The hydrology of the Bois-des-Bel bog peatland restoration: 10 years post-restoration

Abstract

Restoration measures (ditch blocking, bund construction, etc.) were applied to a cutover part of the Bois-des-Bel (BdB) bog peatland in autumn 1999; since then a near complete cover of Sphagnum rubellum (∼15cm) has developed over the old cutover peat, along with a suite of bog vegetation. This research assesses the restored site's (RES) hydrological condition after 10 growing seasons (May 15th–August 15th, 2010) through comparison with an adjacent unrestored site (UNR) and a natural site (NAT) located elsewhere in the peatland. Evapotranspiration (ET) from RES (242mm) has not noticeably changed since the first 3 years post-restoration (2000–2002) still maintaining lower ET rates than UNR (290mm). The highest ET occurred at NAT (329mm), dissimilar to RES despite similar vegetation cover. UNR generates more runoff (37mm) than RES (7mm), similar to the initial assessments. However, since the initial assessments the average water table has continued to rise, from −35.3 (±6.2)cm (2000–2002) to −27.3 (±14.9)cm (2010) below the cutover peat surface but still fluctuates predominantly within the cutover peat and not the regenerated Sphagnum. The regenerated Sphagnum at RES has increased the surface elevation by ∼15–20cm, and with respect to its surface the average water table was at ∼−42.3 (±20.9)cm. However, its water table was still lower (and more variable) than at NAT (33.2±9.0cm), with respect to the moss surface. Average soil water pressures in 2010 were similar to the early post-restoration condition at depths of 10cm (−43.0±12.2 and −44.1±13.1mb) and 20cm (−41.4±13.0 and −40.6±10.5mb) below the cutover surface at RES and UNR, respectively. Volumetric soil moisture contents (θ) at 2.5, 7.5 and 17.5cm depths were higher in the Sphagnum moss at NAT (0.23, 0.31, and 0.71) compared to RES (0.12, 0.11, and 0.23), where the underlying cutover peat had a relatively high θ of 0.74. The low moisture content in the new moss overlying the relatively moist cutover peat indicates there was restricted connectivity between the two layers. Ten years following the implementation of restoration measures and the development of a near complete 15cm thick Sphagnum moss layer, further time is required for the moss layer to develop (increase in thickness and bulk density, hence water retention capacity) and more consistently host the water table, so that the average water content more closely mimics NAT.