METHANE PRODUCTION AS A FUNCTION OF ANAEROBIC CARBON MINERALIZATION -A PROCESS MODEL

Anaerobic carbon mineralization is a major regulator of soil methane p roduction, but the relationship between these processes is variable. T o explain the dynamics of this relationship a model was developed, whi ch comprises the dynamics of alternative electron-accepters, of acetat e and of methanogenic biomass. Major assumptions are: (i) alternative electron-accepters suppress methanogenesis and (ii) the rate of electr on-acceptor reduction is controlled by anaerobic carbon mineralization . The model was applied to anaerobic incubation experiments with slurr ied soil samples from a drained and an undrained peat soil in the Neth erlands to test the model and to further interpret the data. Three par ameters were fitted with a Monte Carlo method, using experimentally de termined time series of methane, carbon dioxide and acetate. The fitte d parameters were the initial concentration of electron-acceptors, the initial concentration of methanogenic biomass and the maximum relativ e growth rate of methanogenic biomass. Simulated and measured time cou rses of methane corresponded reasonably well. The model as such stress es the importance of alternative electron-accepters. At the drained si te initial alternative electron-acceptor concentrations were between 0 .3 and 0.8 mol electron equivalents (el. eqv.) kg(-1) dw soil, whereas at the undrained site they were between 0.0 and 0.3 mol el. eqv. kg(- 1) dw sail, depending on the experimental treatments. The sum of measu red NO3- and SO42- concentrations and estimated maximum Fe-3(+) and Mn 4+ concentrations was much lower than the fitted concentrations of alt ernative electron-accepters. Apparently, reduction of unknown electron -accepters consumed a large part of anaerobically-mineralized carbon w hich, therefore, was not available for methanogenesis. (C) 1998 Elsevi er Science Ltd. All rights reserved.