基于生态系统受扰动程度评价的白洋淀生态需水研究

水是湿地生态系统最重要的影响因子,生态需水核算是对湿地进行生态保护,恢复重建的前提与基础.提出一种基于生态系统受扰动程度评价的适宜生态需水量计算方法.首先根据湿地水面面积变化率最大时对应的关键水位构建初始生态水位方案并将其离散得到一系列离散值；然后应用Mann-Kendall(M-K)法分析历史水位时间序列,找出水位发生突变前自然条件下的水位状态；最后对不同情景水位方案与自然水位状态的差异程度进行修正水文指数(APPFD)评价,确定生态系统受扰动程度在可接受范围之内的多个生态水位方案,进而确定相对应的生态需水量方案.将该方法应用于白洋淀湿地得出了7种可接受的生态水位方案,其中汛期的适宜生态水位在8.31-10.62 m之间,非汛期的适宜生态水位在7.51-9.60 m之间,全年的适宜生态需水量在3.10×108-6.47×l08m3之间.该方法能够为实际的水资源管理和分配提供多种备选方案,有较强的实用性和可操作性.

Study on ecological water demand based on assessment of ecosystem disturbance degree in the Baiyangdian Wetland

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.