Simulation Of Nutrients Transportation And Optimal BMPs Placement In Riparian Agricultural Area Of Typical Yunnan Plateau Lake

The Yunnan plateau lakes are among one of the five biggest zones of lakes in China which are facing the problem of lake eutrophication.Serious non-point source pollution(NPS)is the main reason to lead to the sever eutrophication of Lake Qilu,one of the Yunnan’s nine major plateau lakes.So exploring the refined management of agricultural non-point source pollution is the core of water pollution prevention and control for the 13th Five Year Plan and even the future.Small-scale BMP layout has great significance for the realization of coordinated development of agricultural development and environmental improvement which has been widely applied in other watersheds.However,there were few reports about the research on small-scale BMP layout of Yunnan plateau lakes.Lake Qilu with severe eutrophication and typical agricultural area on the south bank of the lake was selected as the research object to build a scientific and reasonable simulation model of nutrient transportation and transformation for the experimental study of representative BMP layout in our study.Finally BMP layout of agricultural area was made on the south bank of the lake by developing the optimization model.The main innovative points of the study is selecting the certain region to simulate and optimized layout the small-scale BMP with the combination of natural features of the plateau lakes.The content of this paper mainly includes:the specification of main watershed pollutants by water quality evaluation of lakes;the exploration of main features of watershed non-point source pollution by the investigation of agricultural non-point source pollution;the identification of nutrient migration and transformation rule by HSPF modelling;testing soil for formulated fertilization and constructed wetland were chosen to explore the field effect and detailed implementation method of the two BMP technologies according to the selection principles of BMP technology;studying the effects of farming system,testing soil for formulated fertilization and different combining schemes on nutrient reduction of watershed non-point source pollution with the help of uncertainty optimization model and the BMP module of HSPF.The aim of this paper is:to simulate the nutrient migration and transformation of typical agriculture are on the bank of eutrophic plateau lakes,explore the nutrient migration and transformation processes,realize the nutrient erosion process and regularity;to identify the appropriate BMP for research region and obtain the local BMP experimental data;to design eleven BMP combination measures,develop BMP optimization method and small-scale BMP optimization layout to provide technical and decision support for the prevention and control of plateau lake watershed non-point source pollution.The modeling and experiments results showed that:(a)Lake eutrophication is the main water environment problem in the research area.Nutrient is the primary pollutant which urgently needs to be controlled.Agricultural areas on the bank of the plateau lakes need the refinement management of non-point source pollution control.(b)Nutrient concentration of farm wastewater in the research region is higher than that of Lake Qilu.Pollutants concentration of farmland runoff is far higher than that of farm wastewater,and the mean TN,TP and COD concentrations of the farmland runoff is 3.8 times,1.7 times and 1.35 times that of farm wastewater,respectively.Farmland runoff presents the characteristics of "high nitrogen,medium phosphorus and low organic matter".Nitrogen output of regional farmland runoff has the most soluble NO3--N,while P output has the most particle phosphorus,but the dissolved phosphorus concentration is still in a high level.(c)HSPF simulation results showed that dry year,neutral year and wet year of the research region was the year of 2010,2004 and 1984,respectively.The annual runoff was 7.46,8.32 and 9.54 million m3,respectively,and the flux of sediment,TN and TP was 1596,98.5 and 4.78 t/a,respectively in the dry year.Nutrient loss caused by farm water ebb constituted the main pollutants transportation way in the research region.(d)Field experimental study of BMP technology obtained the best soil N,P fertilizing amount and the maximum output of the soil testing for formulated fertilization,and the main influencing factors of artificial wetland on pollution removal.The field experiments showed that the both technologies had ideal removal effects for watershed non-point source nutrients.(e)The assessment and optimization study of BMP technology showed that simply using the cropping system and soil testing for formula fertilization didn’t meet the requirements of the nutrient concentration unless the artificial wetland technique was combined;The multi-objective optimization schemes with different characteristics were proposed for the flexible choice of decision makers based on the decision-making needs.The difference analysis of different schemes with the same reliability can help to better understand the influence factors and accessibility of nutrient reduction targets,specify the different scheme features,and offer various supports for decision-making.