Hydrological regime is the driving factor in wetland ecosystems. Its excessive alteration will lead to severe degradation of wetlands. Assessment of ecological water demands is essential for wetland protection, recovery and restoration.
To solve the existing problems arose in the traditional methods such as simple interval range and lack ecological information, in this paper a new method was developed to determine wetlands' appropriate ecological water demands. This method can maintain the resultant hydrological regime alteration within ecologically acceptable threshold. Firstly, the key water level was determined by analyzing the water level-area curve, and a series of discrete initial water level scenarios were generated based on the preliminary water level. Then, to identify the natural water level condition in a wetland, the time series of historical water level were analyzed by using the Mann-Kendall approach. A hydrological alteration assessment indicator, amended annual proportional flow deviation (AAPFD), was recommended to quantify the hydrological differences between the generated discrete initial water level scenarios and the identified natural water level condition. Each generated discrete initial water level scenarios was evaluated according to its corresponding AAPFD value. Finally, several appropriate ecological water level schemes were identified, which can ensure the corresponding hydrological alteration degree within the ecologically acceptable threshold, and their corresponding ecological water demands can be determined.
We applied the proposed method to the Baiyangdian Wetland, the largest shallow lake and wetland complex in the North China Plain, which is now seriously suffered from water crisis. The key water levels were 7.5 m in dry periods (October to May) and 8.3 m in wet periods (June to September). Seven initial water level scenarios were set up depending on the disperse results of the preliminary water level and actual status of water resources. Hydrological regime before 1960 might be natural condition based on the mutation analysis. The appropriate ecological water level was between 8.31 m and 10.62 m during wet periods, and between 7.51 m and 9.60 m during dry periods, respectively; and the annual appropriate ecological water demand was between 3.10×10⁸ m³ and 6.47×10⁸ m³. This method has high practicability and can offer possible ecological water level schemes for water resources management and allocation.