人类活动和自然变化对长江口-闽浙近海生态结构驱动机制的古-今对比研究

China’s shelf seas and especially coastal environment and ecosystem have been deteriorated very fast during the last 30 years. It is often typified by harmful algal blooms (HAB), especially the increasing dinoflagellate blooms. One accepted conclusion is that this is caused by human activities which significantly increased the input of nutrients (especially DIN) to the coastal region. Eutrophication and increased N/Si ratio are responsible for HAB and dinoflagellate blooms. However, sediment records revealed a decreasing trend of dinoflagellate/diatom ratio over the last 30-40 years in the Min-Zhe coastal region. It has been proposed that this trend was caused by increased coastal upwelling, which brought up Si-rich nutrient to favor the growth of diatoms. Thus, it is critical to quantify the influence of N/Si and N/P ratios on ecosystem growth and dinoflagellate/diatom ratio. In addition, it is also important to quantitatively assess the influences of anthropogenic and upwelling on nutrient ratios and on dinoflagellate/diatom ratio, especially on a spatially-resolved regional scale. To these aims, this project proposes to carry out the following research. The relationship between environment (temperature), nutrient ratio and dinoflagellate/diatom ratio will be determined and quantified by seasonal cruises. High resolution (both temporal and spatial) records of nutrients and ecosystem parameters (dinoflagellate/diatom ratio) will be obtained by synthesis of climatological data and sediment records to reveal the relationship between environment (temperature, upwelling), nutrient ratio and dinoflagellate/diatom ratio. A physical-chemical-ecosystem model will be used to quantify the relationship between nutrient ratio and dinoflagellate/diatom ratio. This model will then be used to assess the influence of anthropogenic and upwelling on the nutrient ratio and dinoflagellate/diatom ratio, to reveal spatially resolved patterns. Our study will provide scientific knowledge for policy make to restore and protect the coastal environment.

过去几十年我国近海生态环境和生态系统恶化的主要趋势是大规模爆发有害藻华，尤其是甲藻藻华相对于硅藻藻华的增加。主要原因是人类活动造成的富营养化尤其是氮/硅和氮/磷比值的增加，导致甲藻藻华增加。然而，近期研究证明，闽浙近海甲藻/硅藻比值在过去几十年也有下降的趋势，可能是上升流增加的结果。美国西海岸近海也有自然变化导致生态结构变化的案例。因此，我国近海生态结构演变机制研究有两个挑战。第一是如何量化氮/硅和氮/磷比对甲藻/硅藻比值的控制；第二是如何在小尺度空间范围内区分人类活动和自然变化对生态结构的驱动。本项目选择长江口-闽浙沿岸为研究区域，通过航次和原位长期监测获得现代数据，整理和同化资料获得气候态数据、沉积记录重建获得长百年尺度演变记录；高分辨率厘清生态系统的时空格局、发现演变规律；古今结合，重点区分长江冲淡水和上升流对生态系统的驱动，模式量化驱动机理，为预测未来生态系统的变化趋势提供案例。

本项目聚焦长江口-闽浙沿岸区域，通过航次和原位观测、实验室分析测定、实验室培养研究、沉积记录和高分辨率物理-化学-生态耦合模型，系统研究了浮游植物生产力和生态结构时空分布的现代过程及其年代际演变及机制，以及人类活动和自然变化对浮游植物生态结构的影响。重要结果及其科学意义如下：.1. 实验室培养研究发现，高营养盐条件下硅藻具有竞争优势，而在较高温度和营养盐条件下转变为甲藻占优势。结合生物标志物重建的记录，可进一步区分浮游植物群落演变的驱动机制。.2. 长江冲淡水对长江口-闽浙沿岸浮游植物生物量和群落结构有较强影响，而黑潮次表层水主要影响群落结构。长江冲淡水贡献高时，对总生物量具有抑制作用并促进甲藻竞争优势，而黑潮次表层水促进硅藻竞争优势。.3. 利用生物标志物重建时间和空间的高分辨率记录，结合三维生物地球化学模型，发现近百年长江口-闽浙沿岸上升流区浮游植物群落结构的主控因素是黑潮流量和黑潮磷酸盐含量，非上升流区主控因素是海水升温与长江的高氮输入。.4. 三维生物地球化学耦合模型表明，浙江沿岸夏季海表温度存在明显年际变化，2013年为上升流强年，2018年为弱年；强上升流年海表温度更低，低温水影响的范围更大，不同强度的上升流使近岸区域底层冷水上涌程度不同。.5. 估算了中国东部边缘海海源有机质的埋藏效率（7-19%），率先量化了总海源生物标志物的埋藏效率（6-24%），发现沉积物粒度越小，越利于海洋有机碳和生物标志物的保存。.项目完成任务、实现目标，为预测未来海洋生态系统的变化及制定相关政策提供重要依据。共发表SCI论文24篇，多篇论文发表在Geochimica et Coamoshimica Acta、Remote Sensing of Environment、Frontiers in Microbiology等国际顶尖期刊。培养多名中青年学术骨干，培养毕业博士生6人、硕士生7人。