Urbanization has accelerated in recent years worldwide, and cropland and woodlands have been converted to roads, buildings, and other paved areas. This development has increased the impermeability of urban surfaces and changed the build-up and wash-off processes of nonpoint source (NPS) pollutants.
As a climate-driven event, NPS pollution can be caused by rainfall- or snowmelt-runoff processes over and through the ground, which would concentrate natural and anthropogenically deposited pollutants and transport them to receiving water bodies, such as rivers, lakes, seas, or groundwater (Hu and Huang 2014). Typically, NPS processes involve rainfall-runoff and snowmelt-runoff, while their driving force is wet deposition, which includes rainfall and snowfall inputs. During the wet season, rainfall NPS originates from direct rainfall-runoff processes. During the winter season, snowmelt NPS results from the natural melting of snow into surface water.
Previous studies on snow and snowmelt mainly focused on three aspects: exporting mechanism, model simulation and control measures. Although these studies have discussed the characteristics of snow and snowmelt from different viewpoints, there was still lack of systematic researches into snowmelt NPS from source to output in urban areas.
Furthermore, the characteristics and mechanisms of snowmelt NPS and rainfall NPS are different. Comparatively, rainfall NPS has attracted more attention, and the management of water quality has mainly focused on rainfall NPS. However, the source and output processes of snowmelt NPS and rainfall NPS are different, and the methods used to manage rainfall NPS are not applicable to snowmelt NPS. Thus, it is also necessary to explore the output process of snowmelt NPS and rainfall NPS.
Exploring the characteristics of snowmelt NPS and rainfall NPS in a typical urban catchment in Beijing, China
In this study, three factors relating to urban NPS, including surface dust, snowmelt, and rainfall-runoff processes, were analyzed comprehensively by both field sampling and laboratory experiments. Considering the city’s dense population, frequent traffic activity, and typical impervious surfaces, we chose the study area around Beijing Normal University (BNU), Beijing, China (Fig. 1), which is located between the 2nd Ring Road and the 3rd Ring Road of Beijing and belongs to the downtown.
Through comprehensive consideration of the impact of land use and geographical location on surface water pollution, our research intends to monitor the surface rainfall-runoff and snowmelt at three sampling sites, including roads from an office area and a traffic-heavy area and the roof of a building. In addition, the pollutant concentrations in surface dust were closely related to the concentration of pollutants in the runoff. Surface dust on impervious surfaces (roads and roofs) was more easily washed off by runoff, and thus, surface dust was also collected to analyze leaching ratios of pollution.
The study revealed that dust deposition contributed more pollutants in winter and spring, and these built-up pollutants showed low leaching ratios, indicating that most NPS pollutants were particulate forms. Underlying snow has higher COD, TSS, Cu, Fe, Mn and Pb concentrations than surface snow, while higher EMCs of most pollutants were observed in road snowmelt. In addition, the snowmelt NPS had higher COD, TSS and metal content than rainfall NPS, indicating the importance of controlling snowmelt pollution for effective water quality management.
These findings are described in the article entitled Comparison between snowmelt-runoff and rainfall-runoff nonpoint source pollution in a typical urban catchment in Beijing, China, published in the journal Environmental Science and Pollution Research. This work was led by Lei Chen, Xiaosha Zhi, Zhenyao Shen, Ying Dai, and Guzhanuer Aini from Beijing Normal University.
- Hu H, Huang G (2014) Monitoring of Non-Point Source Pollutions from an Agriculture Watershed in South China. Water 6(12): 3828-3840