Linking Carbon Fluxes to Flooding Gradients in Sediments of Mediterranean Wetlands

Abstract

This study examines the seasonal variability of greenhouse gas (GHG) emissions from wetland sediments in the Iberian Peninsula in relation to water levels. It included coastal marshes, inland freshwater, and inland saline wetlands, three typical regional types. GHG fluxes peaked in coastal wetlands and were lowest in saline ones. Flux variations were driven by water depth, salinity, and sediment aeration. CO2 emissions peaked in dry zones and declined with water depth, while CH4 fluxes were more variable in waterlogged transition zones, particularly in coastal wetlands during spring and summer. CH4 emissions were lower in well-aerated, less-flooded areas and highest in shallowly flooded zones, where even a thin water layer restricts gas exchange, limiting oxygen and maintaining anaerobic conditions for methanogenesis. However, the lack of a deep-water column prevented methane oxidation, allowing diffusion into the atmosphere. Seasonal variation was higher in saline wetlands due to drought, while patterns in freshwater and coastal wetlands remained spatially more stable. Understanding these gradients is crucial for accurately modeling gas exchanges and assessing their role in climate change mitigation and adaptation. As interest in wetland carbon dynamics increases, integrating this modeling into management is vital to support restoration and long-term wetland sustainability.