Study On Non-point Source Nitrogen And Phosphorus Pollution Loads In The TGRA Based On Improved Output Coefficient Model

The Three Gorges reservoir area(TGRA)is located in the heart of the Yangtze River Basin.In recent years,with the initial control of point source pollution in the reservoir area,Non-point source pollution has gradually become the main cause of deterioration of the water environment in the reservoir area.Therefore,the research on the non-point source nitrogen and phosphorus pollution load in the reservoir area has important practical significance for water quality safety and pollution control in the whole reservoir area.non-point source pollution’s Extensive,random,uncertain,and ambiguous and so on,Leading to fixed point monitoring is difficult,At present,application model to quantitatively estimate non-point source pollution loads is one of the main research methods.In order to clarify the nitrogen and phosphorus pollution load in the TGRA,This paper improves the Jones classic output coefficient model by,Improved output coefficient model,Based on different land use types,agricultural population,and animal husbandry,the non-point source total nitrogen(TN)and total phosphorus(TP)pollution loads of the Three Gorges reservoir area in 2010,2013 and 2015 were simulated;And take the Jialing River as the verification area.The improved output coefficient model is used to simulate the non-point source TN and TP pollution loads in the TGRA.Finally.The main results and conclusions of this study are as follows:(1)Considering that different land use pollution sources are the main source of nonpoint source nitrogen and phosphorus pollution loads,Selecting the intertransformation between different land-use types between 2005,2008,2010,2013 and 2015,Research indicates,During the period of 2005-2015,there has been a gradual decline in dryland.Reduced from 156,1963.30 hm2 to 1,523,197.45 hm2,Mainly converted to woodland 22439.03 hm2,The paddy field has also gradually decreased,from 623,728.03 hm2 to 58,725.87 hm2,mainly to construction land of 15059.13 hm2.The grassland has decreased by 103,136.66 hm2 in 10 years,mainly to forest land,with a number of 69,808.50 hm2.Among them,the conversion to forest land is the largest,and forest land can reduce the loss of nitrogen and phosphorus.Thereby reducing the non-point source nitrogen and phosphorus pollution load.(2)Taking into account the losses of pollutants during the migration process and the erosion effects of rainfall runoff,Incorporated Johnes’ Export coefficient model productivity pollution factor,factor entrapped and leaching factor,constructed an improved output coefficient model.The simulation results show,The total amount of non-point source TN and TP pollution load in the study area showed a decreasing trend.In 2010 years,the output of TN and TP in the reservoir area was 90586.43 t and 9656.16 t respectively.In 2013 years,it was reduced to 90359.86 t and 9595.09 t,and in 2015 years it was reduced to 85222.04 t and 9112.77 t.The TN pollution load is approximately 9.4 times that of the TP pollution load.The verification area with the Jialing River as a model,Using the improved output coefficient model to simulate the non-point source TN and TP pollution loads in the Three Gorges reservoir area in 2010,2013 and 2015 years,respectively.And compare it with the monitored value,Verify the likelihood of the model with relative error size,The error range is controlled within a controllable range.The results show: The relative errors of TN and TP in 2010,2013 and 2015 years were 15% and 23%,9% and 31%,-3% and-11%.This shows,The improved output coefficient model is feasible for the quantification of TN and TP pollution loads in the Three Gorges reservoir area.Provide a theoretical basis for the latter to study the simulation of non-point source pollution.(3)For specific climatic conditions and human activities in the reservoir area,Six types of land use types such as dry land,paddy field,forest land,construction land,water area and grassland in the reservoir area were selected for simulation.analyze The trend of TN and TP pollutants during 2010-2015 years,The results show: The loss of non-point source TN and TP pollutants in different land use types in the reservoir area gradually decreased.The TN load is reduced from 26480.96 t to 26047.35 t,and the TP load is reduced from 3582.72 t to 3524.05t;The order of loss of pollutants in different land use types is dry land > paddy field > grassland > forest land > construction land > water area.Dry land and paddy fields,The concentration of pollutants lost showed a significant reduce and decreased.The changes in forest land and grassland are not obvious;It shows that dry land and paddy fields are the most common source of pollution load in land use types.Nitrogen and phosphorus pollution caused by agricultural activities is the most serious.In 2010-2015 years,the TN and TP loads of livestock breeding in the reservoir area showed an upward trend.From 15630.04 t to 16914.20 t,The order of output of pollution load in animal husbandry is as follows: Pig>Poultry>Cow>Sheep,Among them,the pollution produced by pigs accounts for 46% of the pollution of livestock farming.It shows that pigs in animal husbandry are the most important source of pollution.The order of contribution of non-point source nitrogen and phosphorus in the reservoir area is as follows: Land use>Agricultural population>Animal husbandry,The contribution rates were 55.97%,25.97%,and 18.06%,respectively.Explain that different land use types are the main cause of nitrogen and phosphorus loss.In summary,the pigs in the dry land and livestock breeding in the land use type are the key areas for TN and TP pollution load output.