|Blodau, C; Siems, M (2010): Drainage-induced forest growth alters belowground carbon biogeochemistry in the Mer Bleue bog, Canada, Biogeochemistry|
Impacts of long-term drying and associated vegetation change on anaerobic decomposition, methane production, and pore water composition in peat bogs are poorly documented. To identify some of these impacts, we analyzed peat humification, pore water solutes, in situ and in vitro respiration rates, and Gibbs free energies of methanogenesis in a bog near a drainage ditch established in 1923. We compared drained peat under open bog vegetation and forest with a bog reference site. Drainage and tree growth induced an enrichment in carboxylic, aromatic, and phenolic moieties in the peat. Short-term in vitro respiration rates significantly decreased with humification (R2 > 0.6, p < 0.01). Dissolved inorganic carbon (DIC) and CH4 concentrations also attained lower maxima in drained areas. However, near the water table in situ respiration intensified as indicated by steeper increases in DIC and CH4 concentrations than at the reference site, especially under forest. Maximum in situ CO2 production derived from inverse pore water modeling was 10.3 nmol cm-3 d-1 (forest) and 6.3 nmol cm 3 d 1 (bog) and was one to two orders of magnitude slower than in vitro anaerobic respiration. In the highly decomposed shallow peats under forest, methane production was suppressed and DOC concentration elevated. Raised H2 concentrations (up to 200 nmol L-1) and in situ Gibbs free energies of down to -60 kJ mol-1 (CH4) suggested an inhibition of hydrogenotrophic methanogenesis by an unidentified factor at these sites. The study documents that several changes in biogeochemical process patterns do occur post-drainage, especially when tree growth is triggered. Most importantly, the establishment of forest on intensely humified peats can lower in situ methane production.