Effects Of Typical Submerged Plants On Phosphorus Migration And Transformation From Sediment To Overlying Water

At present,the dredging method is generally adopted for the treatment of sediments in lakes and rivers with severe eutrophication.There are some shortcomings such as large amount of engineering,unstable effect,short effective time,and great damage to the original lake and river ecosystem.Submerged plants,as the main medium for communicating sediments,three phases of overlying water and air in lakes and rivers,play an important role in the material circulation and energy exchange of the entire lake.Submerged plants can directly absorb the phosphorus in sediments,and can also indirectly inhibit the release of phosphorus in sediments by affecting the environment of overlying water and sediments,and is conducive to the stability of lake and river ecosystems.However,there are many kinds of submerged plants,and different submerged plants have different rhizome and leaf structure characteristics,and there are also differences in the effects of phosphorus migration and transformation in sediments.In this study,several typical submerged plants such as Vallisneria,Myriophyllum sp.,Ceratophyllum,and Elodea were planted in the sediment of lakes with severe eutrophication.The plants were statically cultured for 100 days in outdoor greenhouses.The content of various forms of phosphorus in the water,interstitial water and sediments,and the change of environmental factors in sediments.The main findings are as follows:(1)The bitter grass group,the foxtail group,the hornfish group and the Elodea group can effectively reduce the phosphorus content in the overlying water,interstitial water and sediment during the growth period,and maintain it at a lower level.The reduction of phosphorus in the overlying water and interstitial water was better than that of Myriophyllum spicatum and Ceratophyllum sp.,while the release of phosphorus in the sediments of Myriophyllum spicatum and Ceratophyllum sp.was greater than that of Vallisneriae and Elodea.(2)The bitter grass group,the foxtail group,the hornfish group and the Elodea group can effectively reduce the DTP concentration difference in the interstitial water-overlying water,thereby reducing the migration rate of DTP from the interstitial water to the overlying water.Vallisneria and Elodea have the best results.In addition,submerged plants have different effects on the release of various forms of phosphorus in sediments.It is easy to change the release of TP from sediments in each period:in the early stage of the experiment,submerged plants will effectively promote sediment accumulation.The release of TP;in the later stage of the experiment,when the submerged plant grows mature and the sediment environment changes greatly,the effect of each submerged plant on the release of phosphorus in the sediment will be transformed into inhibition of its release by promoting its release.(3)Different submerged plants absorb the phosphorus in some sediment-overlying water systems in the growth process,which effectively reduces the total amount of phosphorus in the sediment-overlying water.At the end of the experiment,the total amount of phosphorus in the submerged plants in the bitter grass group,the foxtail group,the hornfish group and the eucalyptus group increased by 84.54 mg,164.71 mg,175.50 mg and 62.30 mg,respectively.And during the growth process,the changes of pH and Eh in the sediment were affected,and the pH was shifted to neutral in different degrees.Eh continued to rise for a period of time at the beginning of the experiment,and then maintained at a weak reduction potential.Level.Each group of submerged plants indirectly affected the release of Fe/Al-P and the dissolution of Ca-P and OP by changing the pH and Eh in the sediment.(4)Selecting a single submerged plant,bitter grass,as a representative,by changing the initial phosphorus load of different overlying waters,it was found that the initial phosphorus loading of different overlying waters in the initial stage of the experiment affected the absorption rate of nutrients in the overlying water and interstitial water by submerged plants,but At the end of the experiment,the concentration of each form of phosphorus in the different concentration groups and the water in the interstitial water reached the equilibrium of the new dissolved adsorption equilibrium.This is mainly because the different phosphorus loads in the overlying water have different control effects on the growth of submerged plants,which indirectly affects the rate of absorption and utilization of various forms of phosphorus in the sediment.In addition,the initial phosphorus loading of different overlying waters affected the growth rate of submerged plants and the amount of phosphorus in plants.Under the experimental conditions,the submerged plants in the medium concentration group(0.1 mg/L)grew fastest.The highest phosphorus content in the body,and the absorption and utilization of phosphorus in the sediment-overlying water body is better than other groups.