Ecological water level for proposed hydraulic construction locking Lake Poyang based upon wintering waterfowls habitat modelling

After the operation of the reservoirs in the upper basins of the Yangtze River and Lake Poyang, the hydrological rhythm in dry seasons of the Lake Poyang has changed. In order to ease the pressure from low water level in dry seasons, a hydraulic construction locking the outlet of Lake Poyang was suggested. The key point of this project is to determine the suitable control schemes on water level which could maintain a healthy wetland ecosystem. Cranes, Cygnets and Swan Geese feeding with winter buds of Vallisneria natans were selected as the indicator of Lake Poyang ecosystem, a numerical habitat model for wintering waterfowls was developed by integrating an EFDC hydrodynamic model and habitat suitability curves. The water depth was adopted as the key habitat factor, the habitats for the wintering waterfowls feeding in dry seasons and V. natans in wet seasons have been continuously simulated since September in 2008. The variation laws between water level at Xingzi Station and the potential habitat area of V. natans and waterfowls feeding in Lake Poyang were revealed and the quantitative response functions were developed. The potential habitat area of V. natans gets the peak (around 1703 km2) when the water level reaches 14.8 m. The three-stage quantitative response functions between potential habitat area and water level have been developed for wintering waterfowls feeding, the maximum and minimum areas are about 564 and 476 km2, respectively, and the corresponding water levels at Xingzi Station are 11.73 and 9.56 m, respectively. For the proposed Lake Poyang hydraulic construction, a dynamic ecological water level control scheme as following is proposed: the water level should be controlled under 16 m during the refill period of Lake Poyang; then the water level would gradually decrease to increase the waterfowls feeding habitat areas; the maximum water level should be controlled below 12.5 m during December and January for the peak visiting of wintering waterfowls, and then gradually transits to natural state according to the inflow. The results could propose the ecological water control level for Lake Poyang hydraulic construction to protect the food resources and feeding accessibility of wintering waterfowls, and a quantitative basis for the conservation of Lake Poyang wetland ecosystem under new water-sand regime was provided. © 2020 by Journal of Lake Sciences.