潮控型河口-海湾水龄分布及对外部淡水输入的响应

Terrestrial input through river inflow is the major source of pollution to coastal environment and the cause of marine ecosystem degradation. Quantitative analysis on the transport of freshwater in esturaries and bays is critical for unserstanding the environmental impact of terrestrial input to marine ecosystem. Spatio-temporal distribution of water age and its controlling factors is the research focus of the transport processes in region of freshwater influence (ROFI). In this study, we will investigate the water age of the heavilly polluted XiaoQinghe River (XQR) in the Laizhou Bay (LZB), which is a typical eutrophic bay located at the southern coast of Bohai Sea and receives increased anthropogenic inputs of nutrients and pollutants. Constituent-oriented Age and Residence time Theory (CART) will be coupled into a 3D hydrodynamic model to calculate the water age distribution of XQR discharge in LZB. A series of model simulations under various hydrological conditions will be performed to evaluate the influence of river discharge, tides, winds, and barocline on spatial distribution and seasonal variation of water age. Furthermore, the influence of Yellow River (YR) dischagre will be studied because of its dominant impact on the hydrodynamics of the LZB. We will investigate the effects of abrupt change of YR discharge during water regulation event in early summer on the water age of the XQH in the LZB. The research will enhance our understanding of transport process in a tidal region of freshwater influence and eluciate the mechanisms behind the response of water age in ROFI to external freshwater input. The study will make addition to the scientific foundation for effective policy making in pollutant control of estuaries and bays.

陆源物质随河流入海是近海环境污染和生态系统退化的重要原因。定量认识河水在不同海域的输运时间（即水龄），以及不同水文气象要素对水龄分布的控制机制，是理解陆源物质环境效应的关键。本研究以中国北方典型海湾莱州湾及其主要污染来源小清河为例，结合现场观测与数值模拟，采用成分导向水龄和存留时间理论（CART），建立渤海/莱州湾三维斜压水动力-水龄耦合模型，定量描述小清河水在莱州湾的水龄分布，揭示潮、风、径流、斜压等因子对水龄空间分布和季节变化的影响，查明关键因子；重点阐释黄河径流变化，尤其是人类活动导致的调水前后径流急剧变化，对莱州湾流场、要素分布场和小清河水龄分布的作用机制。研究结果将深入认识径流入海的输运过程和潮控型淡水影响区的水龄分布机制，阐明外部淡水输入对河口-海湾水龄分布变化机制的一般性和局地性影响，为河口海湾污染控制提供科学决策依据。

陆源物质随河流入海是近海环境污染和生态系统退化的重要原因。定量认识河水在不同海域的输运时间（即水龄）及其控制机制，是理解陆源物质环境效应的关键。本研究以中国北方典型海湾莱州湾及其主要污染来源小清河为例，采用单宽通量计算发现，径流仍然是其基本贡献因素，主导了向海方向的输运，但潮汐过程引起的Stokes输运和潮脉动输运主导向陆输运，三者的博弈决定了单宽盐度通量的方向和大小。基于muddy-LOICZ模型得到，小清河口夏、秋季水体存留时间分别为0.67天和3.09天，夏、秋季DIP平均收支分别为-2.96×103mol/天、-1.72×103mol/天，夏、秋季DIN平均收支分别为-1.55×106mol/天、-0.77×106mol/天。河口生产力旺盛，有大量的营养盐在此经过生物作用固化，形成氮磷的汇，而由于本身处于磷限制条件下，形成磷汇通量要远远小于氮汇，（p-r）>0暗示小清河口存在净生产过程，即光合作用强于呼吸作用。采用成分导向水龄和存留时间理论（CART），建立渤海/莱州湾三维斜压水动力-水龄耦合模型，定量描述小清河水在莱州湾的水龄分布，小清河水在莱州湾（刁龙嘴-黄河口）全年平均水龄为328天，且存在显著季节变化，径流量大小是其主要控制因子。潮、风是其次要因子，潮汐加大了其水龄，且在河口区尤为明显，风的作用体现在全水域，斜压作用主要体现在河口区；黄河径流量急剧增大，会显著增大小清河水在莱州湾西侧的水龄。研究结果对有助于深入认识径流入海的输运过程和潮控型淡水影响区的水龄分布机制，阐明外部淡水输入对河口-海湾水龄分布变化机制的一般性和局地性影响，为河口海湾污染控制提供科学决策依据。