A kinetic model for microbic organic-matter decomposition in marine sediments

Abstract

Abstract The microbial decomposition of organic matter in marine sediments has been described using a rate law which is linear in the concentration of the metabolizable organic matter, entirely independent of the biomass concentration, and displays a Monod-like dependence on the concentration of the oxidant species being utilized. This paper develops a quasi-reaction mechanism to explain these observed dependencies. The Monod dependence on the oxidant concentration and the biomass independence can both be traced back to the preponderance of occupied sites on the organic matter and pseudo-steady state concentrations of occupied sites during most of the decay process. In the framework of the proposed reaction scheme, the linearity of the rate with the organic matter concentration is possible only if there is a linear proportionality between surface area and mass of organic matter. The rate law described above divides natural organic matter into a finite collection of reactive types. This paper also reformulates this rate law model in terms of a continuum of reactive types as proposed by Boudreau and Ruddick (Am. J. Sci. 291, 507–538, 1991). It is shown that this continuum model can produce a better fit to kinetic rate data than the discrete model.