(Redox-)Biogeochemistry on the Microscale - Biofilms and Model Systems

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We observe reduction and oxidation processes in the environment that cannot be explained by classical geochemical models. Often reactions are coupled that - based on their individual chemical requirements - should not occur together. However, one fundamental aspect that often has not been considered, mostly due to limitations in our experimental possibilities, is the heterogeneity of environmental systems.Die development of innovative experimental approaches, in particular in the fields of synchrotron-based X-ray spectromicroscopy and lab-based in-situ approaches such as the coupling of environmentally sensitive fluorescence probes with confocal laser scanning microscopy now became promising tools to study such heterogeneities.In this project, the influence of structural and chemical sub-micron scale heterogeneity in redox-active biofilms on biogeochemical reactions will be studied systematically. It will focus on the coupling between different redox-cycles (Fe, Mn, S) that - based on the macroscopic conditions - should not occur. The influence of these couplings on nutrient and contaminant cycling will be studied. In addition to studying natural and artificial biofilms, microfluidic model systems will help to gain a fundamental understanding of the underlying processes under controlled laboratory conditions.The goals of this project are:1) to characterize and parameterize both structural and chemical heterogeneities of redox-active biofilms at the micro-scale. This includes the organochemical composition (e.g. redox-active functional groups), inorganic constituents and chemical conditions with a focus on Fe, Mn and S species.2) to identify, to map and to quantify biogeochemical processes that occur in micro-niches, including the adsorption of nutrients or contaminants, mineral-precipitation and -dissolution, but also electron transfer reactions between the different constituents of the biofilm.3) to prove experimentally whether micro-scale heterogeneities can result in the same phenomena as temporal fluctuations, e.g. fluctuations in water levels.4) to identify individual parameters (i.e. pH, potential, metal concentrations, redox potential) that could induce the previously described structural and chemical heterogeneities.5) to characterize the organochemical composition of microbial exopolymers to study their potential for electron conductance and for acting as redox-buffer systems.6) to assess the importance of the previously determined reactions in microenvironments on the macroscopic scale.