Environmental Quality Assessment And Ecological Buffer Zone Setting Method In The Upper Reaches Of Puyang River

Non-point source pollution is a very important environmental problem due to its wide range of influence and complex mechanism.As an effective measure to control non-point source resistance,ecological buffer zone has been widely concerned.Taking the Puyang River Basin in Pujiang County of Zhejiang Province as the study area,this paper investigated and analyzed the land use pattern,spatial vegetation cover and water environment of the basin.Through sampling,monitoring and analysis of field samples,various methods were used to evaluate the status of soil pollutants in riparian zone.Taking the VFSMOD model as a tool,combining with remote sensing images,Digital Elevation Model and land use patterns,the intermission capacity of the ecological buffer zone was analyzed,the minimum width was determined,and the range of the ecological buffer zone in Puyang River was reasonably delimit.（1）In recent years,the overall water environment of the main stream of Puyang River is good,and it can basically meet the Class III surface water standard without TN being used as an assessment indicator.TN is the main index to control the water environment in the main stream.The water quality of the tributary rivers is worse than that of the main stream,among which Wululing Stream,Xixi Stream,Dongxi Stream,Zhonggengxi Stream,Yuetang Stream and Yiwu Stream are the most representative.These tributary rivers are mainly concentrated in the urban centers and agricultural agglomeration areas.Since point source pollution has been basically treated in sewage treatment plants,the main factor affecting their water quality is non-point source pollution.（2）The average values of As,Cr and Cu in the riparian eluvial layer of the study area were 55.71,66.95 and 30.13 mg/kg.As exceeds the national secondary standard,while Cr and Cu do not exceed the national secondary standard.As,Cr and Cu were9.49,1.16 and 1.45 times of the soil background values of paddy soil in Zhejiang Province,respectively.The average contents of heavy metals,nitrogen and phosphorus in the leaching layer of soil were higher than those in the sediment layer,and there was a phenomenon of surface enrichment.The soil acidification is serious.The average content of TN in the nearshore soil is slightly lower than that in the far-shore soil,and the contents of TP,As,Cr and Cu in the nearshore soil are significantly higher than that in the far-shore soil,and the pollutants tend to gather in the surface water.Application of multivariate statistical analysis method,the pollutants in the soil can be divided into three groups,the first group of As,and Cu come mainly from artificial source,the study area soil As pollution is serious,analysis of the main sources should be the local has a larger crystal processing industry,has great potential harm.In the second group,Cr,TP,TN,NH₄⁺-N and AP were affected by both anthropogenic sources and natural conditions.The third group is the soil NO₃^--N content is mainly controlled by natural factors.（3）Sediment inputting ecological buffer is associated with K factor,glue silty loam,sandy loam soil and sediment input quantity is big,need to sediment deposition in the ecological buffer on a regular basis to clean,to avoid the ecological buffer in large amounts of sediment accumulation,affect the uniformity of runoff flow within ecological buffer,and thus the ecological buffer cutting efficiency of pollutants.The higher the slope,the smaller the runoff interception efficiency（RIR）and sediment interception ratio（SIR）.Under the condition of loam soil texture,when the slope is1%～30%,the RIR reaches 60%,and the width of ecological buffer zone is43.9～68.8m.Different soil texture has a great influence on the interjection efficiency of the ecological buffer zone.When the RIR is 60%,the width of the ecological buffer zone required by sandy clay loam,silty clay loam,loam and clay is 56.4～128.7m.Soil texture has little effect on SIR,and the SIR of the 10m-wide ecological buffer zone can reach more than 99%.In practice,due to the limitation of land use space,it is not possible to construct a wide ecological buffer zone.When the main objective is the interception of particulate matter,the 10m-wide ecological buffer zone can achieve more than 90%interception effect.When the main objective is dissolved pollutants,increase the width of the ecological buffer zone to 50～70m,which can achieve more than 40% of the retention effect.