Dynamic Behavior of Micobial Growth and Activity in Mixing-Controlled Contaminant Plumes

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Organic contaminants, e.g. petroleum hydrocarbons, are frequently released into aquifers, forming plumes depleted in dissolved electron acceptors. Biodegradation of such plumes requires a dissolved reaction partner provided by transverse dispersive mixing. Analytical expressions for the plume length and the overall reaction rates have been developed for steady-state conditions. Under field conditions, however, steady state seldom prevails. Both the lateral position of a contaminant plume and the chemical composition of the mixing waters may change over time. For the predominantly immobile, active microbial biomass it may be difficult to cope with these changes so that the overall degradation of mixing-controlled plumes may be hampered. Dynamic changes in local chemical conditions may also induce shifts in the relative abundance of bacterial populations in a microbial community. We will conduct well controlled laboratory experiments of mixing-controlled bioreactive transport in quasi two-dimensional flow-through systems applying dynamic boundary conditions to elucidate the influence of such hydraulic and chemical dynamics on the overall degradation and the microbial communities involved. These experiments will be analyzed by numerical simulation of all relevant processes facilitating the transfer of results to conditions not covered within the experiments. We hypothesize that the importance of dynamic boundary conditions depends on relative time scales of these changes in comparison to the time scales of physical transport, biomass growth/decay and activation/deactivation.