Most estuaries are characterized by non‐uniform axial topography with shallow shoals near the mouth. Previous studies have addressed the impacts of the axial topographic variations on mixing and estuarine circulations yet seldom on material transport and retention. This study investigates the longitudinal structure and mechanisms of exchange flow and material transport of Chesapeake Bay (CB), featuring a shallow sill in the lower bay, by applying total exchange flow (TEF) algorithm, tracer experiments, and partial residence time (PRT) using a validated 32‐years numerical model simulation. A retention coefficient was adopted to quantify the material retention rate using two characteristic PRTs: with and without incorporating water parcels returning to a concerned region. It is found that shoaling from the Rappahannock Shoal to the mouth causes persistent downwelling, strong reflux, and the highest material retention rate in the middle of the bay. The gravitational circulation and the river outflow dominate the transport of salt and riverine dissolved materials (RDMs), whereas the contribution of the tidal oscillatory process is localized near the mouth. The dominance of river outflow over the gravitational circulation for transporting RDMs is confined within the upper bay, where PRTs exhibit distinct seasonality. PRTs show small seasonality in the middle to the lower bay controlled by the exchange flow. The present analysis combining TEF, efflux/reflux theory, and PRT is applicable to other coastal aquatic ecosystems to characterize the water exchange and renewal efficiency along the salinity gradient and understand the contributions of transport to biogeochemical processes.

中文翻译：

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沿长河口盐度梯度的交换流量和物质输送

大多数河口的特征是轴向地形不均匀，嘴附近有浅滩。先前的研究已经解决了轴向地形变化对混合和河口环流的影响，但很少对物质的输送和滞留产生影响。这项研究通过应用总交换流量（TEF）算法，示踪剂实验和部分停留时间（PRT），研究了切萨皮克湾（CB）的纵向结构，交换流和物质输送的机理，该切萨皮克湾（CB）的下部湾为浅湾。使用经过验证的32年数值模型仿真。采用保留系数来量化材料的保留率，使用两个特征性PRT：有或没有合并返回相关区域的水包。发现从Rappahannock浅滩到嘴的浅滩引起持续的向下流，强烈的回流和海湾中部的最高物料滞留率。重力循环和河流流出控制着盐和河流溶解物质（RDM）的输送，而潮汐振荡过程的贡献则位于河口附近。在引力环流中，河水在重力流中的占主导地位被限制在上部海湾内，那里的PRT表现出明显的季节性。PRT在交换流量的控制下，在中海湾到下海湾表现出较小的季节性。目前的分析结合了TEF，外排/反流理论，