[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.

[Spatio-Temporal Distribution and Risk Assessment of Heavy Metals in Middle and Lower Reaches of Le'an River].

The Le'an River is a main tributary of the Poyang Lake, which is the largest freshwater lake in China. The aim of this study is to research the distribution and potential ecological risks of heavy metals in the middle and lower reaches of the Le'an River, which is contaminated by nearby copper mines. Sediment and water samples were collected from 12 stations during the dry, wet, and normal season in 2016, respectively. The geo-accumulation index and potential ecological risk index were used to determine general pollution characteristics of trace metals in sediments. Results suggested that sediments in the Le'an River were considerably polluted by Cd, Pb, Cu, and Zn. Sediment concentrations of heavy metals showed significant spatial variations. The concentrations of heavy metals such as Cu, Zn, and Cd in water are higher in the dry season than in the normal and wet seasons. The distribution of heavy metals along the river is influenced by hydraulic conditions. The flow velocities in wet and normal seasons are positively correlated with the concentrations of heavy metals such as Cd, Pb, Cu, and Cr. There are seasonal differences in the distribution characteristics of heavy metals in surface sediments. In the dry season, the concentration of heavy metals in sediments is the highest in the middle reaches of rivers near mining areas, while during the wet and normal season, it reaches the highest value in the lower reach near the estuary. Except for Cd, whose major form of heavy metal in the sediment is in an exchanging state, the other heavy metals occur mainly in stable states. The assessment of the geo-accumulation index showed significant Cu, Cd, and Cr pollution. Among the heavy metals investigated, Cd was likely to result in more harmful effects.

[Comparison and application of biological indices of macroinvertebrates in river health assessment].

The different biological indices usually result in different results in the river health assessment. It is imperative and valuable to identify the correlation among different indices and their applicability for assessing stream health. In this study, totally five biological indices were selected and compared in the investigation of macroinvertebrate communities in the Taizi river. The results showed significant correlations among the five indices. However, due to the difference in health rating criteria for each biological index, different results of health ratings were obtained when different indices were used. The responding sensitivities to disturbance caused by different types of human activities were studied for each index to determine their applicability in assessment of river health. The data indicated that the BI index had significant correlations with land use and dissolved oxygen and was a good indicator for these two types of disturbance. The FBI index could well reflect the acid and ammonia contamination of the investigated stream. Strong negative correlation was found between the ASPT index and several water quality parameters concerning oxygen consumption. The B-IBI index had a significant negative correlation with the total nitrogen concentration, being a good indicator for nitrogen contamination. Besides, the B-IBI index was also significantly correlated to disturbance caused by other types of human activities and can be used as an indicator for both land use and aquatic pollution. To be concluded, the BI index and ASPT index can be individually used to assess the land use of a riverine and the impact of hydrochemical index on the ecosystems, whereas the B-IBI index could be a suitable indicator for evaluating the stream health correlated with various human activities.