In-situ Ecological Restoration By Aquatic Plants In Dishui Lake

Dishui Lake,which is a multifunctional artificial lake that includes the function of climate regulation,leisure and entertainment,and landscaping,is the representatives and symbol of of Shanghai Lingang New City.However,it has become eutrophication because of the low water quality of its diversion channel.Moreover,the salinity of Dishui Lake is high because it is located near the East Sea.Therefore,it is very important to improve the water quality of the diversion river and inhibit the eutrophication of Dishui Lake.Nine different kinds of indigenous aquatic plants were chosen in this research to investigate their purification ability and salt tolerance of water.The in-situ ecological restoration technology of aquatic plants was used for aquatic plant communities,and water body ecological restoration was carried out in Port C of Dishui Lake.Then the river health assessment was established by comprehensive assessment method.The application of ecological restoration technology in Port C of Dishui Lake could play an important practical role in improving the health of river ecosystems,and provide engineering application guidance in the other polluted rivers.The research results were as follows:All of the nine aquatic plants exhibited obvious purification effects and strong salt tolerance on eutrophic water.The removal rate of TN,TP,NH4⁺-N and CODCr could achieve 50.0%⁹7.9%,75.7%⁹9.9%,55.9%⁹5.9%and 57.2%⁶7.9%respectively.The removal efficiency of emergent and submerged plants is stronger than that of floating plants.The dynamic model was used to simulate the variation tendency of main water quality indext which was influenced by time.The results showed that most of the water qulity index were well fitted,which indicated that the selected aquatic plants have a long-term purification effect on polluted water.According to the results of high-throughput sequencing,the proportion of Proteobacteria was the highest in all of the nine aquatic plants,which indicated that it played an important role in improving water quality.Among the emergent plants,the lethal salinity of Phragmites communis,Canna indica L.,Lythrum salicaria L.and Iris pseudacorus L.were 7,7,5,3 g·L^-1,respectively.The lethal salinity of Myriophyllum verticillatum L.,Hydrilla verticillata,and Potamogeton distinctus were7,5,3 g·L^-1,respectively.The salt-tolerance ability of Hydrocotyle vulgaris was higher than that of Nymphaea L,which was 5 g·L^-1.Nymphaea L possessed a week salt-tolerance ability,which could only survive salt with 3 g·L^-1.Based on the experimental results and the field investigation,the in-situ ecological restoration technology of aquatic plants was used for aquatic plant communities.Using different aquatic plants for different purification and salt tolerance,landscape water buffer zone,emergent and floating plants area,emerging-submerged-floating plants area,underwater area and native plant zone were used in the experiment site.The demonstration water restoration project was designed and applied in Port C of Dishui Lake to improve the quality of the water environment.In general,TN,TP,NH4⁺-N and CODMn were all exihibed a decreasing trend,and the salinity and chlorophyll were decreased.The dissolved oxygen and transparency were increased.The water quality improved gradually with the demonstration function section.Different sections have different purification capabilities for pollutants.The landscape water buffer zone had a better removal effect on NH4⁺-N,the emergent and floating plants area had the strongest removal capability for TP,and the underwater area had a higher removal rate for CODMn,and the native plant zone had relatively strong purification ability for TN.The results showed that the ecological restoration technology had a significant purification effect,and improved water quality effectively.At last,the evaluation index system of river health was established by comprehensive assessment method,which was composed of three criteria layers?water quality characteristics,river structure characteristics,ecological characteristics and social service function?and 19 criteria layers.According to the characteristic of each indicator and Analytic Hierarchy Process,an appropriate scoring standard and weight could be determined.Based on the evaluation of river health and indicator data,the ecological health comprehensive index was used to make an evaluation of Dishui Lake before and after the restoration.The results showed that the ecological health comprehensive index of Dishui Lake before restoration was 3.300,which showed that the river was close to sub-health state.However,the ecological health comprehensive index could achieve 3.887 after restoration,which manifested that the river ecosystem was closer to a healthier state and proved the validity of the water restoration project.