Study On The Periphytic Algae Communitystructure And River Health Assessment In Dahewan River

Dahewan River is located in the downstream of Yalong River.Due to its unique geographical conditions,some stretch of the rivers still maintains the characteristics of the mountainous river after the completion of the dam.The periphytic algae are important key research contents in river ecology research.In this study,the periphytic algae in Dahewan River of Yalong River were investigated to provide guidance or reference for formulating reasonable river ecological protection strategy.From October2020 to October 2021,an annual（four seasons）investigation of the Dahewan River had been completed.In this study,the environment factors,the characteristics of the periphytic algae community structure,and their correlation were analyzed.And the river health was assessed by the index of biological integrity of periphytic algae（P-IBI）.And the sampling method of periphytic algae by an artificial substrate was explored.The results are as follows:（1）According to the results of water quality testing,the water quality was good.And the total phosphorus of the water was low.The water quality of the middle part（D-4,D-5）of the river was better than that of the up part and downs part of the river.The eutrophication index showed that the Dahewan River belongs to oligotrophic water and mesotrophic water.The seasonal differences of physical and chemical factors of the water were obvious.The relevant indicators of water nutrients in summer were the lowest.（2）A total of 173 species from Bacillariophyta,Chlorophyta,Cyanophyta,Euglenophyta,Dinophyta were detected in the samples of periphytic algae.And 122species belong to Bacillariophyta.The density and biomass of periphytic algae in winter and spring were higher than other seasons.In the wet season,the water level of the Dahewan River changes frequently and the turbulence had a great impact on the growth state of periphytic algae and sampling.There were 50 dominant species of periphytic algae.The number of dominant species of diatoms was 40 species.The change of dominant species on a time scale reflected the succession of the periphytic algae community.According to the index,the Biodiversity water quality of other sampling points was good except for some sampling points in the upstream and downstream which were affected by human factors.（3）The results of Pearson correlation analysis showed that the density of periphytic algae was significantly negatively correlated with water temperature（P<0.05）,and positively correlated with dissolved oxygen,nitrite concentration,and conductivity（P<0.05）;The richness index of periphytic algae was significantly positively correlated with total nitrogen concentration and nitrate concentration（P<0.05）.The results of redundancy analysis showed that WT,COD_Mn,TN,nitrate concentration,nitrate concentration,TAN,TP,AP,EC,and DO in water were the main factors affecting the abundance of main dominant species of periphytic algae.（4）The results of index of biological integrity of periphytic algae（P-IBI）showed that the river health in spring was the best,the second in winter and the worse in summer,and the healthy sampling points are concentrated in the middle of the river,which is consistent with the results of water quality result and the biodiversity index of periphytic algae.（5）The species diversity index of artificial substrate algae was close to that of natural substrate algae,and the Shannon-Wiener diversity index and Pielous evenness index of artificial substrate periphytic algae can remain stable within 3-15 days.The sampling results of the artificial substrate were more comprehensive than those of a natural substrate in algae species.And the sampling results of the artificial substrate can reflect the structural changes of the algae population.