[Quantitative Analysis of the Correlation Between Macrobenthos Community and Water Environmental Factors and Aquatic Ecosystem Health Assessment in the North Canal River Basin of Beijing].

Macrobenthos can reflect the cumulative effect of various ecological threats on the water environment and are closely related to the health of river ecosystems. In this study, taking the North Canal River basin, a typical basin in Beijing, as an example, ecological data from 34 stations were investigated in the summer of 2015. Characteristics of the macrobenthos communities were analyzed, and driving environmental factors were identified using typical correspondence analysis. Thresholds and response species of those driving environmental factors were conducted using the thresholds indicator taxa analysis (TITAN). In this study, the health status of the river ecosystem was evaluated by the multi-metrics method and benthic index of biotic integrity (B-IBI). The benthic community was dominated by pollution-tolerant aquatic insects and mollusks, with a low-level Shannon-wiener diversity index between 0-1.01; fluoride, biochemical oxygen demand, ammonia-nitrogen, and total phosphorus were driving environmental factors influencing the community structure of macrobenthos. Indicator species of ammonia-nitrogen were identified by the TITAN in the North Canal River basin with a threshold range of 1.09-6.94 mg·L-1; three indicator species of total phosphorus were identified with a threshold range of 0.48-1.27 mg·L-1, which were all positive response species. According to the health assessment, the river ecosystem in the North Canal River basin was generally unhealthy, and the upstream ecosystem was better than that downstream; the health conditions in the mountainous areas of Changping district were the best, whereas those in Chaoyang and central city districts were the worst. This study can provide a basis for ecological restoration and pollution control of rivers and also provide a reference for the water ecological civilization construction in other cities.

[Impact of Spatial Heterogeneity of Precipitation on the Area Change in Critical Source Area of Non-point Sources Pollution].

Aiming at non-point sources pollution in the agricultural areas with large topographic fluctuations and spatial differences in precipitation, a SWAT model was used to evaluate the spatial variations in the critical source areas (CSAs) of total nitrogen (TN) and total phosphorus (TP) under two precipitation scenarios, i.e., heterogeneous precipitation and uniform precipitation. A change in the CSAs identified based on the two precipitation scenarios during the study period were statistically calculated, and the relationship between the CSAs and precipitation variables was discussed. The study results showed that when the total precipitation was the same, the variation tendency of the identified CSAs for TN and TP under the two precipitation scenarios were similar, and very close for a few years. According to the results of the pair t test, the CSAs of TP were not affected by the spatial variation of precipitation, while the change in CSAs for TN was more significant under different precipitation scenarios, which is likely due to the difference in the physical properties of nitrogen and phosphorus. The correlation analysis between the CSAs of TN and TP with precipitation variables showed that the variation in the CSAs of TP was positively correlated with the precipitation variables in the same year, while the variation in the CSAs of TN was strongly related to the precipitation variables of the previous year. The results obtained in this study are of great significance for further exploring the impact of uncertainty of precipitation, which is an important driving factor, on the CSAs of non-point sources pollution and the governance of agricultural non-point sources pollution.