The DigiBog peatland development model 2: ecohydrological simulations in 2D

In the first of this pair of papers we introduced the conceptual and hydrological basis of the peatland development model-DigiBog. Here we describe the submodels which simulate (i) the production of plant litter, (ii) peat decomposition, and (iii) changes in peat hydraulic conductivity due to decomposition. To illustrate how the model works, DigiBog was applied to three example situations: Bogs 1, 2, and 3. For each, the net rainfall was held constant at 30 cm year(-1) and the oxic decomposition parameter kept at 0.015 year(-1). The anoxic decomposition parameter varied from 5 x 10(-6) (Bog 1) to 5 x 10(-4) year(-1) (Bog 3). Peatland development was simulated for 5000 years. For Bogs 1 and 2, plausible large peatland domes develop. Despite having a higher anoxic decomposition rate, Bog 2 grew thicker than Bog 1. This apparently counter-intuitive result is caused by the feedback between hydraulic conductivity and degree of peat decomposition. For both Bogs 1 and 2, DigiBog also simulates transitions from wet to dry states, demarked by sudden switches from poorly decomposed to well-decomposed peat moving upwards in the peat profile. These regime shifts result from internal peatland dynamics and not from allogenic influences, and challenge the view that peat properties are always a reflection of climate. In Bog 3, a mini-bog developed and persisted near the margin of the peatland; this bog can also be explained in terms of the internal feedbacks within the model. Copyright (C) 2011 John Wiley & Sons, Ltd.