Percolation through peat profiles controls organic matter transformation in different mire types

We hypothesize that organic matter transformation in peatlands will be constrained where there is limited percolation of water through the soil profile. For mire types with more restricted percolation 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 13 peat cores from 8 different peatlands were collected and analysed for their Gibbs free energy of formation, carbon oxidation state, degree of unsaturation, and protein fraction as determined by thermogravimetric analysis. The sites were chosen so that it was possible to examine the difference in peat profile between fens and bogs, and between natural and degraded sites. The study showed that fens and degraded sites showed significantly greater extent of organic matter transformation than observed for either bogs or natural sites. There was a consistent increase in the degree of unsaturation with depth that marked an evolution away from cellulose dominated composition and toward lignin-dominated compositions at depth.

These results support our study hypothesis that greater percolation through sites results in greater transformation and shows that peatlands can be distinguished between the stable and unstable; and the vulnerable and invulnerable. Therefore, stagnant as well as high water tables promote organic matter storage.