北京市河流生态系统健康评价

伴随经济的快速发展,人类活动对河流生态系统的胁迫日益强烈,生态系统健康状况受到严重威胁.以北京市河流水系为例,于2020年秋季至2021年夏季在区域内101个样点进行了4个季度的野外调查,选取涵盖水文、水质、水生生物和栖息环境质量的34个评价指标,采用主成分分析和相关分析进行筛选,利用熵权法确定各评价指标权重,构建北京市河流生态系统健康评价指标体系,并对其健康状况进行评价.结果表明,北京市河流生态系统健康评价指标体系包括：水温、流速、BOD₅、NH₄⁺-N、Cu、浮游植物密度、浮游动物密度、底栖动物Shannon指数和BMWP指数、鱼类Shannon指数和栖息地质量指数11项指标.北京市河流101个点位中,健康状态占比4.95%,亚健康占比23.76%,一般及以下占比71.29%.河流健康状况具有较强的空间异质性,北部和西部地区河流健康状况良好,而中部及东南地区健康状况相对较差.单项指标评价结果显示,北京市河流水质状况整体尚可,为"亚健康-一般"状态,生物和栖息地状况评价均为"一般-差"状态,但水文状况堪忧,为差状态.北京市各水系评价结果显示,潮白河水系健康状况最好,永定河、大清河和蓟运河水系健康状态一般,北运河水系健康状况最差.维持河流生态基流,保障河流水系连通性,改善和恢复河流栖息地环境是今后北京市河流进行生态修复与保护需要重点关注的方面.

Health Assessment of the Stream Ecosystem in Beijing, China

With economic development, the health of river ecosystems is becoming severely threatened because of the increasing effects of human activities on river ecosystems. Here, 101 sites along regional river systems in Beijing rivers were investigated from autumn 2020 to summer 2021. A total of 34 metrics, including aquatic organisms, hydrology, water quality, and habitat, were calculated to be the candidate indicators. Principal component and correlation analyses were used to select the core metrics from the candidate indicators, and the weight of each core metric was estimated using the entropy method. The integrated index of stream ecological health was constructed to assess the health condition of the Beijing rivers. The results of the PCA and correlation analyses revealed that eleven metrics were selected as the core metrics to construct the integrated index of stream ecological health, including water temperature, flow velocity, BOD₅, NH₄⁺-N, Cu, the density of phytoplankton and zooplankton, the Shannon-Wiener diversity index of macroinvertebrates and fish, the BMWP index, and the qualitative habitat evaluation index. According to the health assessment results, 4.95% of the sampling sites were healthy, 23.76% were subhealthy, and 71.29% were in a fair or below healthy state. The river health status showed strong spatial heterogeneity, and the river health statuses in the northern and western regions were relatively good, whereas the river health status in the central and southeastern regions were relatively poor. The results of four aspects stream ecosystem assessment showed that the overall water quality of the rivers was "subhealthy" and the aquatic organisms and habitat were "general poor," but the hydrology was "poor." The evaluation results of five water systems demonstrated that the Chaobai River had the best health status, followed by that of the Yongding River, Daqing River, and Jiyun River, and the Beiyun River had the worst health status. Maintaining river ecological baseflow, ensuring river system connectivity, and improving and restoring the river habitat environment are the key aspects of river ecological restoration and protection in Beijing in the future.