Modeling northern peatland decomposition and peat accumulation

To test the hypothesis that long-term peat accumulation is related to conte mporary carbon flux dynamics, we present the Peat Decomposition Model (PDM) , a new model of long-term peat accumulation. Decomposition rates of the de eper peat are directly related to observable decomposition rates of fresh v egetation litter, Plant root effects (subsurface oxygenation and fresh litt er inputs) are included. PDM considers two vegetation types, vascular and n onvascular, with different decomposition rates and aboveground and belowgro und litter input rates. We used PDM to investigate the sensitivities of pea t accumulation in bogs and fens to productivity, root:shoot ratio, tissue d ecomposability, root and water table depths, and climate. Wanner and wetter conditions are more conducive to peat accumulation. Bogs are more sensitiv e than fens to climate conditions. Cooler and drier conditions lead to the lowest peat accumulation when productivity is more temperature sensitive th an decomposition rates. We also compare peat age-depth profiles to field da ta. With a very general parameterization, PDM fen and bog age-depth profile s were similar to data from the the most recent 5000 years at three bog cor es and a fen core in eastern Canada, but they overestimated accumulation at three other bog cores in that region. The model cannot reliably predict th e amount of fen peat remaining from the first few millennia of a peatland's development. This discrepancy may relate to nonanalogue, early postglacial climatic and nutrient conditions for rich-fen peat accumulation and to the fate of this fen peat material, which is overlain by a bog as the peatland evolves, a common hydroseral succession in northern peatlands. Because PDM sensitivity tests point to these possible factors, we conclude that the st atic model represents a framework that shows a consistent relationship betw een contemporary productivity and fresh-tissue decomposition rates and obse rved long-term peat accumulation.