THE SEASONAL VARIATIONS AND SPATIAL DISTRIBUTION OF THE PRIMARY PRODUCTIVITIES OF PHYTOPLANKTON IN THE THREE GORGES RESERVOIR

In this study, we carried out the field sampling from August 2012 to April 2013 in order to analyze the seasonal variation and spatial distribution of the primary productivity (PP) of phytoplankton in the Three Gorges Reservoir (TGR). Five regions along the longitudinal axis of the TGR (i.e. Zigui, Wushan, Yunyang, Zhongxian, and Mudong) were selected for the measurements of PP with the white and black bottles method. The seasonal average values of PP (according to the dissolved oxygen) followed the order: summer 5.613 mgO2/(Ld) spring 3.630 mgO2/(Ld) winter 0.906 mgO2/(Ld) autumn 0.552 mgO2/(Ld). Light was an important limiting factor in the vertical distribution of PP. The maximum values were obtained between 0 m and 1 m underwater, and the PP decreased along with the increase in the depth from 1 m to 5 m. As for the horizontal distribution, the primary productivity was higher in the head region of the TGR, and the highest was in Zigui, followed by the middle region and the tail region. Moreover, the PP values were higher in the tributaries than in the mainstream. The gross primary productivity was highly correlated with chlorophyll-a, dissolved oxygen, and pH.