Freshwater Composition and Connectivity of the Connecticut River Plume During Ambient Flood Tides
Freshwater Composition and Connectivity of the Connecticut River Plume During Ambient Flood Tides
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DOI：
10.3389/fmars.2021.747191
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发表时间：
2021-10
期刊：
影响因子：
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通讯作者：
M. Whitney;Yan Jia;K. Cole;D. MacDonald;Kimberly D. Huguenard
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作者：
M. Whitney;Yan Jia;K. Cole;D. MacDonald;Kimberly D. Huguenard
康涅狄格河羽流与长岛海湾东部接收水域周围的强潮流相互作用。以潮汐河流羽流进入河口或大陆架高能量环境潮汐环境为例，研究了环境潮汐过程中形成的羽流。应用高分辨率嵌套水动力模式中保守的被动淡水示踪剂，以确定来自潮汐周期不同部分的源水如何促进羽流组成并与边界羽流锋面相互作用。只有在低流量条件下，当潮汐在最大环境洪水后逆流通过河口时，才能切断与水源的连接。当潮汐内部弗劳德数超过1时，上游羽流的范围是有限的，因为环境潮流阻止了相反的羽流传播。潮汐羽流的下游范围始终在距河口20公里以内，不到环境潮汐漂移的两倍。在之前的环境退潮期间，河流中的淡水是在新的洪水羽流中发现的最古老的水。与源水和羽流锋面的连通性表现出强烈的从上游到下游的不对称性。受阻的上游前锋有很高的连通性，因为所有从河口出来的淡水都会立即与这条边界相互作用。下游羽流锋面的整体连通性最低，因为相互作用仅限于最古老的水域，因为较年轻的内陆水域不会超过这一锋面。近海锋面和近岸边界呈现从年轻水域向较老水域的下游发展，与源头水域的总体连通性下降。羽流平均的淡水示踪剂浓度和变化都表现出一个初始增长期，然后是潮汐周期剩余时间的较长衰减期。烟羽平均示踪剂变化由嘴输入增加，由夹带减少，并由内部混合破坏。较年轻水域的最大卷吸速度高于较老水域的峰值卷吸速度，这表明靠近河口的卷吸较强。夹带和混合时间尺度(最大环境洪水时1-4h)都小于半个潮汐周期，表明夹带和混合足够强烈，足以迅速减小羽流内的示踪剂变化。
The Connecticut River plume interacts with the strong tidal currents of the ambient receiving waters in eastern Long Island Sound. The plume formed during ambient flood tides is studied as an example of tidal river plumes entering into energetic ambient tidal environments in estuaries or continental shelves. Conservative passive freshwater tracers within a high-resolution nested hydrodynamic model are applied to determine how source waters from different parts of the tidal cycle contribute to plume composition and interact with bounding plume fronts. The connection to source waters can be cut off only under low-discharge conditions, when tides reverse surface flow through the mouth after max ambient flood. Upstream plume extent is limited because ambient tidal currents arrest the opposing plume propagation, as the tidal internal Froude number exceeds one. The downstream extent of the tidal plume always is within 20 km from the mouth, which is less than twice the ambient tidal excursion. Freshwaters in the river during the preceding ambient ebb are the oldest found in the new flood plume. Connectivity with source waters and plume fronts exhibits a strong upstream-to-downstream asymmetry. The arrested upstream front has high connectivity, as all freshwaters exiting the mouth immediately interact with this boundary. The downstream plume front has the lowest overall connectivity, as interaction is limited to the oldest waters since younger interior waters do not overtake this front. The offshore front and inshore boundary exhibit a downstream progression from younger to older waters and decreasing overall connectivity with source waters. Plume-averaged freshwater tracer concentrations and variances both exhibit an initial growth period followed by a longer decay period for the remainder of the tidal period. The plume-averaged tracer variance is increased by mouth inputs, decreased by entrainment, and destroyed by internal mixing. Peak entrainment velocities for younger waters are higher than values for older waters, indicating stronger entrainment closer to the mouth. Entrainment and mixing time scales (1–4 h at max ambient flood) are both shorter than half a tidal period, indicating entrainment and mixing are vigorous enough to rapidly diminish tracer variance within the plume.