Stormwater runoff pollution in a rural township in the hilly area of the central Sichuan Basin, China

Stormwater runoff in rural townships has a high potential for water quality impairment but little information is available on strormwater runoff pollution from rural townships. To investigate the characteristics of runoff pollution in a rural township, a catchment (2.32 ha) in Linshan Township, Sichuan, China was selected to examine runoff and quality parameters including precipitation, flow rate, and total nitrogen (TN), dissolved nitrogen (DN), total phosphorus (TP), dissolved phosphorus (DP), particulate phosphorus (PP), chemical oxygen demand (COD) and suspended solid (SS) in 12 rainfall events occurring between June 2006 and July 2007. Results show that the annual pollutant loads were 47.17 kg ha⁻¹ for TN, 6.64 kg ha⁻¹ for TP, 1186 kg ha⁻¹ for COD, and 4297 kg ha⁻¹ for SS. DN and PP were the main forms of nitrogen and phosphorus in stormwater runoff. TP, COD and SS showed medium mass first flushes, in which nearly 40% of the total pollutant masses were transported by the first 30% of total flow volume. The peak of pollutant concentration appeared before the peak of runoff due to the first flush of accumulative pollutants in impervious areas and drainage ditches. The EMC values of TN, TP, DN and PP were negatively correlated to the maximum rainfall intensity, precipitation, total flow volume, and runoff duration (P<0.05, n=12), while EMC of COD and SS were not related to any rainfall characteristics. The FF30 (FF, First Flush) for TN, TP, COD and SS were positively correlated to the maximum rainfall intensity (P<0.05, n=12), and TP was also positively correlated to the average rainfall intensity (P<0.05, n=12), indicating that the magnitude of first flush increased with the rainfall intensity in the Linshan Township.