The anthropogenically stressed periphyton of Lake Orta,Italy

A long history of discharge of industrial wastes has left Lake Orta contaminated with high concentrations of acid, ammonia and copper. To study the effect of this chronic pollution on periphyton, I sampled epilithic algae and associated invertebrates at several sites from 1987 to 1988. Although biomass varied both spatially and seasonally, the taxonomic composition of these communities remained relatively stable. The dominant algae were chlorophytes and the dominant invertebrates were trichopterans. Comparisons with nearby unpolluted Lake Mergozzo, and with general equations developed for neutral lakes in North America indicate that these anthropogenic stresses are more clearly reflected by changes in the taxonomic composition and size distribution of the community than by changes in its biomass.Contribution No 375 from the Groupe de recherches en Ecologie des Eaux douces, Université de Montréal.Contribution No 375 from the Groupe de recherches en Ecologie des Eaux douces, Université de Montréal.