Publikationsdatum:
2023-01-18
Beschreibung:
Submitted in partial fulfillment of the requirements for the degree of Doctor of Philosophy at the Massachusetts Institute of Technology and the Woods Hole Oceanographic Institution September 2022.
Beschreibung:
Dispersion in estuaries sets the length of salinity intrusion and the horizontal mixing rate of waterborne constituents, including larvae, nutrients, sediments, and contaminants. While bulk calculations of dispersion are readily estimated using traditional field measurements, the mechanisms contributing to the total dispersion are difficult to identify because they require high temporal and spatial resolution to measure. Recent advances in field techniques and numerical modeling have enabled the isolated study of various mechanisms contributing to dispersion, many of which vary on tidal time-scales and over small spatial scales. The
objective of this thesis is to use a combination of high-resolution field measurements and numerical modeling to determine the mechanisms of dispersion that maintain the salt balance in the North River (Marshfield, MA), a tidally-dominated salt marsh estuary with complex topography. First, a field campaign was conducted to determine the dispersion associated with the out-of-phase exchange between tributary creeks and the main channel. Then, numerical simulations of an idealized estuary were conducted and a novel quasi-Lagrangian approach was applied to analyze the sources of dispersive salt fluxes throughout the estuary.
A second field campaign was conducted to evaluate the spatial variability of shear dispersion, particularly near regions of abrupt topographic variations. The key result from this thesis is obtained through the first application of the theoretical moving plane framework of Dronkers & van de Kreeke (1986), which confirms quantitatively that all landward salt flux at a fixed location must result from spatial correlations in velocity and salinity within a tidal excursion of the fixed location. Based on this result, the sources of the landward salt flux can be directly identified based on the spatial and tidal variations of shear dispersion, which can vary strongly due to its dependence on the local tidal currents, along-channel salinity gradient, and bathymetry. This thesis identifies and quantifies various mechanisms of topographically-induced tidal dispersion and thus highlights the dominant
role of topography in controlling the processes that contribute to mixing and transport in short, tidally-energetic estuaries.
Beschreibung:
The work presented in this thesis was funded largely by the National Science Foundation through a Graduate Student Research Fellowship (No. 1122374) in addition to NSF Grants OCE-1634490 and OCE-2123002. Additional funding was also provided from WHOI through the Michael J. Kowalski Fellowship for Ocean Science & Engineering and from MIT through an OGE Diversity Fellowship.
Schlagwort(e):
Estuary
;
Salinity
;
Dispersion
Repository-Name:
Woods Hole Open Access Server
Materialart:
Thesis
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