长江口及邻近海域营养盐的季节变化特征

2014年2月和7月，采集了长江口及其邻近东海陆架海域106和104个站点的样品，测定了其中的营养盐（NO₃-N、SiO₃-Si、PO₄-P、NH₄-N、NO₂-N）浓度，发现长江口海域营养盐的时空分布具有明显的季节变化特征。在夏季，长江径流量加大，海水层化，含有高NO₃-N、SiO₃-Si、PO₄-P浓度海水的扩散范围明显大于冬季；而在外海，夏季上述营养盐的表层浓度却低于冬季。由于在长江淡水端元NH₄-N和NO₂-N浓度的季节变化较大，这两种营养盐与盐度在长江口的相关关系呈现出"季节性反转"，在夏季其浓度与盐度呈现出正相关关系，而冬季则相反，呈现出负相关关系。长江冲淡水是以"斑块化"的形式向外海传递的，通过在不同斑块中采集样品并比较其中营养盐的浓度，验证了夏季长江口海域对大部分营养盐是一个显著的"汇"。此外，营养盐的不保守行为既发生在盐淡水混合海域，也发生在长江口门以内的淡水端元海域。

Seasonal variation of nutrients in the Changjiang (Yangtze River) Estuary and the adjacent East China Sea

Seawater samples in the Changjiang Estuary and the adjacent East China Sea (ECS) were collected at 106 and 104 stations, respectively, in February and July 2014 during which concentrations of nutrients (including NO₃-N, SiO₃-Si, PO₄-P, NH₄-N, and NO₂-N) were measured.The distribution and variation of nutrients showed distinct seasonal variation pattern.In summer, the coverage area of seawater with high concentrations of NO₃-N, SiO₃-Si, and PO₄-P was obviously larger than that in winter, owing to the increased Changjiang discharge and the seawater stratification.On the contrary, however, the concentrations of the three nutrients in the offshore seawater were generally lower at surface in summer than those in winter.NH₄-N and NO₂-N showed positive correlations with salinity in summer while negative relationships in winter, and this seasonal reverse pattern was largely ascribed to their sharply increased concentrations in the Changjiang freshwater end-member from summer to winter.The Changjiang runoff was transported to the pelagic oceans in separated patches, rather than in continuous plume.Comparison of nutrient concentrations among different patches validated that the Changjiang Estuary and the adjacent areas were a tremendous sink for most nutrients in summer.The non-conservative processes of nutrients occurred not only in the estuarine and shelf areas where freshwater and seawater mixed, but also in the Changjiang freshwater areas within the river mouth.