[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.

[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.

[Effect of environmental factors on macroinvertebrate community structure in the Huntai River basin in the Huntai River basin].

In May-June 2012, macroinvertebrates were investigated at 66 sampling sites in the Huntai River basin in Northeast of China. A total of 72 macrobenthos species were collected, of which, 51 species (70.83%) were aquatic insects, 10 species (13.89%) were mollusks, 7 species (9.72%) were annelids, and 4 species (5.56%) were arthropods. First, 13 candidate metrics (EPT taxa, Dominant taxon%, Ephemeroptera%, Trichoptera%, mollusks%, Heptageniidae/Ephemeroptera; Hydropsychidae/ Trichoptera, Oligochaeta%, intolerant taxon% , tolerant taxon%, Collector%, Clingers%, Shannon-wiener index.) which belonged to six types were chosen to represent macroinvertebrate community structure by correlation analysis. Then, relationships between anthropogenic and physiography pressures and macroinvertebrate community structure variables were measured using redundancy analysis. Then, this study compared the relative influences of anthropogenic and physiographic pressures on macroinvertebrate community structure and the relative influences of anthropogenic pressures at reach, riparian and catchment scales by pRDA. The results showed all environmental factors explained 72.23% of the variation of macroinvertebrate community structure. In addition, a large proportion of the explained variability in macroinvertebrate community structure was related to anthropogenic pressures (48.9%) and to physiographic variables (11.8%), anthropogenic pressures at reach scale influenced most significantly macroinvertebrate community structure which explained 35.3% of the variation of macroinvertebrate community structure. pH, habitat, TN, CODMn, hardness, conductivity, total dissolved particle and ammonia influenced respectively explained 4%, 3.6%, 1.8%, 1.7%, 1.7%, 0.9%, 0.9% and 0.9% of the variation of macroinvertebrate community structure. The land use at riparian and catchment scale respectively explained 10% and 7% of the variation of macroinvertebrate community structure. Finally, the relationships of land use at catchment and riparian scales and water quality factors, hydrological indicators, habitat, substrate types were analyzed. This study supports the idea that human pressures effects on river macroinvertebrate communities are linked at spatial scales and must be considered jointly.

[Effect of environmental factors on fish community structure in the Huntai River Basin at multiple scales].

In June 2012, fishes was investigated at 65 sampling sites in the Huntai River basin in Northeast of China. Forty species were collected, belonging to 9 orders, 14 families,33 genera. Cobitidae and Cyprinidae were the dominant fishes in the community structure in the Huntai River basin, accounting for 13. 21% and 65. 83% of the fish community, respectively. There were two types of spatial distribution of fish community, one was distributed in the head water and tributaries in the upstream, and the other was in the plain rivers. Nemachilus nudus, Cobitis granoei and Phoxinus lagowskii dominated the local community in the upper reaches of the Dahuofang Reservoir and shenwo River, while Carassius ayratus and Hemiculter leucisculdus dominated the local community in the plain rivers. CCA (canonical correspondence analysis) was used to distinguish the primary environmental variables that affected the fish community structure. The results indicated fish community was mainly affected by environment factors at watershed and reach scales. Proportions of woodland and urban land, and altitude were three important environmental factors affecting the fish community at the watershed scale. Dissolved oxygen, total nitrogen, pH and habitat inhomogeneity significantly affected the fish community at the reach scale, whereas substrate didn't show significant influence at the microhabitat scale. Environmental factors at watershed scale explained 7. 66% of the variation of fish community structure, environmental factors at reach scale explained 10. 57% of the variation of fish community structure. Environmental factors at reach scale influenced the fish community more significantly.

[Estimation of nonpoint source pollutant loads and optimization of the best management practices (BMPs) in the Zhangweinan River basin].

