Mechanism Study On The Spatial Distribution Pattern And Vertical Migration And Transformation Of Phosphorus In The Restored Wetland

Study on the migration and transformation of phosphorus and the risk of the release of phosphorus in the wetland is of significance to mechanism research of phosphorus removal in wetland system.The study was carried out in Qixinghu near-natural wetland in Tengzhou,Shangdong province.Samples of surface waters,macrophytes,sediments and overlying water were collected.The study analyzed the distribution regularity of phosphorus and the influences of environmental factors.On this basis,the mechanism of vertical migration and transformation was discussed.The diffusion flux of sediment and overlying water was calculated,and the risk of phosphorus release from sediments was analyzed.The results showed that:(1)In the wetland,the pollution load of various forms of phosphorus decreased along with the flow.1)In the surface water,soluble reactive phosphorus(SRP)concentrations decreased along with the flow.SRP was removed by 80% in plant-free area,94% in reed communities,and 91% cattail communities decreased,respectively,indicating the significant performance of macrophytes in SRP removal.Particle phosphorus(PP)was the main form of phosphorus in the midstream of surface waters,and was lower in macrophytes communities than plant-free area.The various forms of phosphorus in surface water was greatly impacted by pH and dissolved oxygen(DO).2)SRP concentrations in overlying water declinced along with the flow.Its removal efficiency reached 91% and 94% in reed and cattail communities,respectively,which were higher than that of plant-free area(81%).PP percentage was low at the inlet,then increased in the midstream.Phosphorus in overlying water was greatest impacted by pH.3)Along with the flow,various forms of phosphorus concentrations in interstitial water of plant-free area were generally higher than that of the macrophytes communities.The main phosphorus form of interstitial water was SRP which was accounting for 46%~91% of total phosphorus(TP).Phosphorus in interstitial water was greatest impacted by p H and conductivity(C).4)At the inlet section,TP contents in the sediment of plant-free area were as high as 1234.7 mg/kg which was much higher than that of reed and cattail communities.At the effluent section,sediment TP contents of plant-free area were reduced while the TP contents of macrophytes communities were still high.The greater the organic matter content,the greater the TP content of the sediments.The higher the alkaline phosphatase activity,the lower the contents of organic phosphorus.5)The height of reed was pretty large at L1 section with low phosphorus uptake.The stem diamet of cattail was small at X3 section,whilst high phosphorus uptake.(2)The plant-free area and macrophytes communities had different mechanism of vertical migration and transformation.1)At the longitudinal section of plant-free area,reed communities and cattail communities,TP,TDP and SRP were mainly distributed in the overlying water and interstitial water.TP,TDP and SRP in the inlet of the macrophytes communities mainly existed in the overlying water,while interstitial water accounted for a lower proportion.2)Phosphorus was mainly concentrated in the sediment,which was accounted for more than 95%,followed by the macrophytes,and was lowest in the water.3)In the plant-free area,various forms of phosphorus in interstitial water and NaOH-P in sediment had significant correlation.In the reed communities,various forms of phosphorus in surface waters and the overlying water was significant correlated,the same as that various forms of phosphorus in interstitial water and organic phosphorus(OP)in sediment.In the cattail communities,various forms of phosphorus in surface waters and overlying water had significant correlation,the same as that various forms of phosphorus in overlying water and interstitial water.4)The phosphorus in the wetland diffused from sediment into overlying water,because of the positive diffusion flux of sediment-overlying water in general.The maximum phosphate adsorption was small in the upstream because of the low phosphorus sorption index(PSI).The degree of phosphorus saturation(DPS)in macrophytes communities was higher than that in plant-free area,and PSI in macrophytes communities was lower than that in plant-free area,which showed phosphorus in sediment diffused into the ocerlying water more easily in the macrophytes communities.The eutrophication risk index(ERI)of wetland sediment showed the risk of phosphorus released from sediment was high,especially cattail communities.In the restoration of wetland,phosphorus diffusion from sediments to overlying water,suggesting that the wetland had high phosphorus release risk.Phosphorus concentrations in water and sediment in macrophytes communities were lower than the plant-free area,which meant that plants can reduce phosphorus pollution load.This study further correctly understood and evaluated water purification function of the wetland,and could provide the basis for the scientific planning of the sewage treatment ecological project in the near natural wetland.