Impact of human and natural factors on the water environment evolution of Dongting Lake area over the past 500 years

Objective The disputes among humans, water and land have seriously restricted the sustainable development of the Dongting Lake region (TDLR). Methods To address this issue, it is crucial to understand the evolution of the hydrological environment in the TDLR, enabling solutions to the competition for space between human activities and water. By determining the evolution of the human-water relationship in the TDLR over the past 500 years, the influences of natural and human factors on the evolution of the hydrological environment are studied. Results Considering the characteristics of tectonic subsidence and sediment inflow in the TDLR, an evolutionary model of the hydrological environment induced by human activities and the geological environment was obtained, and not only the changing trends in the storage and drainage of water and sediment in the TDLR and Yangtze River but also the possibility of future evolution of the TDLR were clarified. Conclusion The key finding are as follows: (1) The continuous land reclamation has encroached on floodwater retention areas, significantly reducing Dongting Lake's flood storage capacity. (2) The construction of the Jingjiang Dyke has raised flood levels in the Jingjiang River and exerted a backwater effect on Dongting Lake, exacerbating flood disasters during the high-water period. (3) The straightening of the Jingjiang River has led to sediment deposition from Chenglingji to Wuhan, and the decline of the three distributaries of the Jingjiang River, causing shrinkage at the lake's inlets and blockage at its outlets. (4) Since the operation of the Three Gorges Reservoir, the sediment accumulation of the inflow water from Dongting Lake decreased significantly, and that of the Jingjiang reach below Chenglingji increased significantly. Under the influence of human activities, the flood storage capacity of Dongting Lake has decreased annually; therefore, the water inflow during flood periods is difficult to discharge, and dry water replenishment has gradually decreased; therefore, the dry period in the TDLR has lengthened, and water has difficulty flowing. As a result, both flood and drought disasters have intensified. (5) The Jianghan-Dongting Lake Plain is still undergoing rapid structural subsidence, but the rate of sedimentation exceeds the amount of tectonic settlement; hence, Dongting Lake is at risk of morphing into marshes and land.