Nature – Roth et al. (2023): Methane emissions offset atmospheric carbon dioxide uptake in coastal macroalgae, mixed vegetation and sediment ecosystems

Florian Roth, Elias Broman, Xiaole Sun, Stefano Bonaglia, Francisco Nascimento, John Prytherch, Volker Brüchert, Maysoon L. Zara, Lundevall Zara, Märta Brunberg, Marc C. Geibel, Christoph Humborg, Alk Norkko IN: Nature Communications 14, 42,

Knowledge of mechanisms sustaining such CH4 emissions and their contribution to net radiative forcing remains scarce for globally prevalent macroalgae, mixed vegetation, and surrounding depositional sediment habitats. Here the authors show that these habitats emit CH4 in the range of 0.1 – 2.9 mg CH4 m−2 d−1 to the atmosphere, revealing in situ CH4 emissions from macroalgae that were sustained by divergent methanogenic archaea in anoxic microsites. Over an annual cycle, CO2-equivalent CH4 emissions offset 28 and 35% of the carbon sink capacity attributed to atmospheric CO2 uptake in the macroalgae and mixed vegetation habitats, respectively, and augment net CO2 release of unvegetated sediments by 57%.