SPATIAL VARIATION IN RATES OF CARBON AND NITROGEN ACCUMULATION IN A BOREAL BOG

Abstract

Although previous studies hint at the occurrence of substantial spatial variation in the accumulation rates of C and N in bogs, the extent to which rates may vary on high-resolution spatial and temporal scales is not known. A main reason for the lack of knowledge is that it is problematic to determine the precise age of peat at a given depth. We determined rates of carbon and nitrogen accumulation in the uppermost decimeters of a bog ecosystem using the pine method, which enables accurate dating of surface peat layers. We combined accumulation data with numerical and geostatistical analyses of the recent vegetation to establish the relationship between bog vegetation and rate of peat accumulation. Use of a laser technique for spatial positioning of 151 age-determined peat cores within a 20 × 20 m plot made it possible for us to give the first fine-scaled account of spatial and temporal variation in rates of mass, carbon, and nitrogen accumulation during the last century. Rates of C and N accumulation were highly variable at all spatial scales studied. For example, after ∼125 yr of peat growth, C and N accumulation varied by factors of five and four, respectively, from 25 to 125 g/dm2 for C, and from 0.7 to 2.6 g/dm2 for N. It takes ∼40 yr of peat accumulation before significant amounts of C are lost through decay. Hummocks built up by Sphagnum fuscum S. rubellum were able to maintain average rates of C accumulation that exceed 2 g·dm−2·yr−1 during 50 yr of growth. We argue that data on spatial variation in rates of C accumulation are necessary to understand the role of boreal peatlands in the greenhouse effect and global climate.