長江口鋒面附近咸淡水混合對浮游植物生長影響的現場培養

通過2009年6月調查航次,獲得了營養鹽等參數斷面分布,表明咸淡水混合是控制營養鹽分布的主要因素。為了解不同鹽度梯度下浮游植物生長與營養鹽吸收的關系,采集兩個站位水樣分別代表長江沖淡水(C1站)和外海水(I10站),按C1站水樣比例,分100%、75%、50%、25%、0%不同比例混合進行現場模擬咸淡水混合培養,有以下認識:(1)平行結果表明培養過程中活體熒光極大值在100%混合組,且淡水比例越低,指數生長期0—48 h內生長速率越低,100%、75%、50%、25%組分別為1.18/d、1.12/d、1.14/d、0.77/d;(2)低于26鹽度的水體中PO34-在48 h內可被迅速消耗而產生限制作用,是控制浮游植物生長的潛在限制因子;(3)除0%組外,各混合組DIN/P(DIN:溶解無機氮,Dissolved Inorganic Nitrogen,DIN=NO3-+NO-2+NH4+)比值在浮游植物指數生長期有升高趨勢,100%組DIN/P比值增加了一倍。各組培養48 h后DIN/Si比值逐漸降低至原來的0.7左右,初始DIN/Si小于一定時間內硅藻吸收的(ΔDIN/ΔSi)比,是造成各組DIN/Si比值減小的原因。以上結果表明咸淡水混合過程中形成的營養鹽梯度可造成浮游植物生長程度和速率差異,且可因局部浮游植物旺發而改變海水營養結構。The distribution of nutrients and salinity recorded during the June 2009 cruise in the Changjiang Estuary indicated that dilution by Changjiang River water and seawater mixing were the main factors controlling nutrient behavior. To better understand the implications of this variation, phytoplankton growth and nutrient uptake along a salinity gradient representing dilution by the Changjiang River and seawater respectively were recorded. Two water samples were collected from the sampling stations C1 and I10 (as used in the June 2009 cruise) which were representative of the freshwater and saline water end-member. After diluting portions of the two samples by 100%, 75%, 50%, 25% and 0% with freshwater to simulate different levels of freshwater-saline water mixing, the samples were incubated for 3 days. The results were as follows: (1) the higher the percentage of freshwater, the faster was initial growth and the higher the in vivo fluorescence concentration. During the 3 day incubation period, the rate of increase in fluorescence and maximum in vivo fluorescence of the 100% dilution treatment were 2. 9 μg/L/d and 9. 6 μg/L, respectively, whilst the rate of increase in fluorescence and maximum fluorescence of the 25% dilution treatment were 0. 54 μg/L/d and 2. 0 μg/L respectively. The in vivo fluorescence of the 0% dilution treatment was low, probably due to the low nutrient levels in the offshore seawat