[Regular pattern of non-point source pollutants losses in Luxi watershed]

The losses of non-point pollutant combined with natural rainfall events were monitored at outlets of Luxi watershed and several field plots with different land use. The paper probes characteristics of the sediment and chemical losses during a single rainfall-runoff process. The impact of preceding precipitation is also discussed. The results of field experiments show that the concentration of SS in runoff dropped off obviously with the increase of antecedent rainfall. The observed data were 265.6, 145.8, 124.2mg/L respectively with precipitation of 15, 115, 161 mm in preceding 5 days. Compared to the losses of SS, nutrients and COD were not changed greatly by the preceding rainfalls. The fluctuations of pollutant concentration were less than 15%. The results from plots suggested that land use play an important role in pollutant losses. The following is the list ordered according to concentration of pollutant in runoff, from the highest to the lowest: Dry land,residential area, grassland, woodland and paddy land. Vegetation cover is effective on the reduction of soil erosion and sediment loss. About 80% SS could be cut down when the coverage changed from 50% to 90%. Losses of TN were mainly determined by the TN concentration in soil. The ratios of TN concentration in runoff to that in soil were 2.75%, 2.79%, 2.42 % respectively for the land use of dry land, grassland and woodland. Augment of vegetation overage contributed to increment of N losses,including NO3- -N and NH+ -N.