[Health Assessment of the Stream Ecosystem in the North Canal River Basin, Beijing, China].

With increasing urbanization, the stream ecosystem in Beijing has faced great challenges. Phytoplankton, benthic macroinvertebrates, and water quality were investigated based on 25 sampling sites in the North Canal River basin in July 2015, and the quality of the habitat was assessed in situ. A total of 22 metrics, including aquatic organism, hydrology, water quality, and habitat, were calculated to be the candidate indicators. A principal component analysis (PCA) and correlation analysis were used to select the core metrics from the candidate indicators, and the weight of each core metric was estimated by using the entropy method. The integrated index of stream ecological health was constructed to assess the health condition of the North Canal River basin. The results of the PCA and correlation analysis showed that nine metrics were selected as the core metrics to construct the integrated index of stream ecological health, i. e., the Shannon-Wiener diversity index of phytoplankton and benthic macroinvertebrates, water temperature, BOD5, NH4+-N, F-, Zn, petroleum, and the qualitative habitat evaluation index (QHEI). According to the results of the health assessment, 12% of the sampling sites in the North Canal River basin were considered to be healthy (Ⅰ) or sub-healthy (Ⅱ), and more than half were poor (Ⅳ) or bad (Ⅴ). Therefore, the aquatic ecosystem in the North Canal River basin was generally unhealthy. The upstream was better than the midstream and downstream, where the spatial heterogeneity of the health condition was strong. The health condition in the Nansha River, the midstream of the Qinghe River, and the main stream of the Tonghui River were poor, while the upstream of the Liangshui River and the tributaries of the Wenyu River were good. In general, the condition of the stream ecosystem in the North Canal River basin was relatively complicated.