RedoxFlux: Biogeochemical fluxes and transformations at pelagic redoxclines in lakes

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The interface between oxic and anoxic water bodies, the redoxcline, separates, or rather connects two very contrasting habitats and is a hotspot of biogeochemical transformations in many lakes. At the depth of the redoxcline, intense cycling of, e.g. sulfur, iron and manganese, occurs. This cycling involves chemical as well as microbial reactions and the corresponding transformation rates are mainly controlled by (i) vertical transport of dissolved and particulate substances, (ii) reaction and precipitation-dissolution kinetics, and (iii) by the availability of light. In this project we will gain a process-based understanding of the interplay of these processes. Vertical fluxes and biogeochemical turnover rates will be estimated in field experiments at three different lakes, representing three contrasting water bodies in terms of the availability of reduced chemical species, light, and vertical mixing. The detailed kinetics of the underlying chemical and microbial reactions will be studied in laboratory mesocosm experiments, set up for two of the study sites. In an innovative approach, the mesocosms will independently mimic density stratification, vertical fluxes of all relevant constituents and vertical mixing. Results from laboratory and field experiments will be combined into a process-based numerical model, allowing for a transfer of our results to different aquatic systems and to changing environmental conditions.