Study On The Nitrogen And Phosphorus Load Of Non-point Source Pollution In Three Gorges Reservoir Area By Using The Improved Export Coefficient Model

In China, The Three Gorges Reservoir Area(TGRA) is a vital source of fresh water, which offering the important water resource in South-to-North Water Diversion Project. The nitrogen and phosphorus concentration in the secondary river are senior, with the water level promoted and the backwater uplifted, occurring of "bloom". With the point source pollution controlled step by step, non-point source(NPS) pollution has become the main reason that polluting the water environment gradually. Carrying out the research of NPS of TN and TP load in TGRA, will have an important theoretical and practical significance to the water environmental safety and the governance of water pollution.Because NPS has the character of uncertainty 、randomness 、fuzziness and universality, using quantitative model to the numerical simulation has become one of the important method to research NPS. This study will build the improved export coefficient model(ECM),and use the Xiao Jiang Basin to verify the feasibility of the improved ECM.This paper will use the improved ECM which is verified to simulate and analyze the load of TN and TP in TGRA from 2002 to 2012 years, and will predict the reduction of TN and TP load of NPS in TGRA by using the measures of changing the farm which slope above 25 degree to forest or grass or other ways. The main research results are as follows:① Considering the loss of the nutrients in the process of migration and transformation, and the influence of rainfall runoff on the lower bound, this study will introduce the river load ratio and the rainfall influence coefficient to the traditional ECM, and apply the improved ECM to the opening and large scale of the TGRA. By comparing the simulation value of classical and improved ECM and the statistic value,proves the enhance accuracy of the improved ECM.②The declining of the TN, TP load in agricultural population of the TGRA, illustrates that with the growing population in cities, rural population gradually decline, and the large number of rural labor exported to city leading to a fall NPS load in agricultural population. The overall trend of the TN and TP load in the livestock farming of the TGRA is rising and the order of it is: pigs > cattle>sheep > poultries, showing that with the development of economy, the human demand for meat increased year after year, and pigs is the main pollution sources in livestock farming; The order of TN、TP load of per kilometer of the land use in TGRA is :the dry land > forest land > paddy field > grassland > urban land > unused land, illustrating that the dry land is the biggest pollution source in land use, nitrogen and phosphorus pollution caused by agricultural activity is most serious. Also proving that nitrogen and phosphorus loss caused by forest land is less, and it can effectively reduce the loss of nitrogen and phosphorus in the soil, returning farmland to forest is an important way to improve the NPS load in TGRA.③The TN and TP load in TGRA from 2002 to 2012 years is decline. The annual average of TN and TP load is 6.05 and 6.10 times of the corresponding load in Hubei province, the main reason is that the area in Chongqing is 3 times of that in Hubei, and the population and livestock breeding in Chongqing is larger. The contribution rate of TN and TP load order of different pollution source in TGRA is: land use > livestock > agricultural population, showing that land use is the main reason that leading to the loss of nitrogen and phosphorus, and also is the main pollution sources of NPS in TGRA.④ By changing the cultivated land which the slope above 25,the reduced percent of TN and TP is 10.9% and 11.3% of the total amount of simulation, which is over the TN and TP load of agricultural population and livestock.Changing that cultivated land to grassland, the reduction of TN and TP is 8.4% and 7.6% of the total amount, and the reduction of TN load reach 90% of agricultural population and the reduce of TP load is equal to the load of livestock. Changing farmland to land is one of the most effective ways to reduce non-point source pollution, and returning farmland to grassland is the second important way to reduce the NPS.