Multi-proxy paleolimnological evidence for recent environmental degradation of Xingkai Lake, the largest shallow lake in Northeast Asia

Located at the border between China and Russia, Xingkai Lake is the largest shallow lake in Northeast Asia. Current studies based on the lake’s sediments mostly focus on the climatic evolution over the past 10³-10⁶ years, with limited research on high-resolution recent environmental changes. In this study, three short sediment cores were collected from the northern area (in the Chinese part) of the lake and dated using ²¹⁰Pb/¹³⁷Cs radiometric methods. The changes in diatom communities and sediment physicochemical indicators, such as total organic carbon (TOC), Pb, Fe/Mn, frequency-dependent magnetic susceptibility (χ_fd) and sediment accumulation rate (SAR), were analyzed to reconstruct environmental change in the northern part of Xingkai Lake over the last 200 years. Results show that the diatom assemblages were dominated by Aulacoseira granulata prior to the 1990s. Since the late 1990s, eutrophication has emerged, with a shift to Cyclostephanos dubius as the dominant diatom species. Cultivated land area, χ_fd, sediment TP and annual mean wind speed were the four most important environmental variables explaining the shifts in the diatom assemblages, suggesting that agricultural disturbance is the main driver of environmental degradation. Additionally, the study reveals some spatial difference in depositional environments in the lake. The relative stability of the diatom assemblages before the late 1990s suggests that Xingkai Lake experienced low levels of eutrophication prior to the start of the twenty-first century and may thus have a higher ecosystem resilience than is typically seen in smaller lakes. The mean epilimnetic TP concentration of 35 μg/L measured before the significant diatom change can be used as a reference nutrient condition for eutrophication management of this lake. The study provides a scientific basis for the management of Xingkai Lake in China and Russia, and also enriches the research cases of environmental change in the world’s large lakes.