Type of Document	Thesis
Author	Laschet, Matthias
URN	etd-11102008-120451
Title	Oxygen Consumption Rates in Permeable Gulf of Mexico Sediments
Degree	Master of Science
Department	Oceanography, Department of
Advisory Committee	Advisor Name Title Markus Huettel Committee Chair Richard Iverson Committee Member Thorsten Dittmar Outside Committee Member
Keywords	Oxygen Consumption Marine Sediments
Date of Defense	2008-10-22
Availability	unrestricted
Abstract The objective of this study was to investigate oxygen consumption rates in permeable Gulf coast sediments and their link to changes in the water and sediment chlorophyll concentrations. The investigation was initiated to improve our understanding of the biogeochemical functioning of these sediments and their role in the coastal cycling of organic matter. Although sand is the most abundant sediment type on the continental shelf, the decomposition process in sediments affected by advective pore water exchange is not understood. Boundary-layer flows transport organic matter, nutrients and electron acceptors into nearshore permeable sediments thereby affecting benthic photosynthesis, microbial activity and oxygen dynamics. A series of advection chamber measurements was used to determine temporal and spatial variations in O2 consumption at two study sites located in the Northeastern Gulf of Mexico, with one site located at the exposed south side of St. George Island and the other more sheltered site in Apalachicola Bay. A time series analyzing sediment cores and overlying water samples provided data on the temporal and spatial dynamics of sedimentary and water column chlorophyll and oxygen concentrations. Sediment grain size and porosity were similar at the two sites, although Gulf sediments in general were more permeable (Gulf: 1.84 x10-11 to 5.29 x10-11, Bay 7.3x10-12 to 2.11x10-11) and had higher chlorophyll content at the Bay side (Gulf: 1.1 to 10.6 μg cm-3, Bay: 8.8 to 47.2 μg cm-3). At the Gulf site, O2 consumption rates ranged from 2 mmoles m-2 d-1 in winter to 17 mmoles m-2 d-1 in summer, while at the Bay site a maximum of 62 mmoles m-2 d-1 was recorded in August 2006 and a minimum of 11 mmoles m-2 d-1 in the winter. These rates demonstrate high metabolic activity in Gulf of Mexico nearshore sands despite their relatively low content of labile organic matter as reflected by their chlorophyll concentrations. Bay sediment chlorophyll in the upper 3 cm reached highest values in spring (March 2007: 47 μg cm-3), and the Gulf site in summer (July 2006: 10 μg cm-3). Our results highlight the role of filtering sublittoral sands as sites for high benthic organic matter turnover.
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