The Impact of Tracks on Blanket Peat Ecohydrology

Peatlands are subject to multiple uses including farming, forestry, sites for renewable energy (wind farms) and recreation (including gun sports). To facilitate access, roads and tracks, both constructed and unsurfaced, are becoming an increasingly common feature in Northern peatlands. The impact that these linear features have on peatland ecohydrological functioning is poorly understood, especially within blanket peatlands which, unlike other peatland types, often occur on slopes. There is concern that disturbances could negatively impact important physical, hydrological and ecological peat properties, and consequently the wider functioning of these systems. Indeed, the ability of peatlands to capture and store carbon could be compromised following possible reductions in vegetation cover and a deepening of the water table. Likewise, the role of peatlands in flood management could be affected as a result of peat compaction and enhanced surface runoff. With respect to practical applications, the current lack of understanding and evidence for decision-making has made granting permission for track installation problematic. In this thesis, the first comprehensive study of track impacts on blanket peat is presented. A two strand approach was used to investigate the impact of tracks on blanket peat ecohydrology, involving (i) a regional survey of 29 track reaches (aggregate and plastic) across seven sites in the North Pennines and Cheviots of northern England and (ii) an intensive study over two years, covering 1.5 km of plastic mesh track, 30 m of articulated wooden track and 200 m of unsurfaced track located at Moor House in the North Pennines. Key properties for peatland ecohydrological functioning were measured including soil moisture, bulk density, hydraulic conductivity, water-table depth, overland flow occurrence and vegetation composition. The influence of track type, frequency of use and topographic location were considered, in addition to the spatial extent of track impacts. The regional survey found higher volumetric moisture content on the upslope side of stone tracks compared with the downslope side. Such an effect was not found around plastic tracks, where the upslope-downslope gradient was indistinct or did not exist, due to the orientation of the track to the contours. Topographic location and track age influenced spatial patterns in moisture content for stone tracks. Such effects could not be tested for plastic tracks. The influence of distance was considered for the stone tracks however no clear effect was observed. Findings from the intensive study showed variation in the responses to the tracks from the selected key properties for blanket peatland ecohydrological functioning. Clear impacts were observed for surface profile elevation and vegetation characteristics. Following track use a lowering of surface peat elevation directly under the track was recorded for all three track types and at all topographic locations. Compared with before disturbance data, reduced cover in C. vulgaris, E. vaginatum and S. capillifolium, a lowering in the height of the vegetation, and increased bare peat occurrence, were found 22 months after track installation and 13 months after the commencement of driving. These impacts were closely associated with the installation process of the tracks. Track type was a key influential variable in the magnitude of impact observed for both surface peat elevation and vegetation composition and height. Topographic location was influential for vegetation composition but not surface profile elevation. Track frequency of use had minimal influence on the responses of all of the properties measured in the intensive study. Expected impacts to bulk density, hydraulic conductivity, water-table depth and overland flow occurrence were found to occur under some conditions. The intensive study was undertaken over a two year period with 18 months of continuous monitoring (water-table depth and overland flow). The variation in the responses of a number of the key properties measured suggest a need for long-term studies (5+ years) to fully capture the impact of disturbances such as tracks. The results from this study will be used to inform decision-making with respect to the siting and use of tracks in blanket peatland environments. With better informed decision-making the future impacts of track installation and use can be mitigated against; resulting in healthy peatlands, where their multiple functions including carbon sequestration and flood alleviation can be maintained and supported.