AEROBIC DECOMPOSITION OF SEDIMENT AND DETRITUS AS A FUNCTION OF PARTICLE SURFACE AREA AND ORGANIC CONTENT

Abstract

Oxygen uptake by microbial populations on mud, sand, and various types of detritus was measured in short‐term experiments in aerated water at 20C. Sample size had no effect on oxygen consumption per unit weight, but stirring increased uptake. A 2% Formalin solution completely stopped biological uptake of oxygen by microorganisms on sand and detritus; lake muds showed various degrees of chemical uptake of oxygen. Microorganisms on dead Phragmites leaves consumed oxygen at an increasing rate during the first few days of decomposition, followed by a decline to a rate comparable to uptake by freshly collected detritus. Limnaea feces initially consumed oxygen three times more rapidly than detritus, but after 5 days the rates were equal. Detritus consumed up to three orders of magnitude more oxygen per dry weight than sand; uptake rates were inversely related to particle diameter. The logarithm of oxygen uptake was directly related to the logarithm of particle organic content. Particulate oxygen uptake in this and previous studies fell between 0.1 and 10 mg O 2 (g organic matter)−1 hr−1, a rate inversely related to particle diameter. Oxygen uptake per unit weight by particles of ashed mud and sand exposed for 24 hr to decomposing detritus in a nutrient solution and transferred to fresh solution was inversely related to particle size and similar to rates measured with freshly collected samples. On an areal basis all particles consumed between 0.01 and 1.0 × 10−3 mg O 2 cm−1 hr−1. The negative linear correlation on logarithmic axes of surface area, organic carbon and nitrogen and bacterial plate counts with sediment particle size is similar to that observed for measures of oxygen uptake. Bacteria cover only a few percent of particle surfaces. This may result in the narrow range of measures of microbial community respiration on an areal basis.