长江口海域近50a来营养盐的变化及其对浮游植物群落演替的影响

本文根据收集到的1960s到2000s年间东海长江口附近海域(30.5～32°N,122～123°E)的营养盐数据,分析了长江口海域营养盐的季节变化及历史变化趋势。其中根据1959～1960年,1985～1986年和2002～2003年长江口海域营养盐的季节变化数据,发现50 a来,营养盐的季节变化差异不大,均呈现出春夏低,秋冬高的季节变化趋势,其中2002～2003年四个季节之间营养盐含量的变化幅度较其它两年略小。从1960s～2000s年的历史变化可以看出,调查海域的DIN含量呈现出显著上升的趋势,但是在2000年以后,DIN的年平均含量略有降低但变化不大,基本保持在18μmol/L。DIP年平均浓度变化不明显,浓度范围维持在0.39～0.60μmol/L之间。SiO3-Si的年平均含量呈现出明显的降低趋势。就营养盐组成变化来说,DIN/P比例和Si/DIN比值的变化趋势相反,DIN/P比例呈现出升高的趋势而Si/DIN呈现出降低的趋势。生物数据表明从1980s以后该海域赤潮优势种有从硅藻演变为甲藻的趋势,结合营养盐的变化分析认为过量的DIN和持续升高的DIN/P是造成这一藻种长期演变现象的主要原因。

Variation and effect of nutrient on phytoplankton community in Changjiang Estuary during last 50 years

The dissolved inorganic nutrients play an important role in controlling primary productivity in coastal systems.The samples collected in different seasons and years were analyzed in an attempt to understand the processes affecting the seasonal variability in the nutrients concentrations in the Changjiang(Yangtze) Estuary and adjacent sea areas.The concentrations of nutrients are higher in autumn and winter and lower in spring and summer.The long-term trends(from 1960 to 2000) in surface nutrients and Si,N,P ratios and numbers of HAB incidents were investigated at the river estuary as well as in adjacent sea areas.The data showed that the nutrient concentrations and compositions changed significantly after 1960.The annual average concentration of DIN was increased sharply from 1959 to 2000.After 2000,the average concentration stabilized at ～18 μmol/L.For phosphate there was an obviously rising trend.The annual average concentration of Si was decreased in last 50 years.In terms of the nutrient composition,the changes of the N/P and Si/N ratios were opposite and variable.The N/P ratio in the investigation area was increased,however,the Si/N ratio was decreased almost linearly.The dominant species showed a tendency from diatom to dinoflagellate.The excess DIN and the increasing DIN/P were proposed to cause this change.