Abstract
AbstractPeatland 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 the 14C age of methane in surface waters because of the difficulty in collecting sufficient CH4 for analysis. Here, we describe new sampling methods for the collection of CH4 samples from CH4‐oversaturated peatland streams for radiocarbon analysis. We report the results of a suite of tests, including using methane 14C 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 the 14C 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 make 14CH4 dating of surface water more accessible and lead to an increased understanding of carbon cycling within the soil–water–atmosphere system. © 2015 The Authors. Ecohydrology published by John Wiley & Sons Ltd.
Highlights
Inland waters, including streams, rivers and lakes are increasingly recognised for the important role that they play in the transport of carbon from terrestrial ecosystems to the atmosphere (Repo et al, 2007; Dinsmore et al, 2010; Aufdenkampe et al, 2011)
Most of the carbon lost to the atmosphere is in the form of carbon dioxide (CO2), many inland waters and in particular peatland streams contain large concentrations of methane (CH4), another powerful greenhouse gas (e.g. Hope et al, 2001; Billett and Harvey, 2013)
The key methodological advance was to recover sufficient CH4 in the field for routine radiocarbon analysis by accelerator mass spectrometry (AMS) using minimal equipment, providing a robust and rapid method suitable for inaccessible locations. Using this method, a single operator is likely to be capable of recovering 8–10 samples of headspace gas collected in sample bags, which might otherwise require the transport of at least 50–100 l of water if the gas had to be extracted in a laboratory
Summary
Inland waters, including streams, rivers and lakes are increasingly recognised for the important role that they play in the transport of carbon from terrestrial ecosystems to the atmosphere (Repo et al, 2007; Dinsmore et al, 2010; Aufdenkampe et al, 2011). Most of the carbon lost to the atmosphere is in the form of carbon dioxide (CO2), many inland waters and in particular peatland streams contain large concentrations of methane (CH4), another powerful greenhouse gas Hope et al, 2001; Billett and Harvey, 2013) While both gases are sparingly soluble in freshwater, CH4 has a lower solubility and is rapidly lost to the atmosphere (Chanton, 2005). To quantify the role of inland waters in greenhouse gas emissions, it is important to understand the
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