Stagnation in peat profiles controls organic matter transformation in different mire types

Decomposition of organic compounds in peat soils requires atmospheric oxygen, which is limited when water fills soil pore spaces. We examined the thermodynamics of organic matter decomposition in Austrian peatlands and predicted greater thermodynamic constraints deeper in the soil profile where pore spaces are water filled. For mire types with stagnant water we hypothesize that thermodynamic closure of the pore space will occur deeper in the soil profile and there will be a greater extent of organic matter transformation. In this study peat cores from eight different peatlands were collected and analysed for their Gibbs free energy of formation (ΔGf), carbon oxidation state (C_ox), and degree of unsaturation (Ω). The experimental design included bogs and fens, as well as natural and degraded sites. The study showed that decomposition of organic matter was greater in fens and degraded sites than in bogs and undisturbed sites, respectively, and there was a consistent increase in Ω with depth that marked an evolution away from cellulose-dominated compositions and toward lignin-dominated compositions at depth. These results support our study hypothesis that greater water stagnation in sites results in less transformation and shows that peatlands can be distinguished between the stable and unstable, and by relative recalcitrance.