Study On The Relationship Between Water Eutrophication And Aquatic Plants In A Karst Plateau Wetland,Caohai Lake

With the lake eutrophication, the submerged plants died out and aquatic plants diversity were decreased, it becoming a worldwide problem. For the lake ecosystem, diversification and exist of aquatic plant is indispensable. Restoring the ecosystem of eutrophicated lake is the key scientific issues to researchers, and they hold that it is the key point to learn the mechanisms and causes of the submerged plants wither away. In the process of lake eutrophicating, Ottelia acuminate, a plant of the second-class protection, is a classical species. It has be proclaim field perish in a number of lake at the Yunnan-Guizhou Plateau area. But there are differences remain to explain the cause, because the mechanisms and causes is still unclear.For learning the perish causes and eutrophicating sensitivity of Ottelia acuminate, clarifying the die away mechanisms of submerged plants in eutrophicating process, this study chose the Caohai lake as the subject to represent highland lakes on the Yunnan-Guizhou Plateau, adopted field survey of aquatic plants and Ottelia acuminate population, integrated sample determination in laboratory experiment, used principal component analysis(PCA) and sorting and classification of number to analyze the driving factors to change water quality of Caohai lake and the response of aquatic plant community, and applied ecological stoichiometry to research mechanism of Ottelia acuminate population at Caohai. The following are the main conclusions.(1) According to the calculation results of trophic state index, Caohai was divided into three regions, region A, B and C. there are significant differences between any two regions. Trophic state index(TLI) of region A was higher than 50, it consist of city drain area and boats sailing area. TLI of region B was in the range of 40.0 ~ 50.0, it cover the most areas from Caohai upstream Wangjiayuanzi to south-west Baijiazui. TLI of C region was in the range of 30.0 ~ 40.0, it involve the most areas of midstream where weak disturbance and lush aquatic plants. The result of principal component analysis on water quality show that: the main driving factors to change and distinguish water quality of Caohai were TN, TP, Chla and SD.(2) The field survey record that Caohai lake exist 15 families, 21 genera, 26 aquatic plants species. There are 15 species was submerged plants that account of 57.70%, 7 species was merged plants that account of 26.920%, 4 species was floating plants that account of 15.38%. Margalef abundance index change from 0.9478 to 1.8636, Shannon-Wiener diversity index lower and it change from 0.4302 to 1.7545, Simpson dominance index change from 0.3123 to 0.7867, Pielou evenness index change from 0.3877 to 0.7944. All index point that aquatic plants of Caohai has relatively low species diversity.(3) There were no significant correlation between aquatic plant diversity and water environmental factors in Caohai. But there are significant correlation between water environmental factors and submerged plant ? diversity, taxonomic diversity, it show that submerged plant was more sensitive than un-submerged plant. Trophic state index and submerged plant taxonomic diversity index showed a significant negative correlation in Caohai, Trophic state index and taxonomic diversity index aquatic plants showed a significant positive correlation. We hold that eutrophication driver to merged and floating invasive plants expansion, it also increased the level of classification of aquatic plants.(4) The result of redundancy analysis(RDA) show that the change and distribution of aquatic plant community mainly controlled by TN, TP, Chla, CODMn and SD.(5) With TN and TP increased, the population density and community cover of Ottelia acuminate increased at first and then decreased. It was a significant negative correlation with TLI. Combined with field investigation, all result show that Ottelia acuminate was sensitive to the eutrophicated water. Its optimum growth water environment was where TN between 0.60 and 0.70 mg?L-1, TP between 0.010 and 0.015 mg?L-1, Water depth between 30 and 90 cm.(6) Ecological stoichiometry has important ecological significance to reveal extinction mechanism of endangered species. Our research result show that Ottelia acuminate lower nutrient utilization, lower carbon assimilation rate and lower inner stability. In changing water environment, these characteristics can causes its population to reduce or annihilate.