Nitrogen Pollution And Its Control Planning In Shaanxi Reach Of Wehei River

With the fast development of society and economy, the water crisis resulting from lack of water resource and increasingly serious water pollution have become the restrict factor to the sustained developing strategy of our country. The water pollution of watershed contains point source pollution (PSP) and non-point source pollution (NSP). Because less attention is paid to NSP and suitable method to estimate the pollution load is lacked, the work of water pollution control chiefly focus on PSP, which leads to the disjointedness between the practical harnessing effect and the control goal, accordingly, fails to achieve water quality control goal.As the biggest tributary of the Yellow River, the Weihe River is the mother river of Guanzhong region of Shaanxi province. The pollution control level of the Weihe River watershed directly affects the social economy of Guanzhong region. Nitrogen is one of the main pollutants of the Weihe river pollution. Aiming at the character of Weihe's water pollution, based on the real situation and data condition of Weihe River, considering the both PSP and NSP, this thesis studies the synthetically control planning of pollution harnessing in the Weihe River watershed. The main content and innovative achievements of this thesis are as follows:(1) The pollution load calculation methods of watershed are studied. At present, the methods of calculating pollution load are approximately classified as the sum of each section load, product of section average concentration and section water amount, sum ofload distributing frequency and convection-diffuseness model. The result of total pollution load educed by different methods has great difference, sometimes several times difference between one and another method. To estimate the annual pollution load, this thesis selects 8 methods and analyzes and compares their structure characteristic respectively. Then these methods are verified by the real sediment-concentration data of the watershed. The results show that the method of the product of section flux average concentration and average runoff is more rational. In the water quality data collected from the Weihe River, this method is suitable to calculate the annual pollution load for BOD5, P2O5, nitrate nitrogen, total nitrogen and sediment.(2) The Johnes's export coefficient model is improved. Based on the determination of export coefficients and applying Johnes's model, taking account of the deficiency of original model, the thesis puts forward improved models by considering the rainfall affect and the contaminant loss in transport process, and carries out the estimate method of the rainfall affect coefficient a and the watershed loss coefficient A . The applied results of improved models show that the mechanism of the improved export coefficient model is more explicit, and the simulation is more accordant with the fact.(3) The rainfall-deduction method is established to estimate the NSP load. Based on the characteristics of NSP affected by rainfall and the rainfall-runoff process and NPS load being closely correlative with rainfall, this thesis proposed the rainfall-deduction method. Compared with the other methods, rainfall-deduction method can be used to calculate the NSP load, without concerning the contaminant transport mechanism. So it is a practical method with the poor data condition.(4) The pollution load estimating models are applied and compared. Using three kinds of methods (runoff-division, rainfall-deduction, and export coefficient) with 5 models to estimate the load of TN, PSP TN and NSP TN of the watershed. Model 1 of export coefficient method can simulate the multi-annual NSP load; model 2 objectively reflects the rainfall influence on the NSP load; model 3, runoff-division model and rainfall-deduction model can be used to estimate the NSP load from the certain section of the basin. Case study shows that the results of these three kinds of models are very close.(5) The correlationship between nitrogen load and human activities in the watershed isdiscussed. The correlationship b...