Modeling the distribution of acetate in anoxic estuarine sediments

Abstract

Concentrations and rates of production and oxidation of acetate were studied in anoxic, estuarine sediments of Flax Pond, New York. Molecular weight separations by Sephadex gel indicated that in some, but not all, cases pore‐water acetate consisted of multiple “pools.” We developed a one‐dimensional kinetic model that uses measured oxidation rates (14C‐labeled acetate conversion to 14CO2) and production rates (MoO42‐ inhibition experiments) as model parameters. Appropriate diffusion coefficients were calculated with a free‐solution value (1.3 ±0.3 × 10−5 cm2 s−1) measured in this study. In general, oxidation rate constants estimated from modeled profiles agree well with those from [14C]acetate incubation experiments. Results imply that differences in acetate oxidation rates inferred from the two methods (MoO42− inhibition, [14C]acetate oxidation) can be caused by diffusion of acetate along sharp concentration gradients in sediments. [14C]acetate uptake experiments account for such diffusion by using measured steady state acetate concentrations to infer oxidation rates, whereas MoO42− inhibition experiments do not account for in situ acetate diffusion.