Study On The Purification Of Nitrogen And Phosphorus In Agricultural Runoff By The Wetland Project Of The Lakeside Buffer Zone In The Erhai Lake Basin

As the nearest ecological barrier of the lake,the lakeside zone plays an important role in reducing non-point source pollution before into the lake and protecting the water quality of the lake.Erhai Lake is a typical plateau lake with a fragile ecosystem.The construction of the lakeside wetland project is conducive to the restoration of the water environment and its water ecology,as well as the enhancement of the water environment’s carrying capacity.In this study,9 constructed wetland in the Haixi area of the Erhai Lake Basin were selected to analyze the characteristics of water pollution of constructed wetland in different regions of the Haixi area,which was to explorate the microbiological mechanism of nitrogen and phosphorus purification of various process types of wetland projects in the demonstration area.Last but not the least,the types of processes suitable for promotion in the wetland restoration of the Erhai Lake Basin were summarized,which provided a theoretical basis for the restoration of the lakeside wetland in the Erhai Lake Basin.The main conclusions of this research are as follows:（1）The nine wetland projects in the study area are divided into two regional wetlands,i.e.the northern and the southern wetlands,according to the nitrogen and phosphorus concentration of the upstream inflow,and Dali Town is the boundary.The influent of the southern wetlands such asρ（TN）、ρ（NH₄⁺-N）、ρ（NO₃^--N）、ρ（TP）、ρ(PO₄^3--P)ranges of8.32～30.84mg/L、0.177～0.85mg/L、4.99～29.11mg/L、0.208～1.207mg/L、0.192～0.911mg/L,respectively.The influent of the southern wetlands such asρ（TN）、ρ（NH₄⁺-N）、ρ（NO₃^--N）、ρ（TP）、ρ(PO₄^3--P)ranges of 0.97～4.83 mg/L,0.08～0.69 mg/L,0.67～4.62mg/L,0.079～0.792 mg/L and 0.037～0.581 mg/L,respectively.The nitrogen and phosphorus concentrations of incoming water from wetlands in the southern area were high,while those in the northern area were relatively low.（2）During the monitoring period,the overall removal rate of nitrogen and phosphorus pollutants in each wetland project was in the dry season>rainy season.In the dry season,the wetland water intake was small and the HRT increased.From the analysis of removal rate,during the monitoring period,the wetland in Dazhuang Village had the highest TN removal rate in the southern area,the Zhonghegou wetland had the highest NH₄⁺-N and TP removal rate;and the Nanxingdeng wetland had the highest TN and TP removal rate in the northern wetland,Baishixi wetland has the highest NH₄⁺-N removal rate.In terms of pollutant removal per unit area,during the monitoring period,the southern area had the highest TN and TP removal performance in the Jiapeng Village wetland,and the NH₄⁺-N removal performance was the highest in Zhonghegou wetland;the northern area had the highest TN,TP and NH₄⁺-N removal performance.All of them are Yangbogou wetlands.（3）According to Spearman rank correlation analysis and redundancy analysis,wetland inflow conditions（MLR and HLR）are the main factors that significantly affect purification performance in lakeside wetland projects.Appropriate HLR and MLR can obtain better wetlands.Purification performance.Through regression interval analysis based on the influent parameters HLR and purification performance（RE and MRR）,it is obtained that when the HLR of the lakeside wetland system is in the interval of 0.6-1.4m³/m²/day,the wetland system can obtain a relatively good nitrogen and phosphorus reduction effect.However,the wetland has poor resistance to hydraulic load impact,resulting in lower HRT,and the performance of wetland purification of pollutants is still poor.（4）The preliminary exploration results of the nitrogen and phosphorus purification capacity and microbial mechanism of each unit process type in a typical wetland show.During the monitoring period,the surface wetlands showed the highest removal efficiency of TN and NH₄⁺-N,and the ecological gravel ponds were the second.The ecological gravel ponds showed the highest NO₃^--N removal rate,and the removal efficiency of ecological ponds and the surface wetlands were both second to the ecological gravel beds.The highest removal efficiency of TP was in the surface wetland,followed by the ecological gravel pond,and the sedimentation pond is the lowest.In general,the surface wetlands showed the best interception and purification effect of nitrogen and phosphorus,followed by the ecological gravel ponds.The possible reason is that the abundance of Proteobacteria and Firmicutes in surface wetlands was relatively high,which was attributed to the strong nitrification-denitrification ability of the surface wetlands.The abundance ofγ-Proteobacteria in the ecological gravel ponds was the highest,which promoted the removal of NO₃^--N.The dominant bacteria in each unit are Arthrobacter and Bacillus.The relative abundance of Arthrobacter in the LST pond was the highest,which was 20.6%.