Abstract: Studies on the ecologic effect of Cu and Zn on the growth of Chaetoceros mulleri show that when the ionic activities of Cu and Zn are less than 0～10^-7.80 and 0～10^-7.00 mol·L^-1respectively,the growth of C.mulleri is normal. Its optium requirement to the ionic activity of Cu is 10^-13.57～10^-10.53mol·L^-1, but for Zn,it is not essential at lower ionic activity. When the ionic activities if Cu and Zn are higher than 10^-7.80 and 10^-7.00 mol·L^-1 respectively,they will have a harmful effect to C.mulleri. Cu has a higher toxicity than Zn.

Key words: Chaetoceros mulleri, Copper, Zinc, Ionic activity, runoff scouring, riparian zone, slope erosion, hydrodynamic characteristics, interaction