Impact of acid mine drainage on diatom communities of Orijärvi and Määrjärvi, lakes in SW Finland

The top/bottom paleolimnological approach was used to assess (1) the spatial extent of the effect of acid mine-drainage from the Orijärvi mine tailings on diatom communities of Orijärvi and Määrjärvi, and (2) the change that occurred in these communities as compared with the pre-disturbance conditions. Altogether eight cores were retrieved from the lakes and examined for their diatom remains. The compositional change in the diatom communities
was assessed by detrended correspondence analysis and changes in their diversity by the Shannon diversity index (H´). The metal pollution affected diatoms at community levels resulting in a shift in dominant taxa and an overall decrease in diversity (both lakes), and at
the individual level causing alteration in valve morphology (Orijärvi). The proportion of benthic and tychoplanktonic diatoms increased while planktonic diatoms markedly decreased in abundance. This study demonstrates that the used approach is a useful tool in larger-scale assessments of recent change and ecological reference conditions of surface waters.