TEMPORAL SCALE AND THE ACCUMULATION OF PEAT IN A SPHAGNUM BOG

We examined short-term (decadal) and long-term (millenial) processes o f peat accumulation, and the links between them, in a Sphagnum bog in continental Canada. A previously published model of bog growth was fit ted to age profiles of the oxic acrotelm (surface, <60 cm thick) and t he underlying, anoxic catotelm (210 cm thick). Approximately 5300 year s of accumulation were represented in a radiocarbon-dated core that ex tended to the base of the deepest part of the peat deposit. The model estimated that the overall rate at which material entered long-term st orage in the catotelm was 60-66 g . m(-2). a(-1). Although the decay r ate coefficient was near zero, the bog stopped accumulating peat withi n the past 1500 years, resulting from either a decrease in the rate of transfer of material from the acrotelm or an increase in the rate of decay of material at the top of the catotelm. The model of bog growth estimated recent inputs to the acrotelm (90-930 g . m(-2). a(-1)) that were twofold higher than published field measurements of aboveground productivity, and decay rate coefficients (0.005-0.040 a(-1)) that wer e 10-fold lower than published litter-bag measurements of mass loss. T he pattern of mass loss over time, approximated from nitrogen concentr ation data, deviated from the pattern predicted by exponential models of decay. Calculations of the balance between additions to and losses from the acrotelm suggest that the amount of material transferred to t he underlying catotelm differs among microhabitats. Such spatial varia bility in short-term processes is incompatible with long-term processe s determining the position of the acrotelm-catotelm boundary. We discu ss the applicability of the model to continental peatlands and suggest ways to improve modelling of short-term autogenic processes.