Research Of Hydrology, Water Quality, Plankton, And Their Relationship In Pengxi River, Three Gorges Reservoir

After the impoundment of Three Gorges Reservoir in 2003, great changes have taken place in water hydrology, hydrodynamics and nutrition. At the same time, With the proper nutritional conditions and hydrological conditions, many tributaries are able to algal bloom, and algal bloom has become an annual tradition for some tributaries, such as Xiangxi River, Daning River, Pengxi River, etc.. As the tributary of biggest Drainage area in the north bank of Three Gorges reservoir, Pengxi River’s algal bloom particularly frequent, and the extent is increasing year by year. In this paper, as an example, plankton and environmental factors were analyzed in Pengxi River, and the relationship between plankton and environmental factors were discussed.In spring(April 17, 2014) and summer(July 27, 2014), Pengxi River were studied. Draw the following conclusions:(1)The concentration of total nitrogen is 2~10 times of the internationally recognized eutrophication threshold, total phosphorus Exceed more than 50 times. Total phosphorus levels decreased in summer than in spring, but the total nitrogen and total phosphorus levels were still much higher than the internationally accepted threshold of eutrophication. In Pengxi River, high water level period water intrusion effects is stronger than low water level period, to a certain extent, it has affected the concentration of nutrient salt in tributaries.(2) sample points in main stream of The Yangtze river does not hierarchical all the time. In spring, from estuary to upstream, water temperature gradually increased and water gradually stratified, the mixed layer does not occur, or thin; In spring, water temperature generally increased, stratification of tributary significantly, the mixed layer does not occur, or thin.(3) Stratification of the water play a leading role for phytoplankton blooms in spring in. when stratification is not a limiting condition for algal bloom, water temperature, nitrate and pH is the key for growth of Ceratium hirundinella and Microcystis in spring; turbidity, water depth, and redox potential and TN is the key for growth of Anabaena sp..(4) In Pengxi River, occurs of algal bloom has spatial partitioning features. In spring,Ceratium hirundinella was the main dominant species, and Microcystis sp. was the sub-dominant species. Algal bloom in upstream sampling sites PX06(63.4×104cell·L-1) and PX07(145.8×104cell·L-1)were relatively serious. In summer, algal bloom at downstream of the river, PX01(216.44×104cell·L-1), PX02(278.88×104cell·L-1) and PX03(108.12×104cell·L-1) were relatively serious. Anabaena sp. was the main dominant species, and Phormidium sp. was the sub-dominant algae.From January 2015 to June 2015, process of algae bloom was studied, draw the following conclusions:(1)During period of algae bloom, diversity of algae was significantly lower than that of other periods, however, the algae density was much higher than other periods. The average algae density of algae bloom period is about 100 times before algae bloom period, approximately 50 times after algae bloom period.(2) Algae bloom exhibit significant partitioning features in time and space in Pengxi River. Algae bloom take place from April 10 to May 17, PX06(872.9×104cell·L-1) and PX07(976.32×104cell·L-1) have a high density of algae, Microcystis sp. is the main advantages of algae.(3) Water stratification directly induce algae bloom, the ratio of euphotic layer and mixed layer(Zeu/Zmix) is a critical factor for algae bloom in Pengxi River. Their showed a positive correlation between Zeu/Zmix and the extent of algae bloom. Zeu/Zmix has an important guiding significance for the prevention and control of algae bloom in Pengxi River.(4)Water temperature was the key regulatory factors for Microcystis bloom in Pengxi River.During algae bloom in 2015(from April 10, 2015 to May 17, 2015)Water Plankton community structure was studied in Pengxi River, draw the following conclusions:(1) Environment factors and community structure of plankton has typical partitioning features on time and space during algae bloom in Pengxi River. Changes of Environment factors and community structure of plankton in the time dimension is less than the change in spatial dimensions.(2) A、B、C、D is Continuous sample point in Pengxi River.But Plankton community structure of D is remarkably different from A、B、C.(3) In Pengxi River. the main species of plankton in the upstream is heterotrophs, and the main species of plankton in the upstream is autotrophs。...