One of the key techniques in establishing and implementing TMDL (total maximum daily load) is to utilize hydrological model to quantify non-point source pollutant loads, establish BMPs scenarios, reduce non-point source pollutant loads. Non-point source pollutant loads under different years (wet, normal and dry year) were estimated by using SWAT model in the Zhangweinan River basin, spatial distribution characteristics of non-point source pollutant loads were analyzed on the basis of the simulation result. During wet years, total nitrogen (TN) and total phosphorus (TP) accounted for 0.07% and 27.24% of the total non-point source pollutant loads, respectively. Spatially, agricultural and residential land with steep slope are the regions that contribute more non-point source pollutant loads in the basin. Compared to non-point source pollutant loads with those during the baseline period, 47 BMPs scenarios were set to simulate the reduction efficiency of different BMPs scenarios for 5 kinds of pollutants (organic nitrogen, organic phosphorus, nitrate nitrogen, dissolved phosphorus and mineral phosphorus) in 8 prior controlled subbasins. Constructing vegetation type ditch was optimized as the best measure to reduce TN and TP by comparing cost-effective relationship among different BMPs scenarios, and the costs of unit pollutant reduction are 16.11-151.28 yuan x kg(-1) for TN, and 100-862.77 yuan x kg(-1) for TP, which is the most cost-effective measure among the 47 BMPs scenarios. The results could provide a scientific basis and technical support for environmental protection and sustainable utilization of water resources in the Zhangweinan River basin.

[Macrobenthos community structure and its relationships with environmental factors in Weihe River basin, Northwest China].

In October 2011, an investigation was conducted on the macrobenthos at 45 sampling sites in the Weihe River basin of Northwest China. A total of 116 macrobenthos species were collected, of which, 91 species (78.4%) were aquatic insects, 12 species (10.3%) were mollusks, 9 species (7.8%) were annelids, and 4 species (3.4%) were crustaceans. According to the species composition and relative abundance of macrobenthos, the 45 sampling sites could be divided into three groups by using two-way indicator species analysis (TWINSPAN) and detrended correspondence analysis (DCA). In the first group, Serratella sp., Hydropsyche sp., and Antocha sp. were the indicator species. In the second group, Tabanus sp., Alotanypus venustus, one species of Pelecorhynchidae, Liodessus sp., and Limnodrilus hoffmeistteri were the indicator species. In the third group, Ephemera nigroptera and Polypylis hemisphaerula were the indicator species. The canonical correspondence analysis (CCA) indicated that 'cobble + boulder' type substrate, current velocity, water conductivity, water depth, and water total nitrogen content had significant effects on the spatial distribution of macrobenthos in Weihe River basin.

[Transport processes of low-level radioactive liquid effluent of nuclear power station in closed water body].

The transport processes of low-level radioactive liquid effluent of Xianning nuclear power station in the closed water body Fushui Reservoir are simulated using the EFDC model. Six nuclides concentration distribution with different half-lives in the reservoir are analyzed under the condition of 97% guarantee rate incoming water and four-running nuclear power units. The results show that the nuclides concentration distribution is mainly affected by the flow field of the reservoir and the concentration is decided by the half-lives of nuclide and the volume of incoming water. In addition, the influence region is enlarged as increasing of half-life and tends to be stable when the half-life is longer than 5 years. Moreover, the waste water discharged from the outlet of the nuclear power plant has no effect on the water-intake for the outlet located at the upstream of the water-intake and the flow field flows to the dam of the reservoir.

[Spatiotemporal variation analysis and identification of water pollution sources in the Zhangweinan River basin].

In this study, several statistical methods including cluster analysis, seasonal Kendall test, factor analysis/principal component analysis and principal component regression were used to evaluate the spatiotemporal variation of water quality and identify the sources of water pollution in the Zhangweinan River basin. Results of spatial cluster analysis and principal component analysis indicated that the Zhangweinan River basin can be classified into two regions. One is the Zhang River upstream located in the northwest of the Zhangweinan River basin where water quality is good. The other one covers the Wei River and eastern plain of the Zhangweinan River basin, where water is seriously polluted. In this region, pollutants from point sources flow into the river and the water quality changes greatly. Results of temporal cluster analysis and seasonal Kendall test indicated that the study periods may be classified into three periods and two different trends were detected during the period of 2002-2009. The first period was the year of 2002-2003, during which water quality had deteriorated and serious pollution was observed in the Wei river basin and eastern plain of the Zhangweinan River basin. The second period was the year of 2004-2006, during which water quality became better. The year of 2007-2009 is the third period, during which water quality had been improved greatly. Despite that water quality in the Zhangweinan River basin had been improved during the period of 2004-2009, the water quality in the Wei River (southwestern part of the basin), the Wei Canal River and the Zhangweixin River (eastern plain of the basin) is still poor. Principal component analysis and multi-linear regression of the absolute principal component scores showed that the main pollutants of the Zhangweinan River basin came from point source discharge such as heavy industrial wastewater, municipal sewage, chemical industries wasterwater and mine drainage in upstream. Non-point source pollution such as agricultural pollution and runoff pollution caused by heavy rainfalls also showed considerable impact on water quality in the Zhangweinan River basin during flood seasons. These results provide useful information for better pollution control strategies in the Zhangweinan River basin.

