Assessing the effects of restoration and conservation on gaseous carbon fluxes and climate mitigation potential across six European coastal wetlands

Miguel Cabrera-Brufau, Camille Minaudo, Katrin Attermeyer, Alba Camacho-Santamans, Rafael Carballeira, Benjamin Misteli , Jorge Juan Montes-Pérez, Daniel Morant, Biel Obrador, Antonio Picazo, Carlos Rochera, Mihai Adamescu, Raquel Ambrosio, Giancarlo Bachi, Nina Bègue, Martynas Bučas, Lídia Cañas Ramírez, Marco Carloni, Lamara Cavalcante, Constantin Cazacu, Giovanni Checcucci, João Pedro Coelho, Valentin Dinu, Valtere Evangelista, Ilenia Férez Martín, Jonas Gintauskas, Relu Giuca, Anis Guelmami, Mirco Guerrazzi, Samuel Hilaire, Marija Kataržytė, Ana I. Lillebø, Raquel Lizán, Bruna R.F. Oliveira, Vitor H. Oliveira, Marta Pedrón, Jolita Petkuvienė, Tudor Racoviceanu, Michael Ronse, Chiara Santinelli, Ana Sousa, Wouter Suykerbuyk, Edvinas Tiškus, Claudia Tropea, Diana Vaičiūtė, Silvia Valsecchi, Marinka E.B. van Puijenbroek, Mourine J. Yegon, Antonio Camacho, Daniel von Schiller

Coastal wetlands play a substantial role in regulating Earth’s climate through exchanges of greenhouse gases (GHGs). Current European policies promote widespread coastal wetland restoration to reverse historical losses and ongoing pressures. However, substantial uncertainty remains regarding how carbon dioxide (CO2) and methane (CH4) fluxes respond to restoration across different coastal wetland types and whether these responses translate into net climate mitigation in terms of CO2 equivalents (CO2-eq). We measured simultaneous CO2 and CH4 fluxes using static chambers across four seasons at multiple locations spanning preserved, altered and restored sites within six European coastal wetlands of different ecological types. By comparing GHG exchanges and resulting CO2-eq balances across wetlands, we identified dominant biogeochemical drivers of CO2 and CH4 dynamics and assessed the climate mitigation potential of conservation and restoration actions. CO2 fluxes were primarily controlled by landscape-scale vegetation cover and inundation, whereas CH4 emissions responded to less evident changes in water quality, salinity and wetland hydrodynamics. Comparisons of CO2-eq balances between altered and restored sites showed that seagrass replantation was associated with significant mitigation potential under both 100-year and 20-year CH4 warming scenarios, while eutrophication reversal through improved water treatment was only significant under the 20-year scenario. In contrast, other restoration measures modified CO2 and CH4 fluxes in opposing directions, resulting in no significant net change in combined CO2-eq balances. Overall, our results demonstrate that climatic responses to coastal wetland restoration are both GHG-specific and wetland-type dependent, underscoring the need for tailored restoration strategies and robust, multi-GHG monitoring to detect and accurately quantify potential climatic benefits.