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The biogeochemical cycling of methane in Ria de Vigo, NW Spain: Sediment processing and sea-air exchange

Lookup NU author(s): Dr Vassilis Kitidis, Louise Tizzard, Dr Guenther Uher, Professor Robert Upstill-Goddard, Professor Ian Head, Dr Neil Gray, Gillian Taylor

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Abstract

Methane (CH4) concentrations were measured in the water column, in sediment porewaters, and in atmospheric air, in the Ría de Vigo, NW Spain, during both the onset (April 2003) and at the end of (September 2004) seasonal upwelling. In addition, CH4 concentration and stable isotopic signatures (δ13CH4) were measured in porewaters, and sediment methanogenesis and aerobic oxidation of CH4 were determined in sediment incubations. Surface water column CH4 (2 m depth) was in the range 3-180 nmol l- 1 (110-8500% saturation) and followed a generally landward increase but with localised maxima in both the inner and middle Ría. These maxima were consistent with CH4 inputs from underlying porewaters in which CH4 concentrations were up to 3 orders of magnitude higher (maximum 350 μmol l- 1). Surface water CH4 concentrations were approximately three times higher in September than in April, consistent with a significant benthic CH4 flux driven by enhanced sediment methanogenesis following the summer productivity maximum. CH4 and δ13CH4 in sediment porewaters and in incubated sediment slurries (20 °C) revealed significant sediment CH4 oxidation, with an apparent isotopic fractionation factor (rc) of ∼ 1.004. Using turbulent diffusion models of air-sea exchange we estimate an annual emission of atmospheric CH4 from the Ría de Vigo of 18-44 × 106 g (1.1-2.7 × 106 mol). This estimate is approximately 1-2 orders of magnitude lower than a previous estimate based on a bubble transport model. © 2006 Elsevier B.V. All rights reserved.


Publication metadata

Author(s): Kitidis V, Tizzard L, Uher G, Judd A, Upstill-Goddard RC, Head IM, Gray ND, Taylor G, Duran R, Diez R, Iglesias J, Garcia-Gil S

Publication type: Article

Publication status: Published

Journal: Journal of Marine Systems

Year: 2007

Volume: 66

Issue: 1-4

Pages: 258-271

ISSN (print): 0924-7963

ISSN (electronic):

Publisher: Elsevier BV

URL: http://dx.doi.org/10.1016/j.jmarsys.2006.03.022

DOI: 10.1016/j.jmarsys.2006.03.022

Notes: 5th International Symposium on Gas Transfer at Water Surfaces - Selected papers from the 37th International Liège Colloquium on Ocean Dynamics, 37th International Liege Colloquium on Ocean Dynamics


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