Inhibition Of Sediment Phosphorus In Jiuli Lake Rerelease Suspension By Submerged Plants

Coal mining collapsed wetlands have the characteristics of short formation time and high nitrogen and phosphorus content in sediment composition,which are often accompanied by environmental problems such as endogenous phosphorus pollution release and intensified eutrophication.The use of submerged plants to inhibit sediment phosphorus release and control water eutrophication has low cost,high efficiency and broad application prospect.In this thesis,the coal mining collapsed wetland in Jiuli Lake,Xuzhou City,was selected as the research object.Firstly,the water quality and sediment phosphorus content were monitored,and the eutrophication and sediment phosphorus pollution were evaluated.Secondly,the inhibition effect of sediment phosphorus rerelease suspension was tested by three submerged plants,namely,Myriophyllum verticillatum L,Vallisneria natans and Hydrilla verticillata,Myriophyllum verticillatum L was selected as the pioneer species by comparing the inhibition effect of total phosphorus.Finally,the environmental factors of Myriophyllum verticillatum L inhibition of phosphorus release from sediments were analyzed.The response surface method was used to rank the effects of factors with high correlation on the inhibition effect of Myriophyllum verticillatum L on phosphorus release from sediments,and the optimal experimental conditions were determined.The main research results of this thesis are as follows:（1）The investigation of water quality and sediment phosphorus pollution shows that the overall water body of Jiuli Lake presents a mild eutrophication state.Phosphorus is the main limiting factor for algae growth and eutrophication in Jiuli Lake water body.The sediment phosphorus pollution reaches a severe level,and the endogenous release of phosphorus becomes an important source of water pollution in Jiuli Lake.（2）The three submerged plants had good repair effects on particulate phosphorus（PP）,soluble reactive phosphate（SRP）,total nitrogen（TN）and ammonia nitrogen（NH₃-N）in overhanging water,and could significantly increase dissolved oxygen content and p H value;The removal rate of Na OH-P was higher than that of HCI-P,inorganic phosphorus（IP）was higher than that of organic phosphorus（OP）,and the utilization degree of Na OH-P was higher than that of other phosphorus forms.All of them can effectively absorb phosphorus in overlying water,promote the sedimentation of particulate phosphorus（PP）,inhibit the re-release of phosphorus suspension in sediments,reduce the load of endogenous phosphorus,and achieve the effect of repairing eutrophic water and sediment pollution in Jiuli Lake.The inhibition effect of three submerged plants on phosphorus release was ranked as Myriophyllum verticillatum L>Vallisneria natans>Hydrilla verticillata.Myriophyllum verticillatum L showed outstanding inhibition of total phosphorus and could be used as a pioneer species to control internal pollution and eutrophication in Jiuli Lake.（3）The results of single factor experiment showed that the flow rate of 3-6cm/s had the best inhibition effect on phosphorus release from sediments.The flow rate of more than 9cm/s was not only unfavorable to plant growth,but also reduced the inhibition effect of Myriophyllum verticillatum L.The inhibitory effect was optimal when the planting density was 200 plants/m².The inhibitory effect did not increase linearly with the planting density of Myriophyllum verticillatum L.If the planting density continued to increase after reaching a certain limit,the inhibitory effect would decrease due to the competition of light and nutrition.The inhibition effect is best when the water depth is 50cm,and too low water depth will cause stress on Myriophyllum verticillatum L growth,thus reducing the inhibition effect.Response surface experiment results showed that the significant relationship between the three factors on the removal rate of total phosphorus was velocity>planting density>water depth.The optimal experimental conditions after response surface optimization were velocity4.5±1cm/s,planting density 240±20 plants/m² and water depth 45±10cm.Under these conditions,the removal rate of total phosphorus obtained by verification experiment was 70.11%.It is close to the predicted value of 72.19%,indicating that the prediction result of the model is good.The research results have practical guiding value for the ecological restoration project of submerged plants in Jiuli Lake.