Quantitative Lux-Based Assessment of Interacting Microbial Activity and Vadose Hydrology

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9630293 Selker This proposal was reviewed by the Environmental Geochemistry and Biogeochemistry panel (solicitation NSF 96-2) and jointly funded by several divisions at the National Science Foundation: Molecular and Cellular Biosciences, Earth Science, Environmental Biology, and Mathematical Sciences. The dynamic temporal and spatial distribution of microbes in the unsaturated media above aquifers is essentially unknown; though it is recognized that the distribution can be significantly heterogeneous. Since microbial communities in the unsaturated zone degrade the vast majority of contaminants applied to the earth's surface, this lack in understanding presents profound limitations to our ability to predict or enhance this essential contaminant treatment system. These studies involve the development and application of an analytical methodology that allows for direct, continuous observation of microbial distribution and activity, as well as the transport of contaminants through heterogeneous unsaturated porous media. This is made possible through the unification of two new technologies in an interdisciplinary effort between groundwater hydrology and environmental microbiology, namely: (1) the utilization of bioluminescent microbes to quantify microbial activity and contaminant movement; and (2) the use of light transmission chambers to quantify pore water content, pressure, and hydraulic flow paths. The system employs a naphthalene-degrading bacterium, Pseudomonas flourescens HK44, which has a lux gene cassette inserted into the naphthalene degradation pathway such that light is emitted in direct proportion to the rate of degradation of naphthalene or its metabolite salicylate. These experiments will be carried out in two-dimensional glass-walled flow cells containing packed aquifer sands at two scales: 2 x 1.5 m and 60 x 60 cm. The flow cells provide for controlled aqueous flux, illumination, and continuous time-lapse video and digital CCD imaging of the entire experiment. The effect s of geologic heterogeneity will be studied by packing the chambers with fine over coarse sand textural interfaces. Theses studies will: 1) Determine if regions of heterogeneous microbial colonization develop in otherwise uniform porous media under continuous unsaturated flow conditions. 2) Evaluate the effect of geological heterogeneities (textural variation) on localization of microbial development. 3) Investigate the combined and possibly interacting effects of geological and biological heterogeneities on contaminant fate and transport. 4) Assess the predictive capabilities of present microbial and hydrodynamic theory with respect to the experimental results of this research through the use of numerical models which simulate flow and microbial habitat. These studies will provide a powerful new analytical tool for the scientific and engineering communities to gain understanding of subsurface microbial activity and growth in natural and contaminated sites. The ability to make quantitative non-destructive observations on the rate and position of microbial activity, while monitoring water content and pressure, will significantly increase the capability to exploit microbial degradation toward environmental bioremediation. ***