Lowering water level of Dongting lake of the Mid-Yangtze River in response to large-scale dam construction: A 60-year analysis

River-lake systems, crucial to both the ecological environment and societal development, have been affected by increasing anthropogenic activities in addition to climate and environmental changes. Here, annual water discharge and sediment load data (1956–2017) and rainfall data (1960–2016) from Dongting Lake in the middle catchment of the Yangtze River were analysed at four major inlets and one outlet, and their connections with lake level variations were evaluated using multiple analytical methods. The results show that minor fluctuations were found in rainfall and discharge during the study period, but the sediment load entering Dongting Lake decreased significantly from 231 mt/year (before 1969) to 123 mt/year (1970–2002) and then 17 mt/year (after 2003, post TGD). The variation in the sediment was mainly induced by increasing anthropogenic activities in the lake system. During period 1 (before 1969), human impact was weak compared to the dominant natural forces. However, anthropogenic force showed an increasing contribution to the loss of sediment load since then, as it increased from 43.0% (1970–1987, post cut-off engineering) to 64.8% (1988–2002, post Gezhou Dam) and extended to 90.2% during 2003–2017 (post TGD). Nevertheless, continuous sediment accumulation over the past decades in the lake has caused a rising water level. During period 1, high sediment input contributed to an average annual increase of 13.96 cm in the lake level, but it decreased significantly to 1.94 cm year−1 during 1970–2002 due to intensive anthropogenic regulations. Since 2003, the completion of the TGD intercepted abundant sediment, eventually leading to a shift from net deposition to net loss of the sediment budget in Dongting Lake, and consequently, the lake level fell. In the future, if the net sediment supply was kept below ~18 mt/year, the lake level would continue to fall, causing severe problems to the lake ecosystem, especially during drought years.