Restored but Still Emitting: High CO ₂ Fluxes From a Mediterranean Wetland Challenge Inundation‐Based Restoration Strategies

Abstract

Mediterranean wetlands significantly influence terrestrial carbon storage but lack comprehensive, long‐term carbon flux measurements, particularly those that distinguish fluxes between vegetated and open‐water surfaces. Inundation‐based restoration primarily aims to arrest drainage‐driven soil‐carbon loss; whether a re‐flooded wetland also becomes a net CO ₂ sink is not guaranteed and depends on recovery time, wetland design, and vegetation establishment. We conducted a 3‐year (2021–2024) eddy covariance study using dual towers over a restored Mediterranean wetland (Agmon Hula, Israel) to partition CO ₂ fluxes between these surfaces. Results show that the restored wetland acted as a persistent net source of CO ₂ , emitting 3.8 ± 7.2 g C m ⁻²  day ⁻¹ (∼14 t C ha ⁻¹  yr ⁻¹ ), with open water (∼80% area) as a major source (5.0 ± 8.6 g C m ⁻²  day ⁻¹ ; ∼18.3 t C ha ⁻¹  yr ⁻¹ ), especially during summer nights driven by water‐to‐air temperature gradients and atmospheric instability, while vegetated zones acted as a net sink (−1.0 ± 11.3 g C m ⁻²  day ⁻¹ ; ∼−3.7 t C ha ⁻¹  yr ⁻¹ ). When placed in the context of reported Mediterranean wetland fluxes, the Hula wetland exhibits the highest CO ₂ emission rate observed for the region. Our findings indicate that commonly used functional relationships linking CO ₂ to hydrological conditions should explicitly account for surface heterogeneity and nocturnal atmospheric coupling. Furthermore, enhancing vegetation cover may be critical for shifting open‐water‐dominated Mediterranean wetlands toward net carbon sinks under changing climatic conditions.