ALGAL PERIPHYTON OF AN UNSHADED STREAM IN RELATION TO IN-SITU NUTRIENT ENRICHMENT AND CURRENT VELOCITY

The effect of nitrogen and phosphorus enrichment on periphytic algal c olonization was studied in a pool, and at low flow (9-12 cm s-1), mode rate flow (19-24 cm s-1) and high flow (38-41 cm s-1) in an unshaded s tream at Shillong (India). Nutrient diffusing clay pots were used as s ubstrata for algal colonization. The increase of algal biomass was at a maximum at low flow and at a minimum at high flow. Phosphorus supple mentation enhanced periphytic biomass, thereby suggesting phosphorus l imiting conditions in the selected stream. The increased periphytic bi omass after phosphorus enrichment was, however, much less than the lev el ( 100-150 mg chlorophyll a m-2) considered to be undesirable. The b iomass of filamentous green algae was enhanced by phosphorus enrichmen t particularly at low flow and in the pool. The stimulatory effect of nutrient enrichment was inversely related to current velocity.