Date of Completion

4-26-2019

Embargo Period

4-26-2019

Keywords

Long Islands Sound, Dispersion, Coastal Islands, River Water, Mixing, Residence Time, Flushing Time, Hypoxia, Summer

Major Advisor

Michael M. Whitney

Associate Advisor

David Bjerklie

Associate Advisor

Kelly Lombardo

Associate Advisor

Craig Tobias

Field of Study

Oceanography

Degree

Doctor of Philosophy

Open Access

Open Access

Abstract

The Regional Ocean Modeling System, in conjunction with a watershed model, was applied with conservative passive tracers to identify the distribution, mixing, freshwater residence times, and storm response for all of the river systems influencing Long Island Sound (LIS) during the summer of 2013. The Connecticut River was the largest freshwater source throughout the estuary. The Connecticut River strengthened bulk stratification in eastern LIS the most. The Housatonic River (the second largest freshwater source) and the Hudson River had the strongest influence on stratification in central and western LIS, respectively. Smaller coastal rivers were most influential in strengthening stratification near the southwestern Connecticut shoreline. Overall, river water was close to a well-mixed state throughout LIS, but more stratified near river mouths. Freshwater residence time estimates indicated monthly to multi-seasonal time scales and grew longer with greater distance from the LIS mouth.

Effects of islands and shoals on coastal water temperature and salinity, flushing time, and dispersion near small coastal rivers were quantified for summer 2015 for an area along the southwestern Connecticut shoreline, inshore of the Norwalk Islands. Island and shoal effects were isolated through intercomparison of three model runs with islands and shoals either present or removed. The presence of islands (shoals) resulted in cooler (warmer) and saltier (fresher) water immediately inshore of the islands. Shoals influenced a larger area with higher-magnitude water-property differences. Islands altered residual currents by intensifying eddies and creating across-shore exchange through island passes. Islands (shoals) reduced (increased) flushing time. The retention effect of the shoals dominated over the dispersive influence of the islands for two days after dye tracer release, but the effects offset each other for later times.

Temperature fluxes for the Norwalk River estuary were then computed and compared to the results of a related observationally-based study to quantify the importance of advective cooling to embayment temperatures. Model results agreed qualitatively with observationally-based results, with surface heating being the primary source of heating and advection being the primary source of cooling for the Norwalk River estuary.

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