COMPOSITION AND DYNAMICS OF EPILITHIC ALGAE IN A FOREST STREAM AT SHILLONG (INDIA)

The seasonal dynamics of epilithic algae in a third order pristine for est stream were analyzed over a period of 2 years. Stream water was sl ightly acidic and nutrient poor. Encrusting, filamentous flocs, and fi laments were found. Algal standing crop was high (mean concentration o f Chl a 16-43 mg m(-2)) in spring. Filamentous algae contributed most to standing crop. Diatoms made up over 85% by number of the epilithon. Blue-greens were abundant upstream, and chlorophytes downstream. This shift was ascribed to greater light availability downstrean. The comm unity was more diverse during spring. Water current was the most impor tant variable regulating epilithon structure. Total phosphorus (TP), o rthophosphate (O-PO43-), silica (Si4+), nitrate (NO3-) and conductance correlated negatively with flow rate. Green algae showed a positive c orrelation to phosphorus during low and stable flow. During rapid runo ff, diatoms were the most resistant forms. Seasonal change in the epil ithic community was mainly regulated by fluctuations in flow rate.