The Effect Of Wetland Plants On Migration And Transformation Of Phosphorus In Sediments

Phosphorus is an essential and important limiting nutritious element of the wetland ecosystem.The sediments are the important reservoirs of phosphorus.Under certain conditions,sedimentary phosphorus can be released into the water,which is the main reason for endogenous loading that may lead to eutrophic water,thus threatens the stabilization of wetland ecosystem.Wetland aquatic vegetation are important biological groups.There had been some reports on the effects on migration and transformation of sedimentary P of the wetland plants,most of which reported submerged plants instead of emerged plants.Therefore,in this paper,I take Typha orientalis,Phragmites communis,Zizania caduciflora,Scirpus validus,Juncus gracillimus as experimental material,do a research on effects on N.P dissolving in the sediment of emerged plants and phosphorus transformation in the sediment,rhizospheric enzyme activity in related with phosphorus transformation and the total number of rhizospheric bacteria.Moreover,this paper illuminates not only the mechanism of effects on sedimentary phosphorus migration and transformation of the five wetland plants,It also provides guidance for bioremediation of eutrophic water.The main research results are as follows:(1)After planting the five wetland plants,the content of TN and TP in the overlying water are significantly lower than the control.After 60d,the content of TP in the overlying water of T.orientalis is the lowest among the five plants,which fell by 76.44%compared with the control.The content of TN and NH3-N in overlying water of Phragmites is the lowest,the amount of TN fell by 85.31%,while the level of NH3-N declined by 77.61%compared with the control.Although the amount of nitrogen and phosphorus in overlying water of different wetland plants are different,there is no significant difference in statistical analysis.The growth of T.orientalis has obviously advantage compared with Z caduciflora,there was no significant difference among other plants.(2)Phosphorus forms in the overlying water of different wetland plants are different.During the trial period,the content of TP decreases in the overlying water of T.orientalis results from the decline of the amount of DTP and PP,both content decrease in basic each half.And the rate of descend of both are the same.The content of TP in the overlying water of Phragmites,S.validus,Z.caduciflora and J.gracillimus reduced led by the decrease in DTP and PP,moreover,the rate of descend of PP fell even further than that of DTP.In short,the amount of DTP of these five wetland plants declines mainly because of a drop in DOP level,the rate of descend of DIP fell even further than that of DOP.T.orientalis has a stronger effect on DIP than other four wetland plants.After planted,they can effectively lower the pH but increase DO in the overlying water.The result of statistical analysis shows that there is no significant difference on the pH in the overlying water among five wetland plants.As for DO,T.orientalis is more significant than Z.caduciflora and J.gracillimus.There is no significant difference among T.orientalis,Phragmites and S.validus,T.orientalis has a more remarkable effect than Z.caduciflora and J.gracillimus.(3)After planted,these five plants can effectively change the content of TP in rhizospheric soil.There is no significant difference among T.orientalis,Phragmites and S.validus,while comparing with Z.caduciflora and J.gracillimus,T.orientalis'influence on the sedimentary TP is more remarkable.The content of sedimentary TP reduces mainly accounts for the decrease in the organophosphorus in T.orientalis which has different effects on various forms of phosphorus in the inorganic phosphorus.T.orientalis has more influence on total dissolved phosphorus than Z.caduciflora and J.gracillim,it also has a stronger effect of O-P athan Z.caduciflora and Juncus.The content of sedimentary TP of Phragmites and S.validus reduced mainly stems from the reduction in organophosphorus and inorganic phosphorus,of which the proportion has no significant difference.Phragmites has a much stronger effect on total dissolved phosphorus than Z.caduciflora,it and S.validus have a stronger effect on O-P.The content of sedimentary TP reduced mainly comes from the decrease in inorganic phosphorus of Z caduciflora and J gracillimus,and these two plants at the same time have stronger effects on Al-P transformation than the T.orientalis and S.validus.J.gracillimus also has a stronger effect on Fe-P than T.orientalis,S.validus and Z.caduciflora.After planted,the five wetland plants can markedly bring down the pH and increased sedimentary Eh,however,there are no significant difference among these five plants.The correlation analysis showed that the pH and Eh in the rhizospheric soil have positive correlation with pH and DO in the overlying water.(4)After the five wetland plants were planted,enzyme activity and the number of microorganisms have both increased in rhizospheric soil,but the enzyme activity of different plants are different T.orientaliscan can significantly improve acidic phosphatase,phytase and polyphosphate activity,furthermore,it can get the best results.After Phragmites and S.validus were planted,they significantly improved acidic phosphatase and phytase activity in the sediments,there is no significant effect between Phragmites and S.validus.After J.gracillimus was planted,they significantly improved phytase activity in the sediments.These three plants have no significant effects on acidic phosphatase and polyphosphate.J.gracillimus significantly improved polyphosphate activity,but the effect of T.orientalis is stronger than J.gracillimus.The statistical analyses suggested that the total number of the rhizosphere microorganism is the highest if T.orientalis was planted,while the rhizospheric efect of S.validus takes second place,and the other three plants have the least distinct rhizospheric effects.