Study On The Mechanism And Influencing Factors Of Nitrogen And Phosphorus Transport From Lake Water To Groundwater Driven By Pumping

Based on the project of"The key technology of filtration and water extraction in Longhu water supply project",this paper selected the Longhu water body of nitrogen and phosphorus pollution as the research object,analyzes the characteristics of the percolation layer in Longhu and evaluates the water quality indicators of Longhu Lake's two intakes from 2009 to 2016.The analysis was conducted to evaluate the degree of eutrophication and the degree of water pollution by using the scoring method and the improved Nemerow pollution index method.On this basis,the field experiment on the degradation of nitrogen and phosphorus in the lake bed percolation system under the field of pumping water was carried out.The results of the test data were used to analyze the mechanism of nitrogen and phosphorus migration and transformation during the conversion of lake water into groundwater;the factors affecting and controlling the process of nitrogen and phosphorus in the migration and transformation process were analyzed.The characteristics of filter bed and laboratory soil column test and chemical analysis of sediment were mainly selected.The research provides a scientific basis for the selection of the next water quality improvement plan for the Jinmen Longhu Water Supply Project,and has important theoretical and practical significance for the rational use and development of water resources in the N-Pass supertype water source area.Through this study,the following research results have been obtained:?1?Longhu filter bed structure consists of two parts:the upper layer is lacustrine mud and silty clay,and the lower layer is aquifer composed of medium-fine sand,medium coarse sand and sandy viscous.The filter bed in Kunan District is composed of aquifers.The head loss of the lake driven by pumping is mainly controlled by fine-grained soil with a particle size of less than 0.10 mm.?2?According to Longhu's many years of water quality analysis,TP is the main pollutant of Longhu Lake,which is 0.06⁶.96 times higher than that of Category III,which is a trend of increasing slowly year by year.NH₄⁺-N concentration is characterized by high winter and spring and low summer and autumn.The water quality of the eastern half of the lake is better than that of the western half lake.In2016,Longhu was slightly eutrophic,and the degree of eutrophication increased slightly.Using the improved Nemerow pollution index method to evaluate the results,the water quality of Long Lake from 2009 to 2016 was Grade IV each year,the water body was moderately polluted,and the Western Hemisphere was slightly heavier than the eastern half.?3?The use of natural filter bed filtration in Longhu Lake is not suitable for degradation of nitrogen and phosphorus.The experimental results of the degradation of nitrogen and phosphorus by the lake bed infiltration system driven by pumping in the field showed that the total phosphorus in the water seepage after the lake bed was filtered exceeded the standard of 5.579 to 9.09 times,and the ammonia nitrogen was changed from the standard to the standard.The exceeding multiple was 4.69 to9.09.During the experiment,the results showed that the natural lakebed of Longhu Lake had not achieved the expected degradation of nitrogen and phosphorus,and the degradation effect was poor.?4?According to the results of field test,the physical adsorption,cation exchange adsorption,nitrification,denitrification and mineralization of organic matter in the percolation layer were analyzed.The main effects of the percolation layer on total phosphorus are adsorption precipitation,ion exchange adsorption,Phosphate precipitation and dissolution,the biological effects of aquatic plants is weak.The environmental behavior that caused the concentration of effluent nitrogen and phosphorus to be higher than that of Long Lake's surface water is:the mineralization of ammonia nitrogen released by organic nitrogen and the mutual transformation between various forms of phosphorus.?5?The influencing factors of conversion of surface water to groundwater nitrogen and phosphorus include filter bed structure characteristics,infiltration methods,lake water quality,COD_Mn and Fe content in water,sediment and Longhu historical environmental transformation results,including filter bed structural characteristics,lake water quality,Longhu environmental transformation history is the main factor that affects the percolation water above surface water.The experimental results show that the influence of the filter layer characteristics on the migration of nitrogen and phosphorus is reflected in the control of the thickness of the filter layer and the hydraulic retention time of the nitrogen and phosphorus in the filter layer.The contents of nitrogen and phosphorus in Longhu sediments increase with the increase of depth.The organic matter rich is the material source of mineralization of organic nitrogen.