The effect of natural and anthropogenic factors on the evolution of remote lakes in East Siberia for the last 200 years

We performed a regional analysis of the effect of anthropogenic (acid precipitation) and natural (climatic changes, endogenous methane) factors on the hydrochemical composition and phytoplankton of mountain lakes in East Siberia for the last 210 years. The lacustrine diatom community responded to the intense acid precipitation that led to the acidification of lakes in Europe and North America in 1950–1985: Cyclotella-complex was partly replaced by more pH-tolerant species of diatoms, such as Aulacoseira lirata, A. italica, and Tabellaria flocculosa. This anthropogenic impact, however, was not dramatic for the ecosystem of mountain Lake Oron. The diatom records distinctly show a tendency for the reduction of lacustrine-alga population since the end of the Little Ice Age. We assume that the decrease in the Oron bioproductivity was mainly due to a deficit of nutrients caused by the inflow of ultrafresh waters from the thawing glaciers, snow patches, and seasonal snow cover of the Kodar Ridge during the Recent global warming in the Northern Hemisphere. In addition, the changes in the lake ecosystem might have been accelerated by emissions of endogenous methane.