[Relationship between groundwater quality index of physics and chemistry in riparian zone and water quality in river].

Riparian zone hydrology is dominated by shallow groundwater with complex interactions between groundwater and surface water. There are obvious relations of discharge and recharge between groundwater and surface water. Flood is an important hydrological incident that affects groundwater quality in riparian zone. By observing variations of physical and chemical groundwater indicators in riparian zone at the Kouma section of the Yellow River Wetland, especially those took place in the period of regulation for water and sediment at the Xiaolangdi Reservoir, relationship between the groundwater quality in riparian zone and the flood water quality in the river is studied. Results show that, affected by the river and pond water, the highest point of groundwater temperature is near the pond in spring, and near the river in winter; and regulation for water and sediment at the Xiaolangdi Reservoir also affects groundwater temperature in riparian zone, which reaches its maximum at 100 m far from the river bank. There exists a strong zone of nitrification area at 50 m from the river bank, and in this area, the groundwater pH value is lower by 0.2 to 0.4 unit than that of the other regions, with great annual varieties. The turbidity of groundwater is affected by irrigation, which is more obvious than other indicators of groundwater. The turbidity of groundwater and river water increase rapidly during the early phase of flood retreat, and slope stability of river bank is the initial impact of the soil erosion of river bank. Conductivity, chloride and sulfate data show that the range of 50-200 m in riparian wetland is a very important salt accumulation zone, and the width of salt accumulation zone changes with seasons, and this area is also a very important zone of sulfur reduction. The quality of groundwater at 200 m from the river bank is also significantly affected by floods. Physical and chemical indicators of water change strongly in this area. The result indicates that there is a very close relationship between groundwater and surface water, and it is the typical land and water ecotone between groundwater of riparian zone and the river. Rational protection for this region is critical for the conservation of water quality both in the river and groundwater.

[Relationship between groundwater level in riparian wetlands and water level in the river].

The development and degradation processes of riparian wetlands are significantly affected by river hydrological processes. By observing the variation of groundwater levels in riparian wetlands at the Kouma section of the Yellow River Wetland, especially that during the period of regulation for water and sediment at the Xiaolangdi Reservoir, relationship between groundwater level in riparian wetlands and flood water level in the river is studied. The results show that groundwater level in riparian wetlands is significantly affected by water level in the river investigated. There is a negative exponential relationship between groundwater level and the distance between wells and river. The correlation coefficient shows the maximum (R2 > 0.98) during the period of regulation for water and sediment. Affected by the cultivation system in the flooding area, distance between monitoring wells and river bank, water level in the river variation of groundwater level in the wetland changed greatly. In artificial wetland, which is far from the river, the inter-annual variation in groundwater levels show a " (see symbol)" shape, while in the farmland, which is close to the river, the inter-annual variation of groundwater levels show a big peak. The groundwater level 400 m from the river is affected by flood events obviously, that in the area which is less than 200 m from the river is significantly affected by flood events in the area which is especially less than that in the area that is less than 100 m from the river, the groundwater level is affected by flood events intensively. The result indicated that there was a very close relationship between groundwater and surface water, and it was the hydrological ecotone between groundwater of riparian wetlands and the river. It is very important that rational protection for this region (very important for the area which is less than 100 m from the river, important for the area that is between 100 m and 200 m from the river) is critical for the conservation of water quality in the river and groundwater quality.