Modelling long-term peatland dynamics. II. Processes and rates as inferred from litter and peat-core data

The production and decomposition of organic matter are major processes determining peat accumulation dynamics, both of which vary over different time scales. Here we evaluate three types of experimental and observational data related to peatlands, which are from litter, oxic (acrotelm) peat, and anoxic (catotelm) peat. The 210Pb-dated peat-core profiles for the last 100–200 years are used to understand the oxic decomposition processes; 14C-dated peat profiles for the last several millennia are used for understanding anoxic decomposition processes. Analysis of data from litter-bag experiments suggests that a significant portion of the litter is lost in the first few years owing primarily to rapid initial decomposition processes, including movement/leaching of soluble materials. This is also confirmed indirectly by 210Pb-dated peat-core data. Several records of acrotelm peat show similar estimated litter-addition (265±37.3 g m−2 year−1) and decay rates (0.017±0.0047 year−1), despite the climatic difference among study areas. The litter-addition rate of 265 g m−2 year−1 is at most about half of measured net primary production. Warmer climate causes higher production but also higher decomposition. The balance of production and decay processes in the litter and acrotelm determines the peat addition rate to the catotelm, where long-term peat accumulation occurs. Our sensitivity analysis shows that change in the peat-addition rate would affect both young and old peat; in contrast, a change in the decay rate has more influence on old peat. We therefore hypothesize that the wiggles often seen in peat age–depth profiles are caused by changes in peat addition rates, which are determined by climatically sensitive processes including photosynthesis and acrotelm decomposition. Evaluating these litter and peat-core data provides insights useful to the design and implementation of a peatland dynamics simulation model.