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Terrigenous Sediment Dynamics in a Small, Fringing Reef Embayment, Faga
Poster Title: Terrigenous Sediment Dynamics in a Small, Fringing Reef Embayment, Faga'alu, American Samoa
Submitted on 14 Jul 2016
Author(s): Messina, A, Biggs, T, Storlazzi, C, Cheriton, O
Affiliations: San Diego State University, U.S. Geological Survey
This poster was presented at 13th International Coral Reef Symposium
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Poster Information
Abstract: Watershed disturbance can increase sediment stress on corals, but clearly linking sediment sources to reduced coral health poses significant challenges for environmental managers. This study provides a template for managers in remote, sediment-impacted environments, who wish to quantify relationships between watershed sediment sources, water circulation over the reef, and the spatial distribution of sediment accumulation on the reef. In-stream sediment yields were monitored downstream of undisturbed forest, a quarry, and village, before and after sediment mitigation in the watershed. An event-wise sediment budget showed the disturbed quarry and village contributed about 70% of sediment loading to the embayment. Following sediment mitigation at the quarry, sediment loading to the embayment was significantly reduced. An empirical model of water circulation and residence time over the reef was developed from GPS drifters (5 drifters, 30 deployments) and acoustic current meters. Shortest residence times were on the exposed South Reef near breaking waves, and longest over the reef flat close to shore and sheltered northwest corner of the embayment. This circulation pattern explained the significantly higher accumulation of terrigenous sediment on the North Reef, than on the South Reef, as measured by tubes and SedPods. The sediment plume discharged during storms was deflected over the North Reef, leading to increased sediment accumulation on corals and reduced coral health. Conversely the South Reef remains relatively healthy due to the observed circulation pattern that prevents fine, terrigenous sediment from being transported over the South Reef.Summary: A ridge-to-reef assessment of terrigenous sediment dynamics in Faga'alu Bay and watershed, in American Samoa. Measurments of fluvial sediment yield, reef flat water currents, and sediment accumulation on the reef were made to understand where sediment was coming from the watershed and how it was distributed around the bay to negatively impact coral health.References: A.M. Messina, T.W. Biggs, Contributions of human activities to suspended sediment yield during storm events from a small, steep, tropical watershed, Journal of Hydrology, Volume 538, July 2016, Pages 726-742, ISSN 0022-1694, abuse »
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