Influence of atmospheric deposition and climate change on lake eutrophication and environment in Lake Buir (eastern Mongolia) over the last century

• Enhanced river input since the 1940s was caused by increasing rainfall. • Hypolimnion was oxidized after the 1950s with enhanced river input. • Depletion of δ 15 N since the 1960s is due to agricultural activity in NE China. • Primary productivity resulted from climatic warming and atmospheric nutrient supply. • Atmospheric transport of pollutants from NE China began in the 1950s. Multiple proxies from a sediment core taken from the deepest part of Lake Buir in the eastern Mongolian Plateau, situated at the China–Mongolia border, were used in this study to investigate paleoenvironmental changes and climatic and anthropogenic factors that primarily control variability over the past 100 years. A typical upward-fining turbidite bed was found in 1947–1954 CE based on the combined age of excess 210 Pb and 137 Cs, which coincided with high annual precipitation. The median grain sizes of the mineral fraction and TS/TOC ratio indicate enhanced river inflow since the 1940s–1950s with increasing rainfall, leading to changes in the hypolimnion from anoxic to oxic conditions. The gradual increase in carbonate content suggests that regional warming since the 1960s has resulted in a decrease in dissolved CO 2 solubility and an increase in primary productivity in the epilimnion. The C/N molar ratio (8.3–12.0) and Suess-corrected δ 13 C TOC value (–24.9 ‰ to –22.0 ‰) indicate that the sedimentary organic matter mainly originated from algae and phytoplankton. The depletion of δ 15 N (6.5–5.4 ‰) with increasing TN content from the 1960s to the 2000s CE indicates enhanced atmospheric nutrient deposition from northeast China. These findings suggest that climate warming and anthropogenic loading have affected lake eutrophication. Furthermore, the depletion of δ 34 S values (9.1–7.0 ‰) with low TS contents since the 1960s CE indicates that atmospheric pollution of sulfates was transported with the rapid economic and industrial development in northeast China.