Study On The Periphytic Algal And Evaluation Of The River Ecological Integrity In Downstream Of Jialing River

In the present study,artificial substrate periphytic algal samples were collected in downstream of Jialing River,from August 2015 to July 2016.We analyzed the composition,variation of diversity index and structure of periphytic algal on artificial substrates,and evaluated the water quality according with the characteristics of diversity of artificial substrate periphytic algal.Biotic integrity index of artificial substrate periphytic algal(P-IBI)which suits to the downstream of Jialing River was established and used to evaluate the river health.Main results were obtained as follows:(1)The results showed that there were 126 periphytic algal species belonging to 6 phyla and 46 genera found in the investigating region.In the whole year sampling period,the dominant periphytic algal community was Bacillariophyta(73.02%),92 species and 21 genera,Chlorophyta(13.49%),17 species and 14 genera,and then was Cyanophyta(7.94%),10 species and 6 genera.Speices of the Euglenophyta,Pyrrophyta and Xanthophyta were few,and other categories did not appear.The dominant population were composed by Synedra,Nitzschia,Melosira,Navicula,Fragilaria of Bacillariophyta,Ulothri,Stigeoclonium,Oedogonium of Chlorophyta,and Merismopedia of Cyanophyta.Richness of the total number of periphytic algal species was presented as Shuitu > Yanjing > Hechuan > Ciqikou > Jinzi,and as autumn > winter = spring > summer.The density and biomass of periphytic algal showed that the lower reaches of the reservoir area and reservoir area was significantly higher than the upper reaches of the reservoir area.Flow velocity,NO2--N,NH3+-N and N:P were significantly different between the lower and upper reaches of the dam(P<0.05).NO2--N,TP,PO43--P and N:P were significantly different between the Jinzi,Hechuan and Yanjing(P<0.05).Flow velocity was significantly different between the Shuitu and Ciqikou(P<0.05).According to the standard of TP and NH3+-N,water quality of the downstream of Jialing River was Ⅱ~Ⅲ.(2)The Shannon-Wiener diversity index and Pielou index displayed decreasing trend from upper to lower reaches.Shannon-Wiener index showed that Ciqikou was in β-mesosaprobic,others were in light pollution.Pielou index showed that all the sampling sites were in a state of mild pollution.Margalef index showed that all the sampling sites were in a state of heavy pollution.The similarity index of periphytic algal showed mildly similar in the most of surveyed river section,mildly similar between the different seasons and moderately similar between the individual seasons.We can draw a conclusion that the river in a large environmental changes and poor stability in different seasons.The diatom quotient suggests that it is oligotrophic water in the surveying river section,but the periphytic algal pollution index showed that all the sampling sites were in a state of heavy pollution.Wastewater biological system and saprobien indices showed that all sampling sites in the β-mesosaprobic to α-mesosaprobic transitional phase.In total,diatom quotient and pollution index were not suitable for water quality evaluation in downstream of Jialing River,however,wastewater biological system and saprobien indices were more reliable.(3)Based on the distributing range,discriminatory power and Pearson’s correlation analysis of the 30 candidate indexes,eight metrics,including number of genera of Bacillariophyta,percent of Bacillariophyta taxa number,percent of Chlorophyta taxa number,percent of Chlorophyta cells density,percent of Nitzschia cells density,Shannon-wiener index,diatom index,motility diatoms percentage were selected to establish the biotic integrity index of artificial substrate periphytic algal(P-IBI)evaluation system.Three score system,four score system and ratio score system were used to get metrics into a uniform score for all the sampling points,and the results showed that Jinzi and Hechuan in the state of health,Yanjing and Shuitu in the sub-health to good-fair transitional phase,Ciqikou in the state of sub-health.According to the results of three methods,three score system which based on the standard of reference points and four score system which based on the standard of all points more reliable.The Pearson’s correlation analysis showed that the P-IBI was significantly correlated with altitude,oxidation-reduction potential and nitrite nitrogen(P<0.05).(4)On the whole,water quality of the upper reaches of the reservoir area was better than the reservoir area and the lower reaches of the reservoir area.Compared with the results of the biodiversity index and algae biological indicator,P-IBI for river health was more sensitive and accurate.