长江口邻近海域浮游植物群落对黑潮次表层水入侵年际变异的响应特征

The Changjiang (Yangtze River) estuary and its adjacent sea is the most notable region for harmful algal blooms in the coastal waters of China. This area with a complex hydrological environment is influenced by the Changjiang Diluted Water and the intrusion of Kuroshio Subsurface Water (KSSW). Recent studies indicated that the KSSW intrusion in the Changjiang estuary and its adjacent sea has an important impact on the growth of phytoplankton, especially on the timing and scale of dinoflagellate bloom in spring and summer. The KSSW intrusion time, intensity and extent have a significant interannual variation, which influences the spatial and temporal pattern of the phytoplankton community. However, the spatial and temporal responses of phytoplankton community to the KSSW intrusion in long time scale have not been fully understood yet. Thus, this project would be implemented by using the history field investigation data of spring and summer in the past 20 years, combining the physical model data, remote sensing data, and field investigation. Based on these data and methods, we are going to explore the influence of the interannual variation of KSSW intrusion on the phytoplankton abundance, species composition and seasonal succession of key phytoplankton populations in the Changjiang estuary and its adjacent sea. As a consequence, the response of the phytoplankton community to the variation of the KSSW intrusion in the seasonal and interannual scales would be clarified. The study results can help us better understand the influence of the interannual variation of KSSW intrusion on the spatial and temporal variation of harmful algal blooms in the Changjiang estuary and its adjacent sea.

长江口邻近海域是我国近海有害藻华高发区。该区域水环境复杂，受到长江径流输入与黑潮次表层水（Kuroshio Subsurface Water, KSSW）入侵的双重影响。近期研究表明，KSSW入侵对促进长江口邻近海域浮游植物的生长，尤其是春、夏季甲藻赤潮爆发的时间与规模具有重要影响。KSSW入侵时间、强度和范围存在年际变化，并对浮游植物时空格局的变化规律产生影响，但对于两者之间长时间尺度的时空响应关系还欠缺更深入的认识。本项目拟利用近20年春、夏季历史航次数据，结合物理模式数据、遥感数据和现场航次调查方法，研究KSSW入侵年际变异对长江口邻近海域浮游植物丰度、物种组成和关键种群季节演替的影响，在季节与年际尺度上，获得浮游植物群落结构对KSSW入侵变异的响应特征。研究结果有助于从年际尺度上深入理解KSSW入侵对长江口邻近海域藻华爆发时空变化趋势的影响。

长江口邻近海域浮游植物受到长江陆源输入和黑潮入侵的双重影响。比较而言，对长江陆源输入与浮游植物群落的关系的认识更为清晰。综述研究表明，长江口邻近海域营养盐的变化、富营养化的发展及其生态响应过程经历了两个发展阶段：1975-1990s期间的氮磷营养盐缓慢增加阶段和2000年后快速上升阶段，并对浮游植物群落结构的演变产生不同的影响。关于黑潮次表层水（KSSW）入侵对浮游植物影响的研究表明，东海陆架海域KSSW入侵的营养盐贡献春夏季明显高于秋冬季；在近岸区域，春夏季KSSW入侵可以带来丰富的营养盐，其贡献率可以达到～40%，进而可以影响近岸区域的浮游植物分布。另外，2014-2016年东海陆架海域KSSW的入侵强度与近岸海域叶绿素a的浓度变化是一致的，均表现为2016年明显高于2014和2015年，而2014和2015年基本相当的趋势。在长江陆源输入和黑潮入侵的双重影响下，以泥沙锋和羽状锋为边界，进一步探讨了不同区域Chl-a浓度与环境因子的分布特征及相互关系。结果表明浮游植物和环境因子的分布格局与泥沙锋和羽状锋在空间上呈现出明显的响应关系，高Chl-a浓度出现在两锋面之间的过渡区域；长江陆源输入和黑潮入侵依照锋面的位置对浮游植物产生不同影响。本项目对于了解长江口邻近海域浮游植物在长江陆源输入和黑潮入侵双重影响下的响应具有一定的理论价值，对于了解KSSW入侵和锋面的生态效应具有重要意义。