Zonation for nonpoint source pollution control in Hongfenghu reservoir watershed

Abstract: Eutrophication caused by the enrichment of nitrogen and phosphorus is degrading surface water quality throughout the world. Sources of nutrients include over-fertilized agriculture lands, urban areas with excessive usage of herbicides and insecticides, and eroded soils. Due to the variation of nutrient export over the area and time, it is difficult to identify, assess and control nonpoint source (NPS) pollution. The prevention and mitigation of NPS pollution have become priority tasks in water monitoring and restoration programs in many countries. The interaction of human activities with the inherent variations in soil type, climate, topography and hydrology gives rise to large spatial and temporal variation in nutrient concentrations in surface runoff. Many research efforts are made to explore the processes and spatial characteristics of NPS pollution for prevention and mitigation measures. Major pollutants, particularly from agricultural activities, which include nitrogen, phosphorus nutrients and sediment that have been released into aquatic environments, have caused problems in the Hongfenghu Reservoir watershed, Guiyang. It is necessary to identify the spatial and temporal distributions of NPS pollutants and the highly polluted areas for the purpose of watershed management. In this paper, GIS technology, ArcSWAT model, ANOVA (Analysis of Variance) and CA (Cluster analysis) were used to identify the zonation of NPS sources and control in Yangchanghe river watershed which is one of the main tributaries in northwest of Hongfenghu Reservoir watershed, with relative strong intensive agricultural activities. The results showed that the spatial distribution of NPS pollution load in Yangchanghe river watershed was of great heterogeneity, the agricultural land at higher elevation had the highest NPS pollution loads, and the Liu Guang, Huang La, Jiu Zhou and Bai Yun towns were identified as the critical towns for NPS pollution control. In addition, the most important factor for total N (TN) and total P (TP) loss was related to fertilizer application amount. Slope length, land use, and slope degree were also important factors. The content of organic P in soil may contribute to TP loss due to long term cultivation and overuse of fertilizer in Yangchanghe river watershed. Moreover, three zones for NPS control in Yangchanghe river watershed were divided as division zone for eco-agricultural area where the agricultural activities was intensive, pollution treatment zone where was a livestock production area and villages, and ecological restoration zone where there were serious soil erosions at higher elevation. Therefore, optimal strategies and practices were needed to simultaneously control P and N export at the farm and watershed scales. One water quality problem may be aggravated while solving another. In a humid-temperate climate, on-farm practices to reduce surface runoff and P export by increasing infiltration would typically increase ground water P concentration and NO3 leaching. Further, different nutrient control goals require adequate methods for different scales within the Yangchanghe river watershed. For the upstream fresh waters and the fresh water arms of the Yangchanghe river watershed, controlling P export should be the primary concern. For the upstream aquifer systems, and within the Hong Fenghu reservoir, controlling N export should be the primary concern.