Study Of The Non-Point Source Pollution And N/P Loss Characteristic In Changyang Reach Of Qingjiang River Basin

Because of the rapid development in social economy,non-point source pollution(NSP)has becoming a major concern.In this research,we did an investigation of pollution source in Changyang reach of Qingjiang River basin.The investigation result showed that the main nitrogen and phosphorus inputs in this area were agricultural fertilizer,livestock excrement and aquaculture projects.Agricultural fertilizer provided about 9781t TN(total nitrogen)input and 3818t TP(total phosphorus)input while livestock excrement provided about 9781t TN input and 3818t TP input.However,these TN and TP input could not be all transferred into the water because of the migration losses.Compraed with agricultural fertilizer and livestock excrement,the pollution of aquaculture,which contained 813t TN and 133t TP were all discharged into water body directly.To study the characteristic of non-point source pollution in this study area,SWAT model was built up.The model was calibrated and verified with the measured data of hydrology from 2007 to 2013 and the data of water quality from 2011 to 2013.Both in calibration and verification periods,the coefficients of determination(R2)of the following indexes(Flow,TN fulx,TP fulx,NH4+-N fulx)were all higher than 0.6 and the Nash-Sutcliffe coefficients(Ens)were all higher than 0.5.From the SWAT outputs we can learned that:1)the high loss period of TN and TP mainly appeared during April and September,same as the rainy season,and the distrubution of agricultural land would affect the loss modulus distribution of TN and TP spatially.2)For the closed tributaries sub-basins,the amount of TP input amount was huge,but TP output amount was very small compared with input.3)In the study area,the main loss form of TN was nitrate nitrogen,while the main loss form of TP was absorbed phosphorus.4)Among all kinds of pollutant sources,agricultural fertilizer's contribution rate is almost 36%of TN pollution,while aquaculture projects accounted for more than 50%of the TP pollution.The results of regression analysis showed that on both the whole basin and the sub-basin scales,there was a positive correlation between the annual rainfall and the N/P loss modulus.The R2 of regression equation of the relationship between the annual rainfall and the TN/TP loss modulus were mostly higher than 0.6.The result of multivariate regression analysis showed that the percentage of agricultural land and the percentage of some kinds of soil affected the slope(K:N/P loss intensity coefficient)and the intercept(B:correction term)of the regression equation mostly.With the separate analysis into different sub-basins mainly composed of yellow brown soil or limestone soil,it was found out that when taking the different kinds of soil into separate considerations,the slope(K)and the intercept(B)of the regression equation showed generally more positive correlation with the percentage of the agricultural land compared with the results without separately considering.In the terms of TN,the R2 of K and B were increased from 0.6 to 0.9,while in the terms of TP,it were also generally increased but the rising range was concerned with the soil type.After the analysis about the difference of the pollution-loss ability between these two kinds of soil,the reason of the difference between their K-agricultural land proportion regression equations was found.Because of the high amount of the soluble fertilizer used in the agricultural land,soil's soluble N/P loss ability became the most important property to affect the N/P loss modulus.