Sediment Oxygen Demand and Nutrient Release

Benthic oxygen demand rates in rivers ranged from 0.10 gm/m to 5.30 gm/sq m/day and were found to increase linearly with dissolved oxygen concentrations in the water overlying the sediment deposits. The oxygen uptake was found to be more closely related to the nutrient composition of the interstitial water of the sediments than to the nutrient composition of the sediment solids. Ammonia nitrogen release rates ranged from an apparent net uptake of 44 mg/sq m/day to a release of 505 mg/m, whereas total dissolved phosphorus exchange rates varied from a net uptake of 13 mg/sq m/day to a release of 138 mg/sq m/day. The release of ammonia nitrogen was related to the nitrogen content of both the interstitial water and solids portions of the sediment and it appeared that biochemical mechanisms were principally responsible for ammonia nitrogen exchange processes. The exchange of total dissolved phosphorus was unrelated to measured nutrients within the sediments or overlying waters but was related to oxygen depletion, consistent with the widely accepted view that phosphorus exchange is controlled principally by oxidation-reduction reactions with iron, manganese, or sulfur, or all three.