Sediment records of lake eutrophication and oligotrophication under the influence of human activity and climate warming in the Urals metallurgical region (Russia).

The lakes of mining and metallurgical regions are modified not only by climate warming, but also by diverse human impacts. The primary hypothesis of this study was that the response of lakes in the Ural metallurgical region to global warming and human land use was mediated by loading of potentially toxic elements (PTEs) and acidification. To test this hypothesis, we carried out a diatom and geochemical analysis of sediments accumulated through the past 800–1200 years and a hydrochemical analysis of four lakes. All lakes were characterized by shifts in diatom assemblages and changes in diatom indices and planktonic diatoms in the nineteenth and the twentieth centuries. Despite contamination by PTEs, lakes Turgoyak, Tavatui, and Syrytkul experienced an increase in trophic state and in planktonic diatoms. Oligotrophication was inferred only in the record of Lake Ufimskoe which was most contaminated by PTEs, but marked by the least other human impact. We conclude that diatom assemblages in the Middle and Southern Urals lakes primarily reflect the influence of local human activity, rather than the global warming. Industry-related acidification and higher PTEs altered lake development only under the condition of weak influence of other human activities. [ABSTRACT FROM AUTHOR]