Short-term nutrient influences on algal assemblages in three rivers of the Minnesota River basin

Periphyton accumulation variables and diatom assemblage structure were examined on nutrient diffusing pots placed in three rivers in the Minnesota River basin. The Minnesota River, which had the highest accrual of inorganic and organic matter, appeared to have phosphate and light limited algal accumulation. No nutrient effects were observed in the Blue :Earth River although phosphate limitation was predicted by the N:P ratio. Cyclotella meneghiniana responded negatively and Gomphonema parvulum responded positively to ammonia diffusing pots in the Yellow Medicine River. Otherwise no release from nutrient limitation was observed in this stream. Diatom species composition varied independently of algal accumulation rates.