Microbial communities and fatty acid markers across acidification and eutrophication extremes in a river influenced by mining activities

Microbial communities in combination with fatty acid and isotopic markers were studied seasonally to assess the effects of acid mine drainage (AMD) and nutrient loads in the Spree river. Negative values of δ¹⁵N, the bacterial and detrital markers 18: 1(n-7) and 18:1(n-9), pH values ∼3 and bacteria of the genera Ferrovum, Thiomonas, Acidocella, Acidiphilum, Syderoxydans and Galionella were characteristic of the AMD extreme. Potential iron-oxidizers may produce ferric ions and their precipitates may influence biogeochemical processes, while potential sulfur-oxidizers may contribute to elevated sulphate concentrations and challenge drinking water production in the Spree catchment. In this river, eutrophication was linked with polyunsaturated fatty acids (PUFA) enrichment and not with PUFA depletion as occurs in other freshwater systems. Elevated concentrations and proportions of PUFA as well as higher relative sequence abundance of cyanobacteria were characteristic of the highly eutrophic station, particularly during the phytoplankton bloom. The 18:5(n-3) from flagellates or dinoflagellates may indicate lipid anabolism and trophic upgrading processes. The dominance of the classes Bacteroidia, Gammaproteobacteria and Actinobacteria suggested eutrophic and changing hydrological conditions in the river. The microbial communities were better markers of seasonality than the biogeochemical markers and their combination offers an excellent resolution for the study of the ecology and biogeochemistry of water courses. The expected decreased runoff under climate-driven scenarios may worsen the AMD pollution and eutrophication problems and signify a considerable challenge for water management.