The Diffusion and Consumption of Oxygen in Submerged Soils

Abstract

Abstract Six O 2 diffusion models, which included several oxygen consumption processes, were evaluated by measuring O 2 consumption rates under conditions which approached the steady state and under transient‐state conditions. Consumption rates under approximately steady‐state conditions were determined by placing undisturbed lake‐bottom cores in water and measuring the decrease in O 2 concentration of the water. Transient‐state consumption rates were determined from the amount of O 2 gas that had to be injected above an initially reduced soil to maintain a constant O 2 concentration at the soil surface. The distribution of extractable Fe in the cores was obtained by sectioning frozen soil cores and extracting the sections with NaOAc at pH 2.8 and with dithionite in EDTA. Considerable amounts of Fe 2+ were found to diffuse from the reduced zone to the oxidized zone where it accumulated as precipitated Fe 3+ . The oxygen consumption was best described by models which included consumption by microbial respiration in the aerobic zone and oxidation of mobile and nonmobile reductants such as Fe 2+ . The latter components of oxygen consumption accounted for about 50% of the consumption by cores after 11 days when the cores were initially uniformly reduced.