Spatio-temporal Distribution Characteristics And Water Environmental Quality Evaluation Of Macrozoobenthos In The Heihe River

As an important ecological channel between land and water,rivers not only maintain the earth's water cycle and regional ecological balance,but also play important ecological function in regulating climate,reshaping topography and maintaining biodiversity.However,in recent years,with global climate changing,differences in hydrological conditions,and continuous disturbances to the water environment caused by human activities such as dams and interceptions,industrial and agricultural sewage discharges,the self-regulation function of river ecosystems,to a large extent,has gradually weakened.It has substantially altered the original habitat and posed a serious threat to river health.Macrozoobenthos is an intermediate link in the food chain structure of the river water ecosystem.It has the characteristics of wide distribution,poor mobility,small range of activities,and is sensitive and vulnerable to changes in the water environment.Its community structure and diversity can reflect different habitat characteristics,and can accurately reflect the pollution status of the water environment in the past period of time.To this end,this paper conducted field monitoring of macrozoobenthos communities and water environmental factors in the upper and middle reaches of the Heihe River,explored the temporal and spatial distribution characteristics of macrozoobenthos and functional feeding groups and changes in biodiversity,and analyzed macrozoobenthos and the relationship between the community structure of the functional feeding group and the physical and water environmental factors.At the same time,the biological index and water chemical index are used to evaluate the water environment quality in the study area,which provides a theoretical basis for inland river biodiversity protection and water ecosystem restoration.The main findings are as follows:(1)A total of 52 species of macrozoobenthos were collected in the two surveys,belonging to 32 families,3 phyla,7 classes,18 orders.Among them,39 species of arthropods,accounting for 74.00%of the total species,11 species of molluscs,accounting for 22.00%,and 2 species of annelids,accounting for 4.00%.The functional feeding groups of macrozoobenthos are predominantly predators and scrapers,accounting for 44.33%and 32.62%of the total species,followed by gather-collectors,accounting for 18.57%,and filter-collectors and shredders the least,accounting for 2.45%and 2.03%,respectively.There are significant temporal and spatial differences in the density,biomass and biodiversity of macrozoobenthos and functional feeding groups.The spatial change trend from highest to lowest as midstream,upstream main stream,upstream tributary,and temporally ordered as summer and autumn.Argyroneta,Damselfly,Palaemon modestus,Chlaznius sp.,Dytiscidae,Radix auricularia,and Suecinea sp.are the dominant species at this stage.The dominant species in the upstream tributaries and main streams are mainly cleaner types of species,and the middle reaches are pollution-tolerant species.the number of dominant species is the same in summer and autumn,but the composition is different.Argyroneta,Dytiscidae,Radix auricularia,and Suecinea sp.are common species in the two seasons.(2)Redundancy analysis(RDA)results show that the environmental factors affecting macrozoobenthos communities in different periods and regions are different.The main environmental factors affecting macrozoobenthos communities in summer are water temperature,dissolved oxygen,biochemical oxygen demand,salinity,chemical oxygen demand and total dissolved solids.Autumn is WT,Salinity,flow velocity,ammonia nitrogen,permanganate index,total phosphorus.The main environmental factors affecting the functional feeding groups of macrozoobenthos in summer are WT,DO,EC,BOD₅,Salinity,COD_Mn,TDS.In autumn,WT,COD,Salinity,NH₃-N,TDS,COD_Mn.Spatially,the upstream tributary community structure is relatively poorly correlated with environmental factors,individual points in the upstream mainstream are greatly affected by COD_Mn,NH₃-N,TP and Salinity,and the middle reaches are affected by WT,DO,BOD₅,Salinity,TDS,NH₃-N and COD_Mnhave a greater impact.(3)The comprehensive water quality labeling index method and BI index evaluation results show that there are significant temporal and spatial differences in the water quality of the upper and middle reaches of the Heihe River,and the overall water quality standards are Class II to III,which is clean to light pollution level,Some of them are in the middle of pollution.Spatially,the degree of water pollution is in the middle reaches>upstream main stream>upstream tributary;human activities such as industrial,agricultural and urban domestic sewage discharge exacerbate the pollution level of N,P and other elements.In seasons,the degree of water pollution is autumn>summer;the hydrological characteristics(water temperature,flow velocity)and biological activity of rivers in different periods have different dilution effects on water pollutants.Seasonal water quality with strong biological decomposition are relatively better,but the water quality is worse during periods of little precipitation and weak biological effects.(4)The evaluation results of the aquatic ecosystem based on the macrozoobenthos functional feeding groups parameters show that the middle reaches of the Heihe River have strong material circulation and transportation capacity,high coverage of aquatic vegetation,and good habitat stability,but the water quality is relatively poor;the upstream tributaries are affected by climate and river background values is that vegetation is sparse,water quality is good,but the habitat stability is poor;the impact of dams and interceptions in the upstream mainstream on the stability of the habitat is significantly greater than the impact of industrial and agricultural activities.Therefore,when using such indicators to evaluate inland rivers like Heihe,the regional habitat characteristics and climate differences should be fully considered,which has important reference value for accurately evaluating the health of inland rivers.