Modeling Microbially Induced Carbon Degradation in Redox-Stratified Subsurface Environments: Concepts and Open Questions

The degradation of organic matter, including organic contaminants, in subsurface environments is controlled by the abundances and functional capabilities of the resident microorganisms. As a consequence, modeling approaches simulating the fate of organics and related changes in redox conditions have to account for the effects of microbial activity on the degradation kinetics, as well as for the spatial and temporal distributions of the chemical species (e.g., terminal electron acceptors, nutrients or toxic substances) that control microbial activity. The present paper reviews the principal modeling approaches that are used to simulate the degradation of organic matter in water-saturated porous media. Special attention is devoted to modeling the bioavailability of chemical substrates of microbial reactions, and the sequential occurrence of terminal electron accepting pathways. While the various model approaches found in the literature are capable of reproducing field data sets from various environmental settings, they are rarely compared in terms of performance and predictive ability. Most approaches incorporate simplifications or empirical rate laws, which limit their range of application. Thus, there remains a need for further development of more general, process-based modeling concepts to represent microbially mediated reactive processes.