Abstract
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 53genera 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 658.0 × 104cells /L) was considerably higher than that in the rainy season( averaging 459. 3 × 104cells /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( PO3-4) 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 3.3times of that in Xinmiao wetland( 16. 0 mg /L),whilst PO3-4in 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( PO3-4),whereas salinity,phosphate( PO3-4) 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-indicator in water quality evaluation,the results revealed that water quality in Chagan Lake was in β-moderately-polluted category.
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