| In recent years, with the accelerated pace of urban development, the urbanization process continues to improve. The significant improvement of urbanization also results in the increases of the aeras of impervious surfaces and the decreases of rainfall runoff infiltration constantly, which leads to the inceease of urban rainfall runoff. With the sediment from city underlying surface, runoff pollutes urban receiving water.Urban non-point source pollution caused by rainfall flushment has been threatened the safety of receiving water seriously. Urban non-point source pollution is quiet random and can be effected by mounts of factors.Located on the upper reachs of Taihu Lake, Yixing has drawn extensive attentions since the outbreak of cyanobacteria in Taihu Lake. Hense, it is important to know the spatial-temporal distribution of urban rainfall runoff pollution,first flush effect, compositions of pollutants and pollution load to storm management in Yixing. The region of researeh in the paper is the central of Yixing City, which includes different functional areas.Different rainfall runoffs were observed and different samples were analysed. This research is the part of the "twelfth five-year" water environment improvement technology integration in yixing city. The main results are as follows:(1) The initial concentration of rainfall runoff in Yixing of COD, turbidity, TN,NH3-N, NO3-N, NO2-N, TP, DTP and PO4-P are respectively 740-2734mg/L,50.8-1139 NTU, 21.5-53.74mg/L, 5.87-20.1mg/L, 4.54-14.78mg/L, 0.12-0.53mg/L,1.33-4.27mg/L, 0.91-2.99mg/L and 0.28-1.35mg/L. Further more, the initial concentration of COD, TN, NH3-N and TP are respectively 18.5-68 times, 10.75-26.87 times, 2.93-10.1 times and 3.32-10.67 times of class-IV standard values specified in Environmental Quality Standards for Surface Water. The concentration of pollutants decreased and remained stable at the late stage of rainfall. Hydraulic Analysis of runoff indicated that runoff curve was similar with rainfall curve which had little rangevolatility over time and was 5~20mins latter than rainfall curve.(2) The occurrence mode of nitrogen in different areas was basically identical.DIN took about 50-70% in the rainfall runoff in Yixing City, which was highly biodegradable.It need good denitrification conditions to remove nitrogen. Relevance analyse indicated that turbidity shared good linear relationship with COD and TP,however bad linear relationship with TN. The new area made major contribution to COD and TP and the old area made major contribution to TN.Results of Principal component analysis(PCA) indicated that TN and TP were the dominating factors influencing the water quality in Yixing. The PCA analysis indicated that pollution in rubbish area and the new area were serious.(3)First Flushment generally existed in Yixing,and rain influnnced most,which was both flush and dilute to pollutants concentrations.For single peak rainfall, it mainly diluted.For double peak rainfall,the former peak flush and the latter peak diluted.Emission laws varied from areas to rainfalls.Flushment of COD and TP in the new area was most,and TN and COD in the old area took most. |
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