Effects of climate warming and declining water quality on the eco-environmental evolution of Jinmucuo Lake: Evidence from sedimentary diatom assemblages

The problem of lake pollution on the Tibetan Plateau has become prominent in recent years because of the warming climate and increased human activity. However, it is difficult to obtain effective indicators to explain the long-term eco-environmental changes in plateau lakes. In this study, a sediment core from Jinmucuo Lake was taken as the research object, and the ²¹⁰Pb and ¹³⁷Cs isotopes, diatom assemblages, and climatic and environmental factors were analyzed. The results revealed that the lake had a sedimentation rate of 0.47 cm/a, and the age of the 30-cm sediment core was approximately 1876 AD. Diatom abundances at different ages tend to decrease. During 1876-1999, abundant diatom species, such as <i>Cymbella lanceolata</i>, <i>Navicula</i> sp., <i>Surirella ovalis</i>, <i>Synedra</i> sp., <i>Epithemia adnata</i>, <i>Cymbella pusilla</i>, <i>Amphora ovalis</i> and <i>Tabularia tabulata</i>, which included oligotrophic, mesotrophic, and eutrophic indicator species were detected, and the dominant species were <i>Cymbella lanceolata</i>, <i>Navicula</i> sp., <i>Surirella ovalis</i> and <i>Synedra</i> sp. After 2000, diatoms declined dramatically, and were undetected in most samples. Similarly, the species richness and Shannon‒Wiener index plummeted to 0 in approximately 2002. Canonical correspondence analysis revealed that total nitrogen and organic matter were the main influencing factors of diatom assemblages before 2000, whereas As and mean annual temperature were the main influencing factors after 2000. These findings indicate that diatom habitats have been rapidly destroyed by increasing temperatures and As inputs, even in the presence of abundant nutrients in the lake.