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Aquatic Microbial Ecology

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AME 43:139-151 (2006)  -  doi:10.3354/ame043139

Modelling DOC assimilation and bacterial growth efficiency in biodegradation experiments: a case study in the Northeast Atlantic Ocean

Marie Eichinger*, Jean-Christophe Poggiale, France Van Wambeke, Dominique Lefèvre, Richard Sempéré

Laboratoire de Microbiologie Géochimie et Ecologie Marines (LMGEM) CNRS/INSU, UMR 6117, Centre d’Océanologie de Marseille, Université de la Méditerranée, Campus de Luminy, Case 901, 13 288 Marseille Cedex 9, France

ABSTRACT: A Monod (1942) model was used to describe the interaction and dynamics between marine bacteria and labile-dissolved organic carbon (l-DOC) using data obtained from 36 biodegradation experiments. This model is governed by 2 state variables, DOC and bacterial biomass (BB), and 3 parameters, specific maximum assimilation rate (Vmax), half-saturation constant (KS) and bacterial growth efficiency (BGE). The calibrations were obtained from biodegradation experiments carried out in the Northeast Atlantic Ocean over different seasons and at different depths. We also conducted a sensitivity analysis to determine (1) which parameter had the greatest influence on the model, and (2) whether the model was robust with regard to experimental errors. Our results indicate that BGE is greater in surface layers than in deeper waters, with minimum values observed during winter. In contrast, the Vmax/KS ratio is inversely dependent on depth and does not show any seasonal trend. This reflects an increase in bacterial affinity for substrate with increasing depth (decrease of KS) and/or better specific maximum assimilation rates (increase of Vmax). The sensitivity and robustness analyses demonstrate that the model is more sensitive to the Vmax/KS ratio than to BGE, and that the parameters estimated are reliable. However, although the BGE values are close to those estimated experimentally, the use of a constant Vmax/KS ratio and BGE in a 1-dimensional model is not appropriate as these parameters should be described as variables that take depth and season into account.

KEY WORDS: Bacterial growth efficiency · Monod model · Bacterial biodegradation · Northeast Atlantic Ocean

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