Tracking methane emission and oxidation in tropical peatland drainage canals using stable carbon isotopes

Abstract:

Drainage canals are a potentially important source of methane from tropical peatlands. Groundwater flow transports dissolved methane to canals, where it has the potential to escape to the atmosphere. However, these emissions are poorly characterized, and the extent to which methane is oxidised before being emitted to the atmosphere is unknown. In this study, we present data from a deforested tropical peatland in Brunei Darussalam. We measure stable carbon isotopes of methane and dissolved inorganic carbon (DIC) in peat porewater and canal water and create a numerical model which simulates carbon isotope transport through groundwater discharge, degassing and methane oxidation. DIC concentrations and carbon isotopic ratios in the canal are similar to the shallowest porewater samples and are distinct from the deeper porewater. DIC concentration and δ¹³C of DIC are nearly constant along the canal but show slight decreasing trends. Preliminary modelling results indicate that during low-flow conditions, most of the groundwater methane discharged to canals is oxidized to carbon dioxide and that the remainder is degassed to the atmosphere and exported through canal flow.