A Study On The Community Structure Of Benthic Invertebrates And Their Relationship With Environmental Factors In The Mijiang River Of Jilin Province

The Mijiang River Basin is an important river system in northeast China and is rich in biodiversity,including the precious freshwater fish Masu salmon.As a carnivorous fish,the Masu salmon feeds mainly on benthic animals,such as water fleas and mayfly larvae.Macroinvertebrates,as one of the important food sources of benthic fish such as the Masu salmon,also play an important role in the ecosystem of the Mijiang River Basin,affecting nutrient circulation,water quality,aquatic vegetation and so on.In addition,the species and species richness of benthic animals can also show the differences between the characteristics of different habitats.Therefore,the survey of macrobenthic invertebrates in Mijiang River Basin is of great significance for maintaining ecological balance and sustainable development in this area.The sampling points in this study were divided into 5 points of first-class rivers,6 points of second-level rivers,and 4 points of third-level rivers.From June 2021 to February 2022,a combination of qualitative and quantitative methods was used to collect and identify river samples of each grade month by month,and the physical and chemical indicators of water environment were measured.Based on the physical and chemical indexes of river and interseasonal water environment at various levels of the Mijiang River,macrobenthic invertebrate community structure,biological functional traits and biodiversity indices at different taxonomic levels,combined with Generalized Linear Mixed Model,Canonical Correlation Analysis,Principal Component Analysis and other data analysis methods,the distribution characteristics of macrobenthic invertebrate communities in river grade and inter-season distribution were analyzed and significant influencing factors were found.To analyze the comparison of differences between river grades and seasons and the correlation between indices of diversity indices at different taxonomy levels;The main physicochemical factors affecting benthic community structure,biological functional traits and diversity indices at different taxonomic levels were identified,and the following scientific hypotheses were explored:（1）The significant difference of macrobenthic invertebrate community between seasons was greater than that between river classes;（2）The significance of biodiversity indices increased with the seasonal disturbance gradient,and the relationship between the indices showed convergence;（3）Among the environmental factors,permanganate index,water temperature and dissolved oxygen were the main driving factors of benthic community structure.The main research results are as follows:（1）In general,the species composition/density/biomass of different taxa and functional groups were significantly different between seasons than between river classes.A total of 511species of macrobenthic invertebrates were collected in summer,autumn and winter,belonging to 4 phyla,6 classes,17 orders,83 families,234 genera.Arthropods accounted for the largest number of species with 474 species（466 species of insecta,8 species of Phyla）,accounting for95.8%of the total species.The benthic species of other groups were relatively small,including12 species of Annelida（7 species of Oligochetes and 5 species of Bdelloid）,8 species of Mollusca,and 1 species of Nematoda.The dominant species of the Mijiang River are mainly the sensitive taxa Ephemerella sp,Cincticostella sp,Pteronarcys sachalina Klapalek,and Subgenus sp.In this study,29 functional traits of benthic animals were divided.Among them,13 traits,such as monotropism,large size,gill respiration,body wall respiration,precipitation and erosion,cold or hot eurytherm,narrow hypothermia or cold eurytherm,adherent,prostrant,swimmer,predator,predator,predator,and predator,had greater differences between seasons than between river classes.The significant difference of functional groups in summer was greater than that in autumn and winter.（2）The difference between functional diversity and species diversity in seasonal sequence was greater than that in spatial sequence.The functional richness of Functional richness diversity index is positively correlated with the Shannon Wiener index,Simpson index and Margalef index in time and space,which indicates that species richness and function richness show the same trend in time series and decrease with large environmental interference.There was a significant negative correlation between Margalef index and Functional evenness index functional evenness in time and space,and the significant values were summer>autumn>winter,first-class river>third-class river>second-class river,which indicated that both summer and first-class river were affected by tide and temperature,resulting in large disturbance.The lower the species abundance,the higher the functional evenness index.Functional turnover index,functional evenness index were significantly positively correlated,Functional richness diversity index,Margalef index were negatively correlated Significant differences indicated that under low temperature and freezing disturbance,the decline of winter habitat conditions led to species classification The richness and richness of functional groups decreased,and the uniformity of functional groups showed an increasing trend,which was due to the decrease of stream velocity in Mijiang River in winter,which resulted in more single and stable habitat conditions.（3）Seven physical and chemical indexes(WT,Cond,p H,TSS,PO₄^3--P,TN and TP)had significant differences between seasons,but had no significant differences between river grades.The results of Canonical Correlation Analysis showed that WT and TSS were significant factors affecting the zoobenthic community structure in Mijiang River basin in summer,WT and EC were major factors affecting the zoobenthic community structure in autumn,and Dept and COD_Mn were significant factors affecting the zoobenthic distribution in Mijiang River basin in winter.In summer and autumn,with the gradual increase of WT,small individuals and multivoltine groups such as Cricotopus sp and Phaenosectra sp accelerated reproduction,and their individual density and biomass increased accordingly.One-Way ANOVA showed that p H,WT,EC,TSS,TN,TP were negatively correlated with diversity index and functional group characters,while COD_Mn was positively correlated with diversity index and functional group characters.WT was negatively correlated with Semivoltine,Large,Tegument,Depositional and erosional,Climbers,scrapers,Predators,Simpson diversity index,Shannon Weiner index,Pielou evenness index,Functional richness diversity index,functional divergence.It was positively correlated with taxa turnover index and taxa diversity Index.COD_Mn index was negatively correlated with Sprawlers,Shredders,Depositional and erosional,but positively correlated with Simpson diversity index,Shannon Wiener index and Pielou evenness index.There was a significant negative correlation between p H and common and scrapers,and a significant positive correlation between p H and taxa turnover index and taxa diversity Index.The EC was positively correlated with Sprawlers,Shredders and Depositional and erosional,Simpson diversity index,Shannon Weiner index,Pielou evenness index and Functional richness diversity index.TSS were positively correlated with spiracle,Swimmers and Functional dispersion index,but negatively correlated with Small（<9mm）,Bi-or multivoltine.There was a significant negative correlation between TN and taxa turnover index and taxa diversity Index.There was a significant negative correlation between TP and Margalef index,Shannon Wiener index and Simpson diversity index.In this study,the generalized linear mixing model（GLMM）and one-way ANOVA were used to investigate the significant differences of macrobenthic invertebrates community structure among different river classes and seasons in Mijiang River Basin,and the correlation between diversity indices was studied to identify the main environmental driving factors affecting the benthic community structure.The investigation of benthic fauna in Mijiang River Basin is of great significance to understand the characteristics of community structure,biodiversity,water resources management and ecosystem services,and to provide scientific support and decision-making basis for ecological protection and sustainable development in the basin.