Dry habitats sustain high CO₂ emissions from temporary ponds across seasons

Despite the increasing understanding of the magnitude and drivers of carbon gas emissions from inland waters, the relevance of water fluctuation and associated drying on their dynamics is rarely addressed. Here, we quantified CO₂ and CH₄ fluxes from a set of temporary ponds across seasons. The ponds were in all occasion net CO₂ emitters irrespective of the presence or absence of water. While the CO₂ fluxes were in the upper range of emissions for freshwater lentic systems, CH₄ fluxes were mostly undetectable. Dry habitats substantially contributed to these emissions and were always a source of CO₂, whereas inundated habitats acted either as a source or a sink of atmospheric CO₂ along the year. Higher concentrations of coloured and humic organic matter in water and sediment were linked to higher CO₂ emissions. Composition of the sediment microbial community was related both to dissolved organic matter concentration and composition, but we did not find a direct link with CO₂ fluxes. The presence of methanogenic archaea in most ponds suggested the potential for episodic CH₄ production and emission. Our results highlight the need for spatially and temporally inclusive approaches that consider the dry phases and habitats to characterize carbon cycling in temporary systems.