Terrestrial ecosystems contain large amounts of carbon (C) and have the potential to significantly increase atmospheric carbon dioxide (CO₂) concentrations. Peatlands are particularly important for C storage, although little is known about the effects of anthropogenic activities on C balance in these ecosystems. Sheep-grazing and rotational burning are widely practised on blanket peat moorlands in the United Kingdom. The effects of these activities on C sequestration in peat has been investigated with a long-term randomized block experiment with treatments: (a) grazed + unburnt; (b) grazed + burnt every ten years; (c) ungrazed + unburnt. C accumulation under these treatments was compared by identifying a chronologically synchronous horizon within the peat common to all treatment plots. This fixed point was defined by the ‘take-off’ in concentration of spheroidal carbonaceous particles and was supported by the record of charcoal fragments. There was no significant difference in recent C accumulation rates between lightly grazed and ungrazed plots. In contrast, after 30 years there was significantly less C stored in the blanket peat in plots which had been burned every ten years. The results indicate that light sheep-grazing at this site did not affect rates of C accumulation in blanket peat, but decadal burning of moorland reduced C sequestration.