桂江流域附生硅藻群落特征及影响因素

Abstract

The distribution pattern of epilithic diatoms in the Gui River basin in relation to water quality,land use and topography was investigated by principal component analysis(PCA),corresponding analysis(CA),canonical correspondence analysis(CCA) and partial CCA.Twenty-four sites were sampled throughout the basin,ranging from the mainstream to first order streams.The data indicated that electrical conductivity(EC) increased from upstream to downstream,while other water quality parameters varied across wide ranges.A total of 112 diatom taxa were found in the basin,but only 37 taxa or more were observed in more than 5% of the samples.The most abundant species were Achnanthidium minutissimum,A.pusilla,A.tropica and Cymbella laevis,in order of abundance.Three different groups of taxa were identified,located in the headwater,middle and lowland zones of basin.Nitzschia recta was the dominant species in the lowland zone,A.lanceolata,Amphora montan,and Planothidium frequentissimum were more abundant in the middle zone,while high species diversity was typical of the headwaters.Biological Diatom Index(IBD) and specific PolluoSensitivity Index(IPS) were significantly related to many parameters including Chl.a,NH4-N,altitude,sub-basin catchment area and land use.The first two Principal component analysis axes explained 56.20% of the water quality variance,with the first axis significantly related to NH4-N,NO3-N and TN,and the second axis significantly related to water temperature,pH,EC and dissolved oxygen(DO).The first two Canonical correspondence analysis(CCA) axes collectively explained 28.60% of the species-environment variation.The first CCA axis was significantly positively related to water quality(EC,temperature,NH4-N,NO3-N,and TN),significantly negatively related to land use(areas of urban,agriculture and forest),and significantly positively related to topography(basin areas,altitude and slope).The second two CCA axes were significantly positively related to turbidity.Partial CCA analyses showed that water quality explained a high proportion(48.50%) of the variance,while land use and topographic factors explained 7.20% and 17.50% of the variance respectively.The results indicated that the distribution of diatom assemblages in the Gui River basin was strongly related to water quality parameters,as expected,but was also sensitive to land use and topography.