Profiling dynamics of the Southeast Asia's largest lake, Tonle Sap Lake

Lakes, as vital components of the Earth's ecosystem with crucial roles in global biogeochemical cycles, are experiencing pervasive and irreparable worldwide losses due to natural factors and intensive anthropogenic interferences. In this study, we investigated the long-term dynamic patterns of the Tonle Sap Lake, the largest freshwater lake in the Mekong River Basin, using a series of hydrological data and remote sensing images between 2000 and 2020. Our findings revealed a significant decline in the annual average water level of the lake by approximately 2.1 m over 20 years, accompanied by an annual average reduction in surface area of about 1400 km2. The Tonle Sap Lake exhibited episodic declines in water level and surface area, characterized by the absence of flooding during the flood season and increasing aridity during the dry season. Furthermore, the shoreline of the lake has significantly advanced towards the lake in the northwestern and southern regions during the dry season, primarily due to sedimentation-induced shallowing of the lake edge depth and decreased water levels. In contrast, lake shorelines in the eastern region remained relatively stable due to the constructed embankments for the protection of the cultivated farmland. While the seasonal fluctuations of the Tonle Sap Lake are regulated by regional precipitation in the Mekong River Basin, the prolonged shrinking of the lake can be mainly ascribed to intensive anthropogenic activities. The interception of dams along the upper Mekong River has resulted in a decrease in the inflow to Tonle Sap Lake, exacerbating its shrinkage. Moreover, there are minor impacts from agricultural land expansion and irrigation on the lake. This study highlights the driving forces behind the evolution of Tonle Sap Lake, providing valuable information for lake managers to develop strategies aimed at conserving and restoring the ecological integrity of the Tonle Sap Lake.