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La Tour du Valat

Institut de recherche pour la conservation des zones humides méditerranéennes

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Titre :	Microelectrode Study of Oxygen Uptake and Organic Matter Decomposition in The Sediments of Xiamen Western Bay
Auteurs :	Kunming Xu, Auteur ; Liping Zhang, Auteur ; Wenbin Zou, Auteur
Type de document :	Article
Dans :	Estuaries and Coasts (32(3) MAY 2009)
Article en page(s) :	425-435
Résumé :	Sediment cores were sampled from Xiamen Western Bay at five sites during the summer and winter of 2006 and Hg-Au microelectrodes were used to make on board measurements of the concentration gradients of dissolved oxygen, Mn(2+), and Fe(2+) within the sediments. The O(2) concentrations decreased sharply from about 200 mu mol L(-1) in the bottom seawater to zero within a depth of a few millimeters into the sediment. Dissolved Mn(2+) was detected below the oxic zones with peak concentrations up to 600 mu mol L(-1), whereas dissolved Fe(2+) had peak concentrations up to 1,000 mu mol L(-1) in deeper layers. The elemental contents of organic carbon and nitrogen within the sediments were analyzed and their C/N ratios were in the range of 9.0 to 10.1, indicative of heavy terrestrial origin. Sediments from two sites near municipal wastewater discharge outlets had higher organic contents than those from the other sites. These high organic contents corresponded to shallow O(2) penetration depths, high dissolved Mn(2+) and Fe(2+) concentrations, and negative redox potentials within the sediments. This indicated that the high organic matter content had promoted microbial respiration within the sediments. Overall, the organic content did not show any appreciable decrease with increasing sediment depths, so a quadratic polynomial function was used to fit the curve of O(2) profiles within the sediments. Based on the O(2) profiles, O(2) fluxes across the seawater and sediment interface were estimated to be in the range 6.07 to 14.9 mmol m(-2) day(-1), and organic carbon consumption rates within the surface sediments were estimated to be in the range 3.3 to 20.8 mgC cm(-3) a(-1). The case demonstrated that biogeochemistry within the sediments of the bay was very sensitive to human activities such as sewage discharge.

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