Occurrence Mechanism And Characteristics Of Non-point Source Pollution In Typical Hilly Water Source Area Of Reservoir In Yangzi River Delta

Fushi reservoir watershed is located in Anji County,Zhejiang Province,which is one of the important drinking water sources in the upper reaches of Taihu Lake Basin.It is mainly covered by economic forests and secondary forests.Normally,heavy rainfall in this area can cause soil erosion.Runoff generated on the slope after rainfall,then converges in the ecological ditch and migrates to the reservoir,which is an important way for non-point source pollutants migrating into the reservoir.In this study,the changes of pollutants in different spatial levels of Phyllostachys edulis stands,and the water quality changes in the process of ecological ditch migration were monitored in Fushi reservoir watershed in the rainy season.Moreover combined with the soil characteristics analysis,the coupling of non-point source pollution and soil characteristics in different spatial scale were approached.In addition,the quality of the inflow runoff into the reservoir was analyzed,and the pollution sources of the inflow runoff were probed by the PCA-APCS-MLR model.Meanwhile the contribution of each pollution source to the water quality parameters was evalued.As well,the sources of the nitrate into the reservoir was quantitatively analyzed with SIAR model established.Thus this study hopefully could provide scientific data and theoretical basis for ecological control of non-point source pollution and ensuring of drinking water security in Fushi reservoir watershed and even the Changjiang river delta region.The main conclusions of the study are as follows:（1）TN and COD_Mn were the main water pollution parameters in the water source area covered by P.edulis stands in Fushi reservoir watershed.NO₃^--N was the main form of nitrogen loss.The changes of TP in the spatial structure of P.edulis stands was as follow:surface runoff>litterthrough>throughfall>stream flow,and a similar pattern was found of TN.COD_Mn was higher in stream flow,the litterthrough are similar to throughfall,while the surface runoff varies greatly.In addition,the surface runoff was greatly affected by the soil quality,TN concentration in surface runoff is positively correlated with S-NR,but negatively correlated with p H,TN and AN concentration in soil.The contribution of AN to soil nitrogen loss is significantly greater than that of TN,while phosphorus loss is mainly affected by TP.In addition,COD_Mn was positively correlated with S-UE,S-ACP and SOM in soil.（2）Rainfall intensity was the main factor affecting the water quality of ecological ditch in Fushi reservoir basin.The maximum rainfall intensity was significantly positively correlated with CODMn（p<0.05）and total TN（p<0.01）concentration.TN concentration in water of the ecological ditch before rain is closely related to SOM,AN,TP,TN and other factors in soil.While COD_Mn was negatively correlated with TN,TP and AP.NO₃^--N concentration in water was mainly affected by S-NR activity and S-UE activity in soil.Soil moisture content had little effect on TN and COD_Mn,but it was negatively related to NO₃^--N concentration in water.After rain,the concentration of TP in water was positively correlated with the content of TP and AP in soil.COD_Mn in water was positively correlated with S-UE,S-ACP and S-NR activities,as well as SOM,TN and AN content.However,the contents of TN and NO₃^--N were negatively correlated with the activities of S-NR and S-UE,the contents of TN,AN and SOM.（3）Hydrogeology,livestock breeding,domestic sewage and agricultural production pollution were the main pollution sources of inflow runoff into the reservoir.The contribution rate of hydrogeological sources to p H,NH₄⁺-N,Cl^-,SO₄^2-,Mg²⁺,K⁺and Ca²⁺was 52.08%,39.51%,43.92%,52.17%,38.91%,40.69%and 54.67%respectively.The contribution rate of livestock source to COD_Mn was 81.72%,and the domestic sewage source to TP and Na⁺was51.96%and 42.69%,respectively.The contribution rate of agricultural pollution sources to NO₃^--N was 65.08%.The excess rate of total nitrogen in the inflow runoff into the reservoir was 55%and 65%respectively in the flood season and dry season.NO₃^--N was the main form of nitrogen pollution in inflow runoff into the reservoir.The contribution rate of atmospheric precipitation,soil,chemical fertilizer,domestic sewage and manure to the nitrate at the reservoir inlet was 7%,12%,78%,3%respectively in the flood season,and 22%,27%,46%,5%respectively in the dry season.