Comparative Study On The Suitability Of Benthic Algae And Phytoplankton Applied In River Health Assessment

As the primary producer of aquatic ecosystem,algae can more comprehensively reflect the changes of the external environment and the effects of pollutants on the water environment and aquatic ecosystem than the traditional physi-chemical monitoring of water quality.Therefore,algae is often used as an indicator for river health assessment.Algae can be roughly divided into benthic algae and phytoplankton according to their habits in the river.Both phytoplankton and benthic algae have been applied for river health assessment in recent years.However,which of them are more suitable for river health assessment is still poorly studied.For this purpose,the physi-chemical characteristics of water environment and algae communities at 17 monitoring samples of the Jialing River,Wujiang River and Xiaojiang River were investigated from August to September,2015.We assessed tributaries health conditions of the Three Gorges Reservoir based on comprehensive pollution index?CPI?,benthic algae index of biological integrity?Be-IBI?and phytoplankton index of biological integrity?Ph-IBI?.Based on the results of water physi-chemical monitoring,the sensitivity of benthic algae and phytoplankton to the change of physi-chemical factors was compared.The main findings were as follows:During the investigation period,The benthic algae community was composed of 5 phyla,21families and 90 taxa,including 12 taxa?13.33%?of Cyanophyta,11 taxa?12.22%?of Chlorophyta,64 taxa?71.11%?of Diatoma,2 taxa?2.22%?of Xanthophyta and 1 taxa?1.11%?of Euglenophyta.There were 21 benthic algae taxa in each monitoring site,and the average Shannon-Wiener diversity index value was 3.20.The phytoplankton community was composed of 5 phyla,24 families and 87taxa,including 17 taxa?19.54%?of Cyanophyta,22 taxa?25.29%?of Chlorophyta,38 taxa?43.68%?of Diatoma,8 taxa?11.49%?of Pyrrophyta and 2 taxa?11.49%?of Gymnophyta.In addition,14 taxa of phytoplankton were detected on each monitoring site,and the average Shannon-Wiener diversity index value was 2.84.In order to comprehensively reflect the impact of human living,industry and agricultural production on water environment,12 monitoring indexes of water quality were selected,including pH,dissolved oxygen,total nitrogen,total phosphorus,ammonia nitrogen,permanganate index,chlorophyll a,cadmium,lead,hexachlorocyclohexane,parathion-methyl and pentachlorophenol.The comprehensive pollution index was calculated to evaluate the water quality of 17 monitoring samples of Jialing River,Wujiang River and Xiaojiang River.The CPI values of each monitoring site ranged from 0.17 to 0.47,with an average value of 0.31,and the overall water quality grading was"good".Water quality in Jialing River was better,the average CPI was 0.19.Contrastingly,the water quality in Wujiang River and Xiaojiang River were relatively poor,and the average CPI was 0.41and 0.37,respectively.The water quality was ranked as Jialing River?good?>Xiaojiang River?good?>Wujiang River?good?.The Jialing River was mainly affected by pH,TN,TP,COD_Mn and Cd,the Wujiang River was mainly affected by TN,TP and Pb.In particular,the TN content exceeds the Class V standard of the National Surface Water Environmental Quality Standard.The Xiaojiang River was mainly affected by DO,TN,TP,Cd,Pb and hexachlorocyclohexane.According to the least disturbed condition method,the CPI value of J1 and J5 monitoring samples in Jialing River were 0.17,and the water quality grading was"excellent",which can be used as reference samples for algae biological integrity evaluation.The other monitoring samples were damaged.The distribution range analysis,interquartile-range analysis,and correlation analysis of 22algae biological metrics including species composition,relative richness,community diversity and nutritional level were used in this study.Results showed that final Be-IBI included the total taxa number,Cyanophyta taxa number,Chlorophyta taxa number,Cyanophyta cell density,ratio of dominant taxa and Shannon-Wiener diversity index.The Be-IBI scores of all monitoring samples ranged from 9 to 35,with an average of 18.41,and the overall water quality grading was"medium".The final Ph-IBI obtained three core biological metrics,including cell density,diatom proportion and chlorophyll a content of algae.The Ph-IBI index of all sites was in a range of 2-16,with an average of 8.94,and the grading was"medium".As a whole,the results of two types of algae evaluation system showed the same trend,and the algal biological integrity assessment ranked as Jialing River?good?>Wujiang River?middle?>Xiaojiang River?poor?.Correlation between biological integrity of algae and water environmental factors was analyzed.Results showed that there was a significant negative correlation between the values of Be-IBI and CPI?correlation coefficient was-0.551,0.01<p<0.05?,but no significant correlation between the values of Ph-IBI and CPI?p=-0.405?was observed.Be-IBI value was negatively correlated with total phosphorus,permanganate index and lead?correlation coefficients were-0.494,-0.508 and-0.594,0.01<p<0.05?,and Be-IBI value was negatively correlated with hexachlorocyclohexane?correlation coefficient was-0.610,p<0.01?.Ph-IBI value was negatively correlated with hexachlorocyclohexane?correlation coefficient was-0.605,0.01<p<0.05?,and Ph-IBI value was positively correlated with pH?correlation coefficient was 0.657,p<0.01?.Based on the results of comprehensive pollution index?CPI?and the changes of water environmental factors,benthic algae are more sensitive and accurate than phytoplankton.Moreover,there were more core bio-parameters of benthic algae than phytoplankton to construct the biological integrity.Therefore,it is more appropriate and accurate to use benthic algae than phytoplankton in river health assessment.