Interannual Variability in Greenhouse Gas Emissions Challenges Post-Restoration Net Sink Predictions in California Delta Wetlands
Kasak, Kuno (University of Tartu. Department of Geography)
Ahmadi, Arman (University of California Berkeley. Department of Environmental Science Policy and Management)
Dronova, Iryna (University of California Berkeley. Department of Environmental Science Policy and Management)
Arias Ortiz, Ariane (Universitat Autònoma de Barcelona. Departament de Física)
Wang, Tianxin (University of California Berkeley. Department of Environmental Science Policy and Management)
Valach, Alex C. (Bern University of Applied Sciences)
Szutu, Daphne (University of California Berkeley. Department of Environmental Science Policy and Management)
Verfaillie, Joseph (University of California Berkeley. Department of Environmental Science Policy and Management)
Baldocchi, Dennis (University of California Berkeley. Department of Environmental Science Policy and Management)

Date:	2026
Abstract:	Globally, wetlands can sequester and store large amounts of soil carbon over the long term due to high primary productivity and slow decomposition. Yet centuries of drainage for agriculture and development have turned many of these carbon sinks into greenhouse gas (GHG) sources. Restoring degraded wetlands, particularly in peat- rich landscapes, is increasingly promoted as a nature- based solution for climate change mitigation. However, the trajectory and timing of recovery remain uncertain, especially given the complex interplay among vegetation dynamics, hydrology, and GHG fluxes. In this study, we analyzed 44 site- years of continuous eddy covariance measurements of carbon dioxide (CO2) and methane (CH4) fluxes from restored wetlands in California's Sacramento- San Joaquin Delta. Our findings reveal substantial interannual variability in GHG exchange across sites, driven by differences in restoration design, water management, and vegetation establishment. While rapid vegetation growth, especially dense stands of macrophytes, can enhance CO2 uptake, it often elevates CH4 emissions and complicates predictions of when wetlands become net GHG sinks. Crucially, wetlands with delayed vegetation establishment due to high or inconsistent water levels (e. g. , significant drawdown) remained persistent GHG sources, even years after restoration. Conversely, sites with tailored planting or natural and rapid recolonization exhibited earlier transitions to net sink status, including earlier shifts towards net negative radiative forcing since the restoration. The study highlights the importance of adaptive, site- specific restoration strategies and long- term monitoring to capture switchover dynamics from sources to sinks. As global investment in wetland restoration grows, our findings underscore the need to balance climate mitigation goals with ecological realities and the self- designing processes of vegetation succession.
Grants:	Agencia Estatal de Investigación RYC2021-034455-I
Rights:	Aquest document està subjecte a una llicència d'ús Creative Commons. Es permet la reproducció total o parcial, la distribució, la comunicació pública de l'obra i la creació d'obres derivades, fins i tot amb finalitats comercials, sempre i quan es reconegui l'autoria de l'obra original.
Language:	Anglès
Document:	Article ; recerca ; Versió publicada
Subject:	Carbon dioxide ; Carbon sequestration ; Eddy covariance ; Methane ; Radiative forcing ; Switchover time
Published in:	Global change biology, Vol. 32, Num. 1 (January 2026) , art. e70700, ISSN 1365-2486

DOI: 10.1111/gcb.70700
PMID: 41517899

19 p, 5.1 MB

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