Autumnal fluxes of CH4 and CO2 from Mediterranean reed wetland based on eddy covariance and chamber methods

Atmospheric methane (CH4) and carbon dioxide (CO2) concentration have been increasing during the last several centuries due to changes in agricultural practices and other anthropogenic activities. Both greenhouse gases (GHGs), have a significant impact on the Earth's radiative balance. GHG effluxes of CH4 and CO2 were measured in a warm Mediterranean wetland in south of Spain. The dominant vegetation cover at the site was by common reed (Phragmites australis) and the measurements were done during short measurement campaign in early autumn 2015. Gas-flux measurements were carried out applying two methods, the eddy covariance (EC) technique and the chamber method (CM). These two methods representing different ecosystem subsets, with EC representing the plant/ecosystem subset and CM representing the water/soil subset. In our measurement cam- paigns using CM, CH4 emissions ranged from 7.2 to 17.7 mg CH4-C m(-2) d(-1) and CO2 emissions from 0.53 to 1.27 g CO2-C m(-2) d(-1). When using EC, the average fluxes of CH4 and CO2 were 31.4 mg CH4-C m(-2) d(-1) and 1.32 g CO2-C m(-2) d(-1), respectively. Relationships between gas fluxes (CO2 and CH4) measured by the EC method were quite closely correlated with photosynthetically active solar radiation. Our results showed higher CO2 carbon released from the water/soil ecosystem subset in comparison to plants subset. On the other hand, the estimated CH4 carbon balance for the plant/ecosystem subset was about twice that of the water/soil ecosystem subset. Overall, we showed that EC and CM methods cover different areas making EC advantageous for integrated measurements over larger areas, while the CM approach is suitable for local and spatially well constrained flux measurements. Hence, EC and CM methods should be seen as complementary rather than fully comparable methods.