Benthic Oxygen Fluxes Measured by Eddy Covariance in Permeable Gulf of Mexico Shallow-Water Sands

Oxygen fluxes across the sediment–water interface reflect primary production and organic matter degradation in coastal sediments and thus provide data that can be used for assessing ecosystem function, carbon cycling and the response to coastal eutrophication. In this study, the aquatic eddy covariance technique was used to measure seafloor– water column oxygen fluxes at shallow coastal sites with highly permeable sandy sediment in the northeastern Gulf of Mexico for which oxygen flux data currently are lacking. Oxygen fluxes at wave-exposed Gulf sites were compared to those at protected Bay sites over a period of 4 years and covering the four seasons. A total of 17 daytime and 14 nighttime deployments, producing 408 flux measurements (14.5 min each), were conducted. Average annual oxygen release and uptake (mean ± standard error) were 191 ± 66 and -191 ± 45 mmol m day for the Gulf sites and 130 ± 57 and -152 ± 64 mmol m day for the Bay sites. Seasonal variation in oxygen flux was observed, with high rates typically occurring during spring and lower rates during summer. The ratio of average oxygen release to uptake at both sites was close to 1 (Bay: 0.9, Gulf: 1.0). Close responses of the flux to changes in light, temperature, bottom current velocity, and wave action (significant wave height) documented tight physical–biological, benthic– pelagic coupling. The increase of the sedimentary oxygen uptake with increasing temperature corresponded to a Q10 temperature coefficient of 1.4 ± 0.3. An increase in flow velocity resulted in increased oxygen uptake (by a factor of 1–6 for a doubling in flow), which is explained by the enhanced transport of organic matter and electron acceptors into Electronic supplementary material The online version of this article (doi:10.1007/s10498-016-9305-3) contains supplementary material, which is available to authorized users. & Markus Huettel [email protected] 1 Cooperative Institute for Research in Environmental Sciences, University of Colorado Boulder, Boulder, CO 80309, USA 2 Department of Environmental Sciences, University of Virginia, Charlottesville, VA 22904, USA 3 Department of Earth, Ocean and Atmospheric Science, Florida State University, Tallahassee, FL 32306, USA 123 Aquat Geochem DOI 10.1007/s10498-016-9305-3