Carbon fluxes under the littoral wet-dry continuum of natural shallow lakes

Lacustrine littoral zones are generally considered as carbon (C) sources towards the atmosphere because oxygen availability in sediments and dissolved organic matter stimulate bacterial respiration and carbon dioxide (CO₂) emissions. On the contrary, pelagic zones can promote methane (CH₄) emissions linked to anoxic conditions in sediments. These processes can be disrupted by aquatic primary production or by CH₄ oxidation. In the context of climate change and anthropogenic water withdrawals, long-lasting droughts will significantly increase the exposure to the air of lake littoral zones, that likely accelerating the organic matter decomposition and C emissions. In this study, we assess net ecosystem uptake and emission from C fluxes at the scale of two natural shallow lakes (SW of France) related to hydroperiod. CO₂ and CH₄ fluxes were measured seasonally by terrestrial and floating chambers in the littoral zone on soils exposed to the air under different conditions (presence or absence of vegetation, sands or organic sediments, degree of water saturation) and in the pelagic zone according to the depth. Our results reveal significant variations in C fluxes along the littoral wet-dry continuum, that underlying the relevance of considering the lacustrine littoral zone for obtaining comprehensive carbon budgets, especially within climate changing scenarios.