Study On The Relationship Between Periphytic Algae And Environmental Factors During Wet And Dry Periods In Mijiang River

Determining the spatial and temporal pattern of algal diversity in rivers is the central issue of algal ecology,which can provide a scientific basis for the conservation and management of algal diversity.The spatial variation of environmental factors and algae in different river classes is one of the most typical spatial variations of environmental conditions and biomes.Although the taxonomic structure and the vertical gradient pattern of diversity of other biological groups have been extensively reported and some generally applicable rules have been formed,the functional diversity based on algae has been less studied,especially in terms of its relationship with environmental factors.In this context,we choose Mijiang River as the research area.Mijiang River is an ideal spawning place for salmon,and the Tumen River migratory fish breeding and releasing base is built on this river bank.As a natural river,Mijiang River is less disturbed by human beings,so it is of great significance and value to study the relationship between algae biodiversity and environmental factors in Mijiang River.By analyzing the spatial and temporal distribution of algae in Mijiang River and its response to environmental factors,this study provides a scientific basis for the protection and restoration of aquatic ecology in the basin.The following scientific questions can be verified in this study:(1)Does the community structure of algae in rivers of different grades have significant differences,and does biodiversity increase with the increase of river grades?(2)Are there significant differences in physical and chemical factors in rivers with different river grades and hydrological conditions?In this study,from June to August(wet season)and September to November(dry season)in2021,the algae growing in Mijiang River were collected and identified by a combination of qualitative and quantitative methods,and the physical and chemical properties of the water body were also determined.On this basis,the characteristics of hydrological,physical and chemical indexes in wet and dry seasons and among rivers of different grades were analyzed.The algae community structure in Mijiang River was analyzed,including the differences of algae species number,density,biomass and dominant species in space and time.The characters,α-diversity index and β-diversity index of algae were compared in different hydrological periods in Mijiang River.The main physicochemical variables affecting the community structure,biological characters,α-diversity index and β-diversity index of algae in Mijiang River were identified.The response relationship between algae community structure and environmental factors in Mijiang River basin was investigated to provide theoretical basis for water ecosystem protection in Mijiang River basin.The main research results are as follows:(1)A total of 262 species in 64 genera and 6 phyla were identified.The diatoms had the largest number of species,while chrysophyta and Xanthophyta had the lowest number.The algae species in the Mijiang River were different in the wet season and the dry season,but the diatoms were the dominant algae in the two hydrological periods.The density and biomass of algae in Mijiang River were different in both time and space.There were 6 dominant species of algae in Mijiang River in wet season and 5 dominant species of algae in dry season.Achnanthes lanceolata was the most dominant species.(2)In different hydrological periods,the water depth,river width and flow velocity of Mijiang River is significantly different.The water depth,river width and flow velocity of Mijiang River in wet season are higher than those in dry season.The depth,width and velocity of Mijiang River vary significantly among different classes of rivers.The p H and water temperature of Mijiang River have significant differences in different hydrological periods.The permanganate index,total nitrogen concentration and total phosphorus concentration of Mijiang River have significant differences in different hydrological periods.There are significant differences in the conductivity and total suspended solids of secondary streams.There were significant differences in chemical factors among rivers of different grades.(3)The α-diversity of the community,such as functional richness index(FRic)and functional differentiation index(FDiv),was calculated based on the seven biological traits of the biological algae,such as tolerance and sensitivity,and combined with the α-diversity of the biogenic algae,such as Shannon-Wiener.1)Species richness was significantly different in different hydrological periods and river classes.On the contrary,Pielou evenness index was not significantly different in different hydrological periods and river classes.Shannon-Wiener index showed no significant difference in different hydrological periods but significant difference in different river classes.On the contrary,Margalef index showed significant difference in different hydrological periods but not significant difference in different river classes.2)The functional richness index(FRic)and functional differentiation index(FDiv)of algae in Mijiang River were significantly different in wet season and dry season.The functional differentiation index(FDiv)and functional evenness index(FEve)of algae were significantly different among different classes of rivers,while the functional richness index(FRic)was not significantly different among different classes of rivers.The quadratic entropy function and functional dispersion index(FDis)of Rao showed the same distribution trend.Secondary rivers are lower than primary and tertiary rivers.(4)The study on the taxonomic β-diversity and functional β-diversity of algae in Mijiang River showed that the taxonomic β-diversity of algae in Mijiang River was significantly different in wet season and dry season.The functional β-diversity of algae in Mijiang River was significantly different in wet and dry seasons.There was no significant difference in the taxonomic β-diversity and functional β-diversity of algae in Mijiang River.The results showed that the turnover components were higher in different hydrological periods,and the difference in the composition of algae community between wet and dry periods was mainly due to the turnover process.The turnover components accounted for the major contribution of β-diversity in the classification,and the nested components were significantly lower than the turnover components.For functional β-diversity,nested components contributed more than turnover components.For the total β-diversity,taxonomic β-diversity was higher than functionalβ-diversity.(5)The main factors affecting the algae community structure in Mijiang River were p H,conductivity and phosphate.The main factors affecting algae community structure in Mijiang River during dry season were conductivity,total phosphorus,water temperature and dissolved oxygen.The environmental factors in Mijiang River had significant correlation with the functional α-diversity index and the taxonomic α-diversity index of algae in wet season.The environmental factors in Mijiang River had more significant influence on the functionalα-diversity index of algae in dry season.Water depth,velocity,conductivity,dissolved oxygen,p H,total suspended solids,ammonia nitrogen,nitrate nitrogen,phosphate and total phosphorus had no significant effect on any β-diversity index in Mijiang River during wet season.Environmental factors had little influence on the β-diversity of algae in Mijiang River during dry season.The present study showed that there were differences in the community structure of growing algae in different classes of rivers,but the diversity did not increase with the increase of river class,and the biodiversity of growing algae did not show the same trend with the increase or decrease of river class.The physical and chemical factors in different river classes and hydrological conditions are significantly different.In this study,the actual situation of algae in the reach of the river was initially mastered,the gap of algae biological monitoring in Mijiang River was supplemented,the relationship between algae and environmental factors was explored,and the protection and restoration of water ecology in the basin was provided with scientific basis.