A mangrove nitrous oxide sink attenuates methane climate impacts

Abstract

We resolve mangrove nitrous oxide (N₂O), methane (CH₄), and carbon dioxide (CO₂) vertical exchange with the atmosphere and lateral exchange with the ocean. Our new observations in Brazil were combined with literature data to reassess the overall mangrove carbon sequestration potential. The pristine mangrove creek was a source of CO₂ and CH₄, and a sink for N₂O. The CO₂-equivalent N₂O uptake offset up to 71% of local CH₄ emissions. Global mangrove N₂O sinks offset 34% of water–air CH₄ emissions, potentially absorbing 0.6 Tg CO₂ equivalents per year. Overlooking lateral exchange led to a large underestimation of mangrove N₂O and CH₄ fluxes. Previous observations in mangroves receiving nitrogen-rich freshwater may have misattributed N₂O sources. Pristine seawater-dominated mangroves typically act as N₂O sinks while those influenced by anthropogenic inputs are sources. Overall, the observed N₂O sink further enhances the net climate benefit of mangroves.