Design And Development For The System Of Nonpoint Pollution Source Risk Assessment In Tiaoxi Watershed Based On ArcEngine.NET.

As point source pollution was effectively controlled,agricultural non-point source(NPS)has become main pollution source for water eutrophication and also become the hotspot of water quality management.In recent years,information technology has been widely used in environmental management.Due to its spatial and temporal heterogeneity,agricultural non-point source pollution is an important application field of GIS and other information technology as well.In order to carry out the NPS pollution risk assessment effectively,this study designed and developed"non-point source pollution risk assessment system(NSPAS)" for watershed using the object-oriented visual programming language C#and GIS secondary development kit ArcEngine.The assessment system was established by pollution risk assessment index which combined with source factors and transport factors.Furthermore,the NPS nutrient loss of Tiaoxi watershed was evaluated by NSPAS.The main results of this study were as follows:(1)According to the characteristics of agricultural non-point source pollution,multiple agricultural nonpoint sources(i.e.agricultural activity,rural domestic pollution,livestock breeding and aquaculture activity)were integrated and the evaluation system was focused on nutrient loss because nitrogen and phosphorus(N/P)were the main factors leading to eutrophication.The non-point pollution risk assessment index system has involved with source factors and transport factors for NPS pollution.Nutrient discharge load was calculated as the source factors mainly by export coefficient method and the transport factors consisted of soil erosion,surface runoff,soil texture and permeability and the contributing distance were ranked according to the impact of the factors to nutrient loss.According to the influence of each factor on the nutrient migration,the transport factors were weighted in the system.(2)Based on the characteristics of non-point pollution risk assessment index(NPI),combined with the secondary development characteristics of ArcEngine,the overall structure of the system was designed from the logical and functional aspects,and a targeted system’s database composition structure was designed too.Using control and visualization tools of Windows default,CSkin and ArcEngine reasonably,the interface system was developed successfully.With the help of development platform VS2010 and programming language C#,this article selected the appropriate ArcEngine function interface and designed six functional modules,including program settings,data import,parameter determination,risk assessment and auxiliary function,and finally developed the watershed non-point source pollution risk assessment system(WNSPAS)completely.(3)Based on the various social and economic environment data of the Tiaoxi watershed,the non-point source loss risk in the Tiaoxi watershed in 2014 was evaluated by using the developed assessment system.Results of case study showed that the spatial distribution of nitrogen and phosphorus loss in Tiaoxi watershed was similar.The lower and lowest nutrient loss level areas were widely distributed in the middle and western hilly areas of the basin,and the areas with higher and highest nutrient loss level were mainly distributed in the upper reaches of Changxing plain areas,the middle reaches of the East Tiaoxi plain areas and the upper reaches of Jinshan-Pingyao areas in the East Tiaoxi.(4)Using NSPAS,the influence of various factors such as fertilization amount,livestock breeding,aquaculture,rainfall on non-point source pollution loss risk were evaluated by scenario analysis.The results showed that the reduction of cropland fertilization had a significant effect on the loss of nitrogen pollution.After the reduction of livestock breeding,the risk values of nitrogen loss in livestock breeding higher areas were significantly decreased,but the rate of the higher risk areas did not change obviously.The risk values of phosphorusloss were reduced markedly in the areas where aquaculture reduced by 20%.The single effect of rainfall had no significant effect on the rate of each level of phosphorus loss in the Tiaoxi watershed,but the changes on the risk values of phosphorus loss in some sub-basins of Tiaoxi watershed can still be found due to the rainfall every year.(5)The application results of the non-point source pollution risk assessment system(NSPAS)showed that its operation was humanized,and the high calculation efficiency,the diversity of Input/output interface.The case study also showed that it was practicality and feasibility.