| Chaohu lake is one of the five largest fresh water lake in China. Based on its special status of supply water, the eutrophication and contamination of Chaohu lake are always attented by domestic and foreign experts and scholars. Planktonic algae and other aquatic plants are primary producers of aquatic ecosystems, their existence states and abilities of absorption and enrichment of nutrients and pollutants, which are significantly influence by water quality, reflect the state of water eutrophication and pollution.In this dissertation, the basic data and recently related literature were fully studied. Based on Western Chaohu lake was the research object,120 samples were collected systematically in three seasons. Combined with high precision testing technology, and using a variety of theory and methods such as biology, environmental science, geochemical and analysis technology, the characteristics of planktonic algae community structure and the dominant species'spatial and temporal distribution were systematically researched in Western Chaohu Lake, also the contamination status and the degree of the eutrophication were evaluated. Besides, the trace elements occurrence and enrichment coefficient distribution of planktonic algae were analyzed and revealed. What's more, the sources of trace elements and pollutants were preliminary explored.The results show as follows:(1)The pH of water was above 7, the dissolved oxygen content was about 6.37?14.86 mg/L. The algal density and chlorophyll content of planktonic algae were 6-1200×104/L and 0.88?23.15?g/L namely, shows a general change laws of summer> spring> winter. For five water quality parameters, each parameter had a positive correlation with other parameters, only significantly negative correlation was occurred in water temperature and dissolved oxygen content. (2)9 phylum,65 genus and 131 species of planktonic algae were checked out. Chlorophyta had the most species, followed by Cyanophyta, Bacillariophyta, Euglenophyta, Pyrrhophyta, Xanthophyta, Cryptophyta, Chrysophyte and Rhodophyta. What's more, according to the the average number of individuals, Cyanophyta showed the absolutely predominant in all algae phylum, while the numbers of Xanthophyta, Rhodophyta, Chrysophyte and Cryptophyta were lower. Besides, the increasing of species number and individual quantity of each algae phylum were found with the change of three seasons. (3)The absolute advantage species of planktonic algae was Microcystis, but the relative advantage species were not completely same in three seasons, in addition, the individual quantity of advantage algae species existed certain differences between timely and space distribution. (4)Special algae species, which were adapted in polluted environment, had higher proportion than ordinary algae species, among all species, the proportion of Microcystis was the highest. This phenomenon showed that these special planktonic algae species were growed strongly and widely distributed in Western Chaohu lake, also reflected that the eutrophication and contamination status was relative serious. (5)The numerical range of 5 algae community diversity indexes, including abundance, evenness, the advantage species dominance, the Microcystis dominance and the Shannon-weaver Index, were 1.59?7.83?0.61-0.94?0.48?0.81? 0.31?0.69 and 2.02?3.26 separately, the abundance and advantage species dominance were for summer> spring> winter, the evenness, Microcystis dominance and Shannon-weaver Index were increased in three seasons. The larger values of the bundance, evenness and 2 kinds of dominance were easily found in the estuaries of the lake and the vicinity of the island, otherwise, in spring and summer, the Shannon-weaver Index value near the added sampling points is bigger. (6)The Western Chaohu lake belonged to moderate nutritional and contaminated, etherwise, the degree of winter and spring was relatively light. What's more, the elevated degree of eutrophication was found in the estuaries of the lake and the vicinity of the island, but the distribution of contamination status in all regions was quite uniform. (7)The trace elements content of planktonic algae ranged from 0.001 ?g/g to 29882.456?g/g, the algae trace elements enrichment coefficients from water and from sediments were 23?1872397 and 0.001-6291.518 separately, they all showed an absolute seasonal change of winter> spring> summer. There was a big difference between these enrichment coefficients by various kinds of trace element and different lake regions, such as the concentration and the enrichment coefficient of nutrient elements were generally higher than that of toxic elements. (8)According to the result of cluster analysis, algae trace elements could be divided into four groups(1) Fe, Zn; (2) Cr, Ni, Pb; (3) Mn, Hg; (4) Cu, As and Cd. This classification result was similar to that of trace elements correlation analysis. (9) Planktonic algae trace elements were mainly derived from the absorption and enrichment of trace elements from water or sediment, the possible sources were industrial production, agricultural activities and the urban and rural life. |
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