Impact of Aquifer Heterogeneity on Geomicrobial Kinetics
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Rates of microbial reactions are important in understanding groundwater chemistry and bioremediation. In aquifers, microbial rates depend on physicochemical and biological factors and also on how groundwater transport impacts microbial reactions at pore-scale. I numerically simulate microbial acetate consumption in a porous medium, focusing on how physical heterogeneity of the medium impacts the rates. My model is a 3-D cube, which represents a portion of a sandy aquifer. Acetate is supplied by groundwater flow through the cube, and microbes live on randomly distributed grain surfaces by oxidizing acetate. I simulated microbial acetate oxidation under a range of groundwater velocity, acetate concentrations, spatial heterogeneity, and other physicochemical conditions. The results demonstrate a significant gap in microbial kinetics between the pore-scale and continuum model. Specifically, microbial rates are larger in porous media of greater heterogeneity. For this reason, I propose that microbial parameters should not be applied directly to field-scale biogeochemical modeling.