Research On Non-Point Source Pollution Based On AnnAGNPS

As the biggest river in Jiaodong Peninsula, the Dagu river carries the most amount of runoff and sand among rivers emptying into Jiaozhou Bay.As the Dagu river brings annually a large amount of silt and dissolved pollutant into Jiaozhou bay, the Dagu watershed is the main source of inorganic nitrogen and phosphorus of Jiaozhou Bay.With the implementation of synthetically renovating project in Dagu watershed, the point source pollution has been under good control, so non-point source pollution will become one of the main reasons for pollution in Dagu watershed.Therefore the study on non-point source pollution in Dagu watershed has very high theory value and realistic meaning.In order to reflect reliably the runoff producing and sink flow of Dagu basin through getting rid of the influence of external water source and prevent the interference for non-point souce from point souce,the upstream of Dagu watershed is selected as study area.After a large amount of data reflecting basin characteristic were collected and the database was set up, the nitrogen balance model was firstly built to calculate the amount of imported, exported and net nitrogen in the basin, which is theoretical preparation for analysing the mechanism of non-point souce pollution by AnnAGNPS model. The surface flow, sediment and total nitrogen data surveyed were secondly utilized to verify the simulation precision of AnnAGNPS, and the model's suitability was validated in Dagu watershed. The characteristic of non-point source pollution was finally quantitative analysed and the abridged effect of environmental pollution for the best management practices were evaluted by the calibrated AnnAGNPS model. The following conclusions were obtained in the paper:1.The total amonut of imported nitrogen in the upstream of Dagu watershed is 1932.55t.yr^-1, among which the contribution of chemical fertilizer, biological fixation, precipitation and agricultural product is respectively 59%, 14%, 15% and 12%. The total amount of nitrogen output is 668.26t.yr^-1accounting for about 35% of the imported nitrogen, among which the contribution of nitrification and volatilization is 40% and 60% respectively. The net nitrogen is 1264.69t.yr^-1, among which the sharing amount of water body export by point and non-point source, enrichment in soil and living beings is respectively 175.03 t.yr^-1, 579.77 t.yr^-1, 448.68 t.yr^-1 and 60.82 t.yr^-1. The correspondingly contribution is separately 14%, 46%, 36% and 5%. The non-point souce is the main way of nitrogen loss, therefore, it is necessary to carry out some study on non-point source pollution in order to maintain the healthy ecological environment in Dagu basin.2.The correlation coefficient between surface runoff and silt simulated by AnnAGNPS model and surveyed data is respectively above 0.9 and about 0.6.Besides. The lowest correlation coefficient of total nitrogen between simulating and surveying is 0.6 and it is up to 0.8 in small scale.The simulating precision of surface runoff by AnnAGNPS demonstrates in time scale that: annualy >monthly>daily, which prove that AnnAGNPS is not suitable for risk appraisal, however, it is enough to estimate the annually pollutant load and select the best management practices.As the simulating precision of surface runoff and silt in wet year is obviously higher than that of dry year, the AnnAGNPS model is sensitive to the amount of annual rainfall in the basin. The simulation result for the rainfall incident from 30mm to 80mm is better, however, it is unsatisfactory for the extreme and small rainfall incident by AnnAGNPS model.3.The exporting amount of annual surface runoff, silt and total nitrogen is respectively 1.64×10⁸m³, 4.8×10⁴t and 353.3t, and the total nitrogen load of unit area is 5.78kg.hm-2.yr^-1 in Malianzhuang section.The exporting amount of annually surface runoff, silt and total nitrogen is respectively 1.22×10⁸m³, 3.1×104t and 142.47t in Dongdingjia section.The correspondingly value in Xijujia section is separately 16.7×10⁶m³, 8.5×10³t and 195.3t. The amount of surface runoff, silt and total nitrogen entering Jiaozhou Bay is respectively 1120.60×10⁶m³.yr^-1, 377.36×10³t.yr^-1 and 853.59t.yr^-1 through Dagu estuary.The exporting amount of surface runoff, silt and total nitrogen differ significantly in different levels of rainfall that the amount of annual surface runoff, silt and total nitrogen are higher in wet year than that in dry year, which prove indirectly that the model is sensitive to the rainfall.The output amount of surface runoff, silt and total nitrogen concentrate mainly on between June and August.The amount of suface runoff, silt and total nitrogen is separately 301.1×10⁶m³, 83.68×10³t and 97.25t between June and August, which separately accounts for the 96%, 88% and 76% of the total amount and appear the characteristic that July>August>June.There is better positive correlation between surface runoff and pollutant load in July, which the relative coefficient between runoff and sediment is 0.9615 and that of surface runoff and total nitrogen is 0.9225. The trend appear that the output amount of sediment and total nitrogen increase with the increase of surface flow.4.On the basis of designing the best management practices rationally, the cutting down effect of pollutant load from all kinds of measures are simulated and the resut is obtained that returning land for farming to forestry is best for cutting down the pollutant load.