Environmental changes during the past ∼ 400 years in alpine Lake Son-Kul, central Tien Shan, Kyrgyzstan: evidence from sedimentary lipid biomarker records

Environmental and ecological changes recorded in lake sediments can provide valuable information about natural versus anthropogenic effects on the environment, especially in alpine lakes, which are commonly regarded as sensitive indicators of both local and global environmental changes. To reconstruct the past similar to 400 years of environmental history of alpine Lake Son-Kul, central Tienshan, Kyrgyzstan, we measured lipid biomarkers (n-alkanes [n-ALKs] and n-alkanoic acids [n-FAs]) and other geochemical variables (total organic carbon [TOC] and total nitrogen [TN]) in a Pb-210- and Cs-137-dated sediment core. Stratigraphic shifts in lipid biomarkers, TOC and TN indicate three principal environmental stages in the lake over the past four centuries. Stage I (similar to 1600-1900 AD) was characterized by relatively lower and stable terrestrial organic matter (OM) and limited aquatic primary productivity. A period of shallow-water conditions was revealed by increased abundances in long-chain n-FAs ca. 1775 AD. Stage II (similar to 1900-1960 AD) was characterized by increased allochthonous OM inputs, indicating marked development of terrestrial vegetation caused by elevated temperatures. In stage III (similar to 1960-2011 AD), allochthonous OM inputs and aquatic primary productivity in the lake increased significantly compared to previous stages. Warm and dry conditions may be responsible for the rapid increase in allochthonous OM inputs and changes in herbaceous plant communities during the interval similar to 1960-1983 AD. A pesticide spill in 1976 caused a reduction in aquatic macrophytes, as recorded by biomarker indexes, e.g. Paq, LPTP. In addition, greater human-mediated nutrient loading was responsible for increasing phytoplankton productivity, especially in recent decades.