THERMODYNAMIC CONTROL ON HYDROGEN CONCENTRATIONS IN ANOXIC SEDIMENTS

Molecular hydrogen plays a central role in bacterially mediated anoxic sediment chemistry, as both an important electron transfer agent and a key thermodynamic control. We studied the response of hydrogen conce ntrations to changes in temperature, specific electron acceptor, sulfa te concentration, and pH in a series of laboratory experiments using s ediments from Cape Lookout Eight, North Carolina. Hydrogen concentrati ons were found to depend significantly on each of these factors in a f ashion that suggests thermodynamic control. In general, the change in hydrogen concentrations was apparently driven by a necessity to mainta in a constant Delta G for the predominant terminal electron-accepting process. We hypothesize this situation derives from highly competetive conditions that force terminal metabolic bacteria to operate right at their thermodynamic limits. The response of hydrogen to individual co ntrols in the laboratory experiments was reflected in relatively quant itiative fashion in down-core, seasonal, and inter-environmental varia tions observed in sediment cores from Cape Lookout Eight and the White Oak River, NC. Copyright (C) 1998 Elsevier Science Ltd.