Effects of an hypersaline effluent from an abandoned potash mine on freshwater biofilm and diatom communities

Potash abandoned mines cause severe environmental damage to their bordering environment, with significant impacts on freshwater ecosystems mostly through uncontrolled discharge of hypersaline effluents. This study aimed to evaluate the ecological impact caused by a hypersaline effluent from an abandoned potash mine (Menteroda, Germany) on freshwater biofilms and, specifically, on diatom communities. Biofilm from a pristine stream was exposed under controlled conditions in microcosms to a mining effluent (ME), and its structural (algal biomass, community composition, diatom metrics) and functional (photosynthetic activity, nutrient uptake) responses were evaluated over time and compared with unexposed biofilms used as control. Biofilm exposed to ME showed drastic functional responses after one day of exposure, with a significant decrease in photosynthetic efficiency and nutrient uptake, that were recovered over time. Biofilm exposed to ME showed a progressive increase in diatom metrics (abundance, density and growth rate) over time, compared to the control. However, a significant decrease in diatom species diversity, richness and cell size was also observed in biofilm exposed to ME. This study revealed that the ME affected the biofilm causing short-term functional responses, which were recovered simultaneously with a drastic diatom community structure shift. This work was supported by the European Comissio LIFE program throughout the LIFE DEMINE project (LIFE16 ENV/ES/000218).We thank T.S and A.S from the Dresden Groundwater Research Center for the information about Menteroda abandoned mine provided. Lorenzo Proia that has received funding from the Postdoctoral Fellowships Programme Beatriu de Pin?s, funded by the Secretary of Universities and Research (Government of Catalonia) and by the Horizon 2020 Programme of Research and Innovation of the European Union under the Marie Sk?odowska-Curie Grant Agreement No. 801370. This study has been conducted with financial support from the French National Research Agency (ANR) in the framework of the Investments for the Future Programme, within the COTE Cluster of Excellence (ANR-10-LABX-45).