UMD Theses and Dissertations

Permanent URI for this collectionhttp://hdl.handle.net/1903/3

New submissions to the thesis/dissertation collections are added automatically as they are received from the Graduate School. Currently, the Graduate School deposits all theses and dissertations from a given semester after the official graduation date. This means that there may be up to a 4 month delay in the appearance of a given thesis/dissertation in DRUM.

More information is available at Theses and Dissertations at University of Maryland Libraries.

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2008 - 20102

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    The Abundance and Distribution of Transparent Exopolymer Particles in the Turbidity Maximum Region of Chesapeake Bay
    (2010) Malpezzi, Michael A.; Crump, Byron C; Marine-Estuarine-Environmental Sciences; Digital Repository at the University of Maryland; University of Maryland (College Park, Md.)
    Transparent exopolymer particle (TEP) concentrations were measured in the turbidity maximum (ETM) region of Chesapeake Bay during eight research cruises over a two-year period. TEP concentrations ranged from <100 to >2500 ug XG eq l^-1 and accounted for an estimated average of 31% ± 14 of POC. Spatially averaged TEP and chl a concentrations were positively correlated over the two year period, although these parameters were rarely correlated within cruises. Peak TEP concentrations were often separated from chl a maxima, suggesting that formation and concentration processes are more responsible for TEP concentrations than the proximity to precursor source material. Significant correlations between TEP and phaeophytin, POC, DOC, TSS and level of stratification were observed during some sampling periods. Settling tube experiments revealed a positive correlation between TEP concentration and the fraction of settling particulate matter. A hypothetical model for TEP formation and concentration in estuaries is proposed.
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    Density- and wind-driven lateral circulation and the associated transport of sediments in idealized partially mixed estuaries
    (2008-06-06) Chen, Shih-Nan; Sanford, Lawrence P; Marine-Estuarine-Environmental Sciences; Digital Repository at the University of Maryland; University of Maryland (College Park, Md.)
    Lateral circulation and the associated transport of sediments in idealized partially mixed estuaries are investigated using a three-dimensional, hydrostatic, primitive equation numerical model (ROMS). The model simulates a straight estuarine channel with a triangular cross-section. Attention is focused on lateral density (salinity) gradients, the major driving force for lateral circulation. Lateral salinity gradients can result from boundary mixing on a slope and differential advection of axial salinity gradients. Without wind forcing, the numerical experiments suggest that boundary mixing on a slope can drive significant lateral circulation when the water column is stratified. Boundary mixing is at least as important as differential advection for the modeled scenarios, when the two mechanisms are evaluated using the salt balance equation. Sediments are eroded in the channel and preferentially deposited on the right slope (looking seaward), mainly due to tidal pumping. Both stratification and axial salt transport show strong responses to axial wind forcing. While stratification is always reduced by up-estuary winds, stratification shows an increase-to-decrease transition as down-estuary wind stress increases, due to the competition between wind-induced straining of the axial salinity gradient and direct wind mixing. A horizontal Richardson number modified to include wind straining/mixing is shown to reasonably represent the transition. A regime classification diagram is proposed. Axial winds also exert important controls on lateral circulation. When the water column mixes vertically, surface Ekman transport is not a significant contributor to lateral circulation. Instead, wind-induced differential advection of the axial salinity gradient establishes lateral salinity gradients that in turn drive lateral circulation. A Hansen-Rattray-like scaling shows good predictive skill for variations in lateral flow. Event-integrated sediment transport is from channel to shoals during down-estuary winds but reversed for up-estuary winds. Accounting for wind-waves results in an order-of-magnitude increase in lateral sediment fluxes. The effects of wind-waves and seagrass beds on nearshore (< 2m) sediment dynamics are explored separately using a nearshore model (NearCoM). Without seagrass beds, wind-waves greatly enhance sediment resuspension, providing a large sediment source for lateral sediment transport. Seagrass beds attenuate wind-wave energy and trap sediments, thus reducing net sediment loss from the shallow shoal.