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A novel high-resolution in situ tool for studying carbon biogeochemical processes in aquatic systems: The Lake Aiguebelette case study
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  • Roberto Grilli,
  • Tonya DelSontro,
  • Josette Garnier,
  • Frederick Jacob,
  • Julien Némery
Roberto Grilli
Univ. Grenoble Alpes, CNRS, IRD, Grenoble INP (Institute of Engineering), IGE

Corresponding Author:roberto.grilli@cnrs.fr

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Tonya DelSontro
Université du Québec à Montréal
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Josette Garnier
CNRS & University Pierre and Marie Curie
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Frederick Jacob
Electricité de France, Hydro Engineering Centre
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Julien Némery
University of Grenoble Alpes /CNRS/IRD,
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Lakes and reservoirs are a significant source of atmospheric methane (CH4), with emissions comparable to the largest global CH4 emitters. Understanding the processes leading to such significant emissions from aquatic systems is therefore of primary importance for producing more accurate projections of emissions in a changing climate. In this work, we present the first deployment of a novel membrane inlet laser spectrometer (MILS) for fast simultaneous detection of dissolved CH4, C2H6 and d13CH4. During a 1-day field campaign, we performed 2D mapping of surface water of Lake Aiguebelette (France). In the littoral (pelagic) area, average dissolved CH4 concentrations and d13CH4 were 391.9 ± 156.3 (169.8 ± 26.6) nmol L-1 and -67.3 ± 3.4 (-61.5 ± 3.6) ‰, respectively. The dissolved CH4 concentration in the pelagic zone was fifty times larger than the concentration expected at equilibrium with the atmosphere, confirming an oversaturation of dissolved CH4 in surface waters over shallow and deep areas. The results suggest the presence of CH4 sources less enriched in 13C in the littoral zone (presumably the littoral sediments). The CH4 pool became more enriched in 13C with distance from shore, suggesting that oxidation prevailed over epilimnetic CH4 production, that was further confirmed by an isotopic mass balance technique with the high-resolution transect data. This new in situ fast response sensor allows to obtain unique high-resolution and high-spatial coverage datasets within a limited amount of survey time. This tool will be useful in the future for studying processes governing CH4 dynamics in aquatic systems.