| The Yellow River is the mother river of the Chinese nation,I t is an important agricultural and animal husbandry production base and industrial cluster such as energy and chemical industry in China.Due to the high degree of vulnerability of the ecological environment and the impact of human activities such as grazing,water conservancy projects and urban wastewater,there is less biodiversity in the basin,the ability of ecosystem self-repair and renewal is weakened,and the problem of water and soil loss is more serious.The Gansu section of the Yellow River is located in the upper reaches of the Yellow River basin and is an important water conservation and recharge area.Its water ecological health and water pollution level play an irreplaceable role in the ecological construction and stable development of the whole basin.Macrozoobenthos are an important part of the river ecosystem and provide key ecological functions for the material circulation,energy flow and water self-purification of the river.Different species have different sensitivity to environmental changes and tolerance,making the macrozoobenthos community very sensitive to water environmental pollution,human destruction,habitat change,etc,Therefore,it is widely used as indicator species for water ecological health assessment and water quality monitoring.Based on the sampling survey of m acrozoobenthos community and water environment index in Gansu section of the Yellow River,based on the structure and diversity distribution characteristics of macrozoobenthos community,this paper uses the method of combining water quality biological index evaluation and water body physical and chemical monitoring to evaluate the water quality health of the investigated river section,and explores the response of macrozoobenthos on different river sections to environmental factors,for the purpose of water ecological health assessment,biodiversity protection provide scientific basis and reference for water environment investigation and monitoring.The main research results are as follows:（1）The standing stock and biodiversity level of m acrozoobenthos in the Gansu section of the Yellow River are relatively low,and the species composition in the downstream section is significantly richer than that in the upstream section,and the community structure shows significant spatial differences along the route.In the two surveys,36 species of macrozoobenthos were collected,a total of 668,belonging to 3phyla,6 classes,14 orders,26 families,including 25 species of arthropods,a total of447,6 species of molluscs,a total of 209,and 2 species of annelids,a total of 12;The dominant species of the surveyed river reach are five species,namely,hook shrimp,cross striped stink bug,short foot mud beetle,beautiful white shrimp,and egg turnip snail;The density,biomass and diversity of m acrozoobenthos all show that the downstream section is higher than the upstream section,and the biodiversity and abundance of the reservoir and wetland reach the peak;I n terms of community similarity,the similarity of sample points in the upstream section and the downstream section is relatively low,and there are few common species in the community.The difference in species composition between the reservoir and the we tland is very obvious compared with the natural river section.（2）The health status of water quality is evaluated by combining biological index and physical and chemical monitoring of water body.The results show that the BI index and the comprehensive pollution index are consistent in the assessment of water quality,and the biodiversity index exaggerates the risk of water pollution.The BI index results show that the overall water quality in the study area is light pollution level,the water quality in the reservoir and wetland is the best,and the water quality in the upstream section is better than that in the downstream section;The Kalander biomass index shows that the water quality is in the middle trophic level as a whole,and the nutritional status of the water quality in the downstream section is higher than that in the upstream section;The comprehensive pollution index results show that the water environment quality is generally Class II and III,and the water body is at the light pollution level.The upstream pollution source is mainly potassium permanganate,and the downstream section is mainly TP,TN and NH3-N.（3）According to the correlation matrix and redundancy analysis（RDA analysis）,the main environmental factors affecting the benthic co mmunity in the Gansu section of the Yellow River are water temperature（WT）,potassium permanganate(COD Mn),TP,TN,salinity,electrical conductivity（EC）,DO and p H;The key drivers of the disturbance to benthic community in different regions are differe nt.The upstream section is mainly p H,TP and salinity,while the downstream section is mainly p H,water temperature,TP,NH3-N.（4）Through investigation,it is found that the water ecological status of the upstream section is greatly affected by natural factors,while the downstream section is greatly affected by human activities such as water conservancy projects and urban construction.The upstream section has high altitude,bad weather conditions,rapid flow,low coverage of aquatic vegetation,small p opulation and low intensity of human activities,resulting in poor biodiversity and clean water quality;Due to the existence of reservoirs,cascade power stations and constructed wetlands in the downstream section,the river hydrological regime has been i mproved,the habitat conditions are relatively stable,and the biodiversity is high.However,the discharge of urban industrial and agricultural wastewater causes high nutrient content in the water body,and the water quality and health status are worse th an those in the upstream section. |
