Sediment Resuspension and its Possible Link to Harmful Algal Blooms in a Shallow Micro-tidal Estuary
Abstract
The Lafayette estuary is a shallow micro-tidal estuary connected to the Chesapeake Bay. Despite extensive restoration efforts aimed at improving water quality, the estuary still suffers from nearly annual harmful algal blooms (HABs). Recent research suggests that the resuspension of nutrients and algal cysts during summer months leads to HAB initiation and that sediment resuspension, rather than freshwater runoff, could be an important contributing factor to initiation. In an effort to understand sediment resuspension's potential link to HAB initiation, this study was designed to quantify the seasonal variation in magnitude of the forces responsible for sediment resuspension. Current velocity, wave height, and suspended sediment concentration (SSC) were measured using acoustic and optical sensors, in conjunction with measurements of hydrographic properties, and collection of sediment and water samples. Meteorological data, including hourly wind speed and direction as well as precipitation totals, were also examined. Chlorophyll a measurements were used to monitor phytoplankton abundance and were examined for correlation to resuspension events. Results show that during 2017-2018 there were distinct wind patterns such that winds were generally weak and from the southwest during April through August, while from September through March, winds tended to strengthen and come from the northeast. The relatively weak southwest winds may produce just enough force to suspend cysts, nutrients, and some sediment, concurrent with the optimal water temperature and salinity conditions to initiate summer phytoplankton blooms. Although stronger and capable of resuspending more and larger particles, northeast winds occurred primarily during the cooler months so were less likely to result in blooms than summertime storm systems. At the study site, the fetch is greatest when winds are from the NNW, SSW, and east. Despite the greatest fetch nearly aligning with the most common wind patterns, resuspension events did not appear to be solely controlled by the winds. The Lafayette River watershed is fully urbanized and fairly sheltered, and this may limit the wind's effects on resuspension. However, the tide does appear to amplify resuspension as a result of surface gravity waves, leading to significant resuspension events.
- Publication:
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AGU Fall Meeting Abstracts
- Pub Date:
- December 2018
- Bibcode:
- 2018AGUFMOS22A..08M
- Keywords:
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- 0414 Biogeochemical cycles;
- processes;
- and modeling;
- BIOGEOSCIENCESDE: 4806 Carbon cycling;
- OCEANOGRAPHY: BIOLOGICAL AND CHEMICALDE: 4235 Estuarine processes;
- OCEANOGRAPHY: GENERAL