Research On Nitrogen Non-point Source Pollution In Chakou Watershed Based On AnnAGNPS Model

With the high emphasis on the environment problems, agriculture non-point pollution has become the worst problem. Because non-point pollution covers widely range and difficultly prevented, on-point nitrogen pollution has become the major source of pollution. The abundant application of fertilizer has improved the productivity, but ignored the balance between nutrient and environment. It resulted that nitrogen has largely run off.In this paper,through the means of investigations, samplings, labrotart analysis and querying histarical data, information database of Chakou watershed has been built.Methods of quantities and qualitive analysis combination carry out the research of non-point nitrogen pollution in Chakou watershed. The research steps are as follows:1. Based on the data collected from field investigation and GIS build model of nitrogen balance suiting for this watershed. Results show that the total input of nitrogen was946.16t and fertilizer application was the dominant source of input nitrogen accounting for64.05%, while the total output of nitrogen was600.16t and the harvest of crops was the primary of output nitrogen accounting for69.81%. Through the study of input of nitrogen and output of nitrogen, We can predict that the farmland nitrogen load in different district make potential threats to water environment in Chakou watershed.2. Based on the3S technology, database of AnnAGNPS model has been established, and the applicability of AnnAGNPS model has been tested in Chakou watershed. The research conclusions as follows:1)This model has a well simulation precision to runoff, but has a low level precision to nitrogen simulation. Because of landslip, dam and project of slope-to-terrace give rise to the low level of simulation precision of nitrogen.2)Even though the simulation precison of nitrogen is not well, as a whole it has regularity. On the time distribution, rainfall capacity and nitrogen has a uniform trend, and both of them concentrate on the year of July, August, September. Nitrogen losses account for98.7percentage of a year losses in the three months.3)On the space distribution, the sequence of nitrogen load by unit area decreasingly was cultivated land, low density grass, settlement, high density grass, little-forest, high-forest and shrub wood. And the sequence of nitrogen load by unit area of cultivated land decreasingly was slope cropland, dam land, plain land and terrace land. Through the compared analysis, land-use types is most important to the distribution of non-point nitrogen pollution.3. Adoption of cutting down input fertilizer in parallel with no any fertilizer practice can obviously better reduce nitrogen non-point pollution.4. Some suggestions are proposal concerning on the prevention of source and diffusion path of nitrogen. The measures of prevention of source nitrogen involve ecological balanced fertilization, transformation of cultivation method and straw coverage. The measures of prevention of diffusion path involve the adjustment of landscape ecological pattern, for example vegetation buffer strand and wet land.