Oxidation-Reduction Potentials, Oxygen Concentration and Oxygen Uptake of Profundal Sediments in a Eutrophic Lake

Oxidation-reduction potentials were measured with a 1-mm platinum electrode in undisturbed sediment cores and re-settled mud from Lake Esrom, Denmark. Slow stabilization of Eh potentials occurred at the aerobic-anaerobic interface. Seasonal changes in Eh profiles in profundal sediments only occurred in the upper 1 cm during summer stratification. When oxygen disappeared, reducing conditions reached the sediment surface. In artificial mud-water systems, no measurable oxygen occurred when Eh values in either sediment, or water, or both, fell below +100 mv. Oxygen uptake by mud taken from various depths of sediment cores was inversely related to Eh potential. Eh and the square root of oxygen uptake by subsurface mud during aeration showed a similar inverse proportionality, suggesting that intensity and capacity of oxygen consumption are related. Formalin addition reduced oxygen uptake by sediment from the surface of undisturbed cores by 80 per cent. Below 1 cm all oxygen was consumed by chemical processes. Eh potential may index both the intensity and capacity of such reactions.