Study On Non-Point Source Pollution Characteristics Of The Middle Route Of The South-to-North Water Transfer Project Based On Landscape Pattern Analysis

The water quality of the water source area of the Middle Route of the South-to-North Water Transfer Project is mainly caused by non-point source pollution.Nitrogen and phosphorus are the most important factors affecting non-point source pollution,and are affected by vegetation types,land use types and seasonal replacement.This paper will use GIS,remote sensing(RS),landscape pattern analysis,partial least squares regression(PLSR)models,etc.,based on non-point source pollution control approaches(source control,process block and end treatment)The ideas were studied on the landscape pattern of the reservoir area,the source of non-point source pollution,the relationship between landscape pattern and water quality,and the influence of the landscape of the subsidence zone on nitrogen and phosphorus.The conclusions of this study are as follows:(1)By interpreting the remote sensing data of land use/land cover in the water source area,the water source landscape was analyzed.The results showed that the area of forest land,farmland and water area in the water source area was 59.8%,18.0% and 10.7%,respectively,grassland,rural areas and towns accounted for 11.5%.The landscape heterogeneity between the river basins is relatively large.As the landscape matrix in the sub-basin,the forest landscape has a high degree of aggregation,while the farmland and rural landscape are highly fragmented.(2)Through long-term localization monitoring of rainfall runoff with different land use types in typical watersheds,the nitrogen and phosphorus output of farmland,vegetable plots and forest land are quite different,and the nitrogen and phosphorus content of water is significantly affected by rainfall intensity and fertilization period,and the initial fertilization and water At the beginning of the period(April-May),the nitrogen and phosphorus contents in the runoff formed by rainfall were high,and the total nitrogen contents in the farmland and vegetable fields were 116.9 mg/L and 43.76 mg/L,respectively,and the total phosphorus content was 0.42 mg/L and 6.37 mg/L,respectively.,while the loss of nitrogen and phosphorus in forest land is greatly affected by rainfall intensity.The output form of nitrogen in runoff is nitrate nitrogen,which is mainly from farmland and vegetable fields,which are 11.35mg/L and 4.94mg/L respectively.The main output form of phosphorus is soluble phosphate.The average content of total phosphorus in vegetable field is Woodland and farmland are 2 times and 4.82 times.(3)Through continuous monitoring of the water quality of the water source sub-basin,the sub-basin water quality is mostly in Class II,Class III and Class IV,and some in Class V and Class V.Nitrogen is the most important element affecting water quality,and phosphorus is only high in some areas.The water quality of the sub-basin in the dry season and the wet season is quite different.The total nitrogen concentration in the water in most areas is higher than that in the wet season.By establishing the PLSR model of water quality and landscape,the pollution of water bodies in the wet season mainly comes from agriculture and rural areas.It is greatly affected by regional landscape fragmentation and landscape agglomeration.The pollution of water bodies in dry season mainly comes from urban areas and industrial forests affected by some areas.The area ratio of the landscape and the connectivity of the landscape have an inhibitory effect on water pollution.(4)Through the analysis of the water samples in the Library bay and the WLFZ,the average concentration of total nitrogen in the water is the standard of Class IV and total phosphorus as Class III water quality.By studying the physical and chemical properties and enzyme activities of the woodland,farmland and grassland in the WLFZ,the nitrogen,phosphorus and organic matter in the forests of the WLFZ were significantly higher than that of the farmland and grassland.The soil nutrient of farmland and grassland was significantly lower than that of the control zone,while the phosphorus content of forest land was higher.It is higher than the control area,and the enzyme activities of farmland and grassland soil are significantly lower than that of the control area.While the enzyme activities of forest soil is higher than that of the control area,and the forest land of the WLFZ has higher stability than farmland and grassland.In summary,the water source area should strengthen the management of the breeding industry,reduce landscape fragmentation,strengthen forest planting,establish riverside buffer zones,strengthen river pollution monitoring in urban and rural areas,and pay attention to the water quality of small watersheds.