Intact Australian Sphagnum peatland is a strong carbon sink.

Peatlands are important global stores of carbon. However, peatland disturbance, including climate change, can cause stored carbon to be released, shifting peatlands from net carbon sinks to net carbon sources. Yet, there is a paucity of data on the carbon cycling of Australian peatlands from which to inform effective management of the peatland carbon store. Here, we present the first estimation of the seasonal and annual net ecosystem carbon balance (NECB) of an intact Sphagnum-dominated peatland in the Australian Alps. We measured the net ecosystem exchange of CO (NEE), methane emission (CH), and aquatic fluxes of dissolved organic carbon (DOC) and dissolved inorganic carbon (DIC), over a two-year period. Overall, the ecosystem acted as a strong net carbon sink of -292.5 g C m yr. The annual NECB exhibited distinct intra-annual variability, shifting from a strong carbon sink in the growing period (-444.1 g C m period) to a carbon source in the non-growing period (151.6 g C m period). Estimates of non-CO fluxes were relatively small: emission of CH was 2.4 g CH-C m yr; DOC flux was 8.7 g C m yr; and evasion flux was 18.5 g C m yr; together comprising <10 % of annual NECB. The large observed net carbon uptake suggests that the carbon sequestration potential of the study site is exceptionally high, likely due to its occurrence in a temperate region with a relatively long growing period.