Phosphate limitation of phytoplankton growth in the Changjiang Estuary

Laboratory experiments of bioassay with Pltaeodaetytum tricornutum, Chatoceros didymus, Chaetoreros calcitraus and Heterogtoea sp.sampled from the Changjiang Estuary in spring and summer, 1986, indicated that both N and P limit phytoplankton growth in the medium with N:P ranged between 8-30, and N limits phytoplankton production in the medium with N:P<8, while P is the limitary nutrient in the N:P>30.Generally, N:P in the Changjiang Estuary waters is 2 times higher than Redfield ratio.The bioassay experiments with high N:P water samples collected from Changjiang Estuary show that phytoplankton production is limited by P.Phytopiankton appears to give priority to the uptake of P at all periods of time.And the optimum N:P for phytoplankton growth is determined to be 18.