| Since the construction of the Three Gorges Reservoir(TGR), the problem of water eutrophication has become increasingly prominent as all the tributaries which are rich in such nutrients as nitrogen and phosphorus flow into the reservoir. Therefore, the strengthening in monitoring and evaluation of the water environment quality of all the tributaries flowing into the TGR was significant for the control and regulation of the overall water environment quality of the reservoir. The paper, focusing on Pengxi River which is the largest tributary area on the north shore of the TGR, has conducted water sampling at 8 sites, which are Shuangjiang Square, Pengxi Bridge, Huangshi, Kangjiagou, Zhangwangmiao. Gaoyang, Maozhuazi and Quma respectively along the Pengxi River, and then indoor analysis has been conduct from October, 2013 to September, 2014. By the meantime, the water quality parameters(TN, TP and turbidity) and some other parameters related to phytoplankton were monitored, and then the limiting factors that influence the growth of the phytoplankton were selected by using data analysis. At the same time, simulation experiments were conducted in laboratory. Through parallel experiments, the relationship between the influence factors and the growth of phytoplankton were proved. The research findings are as follows:â‘ During the research period, the numerical value of turbidity is little difference among the eight monitoring sections. Take a look at the changes of 8 sites: Quma >Maozhuazi >Gaoyang> Zhang Wangmiao > Huangshi > Kangjiagou > ShuangJiang >Pengxi Bridge. The turbidity show significant seasonal variation: the turbidity in the winter is relatively small, but it increased relatively in the summer. From 2013 to 2014, the concentration of total nitrogen(TN) ranges from 0.054 to 45.079mg/L; the concentration of total phosphorus(TP) is between 0.009 and 0.347mg/L. In late spring and early summer, when the concentration of total nitrogen and total phosphorus were maximum, the concentration surpasses the lower value of eutrophication which is 0.2mg/L. It is illustrated that the water of Pengxi River is in severe eutrophication status. But the concentration of total nitrogen and total phosphorus decreased in the summer time.â‘¡During the study period, 7 phylum 21 genus 38 species of phytoplankton were identified at the 8 sites along Pengxi River. Among them, Chlorophyta accounts for 38.1% of the total amount of phytoplankton; cyanophyta accounts for 23.81%; pyrrophta account for 9.52%, becillariophytceae account for 14.29%; Cryptophyta, Xanthophyceae and Euglenophyta account for 4.76% of the total number of phytoplankton. Chlorophyta and cyanophyta are the dominant species in the study area.In the spatial distribution, the dominant phytoplankton of Shuangjiang is Cyanophyta; those of Pengxi bridge were Chlorophyta and Cyanophyta; that of Huangshi is Chlorophyta; those of Kangjiagou is Cyanophyta and Chlorophyta; that of Zhangwangmiao is Cyanophyta; those of Gaoyang is cyanophyta and Pyrrophyta; those of Miaozhuazi are phrrophyta, cyanophyta and Cryptophyta; and that of Quma is Cyanophyta.In the distribution of time, the study found that, the dominant algae of the sampling sites show obvious seasonal succession rules. The distribution of the dominant algae is: Cryptophyta and becillariophyceae(autumn)-Xanthophyceae(spring)-pyrrophyta and cyanophyta(summer)-Cryptophyta(winter). At the same time, the cyanobacterial bloom and the dinoflagellate bloom were outbreak in Pengxi River during the study period. The Species of phytoplankton caused cyanophyta bloom mainly involved Nostocales; Merismopedia; Oscillatoria wliiei; Oscillatoria anguina; Oscillatoria boryana and Oscillatoria cortiana. The Peridinium willei; Peridinium umbonatum and Ceratium hirundinella which have the large volume caused the Pyrrophyta bloom. The pyrrophyta bloom mainly outbreak in May.â‘¢The change of cell density of phytoplankton is quite obvious as the change of time. The dominant species of phytoplankton are coptophyta and Cyanophyta which plays key roles in the structure of the phytoplankton in Pengxi River. Chlorophyta is observed during the all study period, and it relates to so much species, and its cell density is small. The Chlorophyta mainly emerge in autumn. Xanthophyta and Euglenophyta are also the common species in Pengxi River, but the proportion of cell density have little changes. Becillariophyceae only appeared in individual samples, and it is the regional accident algae.â‘£Getting the correlation between the water quality and the growth condition of phytoplankton through correlation analysis. The correlation analysis showed that, the element of nitrogen and phosphorus is the key factor that affecting phytoplankton proliferation. The laboratory simulation experiments further validated the relationship between these factors and the growth of phytoplankton. It is also found that excessive high or low concentration of nitrogen and phosphorus will inhibit the growth of phytoplankton. |
