The temperature is of major importance for geochemical and biological processes. Despite that, the influence of temperature changes due to geothermal use of the subsurface on the inherent biocenosis and the fluids geochemistry still is largely unknown. Microbiological metabolism can influence, increase or initiate precipitation (scaling). Enhanced process understanding and ecological evaluation of geothermal use of shallow aquifers are in the focus of this work package. The analysis of alterability of the soil system and the assessment of ecological and technical effects on the overall context is a prerequisite for the highly required scientific determination of temperature thresholds for geothermal subsurface exploitation. The influence of temperature on microbiologically catalyzed metabolic processes is studied and additionally the effect of higher temperatures on growth of potential pathogenic microorganisms will be evaluated. Soil inhabiting microorganisms and their metabolism will be analyzed with different molecular biological and geochemical methods.