Increase in CH ₄ Emissions in a Pantanal Wetland Lagoon Due to Extreme Drought and Sediment Exposure

ABSTRACT The Pantanal, one of the largest wetlands on Earth, stores substantial carbon in its diverse ecosystems but faces increasing threats, such as fires, poor soil management, deforestation, and climate change impacts that may elevate CH₄ emissions. Given the importance of this ecosystem, we investigated methane (CH 4 ) emissions from the limnetic zone and marginal soils in a drying lagoon in the Pantanal during a drought period unprecedented in over 75 years. To this end, CH₄ flux measurements were conducted along a transect with three replicates in each of the evaluated compartments, with four samples collected per day during both a dry‐season and a wet‐season campaign (2019–2020). The highest emissions occurred during the drying event, primarily in the aquatic compartment (7.43 mg ± 5.51 CH₄ m⁻² day⁻¹, mean ± SD, n = 20), representing a 56‐fold increase in CH₄ emissions compared to the wet season, and along the margins (3.43 ± 3.55 mg CH₄ m⁻² day⁻¹, n = 12). This indicates that the lowering of the water column and exposed sediments became a significant source of CH₄ emissions. Our results suggest that these environments can become large CH₄ emitters during drying events. Accordingly, current CH₄ emission models underestimate their contribution due to neglecting sediment exposure effects. With the expected increase in drying events in the Pantanal, CH₄ emissions will likely rise in the coming years, exacerbating global warming and intensifying climate change.