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La Tour du Valat

Institut de recherche pour la conservation des zones humides méditerranéennes

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Titre :	The Effects of Oxygen Transition on Community Respiration and Potential Chemoautotrophic Production in a Seasonally Stratified Anoxic Estuary
Auteurs :	Dong Y. Lee, Auteur ; Michael S. Owens, Auteur ; Mary Doherty, Auteur ; Erin M. Eggleston, Auteur ; Ian Hewson, Auteur ; Byron C. Crump, Auteur ; Jeffrey C. Cornwell, Auteur
Type de document :	Article
Dans :	Estuaries and Coasts (38(1) JAN 2015)
Article en page(s) :	104-117
Résumé :	To assess the effects of seasonal oxygen transition on microbial metabolism, we measured spatiotemporal changes in total dissolved inorganic carbon, respiratory products, and geochemical constituents in the mesohaline region of Chesapeake Bay from May to October 2010. Vertical redox zonation was examined, and a spatial transect survey was also conducted from the southern to northern limit of the mesohaline region in July providing an alternative approach for assessing the temporal dynamics of oxygen transition. The transitions from oxic to hypoxic to anoxic and back to oxic were illustrated by the pattern of nitrogen redox species. Respiration, measured from changes in total dissolved inorganic carbon (Delta DIC) and dissolved oxygen (Delta DO) during incubations, had an average respiratory quotient (Delta DIC/Delta DO) of 1.04 +/- 0.06 under oxic conditions and 1.58 +/- 0.48 under hypoxic conditions. The difference in the respiratory quotients suggested that oxygen-based respiration measurements would underestimate community respiration rates in hypoxic conditions. In the present study, we observed within the surface-mixed layer three-to sevenfold differences in temporal and vertical variation of community respiration, while net respiration across oxyclines and anaerobic respiration in deep waters had lower rates and variability. In some anoxic samples, there was a net decrease in dissolved inorganic carbon that was exacerbated with experimental augmentation of terminal electron acceptors. Potential carbon fixation rates of chemoautotrophs within and below oxyclines were estimated and ranged from 0.63 to 116.9 mg C m(-2) day(-1) depending on growth conditions. These results indicate that anaerobic metabolism during the seasonal anoxic transition and at oxic/anoxic interface can play an important role in the estuarine carbon cycle.

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