Abstract: In order to clarify the effects of water velocity on the growth of diatoms in the middle route of South to North Water Diversion Project, we examined specific growth rate, nutrient uptake, photosynthetic pigment, the activity of photosynthetic system II (PSII) of algal cells and alkaline phosphatase activity of the dominant species Cyclotella meneghiniana under different water velocity in microcosm experiments. The results showed that low water velocity (0.3 m·s^-1) could promote the growth and nutrient uptake of C. meneghiniana, photosynthetic pigment content, the PSII activity and alkaline phosphatase activity. High water velocity (>0.5 m·s^-1) inhibited the growth and nutrient uptake, and reduced the photosynthetic pigment content, PSII activity, and alkaline phosphatase activity. The higher the flow velocity, the stronger of the inhibition effect. Compared with other flow velocity, the flow velocity of 1.0 m·s^-1 showed significant inhibitory effects on growth of algae cells and the photosystem II activity (P<0.01). Such a water velocity could be used as the threshold of water velocity for inhibiting the proliferation of diatoms. The results provided a basis for controlling the growth of diatom through water velocity regulation in the SouthtoNorth Water Diversion Project.

Key words: water velocity, middle route of the SouthtoNorth Water Diversion Project, Cyclotella meneghiniana, growth, photosynthetic activity.