title: Historical peat loss explains limited short-term response of drained blanket bogs to rewetting.
abstract: This study assessed the short-term impacts of ditch blocking on water table depth and vegetation community structure in a historically drained blanket bog. A chronosequence approach was used to compare vegetation near ditches blocked 5 years, 4 years and 1 year prior to the study with vegetation near unblocked ditches. Plots adjacent to and 3 m away from 70 ditches within an area of blanket bog were assessed for floristic composition, aeration depth using steel bars, and topography using LiDAR data. No changes in aeration depth or vegetation parameters were detected as a function of ditch-blocking, time since blocking, or distance from the ditch, with the exception of non-Sphagnum bryophytes which had lower cover in quadrats adjacent to ditches that had been blocked for 5 years. Analysis of LiDAR data and the observed proximity of the water table to the peat surface led us to conclude that the subdued ecosystem responses to ditch-blocking were the result of historical peat subsidence within a 4-5 m zone either side of each ditch, which had effectively lowered the peat surface to the new, ditch-influenced water table. We estimate that this process led to the loss of around 500,000 m3peat within the 38 km2study area following drainage, due to a combination of oxidation and compaction. Assuming that 50% of the volume loss was due to oxidation, this amounts to a carbon loss of 11,000 Mg C over this area, i.e. 3 Mg C ha-1. The apparent 'self-rewetting' of blanket bogs in the decades following drainage has implications for their restoration as it suggests that there may not be large quantities of dry peat left to rewet, and that there is a risk of inundation (potentially leading to high methane emissions) along subsided ditch lines. Many peatland processes are likely to be maintained in drained blanket bog, including support of typical peatland vegetation, but infilling of lost peat and recovery of original C stocks are likely to take longer than is generally anticipated.
authors.affiliation: Centre for Ecology & Hydrology, Environment Centre Wales, Deiniol Road, Bangor LL57 2UW, UK. Electronic address: jwl@ceh.ac.uk.
authors.forename: Jennifer
authors.initials: J
authors.lastname: Williamson
authors.affiliation: Centre for Ecology & Hydrology, Environment Centre Wales, Deiniol Road, Bangor LL57 2UW, UK.
authors.forename: Edwin
authors.initials: E
authors.lastname: Rowe
authors.affiliation: Natural Resources Wales, Maes y Ffynnon, Penrhosgarnedd, Bangor LL57 2DW, UK.
authors.forename: David
authors.initials: D
authors.lastname: Reed
authors.affiliation: Natural Resources Wales, Maes y Ffynnon, Penrhosgarnedd, Bangor LL57 2DW, UK.
authors.forename: Lucia
authors.initials: L
authors.lastname: Ruffino
authors.affiliation: Natural Resources Wales, Maes y Ffynnon, Penrhosgarnedd, Bangor LL57 2DW, UK.
authors.forename: Peter
authors.initials: P
authors.lastname: Jones
authors.affiliation: National Trust, Dinas, Betws-y-Coed LL24 0HF, UK.
authors.forename: Rachel
authors.initials: R
authors.lastname: Dolan
authors.affiliation: National Trust, Dinas, Betws-y-Coed LL24 0HF, UK.
authors.forename: Helen
authors.initials: H
authors.lastname: Buckingham
authors.affiliation: Centre for Ecology & Hydrology, Environment Centre Wales, Deiniol Road, Bangor LL57 2UW, UK.
authors.forename: David
authors.initials: D
authors.lastname: Norris
authors.affiliation: Centre for Ecology & Hydrology, Environment Centre Wales, Deiniol Road, Bangor LL57 2UW, UK.
authors.forename: Shaun
authors.initials: S
authors.lastname: Astbury
authors.affiliation: Centre for Ecology & Hydrology, Environment Centre Wales, Deiniol Road, Bangor LL57 2UW, UK.
authors.forename: Chris D
authors.initials: CD
authors.lastname: Evans
mesh_terms: D002244:Carbon; D060587:Groundwater; D008697:Methane; D012987:Soil; D053833:Wetlands
chemical_list: D012987:Soil; D002244:Carbon; D008697:Methane
keywords: Ditch blocking; Drainage; Peat subsidence; Peatland vegetation; Restoration; Water table