The connectivity threshold of the wetlands based on water environment response, and a case study of China’s Baiyangdian wetland

The quality of the water environment of wetlands is closely related to the changes in hydrologic connectivity, so wetland responses to changing connectivity exhibit a range of optimal connectivity values. Identifying these ranges of values is of great significance for wetland ecological restoration. Current studies mostly determine the hydrologic connectivity ranges based on a single target, even though connectivity simultaneously affects multiple water environment targets. Hence, the optimal hydrologic connectivity should be determined by accounting for multiple targets. With the Baiyangdian Wetland as the study area, we developed a method to model how the water environment responded to changes in hydrologic connectivity from three perspectives: hydrodynamics, water quality, and aquatic habitat. To do so, we used the BP neural network model and a non-dominated sorting genetic algorithm to calculate the hydrologic connectivity values in a context with multiple targets. We found that under the optimal hydrodynamic target, the integral index of connectivity (IIC) threshold was [0.23, 0.61] and the probability connectivity (PC) threshold was [0.32, 0.68]; under the optimal water quality target, the IIC threshold was [0.42, 0.70] and the PC threshold was [0.48, 0.82]; under the optimal aquatic habitat target, the IIC threshold was [0.38, 0.69] and the PC threshold was [0.35, 0.71]; and under the comprehensive optimization target, the IIC threshold was [0.48, 0.64] and the PC threshold was [0.51, 0.73]. These ranges of values will help wetland managers determine the optimal ecological water releases to meet the ecosystem quality targets.