Sedimentary records of polycyclic aromatic hydrocarbons and organochlorine pesticides to reconstruct anthropogenic activities in Lake Issyk-Kul region (Kyrgyzstan), and their effects on the lake environment

Vertical distributions of polycyclic aromatic hydrocarbons (PAHs) and organochlorine pesticides (OCPs) in a sediment core from Lake Issyk-Kul are powerful tools for reconstructing historical anthropogenic activities over the past 350 years. Four periods were identified according to the variations in these environmental proxies. Period I (1670s-1800s) corresponds to a phase of limited anthropogenic activity reflected by the lowest sigma PAH16 concentrations, mainly from biomass combustion and petrogenic processes. Along with pronounced deforestation due to wildfires documented in the pollen record, a similar decrease in PAHs suggests that PAHs were most likely generated by natural sources around Lake Issyk-Kul during this period. Period II (1800s-1930s) reflects increasing agricultural activities with fluctuations in various PAH concentrations. Anthropogenic biomassderived PAH inputs from agricultural activities gradually replaced natural inputs to Lake Issyk-Kul, coinciding with several historical events. However, natural factors still mainly controlled changing lake levels before the 1930s. Period III (1930s-1970s) corresponds to rapid development of agricultural activities, inferred by slight increases in sigma PAH16 concentrations dominated by coal -derived PAHs and a considerable increase in sigma OCP18 concentrations. Concentrated agricultural activities around Lake Issyk-Kul significantly influenced environmental changes in grain size and water level in the lake. Period IV (post -1970 s) corresponds to intensive industrial and urban activities, including a 10 -year economic depression (1990s-2000s), characterized by the highest sigma PAH16 concentrations mainly from petroleum combustion followed by a sharp drop after the 1990s as the dissolution of the Soviet Union. Industrialization and urbanization in study area have changed the trophic state of Lake Issyk-Kul, particularly in recent years. Climate change has also induced "lateral remobilization" of contaminants, increasing pollution levels in this mountain lake.