Driving and limiting factors of CH₄ and CO₂ emissions from coastal brackish-water wetlands in temperate regions

Abstract. Coastal wetlands are fundamental for climate-change mitigation thanks to their ability to store large amounts of organic carbon in the soil. They also represent the first natural emitter of methane (CH₄). Salinity is known to inhibit CH₄ production, but its effect in brackish ecosystems is still poorly understood. Our study aims to understand how environmental variables may affect greenhouse gas emissions (GHGs) in coastal temperate wetlands. We present the results of over one year of measurements performed in four wetlands located along a salinity gradient on the northeast Adriatic coast near Ravenna, Italy. Soil properties were determined by collecting soil samples, while carbon dioxide (CO₂) and methane (CH₄) fluxes from soils and standing waters, water levels, surface, and groundwater physical-chemical parameters (temperature, pH, electrical conductivity, and sulphate concentrations of water) were monthly monitored by a portable gas flux-meter and multiparametric probes, respectively. Principal component analysis (PCA) was used to investigate emergent relationships between GHGs fluxes and environmental variables. Our results suggest that, among all variables, temperature and irradiance play a significant role in CH₄ emissions from water and soil whereas water column depth and salinity are limiting factors of GHGs emissions.