Study On Health Assessment And Health Influencing Factors Of Typical Small And Medium Rivers In Yichang City

There are a large number of small and medium rivers in China,which are widely distributed and closely related to human.As the “capillaries” of large river basins,small and medium rivers are of great significance in the material and energy cycle of the basin and maintaining the diversity of the ecosystems.Due to the relatively lower order of river,the selfregulation ability of the ecosystem of small and medium basin is generally weak,and practical problems such as frequent floods and unreasonable hydropower arrangements are more prominent.Relevant research on the health assessment of typical small and medium rivers can provide a theoretical basis for the protection and restoration of ecosystems.The research took three representative small and medium rivers(including Xiangxi River,Qiaobian River,and Manao River)in Yichang City as the research objects to conduct ecological system health diagnosis application research.First of all,the main stream was divided into some sections according to space and types,and the characteristics of the temporal and spatial distribution of basic elements of the water environment and water ecology of the basin are analyzed.Secondly,the ecosystem health index system of different types of small and medium rivers were constructed on the base of the classification of rivers(river sections).The subjective and objective combination weighting method and the fuzzy matter-element model are used to obtain the health assessment results of the river sections during the wet and dry seasons.The main external factors and corresponding mechanisms of the health of small and medium rivers have been comprehensively analyzed.The main research results are as follows:(1)Investigation of current status of water ecology.Based on the measured data of three rivers,the biological and habitat status of the regional water ecosystem is analyzed.The chemical aspect focuses on the analysis of the basic physical and chemical parameters and characteristic nutrient indicators of the water environment;the physical factors include basic hydrological elements,river sediments and riparian vegetation coverage related indicators;the biological aspect mainly discusses temporal and spatial distribution characteristics of the community structure of macrobenthos and phytoplankton.The results show that most of the parameters exhibit different degrees of temporal and spatial heterogeneity,among which the differences in nutrient concentration,channel sediment composition and structure characteristics of indicator species community are the most obvious.(2)Construction of health evaluation system for small and medium rivers.Based on the health connotation and the selection principle of evaluation indicators,a general indicator system for the health evaluation of small and medium river ecosystem is established,which is composed of common and individual indicators.Among them,there are 5 common(required)indicators and 17 individual indicators,which belong to different categories(including urban and rural sections,mountain sections and plain sections,flowing water sections and static water sections).The fuzzy matter-element model combined with subjective and objective combination weighting method is selected as the comprehensive evaluation method.At the same time,the set of weight coefficients of the criterion layer and the index layer in the evaluation system and the grading standard of evaluation indicators are determined.The relative value of the weight of the criterion layer is: water environment quality > indicator community structure > hydrology and hydrodynamics = river morphology and structure > pressure and service function.In order to improve the operating efficiency of the evaluation system and make up for the existing shortcomings,the ecological flow guarantee rate,flood control safety guarantee rate and eutrophication index are set as controlling indicators in the evaluation process.(3)Application of health evaluation model for small and medium rivers.According to the comprehensive membership degree value,the ecological quality grade and stable status of the river sections are judged in the wet and dry seasons.The evaluation results show that the overall health status of the study area during the dry seasons is slightly better than that in the wet seasons.There are 2 “sick” river sections throughout the year.Compared with the other two classification methods,the health differences between different land use conditions are the most significant.The comparison result with the biological evaluation method shows that the established comprehensive evaluation method is overall reasonable and has comparative advantages.Finally,based on the diagnosis results,the impact of human driving forces(including urban construction,agricultural non-point source pollution,water conservancy project construction and operation,and management mechanism)on the health of small and medium rivers is discussed from multiple perspectives,and management countermeasures and restoration measures for small and medium rivers are summarized.