UK peatland streams release old carbon dioxide to the atmosphere and young dissolved organic carbon to rivers

Abstract

Since the end of the last ice age, sequestration and storage of CO2 from the atmosphere by peatlands in the northern hemisphere has produced a terrestrial C pool of comparable magnitude to that of the global atmosphere. Destabilisation of the peatland C pool will have significant positive climate change feedbacks both directly (via the atmospheric pathway) and indirectly (via the aquatic pathway). Streams and rivers draining peatlands are supersaturated with CO2 and contain high concentrations of dissolved organic carbon (DOC); these are often associated with large lateral (downstream) and vertical (evasion) fluxes, which may produce significant changes in the sink/source relationships of individual peatlands. Here we present isotopic evidence from four UK peatlands to suggest that whilst the age of DOC released in the drainage system of peatlands is consistently young (modern to 202 years BP), the age of CO2 lost by evasion from the water surface is much older, varying from modern to 1449 years BP. δ13C data suggest that the sources of DOC and CO2 are different. Whilst antecedent moisture conditions affect within‐ and between‐site differences in the isotopic signature of DOC and CO2, we suggest that the release of CO2 (in contrast to DOC) into the aquatic system is related to a significantly older C pool. The source of this CO2 is likely to be both geogenic (carbonate weathering) and biogenic (decomposition of soil organic matter).

Carbon balance of UK peatlands: current state of knowledge and future research challenges

“…Measurements of DOC-14 C from UK peat catchments suggest that the majority is derived from recently fixed plant material rather than older peat (C. D. . On the other hand, 14 C measurements of evaded CO 2 suggest that significantly older C is being released in some peatland streams, some of which may be geogenic rather than biogenic in origin (Billett et al 2007). …”

Assessing the Effect of Sterilization on the Radiocarbon Signature of Freshwater Dissolved Organic Carbon

“…Diurnal fluorescence cycles in a Californian agricultural stream (Spencer et al 2007) suggest significant DOC processing over short time periods. Billett et al (2007) and Billett and Moore (2008) have shown that peat headwater streams are hotspots for CO 2 release. The recognition of the relative lability of dissolved organic matter in freshwater systems has therefore led to the increased interest in the use of radiocarbon analyses to understand the relative age and processing of DOC (Evans et al 2007;Tipping et al 2010).…”

Radiocarbon dating of methane and carbon dioxide evaded from a temperate peatland stream

“…Time-concentration changes (Figs 1 240 and 2) confirm that the build-up of CO 2 and CH 4 concentrations within the chambers was mostly linear and typical of diffusive emissions (Hornibrook 2009). In contrast, ebullition 242 events produce more temporally and spatially variable gas concentrations in collection chambers (Hornibrook 2009;Walter et al 2006Walter et al , 2008 (Billett et al 2006(Billett et al , 2007. CH 4 emitted by ebullition 330 from tundra and boreal lakes (Walter et al 2008) and Siberian thaw lakes (Walter et al 2006) has been reported to have considerably wider ranges in 14 C age, from > 40 000 years BP to 332 modern (e.g.…”

“…Mayorga et al 2005). Studies applying these techniques have shown that evaded CO 2 can vary considerably in age, ranging 58 from a few years for CO 2 degassing from Amazonian rivers (Mayorga et al 2005), to over 1000 years BP for some UK peatland streams (Billett et al 2006(Billett et al , 2007.…”

“…The 14 C content of CO 2 lost by evasion can be established using a direct method whereby the headspace of a floating chamber is sampled and the CO 2 component recovered 54 for analysis (e.g. using molecular sieve techniques; Billett et al 2006Billett et al , 2007. Alternatively, the 14 C content of evaded CO 2 can be inferred from analysis of the total DIC component of a…”