A series of experiments were conducted to test the hypothesis that the concentrations of suspended algal populations in central Iowa streams are not limited by nutrient concentrations. River water samples with their natural plankton populations were collected from the Des Moines River, Skunk River, and Squaw Creek and were cultured under controlled conditions without the addition of nutrients. In 23 of 24 experiments significant increases in algal chlorophyll a were found with an average replication factor of 14 times. The data indicate that nutrients are not limiting suspended algal densities in the streams. A second series of experiments indicated that nitrate concentrations of up to 20 mg/I nitrate-nitrogen did not inhibit algal growth in these river waters
