Impacts of road construction and removal on the hydrologic and geochemical function of a fen peatland

Abstract:

Linear disturbances such as roads cover vast swaths of northeastern Alberta, the majority of which are wetlands with shallow and local hydrologic connections. Thus, the effects of road construction on wetland hydrological pathways can have significant implications on water movement within the region, and by extension the productivity of vegetation communities and carbon sequestration. However, little is known about the effect that roads have on wetland hydrology. In 2013, a gravel road built within a fen peatland was reclaimed to evaluate hydrologic impacts post removal. Prior to removal, ground and surface water flow was obstructed leading to surface ponding, and vegetation mortality was observed on the up-gradient (wet) side of the road. Rebounding of the peat column was observed throughout the fen immediately following road removal in 2013 (maximum of 12 cm, mean of 2 cm), with modest but slightly smaller expansion in 2014. For both years, peat rebound was greatest in areas where the road was removed. Peat physical properties contrasted sharply between the reclaimed road (RR) peat and the adjacent, unimpacted peatland (UP). Surface bulk densities (pb, 0-10 cm) ranged from 0.1-0.25 g cm^-3 along the RR compared to 0.02-0.07 g cm^-3 for the UP and on average, pb for all depths were lower at the RR compared to the UP. Similar spatial patterns were observed for peat porosity. Correspondingly low horizontal saturated hydraulic conductivities (K_h) were observed along the RR compared to the UP, averaging 5.7x10^-4 m s^-1 and 1.7x10^-3 m s^-1, respectively. The local flow system across the RR and thus subsurface flow was impeded by almost half (0.4 m d^-1) compared to flow observed within the UP (0.8 m d^-1), leading to ponding on the upgradient side. A marked change in hydrophysical properties and ground and surface water flow patterns post road removal has implications for plant reestablishment and restoration and will form the basis of further study.