A rapid method to collect methane from peatland streams for radiocarbon analysis

Abstract

Peatland streams typically contain high methane concentrations and act as conduits for the release of this greenhouse gas to the atmosphere. Radiocarbon analysis provides a unique tracer that can be used to identify the methane source, and quantify the time elapsed between carbon fixation and return to the atmosphere as CH4. Few studies – those that have focus largely on sites with bubble (ebullition) emissions – have investigated the14C age of methane in surface waters because of the difficulty in collecting sufficient CH4for analysis. Here, we describe new sampling methods for the collection of CH4samples from CH4-oversaturated peatland streams for radiocarbon analysis. We report the results of a suite of tests, including using methane14C standards and replicated field measurements, to verify the methods. The methods are not restricted to ebullition sites, and can be applied to peatland streams with lower methane concentrations. We report the14C age of methane extracted from surface water samples (~4–13 l) at two contrasting locations in a temperate raised peat bog. Results indicate substantial spatial variation with ages ranging from ~400 (ditch in afforested peatland) to ~3000 years BP (bog perimeter stream). These contrasting ages suggest that methane in stream water can be derived from a wide range of peat depths. This new method provides a rapid (10–15 min per sample) and convenient approach, which should make14CH4dating of surface water more accessible and lead to an increased understanding of carbon cycling within the soil–water–atmosphere system.