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

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. 13C 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).