Modeling microbially driven reactions at the pore scale

Abstract:

Microbial communities provide a large variety of ecosystem services including the degradation of bioreactive chemicals in subsurface environments. Soils and aquifers are characterized by a high heterogeneity of the solid matrix. This leads to extremely high spatial variabilities of the various factors/constraints controlling the distribution of chemicals and of microbial abundance and activity at the pore scale (e.g., water activity, oxygen availability, substrate and nutrient supply or spatial habitat configuration). The ability of the microbial community to provide a given function such as the degradation of a chemical is thus controlled by both, a) the properties of the chemical determining its degradability and its distribution within the pore space, and b) the combination of individual constraints for microbial activity within each pore. These are major challenges for a sound prediction of the functional performance of the subsurface microbial community including its response to environmental changes or certain management practices.

Although there is an increasing process understanding on how individual factors influence the activity of microorganisms there is still a lack of knowledge on the influence of different factors controlling the in-situ ability of microbial communities to degrade a given chemical in heterogeneous pore systems. The presentation will cover numerical modeling approaches combining pore-scale flow and transport simulations with the simulation of biogeochemical processes to determine which properties of the solid matrix environment will facilitate or prohibit the microbial degradation of a chemical. This includes results from simulating simplified pore geometries showing the relevance of pore-scale mass-transfer processes as well as results obtained from a direct numerical simulation of variably saturated real world pore spaces.