Characterizing ecosystem-driven chemical composition differences in natural and drained Finnish bogs using pyrolysis-GC/MS

Abstract

Aerobic decomposition increases in drained peatlands; releasing stored organic matter (OM) and shifting greenhouse gas fluxes from sink to source. This study explored how drainage influenced peat OM chemical composition by investigating paired sites from a Sphagnum-dominated ombrotrophic Finnish bog undergoing contrasting hydrological management (natural and drained). Peat OM was investigated in replicate cores using analytical pyrolysis, compared with observed vegetation, elemental analysis (O:C, N:C), stable isotopes (δ13C, δ15N), and fraction radiocarbon. Principal component analysis of quantified pyrolysis products separated four primary components: vascular plants vs Sphagnum, aerobic degradation of fresh plant biomass, anaerobic processes in water-saturated depths, and pine vs Eriophorum. The largest influence of drainage on peat chemistry was via aerobic decomposition (decreased abundance of Sphagnum phenols and simple polysaccharides; accumulation of macromolecular polysaccharides) (p < 0.05, 0–2 cm). Drainage-induced shifts in vegetation (from Sphagnum to Pinus sylvestris (p < 0.01, 0–2 cm) were reflected by increased abundance in lignin, N-compounds, and lipids, and decreased abundance in phenols and polysaccharides. Anaerobic processes also differentiated the natural and drained sites and primarily affected polysaccharides (p < 0.05, 0–2, 8–10 cm). Vegetation shifts and aerobic decomposition similarly affected many of the same compounds upon drainage– demonstrating the simultaneous influence of different processes on the same OM. Pre-drainage inter-core variation illustrated the importance of replicate cores in disentangling anthropogenic changes from natural biodiversity. These findings suggest that even short-term and moderate alterations in peatland hydrology strongly influence the chemical composition of peat OM, and that its chemistry serves as an effective indicator to assess decomposition status.