The future stability of upland blanket peat following historical erosion and recent re-vegetation

Abstract

The importance of fluvial dissection in upland blanket peat erosion is well-established but knowledge of the significance of peatland gully system development is limited. This thesis investigates the stability of upland blanket peat in relation to recent re-vegetation and historical erosion of peatland gully systems. It combines regional morphological surveys in a GIS framework with detailed field and laboratory analyses. Detailed research was carried out at three study areas across Northern England: The Cheviot (Northumberland), Moor House (North Pennines) and Wessenden Head Moss (Southern Pennines). A regional-scale investigation into gully development at the three sites demonstrated that the end members (Type 1 and Type 2 dissection) in Bower's 1960 classification of dissection types could be identified but a revised dissection classification including a third category of anastomosing dissection was needed. Regional variations in erosion and gully form were observed. The most extensive aerial erosion was on The Cheviot (80 %) and least at Moor House (48 %). Re-vegetation was most well-established at Moor House (80 % of the eroded peat) and least on Wessenden Head Moss (45 % of the eroded peat). The local topography of each site was the key in explaining erosion patterns. Linear dissection dominated on steeply sloping ground and anastomosing dissection on gentle sloping summit areas. Dendritic dissection occurred on intermediate slopes. Approximate slope angles for the dentritic transitional zone vary in relation to the local topography; however, the means for the three study sites are 3.7 (Moor House), 4.9 (The Cheviot) and 1.4 (Wessenden Head Moss).Local-scale variations in erosion were observed on the interfluves and within existing gully systems. On the interfluves peat accumulation rates were estimated from Spheroidal Carbonaceous Particle deposition. Average rates were 0.5 mm yr(^-1) under moorland grass and 1.2 mm yr(^-1) under heather. Erosion potential of these sites was estimated from rainfall simulation experiments. The potential for erosion was high (243 t km(^-2), 0.243 mm yr(^-1)), though not atypical of local directly measured erosion rates. However, experimental results showed that sediment production rarely occurred below a rainfall intensity of 12 mm hr(^-1) (high intensity for the Pennines) and with a presence of an intact vegetation cover sediment is only locally entrained and re-deposited and actual erosion under current climatic conditions is likely to be low. The onset of peat erosion was estimated by comparing eroded and uneroded cores. It is thought the most recent phase of erosion resulted from climatic change and land management and occurred some 570 years ago on Wessenden Head Moss and between 300 - 330 years ago at Moor House and on The Cheviot. Over the last approximate 50- years, infilling and re-vegetation of the bases of gully systems has been observed. The peat within the gully stratigraphy appears to be eroded, re-deposited or grown in situ. The future of upland blanket peat will likely involve further stabilisation of the gully systems; however, in severely eroded areas where the peat is totally stripped and surface hydrological regime destroyed, the peat will not recover.