Enhanced methane oxidation in an estuarine turbidity maximum

Methane and suspended particulate matter (SPM) concentrations, monitored bimonthly during one hydrological year (2003–2004) along 70 km transects in the tidal regions of the Garonne and Dordogne rivers (SW France), showed a significant negative correlation, both spatially and temporally. During spring in clear waters (SPM 2,000 mg L−1, but not after removing the SPM by settling (SPM = 16 mg L−1), nor in a sample collected few kilometers upstream, with SPM = 3 mg L−1. Methane oxidation was also able to draw down methane concentrations below half the atmospheric equilibrium value in an ETM sample. Suspended clays in the ETM enhance methane oxidation and strongly reduce methane fluxes to the atmosphere.