Study On Distribution Characteristics Of Benthic Diatom Communities And Correlation Between Benthic Diatom Communities And Environmental Variables In Rivers Of QianGui ZhuJiang Watershed

According to the special hydrological and geological characters of QianGui ZhuJiang Watershed,35 sampling sites were ascertained.The structure of compositions, relative abundance,abundance,dominant species,biological diversity of benthic diatom communities were studied and the relationships among the compositions,abundance of benthic diatom communities and environmental paramenters were analyzed using multivariate analysis such as PCA,CCA.Meanwhile,the transfer-function models of the relationships between the distribution,abundance of benthic diatom communities and physic-chemical factors were developed.The study on structure of the regional benthic diatom communities showed that benthic diatoms identified belonged to 2 Classes,6 Orders,9 Families,60 Genus and totally 470 species(including subspecies and varieties) were identified.The dominant species were different in different sampling sites,but universal species were generally the same.Navicula genus was firstly the dominant genus,secondly Nitzschia and Gomphonema.Navicula parabilis had the highest species numbers,Navicula cryptotenella the next.The frequency and abundance of Nitzschia amphibian and N.inconspicua were much higher in waterbody in the genus. The frequency of Gomphonema parvulum and G.pumilum arisen was high in Gomphonema genus.The frequency of Achnanthidium biasolettiana var.subatomus and A.minutissimum was the highest in Achnanthes genus,which became the dominant species.TP was the most prominent factors influencing the distribution of benthic diatom communities.With further analysis using weighted average inference models,the results showed good predictive statistics for diatom composition and TP(R²=0.654,RMSE = 0.036;R_boot²=0.483;RMSE_boot=0.048).Indicator diatom species for TP was identified and assessed using weighted average optima and tolerances.Fifty-seven taxa were identified as biological indicators,which included Fragilaria vaucheriae, Achnanthidium convergens,A.lineare,Kolbesia suchlandtii and Nitzschia frustulum for high TP(>200μgl^-1)and Reimeria sinuata,Achnanthidium minutissimum var.scoticum, A.exile,Cymbella leptoceris,and Navicula cf.pseudokotdchyi for low TP(50-97μgl^-1). Velocity was the second significant factor influencing the distribution of benthic diatom communities.At least 76%of the species used in this inference model belong to genera that have selected adaptations for attachment to solid substrates.The most prominent diatom adaptation was short attached stocks.Achanthidium sensu stricto was the dominant genus(19%of the taxa selected) with this living form and mostly found at the velocity(current) optima of 0.11 to <0.5 ms^-1.Diatom richness followed a Gaussian distribution with the most taxa observed in waters with moderate levels of TP.This distribution supports the intermediate disturbance hypothesis which predicts that species richness and diversity will be highest under moderate environmental conditions.A Gaussian distribution was also observed for species richness under changing current flow.The relationships between major ions,conductivity and the distribution of benthic diatom communities from ZhuJiang Watershed within a Karst region of southwest China were quantitatively studied.The results showed that conductivity ranged from 20μS·cm^-1 to 2070μS·cm^-1 and Ca²⁺,(HCO₃^-+CO₃^2-) in calcific water columns were the dominant ions.Principal component analysis(PCA),correspondence analysis(CA), weighted averaging(WA) and correlation between ions,conductivity and communities of benthic diatoms showed that the content of major ions and conductivity all explained a statistically significant amount of the variation in composition of benthic diatoms communities.Ca²⁺,(HCO₃^-+CO₃^2-) and Na⁺ were the most significant factors affecting changes of diatom compositions.The corresponding indicator values(optima) for conductivity,major ions and the distributed character of diatom communities influenced by eight ions were ascertained.The correlation between content of heavy metals and benthic diatom communites distribution showed that As is the prominent factor affecting distribution of benthic diatom assemblages.The transfer-function model was established through linear correlation:Y=0.195+0.62X(P<0.01),species abundance and diversity reduce in samples of high As,Cu contents.However,the abundance of Achnanthes curtissima Carter,A.biasolettiana vax.subatomus Lange-Bertalot increase with the increase in concentration of As,Cd;relative abundance of Achnanthidium macrocephalum reach the highest in sites of high As,Cu contents,so they are indicative species tolerating high concentration of As,Cu.In sites of high Pb,abundance of Gomphonema spp., Gomphonema pumilum,Amphora montana are high,which stand for the indicative species assemblages of rivers polluted by Pb.COND,Na+and Hg elements were ascertained to be the prominent factors influencing the abundance of benthic diatoms using correlation and cluster analysis and the transfer-function model between COND,Na⁺,Hg element and abundance of benthic diatom were established through curve regression(y=1.61-70.51t+1178.68t²-1533.68t³,y=8.55-0.14t+0.001t²-2.34×10^-7t³å’Œy=-7.82+5.72t-0.09t²).This could be regarded as the criterion for evaluating the water quality of Karst region of Southwest China and provide theriocal basis for water-quality warning of diatoms.