Land-ocean interaction plays an essential role in the transport fate of terrestrial matters in the coastal and shelf regions. Flood discharge from a mega river, containing massive water, sediment, and nutrient loads, could result in substantial and complex impacts on the physical and biogeochemical dynamics of coastal systems. In this study, field campaigns were conducted in a region from the Changjiang River Estuary to the East China Sea (ECS) before and after a significant flood. The impacts of the flood on physical and biogeochemical environments were assessed. The results revealed that the fluvial flood enhanced the offshore expansion of the low-salinity river plume and associated sediment/nutrient fronts. However, the area of elevated chlorophyll-a at the river mouth did not expand noticeably. A numerical model was applied to quantify the contribution of the Three Gorges Dam (TGD) to the spatial intensity and temporal duration of fluvial flood effects on estuary–shelf continuum. The results predicted a maximum of 2° latitudinal offshore displacement of the shelf water. Salinity and nitrate exhibited conservative expansions, with a longer relaxation time (∼ 2 months) than chlorophyll-a and phosphate. After the TGD-regulated flow event ceased, salinity and nitrate effects persisted, but phosphate and chlorophyll-a recovered rapidly. The flood decreased the dissolved oxygen (DO) concentration around the river mouth and the offshore region, but not in the nearshore transient area. In contrast, the non-TGD regulation increased the regional DO concentration, which reduced the hypoxia risk. The TGD has become a crucial anthropogenic driver of environmental changes in the Changjiang Estuary-ECS continuum.

陆地与海洋的相互作用在沿海和陆架地区的陆地运输命运中起着至关重要的作用。包含大量水，沉积物和营养物的巨型河流的洪水排放可能对沿海系统的物理和生物地球化学动力学产生实质性和复杂的影响。在这项研究中，在大洪水发生前后，在从长江口到东海（ECS）的区域进行了野战。评估了洪水对物理和生物地球化学环境的影响。结果表明，河流洪水增强了低盐度河羽的近海扩张以及相关的沉积物/养分前沿。但是，河口的叶绿素-a升高区域并未明显扩大。应用了一个数值模型来量化三峡大坝（TGD）对河口-陆架连续体上河道洪水影响的空间强度和时间持续时间的贡献。该结果预测了架子水的最大纬向离岸位移为2°。盐度和硝酸盐显示出保守的膨胀，比叶绿素a和磷酸盐具有更长的弛豫时间（〜2个月）。在TGD调节的流量事件停止后，盐度和硝酸盐效应仍然存在，但磷酸盐和叶绿素a迅速恢复。洪水降低了河口和近海区域的溶解氧（DO）浓度，但没有降低近岸过渡区的溶解氧（DO）浓度。相反，非TGD法规增加了区域DO浓度，从而降低了缺氧风险。