2012年长江口及其邻近海域营养盐分布的季节变化及影响因素

VARIATION AND CONTROLLING FACTOR OF NUTRIENT DISTRIBUTION IN CHANGJIANG RIVER ESTUARY AND ADJACENT AREAS IN 2012

根据2012年3、5、8和12月4个航次长江口及邻近海域的调查数据,研究了氮、磷、硅营养盐及总氮(TN)、总磷(TP)的浓度特点,及其与盐度的相关性和叶绿素a的变化特征。结果表明,总溶解无机氮(DIN)、硅酸盐(Si O3)和TN的浓度分布均表现出自长江口至外海迅速降低的特征,且与盐度呈现显著负相关性。磷酸盐(PO4)的浓度降低程度随远离河口而减弱,且与盐度的相关性相对较弱,可能存在外海水补充;而TP则在长江口浑浊带海域呈现出较高浓度,且与盐度的相关性不明显,可能是受浑浊带泥沙吸附所致。在调查海区内,DIN与TN的平均值在夏季较低,结合叶绿素a数据分析,认为浮游植物吸收作用降低了DIN和TN的浓度。通过分析各营养盐之间的比值特征,进一步考察了营养盐来源及其对浮游植物生长的可能限制情况,其中N/P比值的变化同样揭示了N主要来自于长江水而P有部分来自于外海水的特征。该比值呈现远离河口而降低的特征,且在浑浊带无明显季节变化。春季和夏季有超过90%的调查站位显示潜在P限制,且均位于外海区。与历史资料对比发现,春季和夏季潜在P限制站位的比例明显升高,而潜在Si限制站位比例在春季和夏季降低。本文研究认为,营养盐含量及组成结构反映了该海域浮游植物群落组成和优势种的演替。

Four cruises（March, May, August, and December, 2012） were conducted in the Changjiang River estuary（CRE） and adjacent areas（AA） to study the characteristics of nutrient distribution and their correlation with salinity. Indices included dissolved inorganic nitrogen（DIN）, phosphate（PO4）, silicate（Si O3）, total nitrogen（TN）, and total phosphors（TP）, as well as chlorophyll a（chl a）. Results show that average concentrations of DIN, Si O3, and TN decreased from the CRE to AA rapidly, displaying significant negative correlations with salinity. PO4 showed a relatively weak correlation with salinity, and decreased off the estuary mouth slightly due to supplement by ocean current. TP presented unobvious correlations with salinity but high concentration in the turbidity maximum zone（TMZ）, indicating absorption by suspended sediments in the TMZ. The lowest average concentrations of DIN and TN were observed in summer. In addition, as chl a data reflected, DIN and TN were assimilated by phytoplankton. Furthermore, nutrients sources and potential limitations for phytoplankton growth were studied according to the ratios between various nutrients. As N/P ratio reveals, N was originated mainly from the Changjiang River and partial P was from the open ocean. Most of the stations（〉90%） showed potential P limitation in spring and summer, and these stations were all in the ASA. Compared with historical records in spring and summer, the number of the stations showing potential P limitation increased obviously, while that of potential Si limitation decreased. We believe that these changes were resulted from the shift of dominant phytoplankton species.