Surface peat mass and carbon balance in a hypermaritime peatland

Net primary production (NPP) and decomposition were measured in a suite of representative microsite types, and Ph-210 age was determined on near-surface peat in a hypermaritime sloping peatland in British Columbia, Canada. Hummock and depression communities had significantly higher aboveground NPP, and were characterized by higher moss NPP than other communities. Mass loss of a standard litter material was significantly different among the microcommunities, possibly because of the differences in microsite oxic conditions and water movement. Incubated litter material lost C and gained N during the 2-yr trial in all microcommunities, except for the Sphagnum austinii hummock, where N was lost at shallow depth. Low N content in the living Sphagnum and further N depletion in hummocks suggest that the hummock Sphagnum peat is recalcitrant to decomposition. Peat accumulation was found to be faster in hummock than in lawn communities. The hummock Sphagnum NPP and mass loss values were higher than published values for continental peatlands, possibly due to the wet and mild hypermaritime climate in this region. The recalcitrant nature of the litter and high NPP in hummocks likely account for rapid peat accumulation at the surface, whereas peat decomposition is most pronounced with depth, resulting in similar C sink strength as in hummocks in continental peatlands. Given that lawn community predominates, overall C sequestration capacity at the study site was estimated to be smaller than in continental peatlands. Possible range of C sink strength in sloping open peatlands in the hypermaritime region, therefore, is lower than or close to that in continental peatlands.