查干湖湿地浮游植物与环境因子关系的多元分析

Multivariate analysis of the relations between phytoplankton assemblages and environmental factors in Chagan Lake Wetland

采用野外采样调查的方法,结合聚类(Cluster)、多维排序尺度(MDS)、冗余度分析(RDA)以及Shannon多样性指数、Pielou均匀度指数、Margalef丰度指数等手段,研究了查干湖湿地2012年平水期(5月)和丰水期(9月)浮游植物的种群结构特征、多样性及其与环境因子的相关性。调查期间共发现浮游植物127种,隶属于5门53属,其中硅藻门52种,占40.94%,绿藻门46种,占36.22%;蓝藻门25种,占19.69%。从浮游植物丰度看,平水期蓝藻最为丰富(占丰度的39.85%),其次为硅藻(占36.19%)和绿藻(占21.33%),而丰水期绿藻(占70.84%)占绝对优势。查干湖湿地研究区可划分为主湖区和新庙泡两个区域,浮游植物丰度时空差异显著:其平均值为平水期(658.0×104个/L)>丰水期(459.3×104个/L),主湖区丰度是新庙泡的8—10倍。相关分析表明:平水期和丰水期浮游植物丰度均与盐度呈显著正相关;平水期浮游植物丰度与pH值、磷酸盐(PO3-4)显著负相关,说明平水期浮游植物丰度空间差异主要受盐度和营养盐的影响,主湖区盐度(52.0 mg/L)是新庙泡(16.0 mg/L)的3.3倍,同时主湖区的磷酸盐(PO3-4)(0.045 mg/L)是新庙泡(0.012 mg/L)的3.8倍;而丰水期由于营养盐没有显著差异,浮游植物丰度空间差异主要受盐度影响。除野外调查结果外,基于Bray-Curtis相似性计算的聚类和多维排序尺度分析也表明据研究区可划分为主湖区和新庙泡两个区域。RDA显示:影响查干湖湿地浮游植物分布的关键环境因子,平水期是pH值、TN和BOD5,丰水期是盐度、PO3-4和BOD5。平水期优势属喜低碱、低磷素、高氮素的生境,而丰水期优势属则喜欢微碱性、高盐度、高磷素、高BOD5的生境。调查期浮游植物优势种群为温带小型藻类,能迅速吸收营养盐并进行繁殖生长,在较高营养盐条件下可以形成较高的相对丰度。根据浮游植物生态指标对查干湖湿地水质污染程度进行现状评价表明查干湖湿地处于β-中度污染水平。

This study investigated the biodiversity and community structures of phytoplankton and their relations with environmental factors in Chagan Lake during the intermediate （May） and rainy season （September） in 2012. Combining field investigations with cluster analysis, multi-dimensional scaling （MDS） analysis and redundancy analysis （RDA）, and applying Shannon, Pielou and Margalef indices, the study identified a total of 127 phytoplankton species （belonging to 53 genera and 5 phyla）. Among these species, 52 were members of Bacillariophyta, 46 Chlorophyta, and 25 Cyanophyta, accounting for 40.94%, 36.22%, and 19.69% of the total phytoplankton species, respectively. In terms of algal populationdistribution, in the intermediate season Cyanophyta was the most abundant phylum of planktonic algae （ accounting for 39. 85% of algal population）, followed by Bacillariophyta （36.193%） and Chlorophyta （21.33%）, whereas in the rainy season Chlorophyta （70.84%） was the dominant phylum. Consisting of two connected parts （the main lake body and Xinmiao wetland）, Chagan lake was found to sustain significant temporal-spatial variations of phytoplankton populations. The abundance of phytoplankton in the intermediate season （averaging 658.0x 10^4 cells/L） was considerably higher than that in the rainy season （averaging 459.3x 10^4 cells/L）. In both seasons, phytoplankton abundance was found to be positively correlated with water salinity （i.e. greater salinity coinciding with higher phytoplankton populations）, and negatively affected by pH and phosphate （PO34-） concentration in the intermediate season. In either season, the abundance of phytoplankton in the main lake was 8-10 times of that in Xinmiao wetland. In the intermediate season, such discrepancy was caused by different salinity and nutrients in these two water bodies; salinity in the main lake （52.0 mg/L） was 3.3 times of that in Xinmiao wetland （16.0 mg/L）, whilst PO- in the main lake （0.045 mg/L） was 3.8 times of its concentration in Xinmiao wetland. In the rainy season, there was no significant difference in nutrient levels in the whole lake, so water salinity was the main factors affecting the distribution of phytoplankton. In addition to field investigation results, cluster and MDS analyses based on Bray-Curtis measures of similarity also illustrated significant discrepancy between the main lake and Xinmiao wetland in terms of phytoplankton abundance. RDA results indicated that in the intermediate season the key environmental factors influencing the phytoplankton assemblages were pH, total nitrogen （TN） and phosphate （PO34-）, whereas salinity, phosphate （PO34-） and 5-day biological oxygen demand （BOD5 ） were the key factors in the rainy season. In the intermediate season, dominant phytoplankton genera were those favoring low alkalinity, low phosphorus and high nitrogen levels. Rainy season benefitted genera that were more tolerant alkalinity, salinity, phosphorus and BOD5. Most dominant genera indentified in this study were micro-phytoplankton, common in temperate climate and capable of rapid multiplying and fast growing through nutrient assimilation, could form a higher abundance in rich nutrients. When phytoplankton was used as a bio-indieator in water quality evaluation, the results revealed that water quality in Chagan Lake was in β-moderately-polluted category.