EFFECTS OF A PULP AND PAPER-MILL EFFLUENT ON THE STRUCTURE AND METABOLISM OF PERIPHYTIC ALGAE IN EXPERIMENTAL STREAMS

The impact of a pulp and paper mill effluent on periphytic algae growing under controlled conditions in experimental streams was manifested as a drop in species richness and diversity, and changes in the taxonomic structure of the algal community. The decrease in diatom density was compensated by the relative contribution of Chlorophyceae, which increased with increasing effluent concentration (0.5%, 2.5% and 10% v/v). The presence of effluent also led to a rise in heterotrophic biomass and activity. However, the stream with the highest effluent concentration (10% v/v) showed a greater autotrophic biomass, and had the lowest photosynthetic efficiency, suggesting that algal species which develop under such conditions exhibit important heterotrophic activity. This hypothesis was supported by micro-autoradiographic studies, which showed that Chlamydomonas sp. cells were very strongly marked after incubation in the presence of amino acids, while diatoms showed little or no radioactivity. This suggested that the dissolved organic carbon in the effluent acted as a eutrophication factor for periphytic algal communities.