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Risk Assessment For Nutrient Loss Of Agricultural Non-point Pollution Source In Tiaoxi Watershed

Posted on:2016-07-03Degree:MasterType:Thesis
Country:ChinaCandidate:Z L SunFull Text:PDF
GTID:2191330461959584Subject:Environmental Engineering
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Eutrophication is one of the main characteristics of surface water environment problems. With the effective control and reduction of point source pollution, agricultural non-point pollution sources (NPS) composed of farmland, livestock and poultry breeding, aquaculture and rural domestic pollution have become the major sources of eutrophication. Therefore, controlling agricultural non-point pollution is more significant for improving water quality in rivers and lakes, protecting ecological environment and even achieving the sustainable development of agricultural resources and environment in China.Located in the south of Taihu Basin, Tiaoxi Watershed was selected as the study area. Based on the migration and loss mechanism of agricultural non-point pollution sources, the comprehensive risk assessment index system of nutrient loss for agricultural non-point pollution source was established, The nitrogen and phosphorus loss risk assessment for Tiaoxi Watershed was carried out by the application of the risk assessment index system, and the main research work was made up of:(a) comprehensive evaluation for the spatial distribution features of nitrogen and phosphorus loss risk from each agricultural non-point sources, (b) identifying the critical areas of nitrogen and phosphorus losses, and (c) zoning the key nitrogen and phosphorus loss control areas and the corresponding control measures for each key control areas was put forward. The main results were showed as following:(1) The basic attribute database composed of meteorological data, soil property data and socioeconomic data was established based on investigation, statistics and data classification. With the support of ArcGIS technology, the spatial database including the Digital Evaluation Model (DEM), soil type map and land use type map was built. Moreover, the channel network was extracted and sub-basin was generated with the SWAT model.(2) The comprehensive risk assessment index was established from the aspect of source factor and transport factor, based on the natural geographical conditions, socioeconomic development and the production and loss characteristics of each agricultural non-point sources. Source factors were composed of farmland fertilizer rate, fertilizer loss rate, nitrogen and phosphorus (N/P) concentrations in forest surface runoff, N/P discharge load of rural life, N/P discharge load of livestock breeding and aquaculture. Transport factors include soil erosion, surface runoff, soil permeability, soil texture and the distance from river. The assessment index has the advantage of low data requirement, simple operation and large scale watershed application.(3) By using of the comprehensive risk assessment index, N/P loss risk in Tiaoxi Watershed was evaluated. Results showed that the integrated N/P loss risk in the watershed was mainly composed of low risk degree, accounting for 75.05% of the whole watershed, and high risk areas only accounted for 11.18% which were mainly distributed in East Tiaoxi Watershed. The critical areas of integrated N/P loss risk distributed in three regions:Jingshan-Pingyao region in the upstream of East Tiaoxi Watershed, middle reach plain of East Tiaoxi Watershed and Changxing Plain. The spatial distributions for N/P loss risk of farmland, rural living, livestock breeding and aquaculture were all mainly composed of middle and low risk areas. The N/P loss risks of farmland and rural living were evenly distributed, with a large scale of middle risk areas and no outstanding high risk areas. While the condition was different with regard to livestock breeding, most areas of the watershed showed low risk, and high risk areas only accounted for 11.39% with outstanding high risk values, which were 5-8 times of the mean value in Tiaoxi Watershed.The nitrogen loss risk of farmland was mainly connected with the nitrogen fertilizer quantity and the distribution density of farmland; while phosphorus loss risk of farmland was not only impacted by phosphorus fertilizer quantity but also influenced by surface runoff, soil erosion and the distance to rivers. The N/P loss risk of livestock breeding was dominated by breeding density and scale, and N/P loss risk of rural living was mainly influenced by the distribution of rural residential areas and population size.(4) Three key control areas of N/P losses in Tiaoxi Watershed were zoned based on the risk assessment results, including:Changxing Plain (area A), the middle reach plain of East Tiaoxi Watershed (area B) and Jingshan- Pingyao Region in the upstream of East Tiaoxi Watershed (area C). Risk order of the three key control areas was as following, B> C> A. Area A was the integrated control area of farmland, rural living and livestock breeding, area B was the key control area of livestock breeding, and area C was the integrated control area of farmland and livestock breeding. Finally, the control and management scheme was worked out based on the compositions of pollution sources, geography position and the industrial situation, which was guided by the general idea of total pollution control and industrial adjustment.
Keywords/Search Tags:Agricultural non-point pollution, nitrogen and phosphorus losses, risk assessment, critical area, zonal and classification control
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