Study On The Countermeasures Of Reducing Agricultural Non-point Source Pollution Around Baima Lake

In recent years,The agricultural non-point source pollution is becoming more and more serious in the surrounding areas of Baima Lake,its contained nitrogen,phosphorus pollutants into the air,soil and water,the water environment and the ecological system caused serious damage.According to the field investigation,the non-point source pollution around the Baima Lake mainly comes from crop production,breeding industry and rural domestic waste water.The non-point source pollution goes through 3 steps of "source-flow-sink".Around the 3 steps,the paper put forward 3 technology:the controlling of pollution source,the retaining of pollutant from moving into the water nearby and the tail end sewage purifying.The area of Baima Lake grows paddy rice with a crisscross network of irrigation channels and drainage ditches in it.Waste water from farmland and villages initially flow into drainage ditches,what makes drainage ditches become the passage for the non-point source pollution to reach the rivers.Therefore,the study of the moving and the transformation of nitrogen and phosphorus in drain system is the key to controlling and treating the non-point source pollution.To stop nitrogen and phosphorus from the farmland getting into rivers,the paper put forward a kind of new ecological permeable weirs in drainage ditches,after summarizing the ways to control farmland non-point source pollution worldwide.The permeable weirs retains and purifies waste water while daily drainage won't be influenced.It's a new method to save land.Firstly,experimental installations of ecological permeable weirs was placed in drainage ditches.Then,the writer did orthogonal experiments on static conditions.Finally,the removal effects of CODcr,TN,NH4+-N,NO3--N and TP were taken as the index of evaluation and the length of purification tankA,grain size of sand B,filling rate C and infilling D were taken as 4 influencing factors to analyse how the ecological permeable weirs remove nitrogen and phosphorus from waste water.Meanwhile,the writer studied which is the major factor that affect the purifying capacity of the weirs and the best combination.The result of this test shows that:the ecological permeable weir has better retention and remove ability for nitrogen and phosphorus pollutants,The concentration of pollutants in the drainage ditch decreases with the hydraulic retention time.Apply the methods of range analysis,variance analysis and matrix analysis on the result of orthogonal tests,the writer found the sand grain size(B)of the permeable weirs played the biggest part in purifying farmland sewage and the sequence of influencing factors is grain size of sand(B)>filling rate(C)>infilling(D)>the length of purification tank(A).The optimal level combination of the weirs to purify pollutant is A3BIC3D1,which means fill it with bamboo chips when the length of purification tank is 3m,the sand grain size ranges from 0.8mm to 1.2mm and the filling rate is 65%.Therefore,building the ecological permeable weirs in the farmland drainage ditches around the Baima Lake can effectively intercept nutrient loss from farmland and reduce the migration and transformation of nitrogen and phosphorus contaminants to downstream water.At the same time,the results of this paper provide theoretical basis and technical support for the popularization and application of ecological permeable weir in rural areas.