[Analysis of Pollution Characteristics and Sources of Rainfall Runoff from Roofs in the Central District of Beijing].

The rainwater and rainfall runoff of roofs in the central district of Beijing from June to September in 2019 were sampled and analyzed to study the characteristics of the water quality, the first flush effect, and the main influential factors and sources of pollutants. The results showed that the roof runoff was seriously polluted by total nitrogen, ammonia nitrogen, chemical oxygen demand, and total suspended solids whose event mean concentration (EMC) exceeded the fifth level of environmental quality standards for surface water (GB 3838-2002) (the EMC of suspended solids exceeded the second level of discharge standard of pollutants for municipal wastewater treatment plants (GB 18918-2002)). The rainwater was relatively less polluted than the rainfall runoff, but the EMC of ammonia nitrogen and total nitrogen of the rainwater also exceeded the standard in some rainfall events. The first flush intensity of the rainfall runoffs was between weak and medium. The sequence of strength of the first flush of different pollutants was ammonia nitrogen>total suspended solids>chemical oxygen demand>total nitrogen>mercury>zinc>total phosphorus>lead. The concentration of total suspended solids, chemical oxygen demand, and total phosphorus in roof runoff were significantly positively correlated with the length of rainfall and the dry period and negatively correlated with the rainfall intensity. According to the results of principal component analysis, the main pollutant in rainwater was nitrogen emitted by vehicles, and the main pollutants in roof runoffs were suspended solids, organic matters, and phosphorus pollutants released from the aging of roofing materials and the corrosion of metal down pipes.

[Spatial Distribution, Contamination Assessment, and Sources of Heavy Metals in the Urban Green Space Soils of a City in North China].

To study the condition of urban green space soils in the central parts of a city in North China, the spatial distribution, sources, and pollution levels of heavy metals (Cd, Hg, As, Pb, Cr, Cu, Zn, and Ni) within green space soils in the central urban districts of the city were investigated. The results showed that the soil quality was high overall. The mean concentrations of Cd, Hg, As, Pb, Cr, Cu, Zn, and Ni were 0.172, 0.202, 9.02, 34.7, 57.0, 31.2, 85.7, and 26.3 mg·kg-1, respectively. The mean concentrations of Cd, Hg, Pb, and Zn in urban soils exceeded the background value of the Beijing-Tianjin-Tangshan region. All of the samples' heavy metal concentrations were lower than the risk screening values for soil contamination of development land in the national soil environment quality standards. With respect to the spatial distribution, the concentrations of As, Cr, and Ni were higher in the northwest of the study area, the concentrations of Cd and Zn were higher in the northeast, and the concentrations of Hg, Pb, and Cu were higher in the urban core area. As for the different land use types of the soils, the concentrations of Cd, Zn, and Ni were higher in the enterprise soils, while the concentrations of Hg, Pb, and Cu were higher in park and residential soils. Assessments of soil quality showed that 97.2% of soil samples' Nemerow integrated indices were less than 1, indicating that the soils were clean. Indices of potential ecological risk for all soil samples were less than 80, indicating that they posed a slight ecological risk. Multivariate statistical analysis (correlation and principle component analyses) showed that Cu, Pb, and Hg may originate from an anthropogenic source via the painting of ancient buildings and pesticides used to protect ancient trees. Chromium may originate from natural sources via geochemical activity and soil parent material; Cr, Zn, Ni, and As were derived from mixed sources through human and geochemical activities. The receptor model was used for identification and apportionment of pollution sources of elements over the standard. The contribution rates of sources were as follows:source 2(46.1%), source 3(33.1%), source 1(17.7%), and others (3.1%) for Cd, source 1(93.0%) for Cu, source 1(52.4%), source 3(24.2%), source 2(20.0%), and others (3.4%) for Zn, source 1(56.3%), source 2(37.8%), and source 3(5.8%) for Ni. Sources 1 and 3 were anthropogenic, while source 2 was natural.

[Concentration and Carbon Isotope Composition of DOC and DIC in the Miyun Reservoir Watershed in Summer].

This study aims to complement existing research on the carbon cycle of water in reservoirs, for the effective control of nutrient input in drinking water. The content and isotopic compositions of water dissolved organic carbon (DOC) and dissolved inorganic carbon (DIC) from the Miyun Reservoir watershed in Beijing were studied, and water from the Jingmi diversion canal was also studied as a baseline reference. The results showed that the content of DOC in the Miyun Reservoir watershed in summer varied from 1.07 to 5.19 mg·L-1, with an average value of 2.61 mg·L-1. DOC in tributaries was lower than that of most rivers in China and globally, while DOC in reservoirs, particularly in Miyun Reservoir, was high. The high water level might be the main reason for the high DOC in the Miyun Reservoir. In summer, the δ13CDOC in the Miyun Reservoir watershed ranged from -27.4‰ to -24.3‰, with an average value of -25.8‰. Results from the isotopic analysis showed that the water in the Miyun Reservoir watershed was less affected by human sources, with the exception of some points. In summer, DOC in tributaries and in the Miyun Reservoir was mainly derived from soil organic matter and terrestrial C3 plants. In addition, endogenous substances also contributed to DOC in the watershed. DOC concentration increased along the Chao and Bai Rivers, and DOC from soil erosion and human sources was higher in the Chao River. The δ13CDIC in the study area varied from -12.6‰ to 5.75‰, with a mean value of -9.44‰. The weathering of carbonate rocks accounted for the major river DIC, and DIC had been clearly assimilated by the phytoplankton by photosynthesis. DOC and DIC in the Miyun Reservoir were significantly higher than in the Jingmi diversion canal (P<0.01), and the δ13CDIC in the Miyun Reservoir showed a clear positive deviation. This indicated that there were differences in carbon concentration and components in the two kinds of water, which might affect the denitrification capacity of the water in the Miyun Reservoir after mixing. In general, the dissolved carbon in the water of the Miyun Reservoir watershed is less affected by human sources. The conversion of DIC to DOC may also be a potential source of DOC in the study area.