Characterization of rainfall-runoff pollution in a small rural township in a hilly area with purple soil

A small catchment of the Linshan township(area 2.32 hm2)in Yangting county,Sichuan basin was selected to examine runoff discharge and content of total nitrogen(TN),dissolved nitrogen(DN),total phosphorus(TP),dissolved phosphorus(DP),chemical oxygen demand(COD)and suspended solids(SS).Data was collected from the stormwater of 8 rainfall events from June 2006 to April 2007.Results showed that the averages of event mean concentration(EMC)for TN,TP,COD and SS were 25.52,3.63,714 and 2396 mg · L-1,respectively.And the annual loads for TN,TP,COD and SS were 39.21,5.57,993,and 3335 kg · hm-2,respectively.The peak pollutant concentrations in the storm water occurred 3-45 min before the peak concentrations appeared in the runoff.TN,TP,COD and SS showed medium mass first flushes,in which nearly 40% of the total pollutant loads were transported by the early runoff,comprising 30% of the total flow volume.Soluble nitrogen and particle-bound phosphorus were the main forms of nitrogen and phosphorus output.Soluble nitrogen was negatively related to the maximum rainfall intensity(r=-0.825,p0.05),while particle-bound phosphorus was not related to rainfall parameters.The rainfall-runoff pollution of Linshan township was characterized by both non-point pollution from impervious areas and accumulative point pollution in the drainage ditches.Soil erosion and runoff from pervious forestland and slopeland intensified the runoff pollution.