Sources and Age of Aquatic DOC, CO2 And CH4 Exported From a Swedish Peatland

Abstract:

Northern peatlands store as much organic matter as the equivalent of all the CO₂ currently present in the earth’s atmosphere. The peat carbon storage results from the progressive accumulation of organic matter since the end of the last glaciation (~10 000 years). The stability of these large carbon storages, under the influence of climate change, is unknown. Runoff represents one of the major C fluxes out of northern peatlands, and is particularly sensitive to changes in climate and hydrological regimes. Identifying the sources and age of aquatic C export will help assess the stability and future role of northern peatlands as active components of the global C cycle. We have characterized both radiogenic (¹⁴C) and stable carbon isotopes (δ¹³C) of DOC, CO₂ and CH₄ across a four-meter deep ombrotrophic peatland and its stream outlet. Previous studies have shown that about 34% of the estimated net ecosystem exchange from this peatland system, is lost through aquatic C export. We determined that fermentation processes in the peat acts as the main production pathway for stream CO₂ (mean δ¹³C =-4.9‰) and CH₄ (mean δ¹³C = -67.8‰). The seasonal variability in both sources and age of C was high. Despite this dynamism, the application of carbon isotopes allowed us to trace back the origin of aquatic C exports from the peatland.