Benthic production, respiration and methane oxidation in Lobelia dortmanna lawns
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Isoetid macrophytes such as Lobelia dortmanna and Littorella uniflora are engineering species with an extensive root system and high radial oxygen loss. Despite several studies on these macrophytes, the effect of their oxygenation on methane dynamics has never been investigated. In this study, we hypothesise that isoetids promote dissolved inorganic carbon fixation and methane oxidation in sandy sediments. Our whole-ecosystem approach study lasted 2 years (2013–2014) on two oligo-mesotrophic shallow lakes. Benthic chamber incubations confirmed that, as a result of primary production and methanotrophy, isoetid lawns had consistently lower benthic carbon fluxes than bare sediments. On a daily basis, vegetated areas acted as a carbon sink (−0.7 ± 0.4 g C m−2 days−1, as DIC + CH4), whereas bare sediments acted as a net source (0.6 ± 0.5 g C m−2 days−1, as DIC + CH4). Photosynthetic quotients of <1 indicated that photosynthetically produced oxygen was not released into the water column, but accumulated in leaf lacunae or was transferred to the rhizosphere, that contributing to the alteration of net benthic fluxes at the sediment–water interface. This preliminary study highlights the necessity of further investigating the role that isoetids play in mitigating greenhouse gas emissions from temperate shallow lakes.
KeywordsSubmerged aquatic vegetation Isoetid Radial oxygen loss Shallow lakes Greenhouse gas emissions Net ecosystem metabolism
Authors wish to thank K. Madarassou and M. Eon for nutrients analyses. T. Huguet, S. Moreira, G. Ducasse, J. Chabanne, J-C. Gregoire and D. Poirier also participated to field and laboratory activities. M. Bartoli (University of Parma, Italy) and A. Dutartre (Agence Régionale pour la Biodiversité - Aquitaine) provided technical and experiential expert advice. This work was funded by AEAG (Agence de l’Eau Adour-Garonne), within the conventions #310330085 and #310330109, by Irstea (Institut de Recherche Sciences et Technologies pour l’Environnement et l’Agriculture) and by Université de Bordeaux - CNRS UMR 5805.
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