Characteristics Of Non-point Source Pollution And Quantification Of Pollution Load Study In Dong River Basins

With the improvement of the pollution control, point source pollution had been well controlled, but non-point source pollution problems have become increasingly prominent. “Water pollution prevention action plan”(hereinafter referred to as the “water ten”) had been published and refered to the aim of control Pearl River pollution, which stressed the importance of non-point source pollution research in river basin. Dong River is one of the four major tributaries of the Pearl River Basin, which also has important socio-economic status. In this study, field studies were conducted to evaluate the emission characteristics of conventional contaminates and typical heavy metals in the runoffs due to the rainfall for different types of land use in Dong river basin. Non-point source pollution model of Dong River Basin is established in ArcSWAT to calculate non-point source pollution load. The main results were as follows:(1) The runoff from the agricultural land was the main non-point pollution source for Dong River Basin, while the heavy metal emission from the traffic way cannot be ignored. There is a significant correlation between the concentration of pollutants and runoff in courtyard, road and vegetable land, but not in cropland and woodland.(2) On the courtyard, the first flush effect(FFE) was significant for suspended solids(SS) and chemical oxygen demand(COD), but insignificant for the contaminates of total nitrogen(TN), total phosphorous(TP) and heavy metals(e.g., As, Cu, Pb and Zn). For the traffic road, vegetable field, paddy field, and woodland, however, FFEs were observed for most of the contaminants, and the secondary flush effect was observed in the late stage of rain. Pearson correlation analysis showed that the correlation between pollution load and runoff flow was significant for the courtyards, traffic road and vegetable fields, but insignificant for the cropland and woodland, mainly due to the great difference in the rainfall interval and characteristics. The FFE for the contaminates followed a order of SS>COD>Pb>TN>Zn>TP>Cu>As. In general, FFE was more obvious for the conventional pollutants than the heavy metals. The key influence factor of toxic pollutants is land use type. For different types of land use, FFE is more obvious on agricultural land. However, for traffic road, FFEs were found mainly for the heavy metals. In conclusion, rainfall, rainfall intensity and rain interval are the significant factors for FFE.(3) Non-point source pollution model of Dong River Basin which was established in ArcSWAT has better performance in Monthly time scale simulation. The determination coefficient(R2) and Nash coefficient(NS) were respectively 0.85 and 0.40 above, which showed that the model has high adaptability. Daily time scale simulation about flow and SS also met the basic requirements of basin modeling.