Research Of TMDLs Of Erhai Lake Based On Ecological Carrying Capacity

With the continuous development of human in Erhai Basin, the basin appears ecological imbalance, poor water quality and eutrophication phenomenon gradually. The problem that how to control the Erhai basin’s water ecological environment have been concerned by people. This research formulats the TMDLs plan based on the water ecological carrying capacity of Erhai Basin. Controling the main pollutants can interference algal bloom broke out indirectly and I can realized the protection of Erhai Lake water ecology. The management measures of main pollutants in the basin can provide a theoretical basis and decision support. This paper consists of seven chapters, can be divided into five parts. The first part is the first chapter, the main research content is discussed the related knowledge. The second part is the second chapter and the three chapter, I analysed the influence factor of main pollutants and phytoplanktons, and seta main pollutant control standards. The third part is the fifth chapter and the sixth chapter, based on the control standards, to calculate the total amount of TMDLs and MOS. The fourth part is the sixth chapter, combining the SWAT model and the measured data to account the area of point source and non-point source pollution load, and distributed the load based on its contribution rate. The fifth part is the seventh chapter, is the conclusion and prospect. By studying this paper, get the following conclusions:(1) Using the gray correlation to assess water quality of Erhai basin, the grade is II, the best water quality is 1997, the worst water quality is 2006. It can be seen from the Carlson nutritional index method that the 1987-1998 years of Erhai in the poor nutritional status and the 1999-2012 years of Erhai in nutrition state stage, which shows that Erhai has started to deteriorate water quality. To further investigate the cause of algae bloom in Erhai lake, I used RDA method to know the ecological relationship between of phytoplankton and water quality factors, the results show that the greatest impact on phytoplankton community is turbidity, followed are TN, TP, temperature, pH and DO, the smaller impact is CODMn and ammonia nitrogen, therefore the water quality factor TN, TP, CODMn and ammonia nitrogen should be control.(2) Using statistical methods, I got TN, TP and CODMn control standard, the calculated results are 0.36mg/L, 0.026 mg/L and 2.9 mg/L respectively. Aquatic biological control standard of ammonia nitrogen is obtained by ecological species sensitivity distribution theory calculation method, the calculation results is 0.28 mg/L.(3) Based on MIKE21 model of two-dimensional hydrodynamic and water quality I calculated water environmental capacity of major pollutants by linear programming method in Erhai which the control standard as the water quality target value. Results showed that TN, TP, CODMn and ammonia nitrogen’s TMDLs of Erhai are 1439.906 kg/day, 100.623 kg/day, 9673.589 kg/day and 934.148 kg/day respectively.(4) Using the first-order error analysis(FOEA) method to calculate MOS, TN, TP, CODMn, ammonia nitrogen’s MOS, the results are 142.191 kg/day, 8.493 kg/day, 542.205 kg/day and 68.286 kg/day respectively.(5) Combining the SWAT model and the measured data phase, accounted the pollution load in Erhai basin. Erhai point source of TN, TP, CODMn and ammonia nitrogen are 82.1t/a, 6.9 t/a, 177.76 t/a and 56.8 t/a respectively. Non point source of TN, TP, CODMn and ammonia nitrogen are 2089.16 t/a, 123.209 t/a, 5447.277 t/a and 507.748 t/a respectively. According to the contribution rate of the maximum permissible pollution load distribution, finally get the TN, TP, CODMn and ammonia nitrogen reduction rate was 78.18%, 74.15%, 40.75% and 44.02% respectively.Innovations of this paper are:(1) Putting forward the concept of TMDLs of Erhai Lake based on ecological carrying capacity. It is a scientific guidance on water ecological protection of Erhai basin, which can achieve the goal of sustainable development of the basin effectively.(2) I made the target of water quality by the ecology of Erhai basin, which are no longer according to the evaluation standard of surface water quality target simply. It can avoid the water quality objectives are too broad which chould lead to inconsistent with the actual problem.(3) The MOS of Erhai basin was formulated by the characteristics of model of the ecological carrying capacity of water. The value of the objective is in line with the actual situation of Erhai basin. It can avoid the subjective determine lead the lack or excess of the MOS estimation directly.It also ensure the safety of the TMDL plan and effective cost savings.