Study On Phytoplankton In And Near The Jiuduansha Wetland Nature Reserve Waters

The Jiuduansha Wetland Nature Reserve which is located in the Yangtze River estuary, generally keeping the state of native estuarine wetland, has great value for conserving and researching. The phytoplankton of ten sampling sites between Wusongkou and Lower Jiuduansha was investigated seasonally in February, May, September and December in 2005, two sampling sites in the Taihai ferry dock and the Changtong ferry dock of Yangtze River in Jiangsu province were added in September and December. The diurnal change of phytoplankton in one sampling site near the dock of Upper Jiuduansha were stratified investigated in August 2006; meanwhile, the phytoplankton of six sampling sites in the north and south troughs was investigated. Community structure and changing rules of the phytoplankton were analyzed, they relationship with environmental factors were also discussed in this paper. The main results are summarized as follows:1. 304 species of phytoplankton belonging to 119 genera were found in this investigation. The species of diatom, including 142 species in 56 genera, was the most and took 46.71% of all species. Green algae involving 99 species in 36 genera, and 27 genera of other algae were also detected.The amount of species was the most in winter and the fewest in autumn. The amount of species in daytime was more than night. The amount of species was similar in the six sampling sites in the north and south troughs.2. The yearly average amount of phytoplankton was 44.33×104 ind/L in the seasonal investigation. The quantity of phytoplankton was similar in spring, autumn and winter, but was significantly higher in summer. The quantitative distribution of phytoplankton in the survey area was low-high-low pattern, but winter. The specific distribution and its affecting factors are summarized as follows:The quantity of phytoplankton in the sampling sites between Wusongkou and South Jiangyasha were less abundant than that in Upper Jiuduansha and Middle Jiuduansha in spring, summer and autumn, as the salinity in this area was not suitable for algae to grow plentifully. The quantity of phytoplankton in the sampling sites in Upper Jiuduansha and Middle Jiuduansha were obviously more abundant than that between Wusongkou and South Jiangyasha because of difference of nutrient salt and besides the above reason and water temperature. The growth of the dominant species (Skeletonema costatum) in the sampling sites in Upper Jiuduansha and Middle Jiuduansha was limited by the low temperature in winter, so the quantity of phytoplankton in the sampling sites between Wusongkou and South Jiangyasha were more abundant.The Yangtze River in Jiangsu province was less affected by seawater, freshwater phytoplankton could grow plentifully, so the quantity of phytoplankton here was more abundant than that in the sampling sites between Wusongkou and South Jiangyasha. But it was less abundant than the sampling sites in Upper Jiuduansha and Middle Jiuduansha in summer, because of the limit of nutrient salt, and it was not less than that in the sampling sites in Upper Jiuduansha and Middle Jiuduansha in autumn because of rich nutrient salt.The quantity of phytoplankton in the sampling sites in Lower Jiuduansha were less abundant than that in Upper Jiuduansha and Middle Jiuduansha in four investigation, would be affected by the seawater from off coast bringing by tides.3. The average quantity of phytoplankton was 158.90×104 ind/L in the diurnal investigation. There were two quantitative peaks in 24 hours, both in upper layer and in lower layer. The average quantity of phytoplankton in upper layer was more abundant than that in lower layer in vertical distribution.Tidal current was the main factor which affected on the diurnal quantity change of phytoplankton. Meanwhile, this change was related to the horizontal distribution of phytoplankton in the Yangtze River estuary.4. The average quantity of phytoplankton was 186.19×104 ind/L in the six sampling sites in the north and south troughs. The average quantity of phytoplankton in the north trough was more abundant than that in the south trough, but it might be caused by tides.5. Skeletonema costatum was the main dominant species in the investigated area (except the Yangtze River in Jiangsu province).The distribution characters and seasonal change of the quantity of phytoplankton in this area were decided by the quantity of Skeletonema costatum. And the diurnal change, the horizontal distribution and the distribution in the north and south troughs of the quantity of phytoplankton were also decided by it.Skeletonema costatum was the single dominant species and took over 70% of the total quantity of phytoplankton in each sampling sites between South Jiangyasha and Lower Jiuduansha. Three diversity indexes of phytoplankton were analyzed and these indexes were negatively correlated with the percentage of quantity of Skeletonema costatum in the total. The three diversity indexes were lower in the sampling sites between South Jiangyasha and Lower Jiuduansha. It showed that Skeletonema costatum destructed the biodiversity of phytoplankton in this area. The reason why Skeletonema costatum grew plentifully and became the single dominant species was the complex environment in this area, the wild tolerance ability of Skeletonema costatum and the rich nutrient salt in the Maximum Turbidity Zone.The Yangtze River in Jiangsu province was only investigated in summer and autumn, The three diversity indexes were higher in this area(except the Taihai ferry dock in autumn).In conclusion, the species were abundant in and near the Jiuduansha Wetland Nature Reserve waters, but most of them couldn't grow plentifully because of the complex environment, only Skeletonema costatum could grow plentifully and become the main dominant species. Tides, flows, water temperature and nutrient salt et al. affected the quantity distribution characters of phytoplankton through Skeletonema costatum. This research was one part of the entirety environmental information research of the Jiuduansha Wetland Nature Reserve, would provide a scientific basis for the research on the current characteristics and ecological restoration of community structure of phytoplankton.