Geoökologisches Kolloquium WS 2002/03

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Prof. Rasmus Jacobsen
Technical University of Denmark, Lyngby
Thursday, 17.10.2002 16:15 H6

Hydrogen, the common Currency of anaerobic Processes? Sampling Methods, Bioenergetics, and the Application in partial Equilibrium Models of Redox Processes

Hydrogen (H2) is a major intermediate in the oxidation of organic matter. It is present in all natural environments, typically in extremely low concentrations of ~0.01-20 nmol/L in water. H2 is produced by fermentation of organic matter and used in terminal electron acceptor proccesses (TEAP\'s) e.g. reduction of sulfate to sulfide. In-situ concentrations of reactants, of which H2 is one, and products enable the calculation of the Gibbs energy available for the TEAP\'s. This has shown that the fermenting microorganisms and the TEAP microorganisms form a thermodynamically optimized eco-system enabling sustained oxidation of organic matter. The energy available for the TEAP processes, when they occur, is small, and close to constant in a given system. Some studies indicate that this is also the case for the degradation of xenobiotic compounds. The small energy involved means that the processes occur close to equilibrium. This makes it possible to view redox processes as taking place at partial equilibrium, implying that the overall rate of the TEAP\'s is controlled by the rate of supply of fermentation products, while the TEAP\'s can be handled as equilibrium reactions. This approach greatly simplifies numerical modelling of redox processes in natural environments.

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