Study And Application Of Ecological Restoration Effect Evaluation Method For Medium And Small Rivers Reach

Medium and small rivers are widely distributed in China.As the “capillary” of aquatic ecosystems,they play an important role in contributing water and nutrients to the “The Great Artery——big river”.Compared with the big river,the medium and small rivers in more cities are more seriously disturbed by human activities,and the role of providing a better living environment for the people is more prominent.Different from the previous water pollution control that focuses on the improvement of water environment quality,river ecological restoration pays more attention to the functional restoration of ecosystems.The function orientation of river is closely related to its own ecological characteristics and the surrounding human activities.The key points of ecological restoration in different functional river reaches should also be differentiated.It is of great significance to formulate the evaluation method of ecological restoration effect at river section scale for scientific guidance of river ecological restoration.Based on the different functions of medium and small rivers,this paper constructs the evaluation methods of ecological restoration effect of different types of rivers,and applies them to the typical medium and small river——Qingyi River.The main research contents and conclusions are as follows :(1)A method of river section classification is proposed,which conforms to the dual attributes of “natural-social” of medium and small rivers.Firstly,according to the region where the river flows,the river reaches that flow through the built-up areas of cities at the county level and above(including county towns)are divided into urban river reaches,and the river reaches that flow through the built-up areas of township governments and other areas are divided into rural reaches.Secondly,based on the water function zoning and water environment function zoning,combined with the river function survey results,the dominant function of the river is determined,and the river is further divided into “ecological/service/dual” functional “urban/rural” river reaches.(2)The evaluation method of ecological restoration effect for different types of river reaches is established.Firstly,using the method of frequency analysis and theoretical analysis,an evaluation index system covering 17 indicators is constructed from6 criteria layers of hydrology,water quality,habitat,riparian zone,aquatic organisms and water services.Secondly,according to the results of the questionnaire survey,the importance of indicators is sorted,and the characteristics of different types of river sections are identified and weighted differently.Thirdly,two sets of comprehensive evaluation criteria of ecological restoration effect based on restoration status and restoration degree are established.When the evaluation results obtained by the two methods are inconsistent,the poor evaluation results are the criterion.Finally,the cluster analysis method is used to identify the factors that affect the effect of ecological restoration,which provides a reference for improving the effectiveness of ecological restoration.(3)The types of Qingyi River reach and the causes of ecological environment change were analyzed.Firstly,the Qingyi River and its main tributaries were divided into five reaches,namely,the upper reaches of the Qingyi River in Changge City,“ecological functional rural reach”,the middle reaches of the Qingyi River in Changge City-Xuchang City,“service functional urban reach”,the lower reaches of the Qingyi River in Xuchang City,“dual functional rural reach”,the tributaries in Baling River,“dual functional rural reach”,and the tributaries in Xiaoni River,“ecological functional rural reach”.Secondly,the investigation results of the ecological environment of different reaches before the restoration in 2017,after the restoration in 2019 and during the operation period in 2021 showed that the engineering restoration had achieved remarkable results,but the water quality of the tributary Baling River couldn’t reach the standard stably,and the biological structure still showed a trend of degradation.The ecological structure of the lower reaches of Xuchang City in the Qingyi River was not stable.(4)The ecological restoration effect evaluation and factor diagnosis of Qingyi River were carried out.Firstly,based on the ecological environment survey data of different river reaches after restoration in 2019 and during the operation period in 2021,unified weighting before method optimization,single standard evaluation based on restoration status,differential weighting after method optimization and double standard evaluation based on restoration status and restoration degree were carried out.The evaluation results before and after the optimization of the method show that the repair effects of urban and rural reaches after repair and during the operation period were medium,but the non-differentiation of the weights before optimization leads to the high score of the indexes with low importance after weighting,which made the total score after optimization higher than that before optimization.Secondly,the identification results of the optimal factors after restoration based on clustering show that the optimal factors of Qingyi River and Xiaoni River were aquatic organisms,and the optimal factors of Baling River are aquatic organisms and water quality.It was necessary to further strengthen the control of pollution sources into the river,implement water quality maintenance and improvement,optimize the recovery of aquatic organisms,carry out continuous monitoring and evaluation,and improve the consolidation effect.