Effect of Restoration on Physical and Chemical Peat Properties in Previously Drained Boreal Peatlands

There is a societal demand to restore drained boreal peatlands for purposes of improving water quality and biodiversity and lowering emissions of greenhouse gases. Restoration measures are costly and neither the effects of drainage nor restoration on biogeochemical processes in the peat, and in downstream environments are well understood. This study assesses how 60-100 years of drainage followed by 6-9 years of restored conditions have changed the physical and chemical peat properties in restored boreal peatlands. Eight pairs of restored and natural peatlands were sampled down to 50 cm (n = 3 for each site). Each of the 50 cm peat cores was sliced into 25 two-centimetre discs, generating high-resolution records of the dry bulk density (BD), organic matter content (OM), C- and N- content, delta 13C, and delta 15N. Peat from the restored sites showed significantly higher BD and lower C:N ratio and OM content than the reference sites. Furthermore, peat from restored peatlands was systematically depleted in delta 13C, and the OM was enriched in C and N. Long-term drainage could cause increased peat decomposition, leaving altered physical and chemical peat properties. For example, the C content in OM increases as the residual peat is enriched in aromatic and aliphatic moieties following decomposition. For the same reason, degraded peat can be delta 13C depleted. Interestingly, differences between the restored and pristine sites were mainly found at 20-50 cm depth. Given the low peat formation rates in nutrient-poor peatlands, the superficial 20 cm peat was potentially recovering from drainage even before restoration.