Ecohydrological feedbacks in peatland development: a theoretical modelling study

1. Peatlands are complex ecohydrological systems. In a theoretical modelling study we identify three ecohydrological links - commonly omitted from existing models - as potentially important to long-term peatland development, namely those between: I oxic-zone thickness and the rates of litter addition and depth-integrated decay; II time-integrated decay and hydraulic conductivity; and III drainage and peatland lateral expansion via paludification. 2. In a simple model that includes none of these links, total peat thickness increases monotonically with annual rainfall, while oxic-zone thickness is controlled by the rates of litter addition and depth integrated decay. 3. In an intermediate model that includes Link I, bi-stable behaviour occurs, with both 'dry' and 'wet' peatland forms possible at low rainfall, but only 'wet' peatland forms possible above a threshold value of rainfall. This finding agrees with those from a similar published model. 4. In a more complicated model that includes both Link I and Link II, the bi-stability of the intermediate model is lost. Increases in net rainfall lead to little change in oxic-zone thickness because the model's feedbacks confer self-dampening (stabilizing) behaviour. Bog height after 5000 years is maximal at an intermediate anoxic decay rate, an initially counter-intuitive finding that reflects complex behaviour arising from the interacting feedbacks represented within the model. 5. In a final model that includes Links I, II and a partial representation of Link III, the mode of peatland lateral expansion (i.e. linear, logarithmic or step-wise expansion) has a strong effect on patterns and rates of peat accumulation. 6. Synthesis. Understanding long-term peatland development requires consideration of ecohydrological feedbacks; models without such feedbacks are likely to misrepresent peatland behaviour. Down-profile changes in peat properties, commonly taken to indicate external (climatic) influences in palaeoclimatic studies, may in some cases be consequences of internal peatland dynamics under a steady climate.