Epiphytic Diatoms In The Middle And Lower Reaches Of The Yangtze River And Their Environmental Significance

It is of great significance for epiphytic diatoms to reconstruct the past environment changes, restore the ancient variation, test and cope with environment pollution in modern world, especially in lower reaches of the Yangtze Rive,where is relatively weak in the research of epiphytic diatoms. This thesis focuses on studying the relationships between bepiphytic diatoms and aquatic plants, the seasonal variation of epiphytic diatoms, the relationships between epiphytic diatoms and environment and so on.The record of epiphytic diatoms can be used to reconstruct the change history of aquatic vegetation in macrophytic lake.According to the research on the similarity coefficient of epiphytic diatoms in the lakes of the middle and lower reaches of the Yangtze River,it is found that epiphytic diatoms from the same type of aquatic plants represented high similarity coefficient, indicating strong similarity between epiphytic diatoms in aquatic plants and its dominant species in the lakes of the middle and lower reaches of the Yangtze River.For the middle and lower reaches of the Yangtze river lake aquatic vegetation and pick the diatoms in the different correlation analysis, found that different choices of accessory diatom to aquatic vegetation are significantly different, main show is Achnanthes minutissima, Cocconeis placentula and Gomphonema kinds of low plant crown plants showed a greater selectivity; Nitzschia palae, Fragilaria capucina and Navicula species in high plant crown on the submerged plant distribution, most has obvious selectivity; Cymbella affinis and Eunotia pectinalis on floating plant distribution, most showed very obvious selectivity for floating leaf plants; Synedra ulna and Achnanthes hugarica on floating vegetation distribution, most show of floating plants strong preferences; Epithemia adnata and Gyrosigma acuminatum in a water plant to the distribution of most, showed a greater selectivity.Except for the impact of aquatic plants, the epiphytic diatoms are closely related to water environment fators. CCA analysis showed that temperature which well distinguished epiphytic diatom assemblages of winter, spring and summer was the main factors that influenced diatom seasonal succession.For example, Fragilaria capucina,Nitzschia palae,Nitzschia perminuta and Gomphonema parvulum had the highest content in the late spring and summer; Cymbella sistula,Navicula menisculus,Navicula trivialis and Synedra nana appeared in low temperature season.Monte Carlo test showed that the conductivity was also significant factors to influence the diatom community(p<0.05).With the decline of lake eutrophication in in the lakes of the middle and lower reaches of the Yangtze River,the study of epiphytic diatoms above will lay theoretical foundation for restoring the ancient variation of lake and controlling lake pollution, showing a certain environmental significance.