Study On Non-point Source Nitrogen And Phosphorus Loads In Lianjiang River Basin

Lianjiang is one of the important mother rivers in Chaoshan area.Since the 1990 s,industrial and agricultural and economic development in the basin has been rapid.A large amount of industrial wastewater and domestic sewage are directly discharged into the Lianjiang water system without treatment.The pollutants produced by farming,livestock and poultry farming are seriously lost,and the water quality is always inferior to Class V,Making Lianjiang one of the most polluted black and odorous water bodies in Guangdong Province and even the whole country.In recent years,under the general situation of resolutely winning the battle of water pollution,relevant departments at all levels have actively launched the prevention and treatment of water pollution in Lianjiang.The treatment of industrial wastewater and urban domestic sewage as point source pollution has gradually been standardized,and the problem of non-point source pollution has gradually increased protruding.Therefore,in order to achieve the Lianjiang water functional zoning goal,carrying out qualitative and quantitative research on non-point source pollution in the river basin is of great significance for the reconstruction of Lianjiang ’s ecological civilization and the sustainable development of the social economy.In this study,on the basis of obtaining water quality data,the comprehensive water quality index method is used to evaluate and analyze the water quality of the main stream of Lianjiang River;on this basis,the output coefficient model is improved by introducing the terrain influence coefficient,rainfall influence coefficient and river inflow coefficient,Build an improved model of output coefficients;use the spatial processing function of GIS and apply the constructed model to the non-points of the four major pollution categories such as land use,agricultural population,livestock and poultry breeding and atmospheric subsidence from 2014 to 2018 in the Lianjiang River Basin Simulation and analysis of source nitrogen and phosphorus pollution load.The main research results are as follows:(1)The three most polluted indicators of the main stream of the Lianjiang River are:TN,ammonia nitrogen and TP.Under the joint efforts of multiple departments,the water quality from 2009 to 2019 will gradually change from black and odorous water to Category V from 2016.There is no obvious difference between the upstream and downstream sections.The water quality assessment of the Lianjiang estuary shows that the overall water quality in 2018 is better than the same period in 2015,and the water quality in the flood season is better than that in the dry season.(2)The average TN and TP loads in the Lianjiang River Basin from 2014 to 2018 were 4716.43 t and 240.25 t,accounting for 95.15% and 4.85%,respectively.The pollution was mainly non-point source nitrogen.The load change in the past years is relatively small,and the load in Shantou section is more than 1.7 times higher than that in Puning section.The area of Shantou section in the river basin accounts for about 3/5,with a large agricultural population,a more active livestock and poultry industry,and a more developed economy.Among the four major pollution categories,the TN load is:land use> agricultural population> atmospheric subsidence> livestock and poultry breeding,and the TP load is: agricultural population> land use> livestock and poultry breeding> atmospheric deposition.Land use and agricultural population are the main output sources of non-point sources of nitrogen and phosphorus load,because the fertilizer application rate in the basin is high,and the agricultural population base is large,the domestic sewage generation is large,but the treatment efficiency is not high.(3)Among different land use methods,the output intensity of non-point source pollution is the largest in human agricultural activities and urbanization construction,and the output load density of forest land and grassland is small.Before 2016,a large number of people in the river basin changed from agricultural to non-agricultural.After2016,changes in the agricultural population have stabilized,and their contribution to non-point source pollution has generally declined.Among all kinds of livestock and poultry farming,pigs make the largest contribution,and non-point sources TN and TP account for 79.23% and 74.06% of the total livestock and poultry farming load.The contribution of atmospheric subsidence exceeds that of live pigs,indicating the need to pay attention to non-point source pollution of water bodies caused by air pollution.