桂江流域附生硅藻群落特征及影响因素

研究了桂江流域水质、土地利用、地理因素对河流附生硅藻群落的影响。结果显示,桂江流域电导率(Conductivity,Cond.)由下游至源头呈降低趋势,其它水质参数变化趋势不明显。主成分分析(Principle Component Analysis,PCA)显示前两个主成分共解释了56.2%的水质特征,第一轴反映了氨氮(NH4-N)、硝氮(NO3-N)、总氮(Total Nitrogen,TN)的变化梯度,第二轴反映了水温(WT)、pH、Cond.、溶解氧(Dissolve Oxygen,DO)的变化梯度。桂江流域硅藻特定污染敏感指数(Specific PolluoSensitivity Index,IPS)和硅藻生物指数(Biological Diatom Index,IBD)下游低于源头,差异不显著,与多项水质、土地利用以及地理因子呈线性显著相关。24个样地共发现112种硅藻,丰富度大于5%的37种,丰富度最大的几个种类依次为Achnanthidium minutissimum,A.pusilla,A.tropica,Cymbella laevis。对应分析(Corresponding Analysis,CA)显示桂江流域存在3个差异较大的硅藻群落,流域下游以Nitzschia recta为优势种,A.lanceolata、Amphora montan、Planothidium frequentissimum在中下游丰度较高,上游区域种类较多。典型相关分析(Canonical Correspondence Analysis,CCA)排序前两轴解释了硅藻群落变异程度的28.60%,CCA排序轴1与水质(Cond.、WT、NH4-N、NO3-N、TN)和土地利用(城市面积、农田面积、植被覆盖)显著负相关,与地理因素(流域面积、海拔、坡度)显著正相关,第二轴与浊度(NTU)显著正相关(P<0.05)。偏典型相关分析(Partial CCAAnalyses)显示,土地利用、地理因子、水质分别解释了桂江流域硅藻群落变异的7.20%,17.50%,48.50%。结果表明,桂江流域附生硅藻群落结构是水质、地理因子和土地利用共同作用的结果,水质起决定性作用,电导和不同形态的氮是影响附生硅藻群落结构的主要水质因素。

Epilithic diatom assemblages distribution in Gui River basin, in relation to chemical and physiographical factors

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.