species are not available.

SUMMARY. 1. Changes in species composition of the periphyton of an oligotrophic. Sierra Nevada stream continuously dosed for 1 year at three concentrations of copper (2.5, 5 and 10 μg 1−1 CuT; approximately 12, 25 and 50 ng 1−1 Cu2+) were determined. 2. The numerically most abundant taxa were Bacillariophyceae (Achnanthes minutissima, Cocconeis placentula, Cymbella microcephala, C. sinuata, Fragilaria conslruens, F. crotonensis. Navicula spp., Synedra acus and S. rumpens), and the Cyanophyta Lyngbya spp., a co‐dominant during spring and summer. 3. Population densities of Lyngbya spp. were markedly reduced at all test concentrations of copper. Population densities of the principal Chlorophyta (Spirogyra spp. and Cladophora spp.) and the diatom Amphipleura pellucida were reduced at 5 μg 1−1 CUT. Of the twenty‐two most abundant taxa, sixteen were reduced in abundance by continuous exposure to 10 μg 1−1 CuT. 4. There was no commensurate reduction in standing crop (total number of individuals of all taxa). Achnanthes minutissima, a co‐dominant in the control, was the primary replacement species. Other taxa that were more abundant at 5 μg1−1 CuT than in the control were Ceratoneis arcus, Cocconeis placentula, Navicula spp. and Synedra rumpens. Only A. minutissima and Calothrix spp. were more abundant at 10 μg 1−1 than in the control. 5. Three resemblance measures (Canberra metric, Bray‐Curtis and Dice) and diversity (Brillouin's) were evaluated for detecting differences in species composition among experimental stream sections. The Canberra metric, an index sensitive to proportional rather than absolute differences, was the most informative of these indices.

1. Effects of copper on species composition and production of benthic insects in an oligotrophic stream dosed at low concentrations {2.5-15 ^g 1"' Cu,; approximately 12-75 ng I"' Cu-+) were determined. Dosing was initially in autumn-early winter when peak densities of many species occur. It was resumed the following summer near the time of egg hatch of most species and continued through the remaining aquatic stages of univoltine and multivoltine taxa.2. Declines in population density of species representing all major orders {Ephemeroptera. Plecoptera, Coleoptera. Trichoptera and Diptera) occurred at 5 and/or 10 /^g 1"' Cu^. Differences in sensitivity among families existed in the Plecoptera, Trichoptera and Diptera. These differences were apparently related to the trophic preferences of taxa, with herbivores and detritivores more sensitive than predators.3. Equivalent percentage declines in annual production occurred for herbivores/detritivores and predators exposed to copper, suggesting an adjustment in total predator production in response to the reduction in prey abundance.4. Possible examples of reiease of benthic insects from competition with less tolerant species were rare. Of the thirty-seven most abundant taxa, only the predators Rhyacophila vaccua and Rhyacophila angelita were more abundant [than in the control] at copper concentrations (5 and 10//gl"' Cuj) causing population declines of other species. 5. Species richness and percentage similarity were sensitive communitylevel indices of copper toxicity, whereas Brillouin's diversity was insensitive to differences among the control and copper-treated stream sections.

SUMMARY. Production of periphyton, nitrogen fixation and processing of leaf litter were examined in an oligotrophic Sierra Nevada stream and the responses of these processes to copper (2.5, 5 and 10μg 1‐1 CuT [total filtrable copper]; approximately 12, 25 and 50 ng 1‐1 Cu2+) were determined. Autotrophic and total production were estimated from 3‐week accumulations of biomass on artificial substrates. Mean autotrophic production in the control ranged from 0.22 to 0.58 mg C m‐2 h‐1 in summer‐autumn 1979, but declined to 0.08–0.28 mg C m 2 h‐1 after peak discharge in summer 1980, apparently due to phosphorus‐limited growth. Total production in the control ranged from 0.30 to 0.82 mg C m‐2 h ‐1 in summer‐autumn 1979 and from 0.16 to 0,68 mg C m ‐2 h ‐1 in 1980. Mean autotrophic productivity, estimated by l4C‐bicarbonate uptake in daylight, ranged from 0.30 to 2.8 mg C m‐2 h‐1. Autotrophic productivity was reduced by 57–81% at 2.5μg 1‐1 CuT, 55–96% at 5μg 1‐1 CuT, and 81–100% at 10μg 1‐1 CUT, Heterotrophic productivity (based on dark 35S‐sulphate uptake) was inhibited to a lesser extent (28–63% at 2.5μg 1‐1 CuT, 24–84% at 5μg 1‐1 CuT, and 67–92% at 10μg 1‐1 CuT), The inhibition of autotrophic and heterotrophic productivity persisted through the year of exposure. Production in stream sections previously exposed to 2.5 and 5μg 1‐1CuT increased to control levels within 4 weeks after dosing, but remained depressed for more than 7 weeks after exposure to 10μg 1‐1 CuT. The specific rate of photosynthesis (mg C mg chlorophyll a‐1 h‐1) of mature periphyton communities declined at all test concentrations of copper, but the rate for periphyton on newly‐colonized surfaces did not change. The species composition of benthic algae shifted during exposure to an assemblage more tolerant of copper. Achrtanthes minutissima and Fragilaria crotonensis were the primary replacement species on newly‐colonized surfaces. The nitrogenase activity of blue‐green algae was low. with controls ranging from 2.4 to 12 nmol C2H2 m‐2 h‐1. Nitrogenase activity was inhibited during the initial weeks of exposure by 5 and 10μg 1‐1 CuT. However, after 9 months of exposure, control and copper‐treated sections did not differ. The rate of processing of leaf litter, estimated by microbial respiration and nutrient quality of litter of resident riparian woodland taxa, was inhibited at all test concentrations of copper.

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