中文摘要：

根据2005年4—5月（春季）、8月（夏季）和11月（秋季）对大亚湾大鹏澳海区表层的现场调查结合营养盐加富实验，探讨了不同季节硝态氮（NO3^-）、脲氮（urea）和无机磷（PO4^3-）等营养元素对该海区浮游植物叶绿素a含量与初级生产力及它们的粒级结构的潜在影响。调查海区表层海水叶绿素a含量在近岸养殖区较高，季节变化不明显，但其粒级结构有较大的季节差异；初级生产力的平面分布与叶绿素a含量在春、秋季均较一致，其粒级结构与叶绿素a的粒级结构在春季基本一致，但在秋季有较大差异。实验结果表明，NO3^-、urea和PO4^3-对该海区浮游植物叶绿素a、初级生产力及它们的粒级结构有不同的潜在影响，并存在季节差异。尽管磷被认为是该海区浮游植物生长的主要限制因子，结果显示氮（NO3^-或urea）对浮游植物生长仍有潜在限制作用，其中NO3^-和urea作为不同氮源的潜在影响有明显区别。

英文摘要：

In situ surveys in the surface water of Dapeng＇ao area of the Daya Bay, combined with nutrient enrichment bioassays, were conducted in April-May （spring）, August （summer） and November （autumn） of 2005 in order to better understand the potential impacts of NO3^- , urea and phosphorus （PO4^3-） on the size structure of chlorophyll a and primary productivity of phytoplankton in this area in different seasons. The concentration of chlorophyll a was higher in the aquacultural area, and had no distinct seasonal changes, whereas its size structure had seasonal variations. The distribution of primary productivity in the area was accordant with that of the chlorophyll a in both spring and autumn, while the distribution of its size structure was similar to that of chlorophyll a in spring but was quite different in autumn. The experimental results showed that the potential impacts of NO3^- , urea and PO4^3- on chlorophyll a concentration, primary productivity and their size structures were different and had seasonal variations. Although phosphorus is considered to be the main limiting factor to the growth of phytoplankton in this area, it is showed that nitrogen （NO3^- or urea） still has potential limitations to phytoplankton growth, and as different nitrogen sources, the potential impacts of NO3^- and urea are different.