Main content area

Source and age of dissolved and gaseous carbon in a peatland–riparian–stream continuum: a dual isotope (14C and δ 13C) analysis

Leith, F. I., Garnett, M. H., Dinsmore, K. J., Billett, M. F., Heal, K. V.
Biogeochemistry 2014 v.119 no.1-3 pp. 415-433
C3 plants, carbon, carbon dioxide, carbon sinks, dissolved organic carbon, emissions, hydrology, methane, peatlands, riparian areas, soil organic matter, soil profiles, stable isotopes, temperature
Radiocarbon isotopes are increasingly being used to investigate the age and source of carbon released from peatlands. Here we use combined¹⁴C and δ¹³C measurements to determine the isotopic composition of soil and soil decomposition products [dissolved organic carbon (DOC), CO₂and CH₄] in a peatland–riparian–stream transect, to establish the isotopic signature and potential connectivity between carbon pools. Sampling was conducted during two time periods in 2012 to investigate processes under different temperature, hydrological and flux conditions. Isotopic differences existed in the peatland and riparian zone soil organic matter as a result of the riparian depositional formation. The peatland had a mean radiocarbon age of 551 ± 133 years BP, with age increasing with depth, and δ¹³C values consistent with C3 plant material as the primary source. In contrast the riparian zone had a much older radiocarbon age of 1,055 ± 107 years BP and showed no age/depth relationship; δ¹³C in the riparian zone was also consistent with C3 plant material. With the exception of DOC in September, soil decomposition products were predominately >100 %modern with¹⁴C values consistent with derivation from organic matter fixed in the previous 5 years. Emissions of CO₂and CH₄from the soil surface were also modern. In contrast, CO₂and CH₄evaded from the stream surface was older (CH₄: 310–537 years BP, CO₂: 36 years BP to modern) and contained a more complex mix of sources combining soil organic matter and geogenic carbon. The results suggest considerable vertical transport of modern carbon to depth within the soil profile. The importance of modern recently fixed carbon and the differences between riparian and stream isotopic signatures suggests that the peatland (not the riparian zone) is the most important source of carbon to stream water.