Methane in pristine and impaired mangrove soils and its possible effect on establishment of mangrove seedlings

Pristine and impaired mangrove soils (from road construction, aquaculture, and sewage) in Baja California Sur, Mexico were investigated for methane dynamics, related soil properties, and their impact on initial establishment of black mangrove propagules. All soils (Salic Fluvisols and Histosols) had neutral to alkaline pH, were saline, and had variable organic carbon content, and redox potentials. Most pristine mangrove soils showed low methane concentration, low methane production rates, and no methane emission. Impaired mangrove soil (from aquaculture) and mangrove soil affected by sewage water showed high methane concentration, high methane production rates, and high methane emission, thus acting as a methane source. Elevated methane concentrations, similar to levels detected in the impaired mangrove soil, reduce the growth of seedlings under closed chamber conditions. Addition of sulfate to the soil reversed the trend. These results indicate that impaired mangrove soils in dry climatic regions produce and emit methane and that elevated methane concentration in the vicinity of propagules may affect establishment of mangrove seedlings in impaired mangrove soils.