Phosphorus and major cation mass balances for two rivers during low summer flows

SUMMARY. Soluble reactive phosphorus (SRP) mass balances showed that phosphorus retention occurred during low summer flows in reaches of Duffin Creek and the Nottawasaga River, two phosphorus‐rich streams in southern Ontario. The average daily removal in Duffin Creek was 6.1 ± 1.6 kg SRP which represents the retention of about 92% of the phosphorus input. Approximately 5.3 ± 3.5 kg SRP (about 44% of the daily input) was removed from stream water in the Nottawasaga River. Laboratory experiments indicate that sorption by stream‐bed sediments is an important mechanism for phosphorus retention in both rivers. Uptake by benthic algae may also act as a temporary phosphorus sink in Duffin Creek. Major cation inputs and outputs are generally in balance, implying that these elements act in a relatively conservative manner in both rivers.