Spatial and temporal fluctuations of methane production in anoxic coastal marine sediments

Abstract

In vitro rates of net methane production and sulfate reduction were measured at various depths from October 1979 to November 1981 in anoxic coastal marine sediments from Cape Lookout Bight, N.C. In sulfate‐rich surface sediments at 1–4 cm, calculated methane production rates were within the experimental error of 0.011 mM CH₄·d^‒1. The depth of maximum methane production rate varied from 7–30 cm from summer to winter with summer maxima at the shallower depth. A maximum rate of 0.305 mM CH₄·d^‒1 was measured at 7–10 cm during July 1981. At intermediate depths low rates of methane production were observed in the presence of low concentrations of dissolved sulfate; however, these rates were near or within experimental error. Integrated rates of sediment column methane production ranged from 20 µmol·m^‒2·h^‒1 in April to 2,000 in August. These rates compared well with previously measured CH₄ sediment— water fluxes measured in sediments from the same field site in 1977. The total methane flux then ranged from 50 to 2,600 µmol CH₄·m^‒2·h^‒1.