The Development of a Hydrological Buffer Zone Strategy for Designating the Mesotope Protection Zone of Raised Mire Systems

Abstract

The overall aim of this thesis has been to develop a pragmatic strategy to aid decisionmaking concerning the management of raised bogs for future sustainability, and specifically to provide a tool to identify the extents and locations of those areas around the bog margins within which water tables need to be managed.
Undesirable water losses resulting from damage to peripheral lagg fens that would once have surrounded intact mire systems will be associated with a steepening change in hydraulic gradient. Although steep hydraulic gradients are frequently cited as a problematic threat to a raised bog there has been a lack of previous attempts to quantify a suite of indicative gradients to form a predictive model. This thesis has considered the possibility of identifying key areas of threatened lagg fen from analysis of topographic and hydraulic gradient data across the mire surface of surviving peat domes and their adjacent landscapes. These marginal lagg areas are important to the overall sustainable hydrology of raised bogs, but the identification of land judged necessary to the hydrological integrity of these habitats has received little attention in the scientific literature.
Acquisition of the necessary indicative data, carried out at the landscape scale at a range of raised mires, was made feasible by the use of differential Global Positioning Systems (dGPS) for accurate and rapid surveying of transects across a suite of UK raised mires. It may be that developments in dGPS and remote sensing methods such as LiDAR will offer opportunities for future development of this approach.
An early product of the strategy was the development of a methodology for carrying out rapid assessments of the condition or "health" of the sites. Profiles of the raised bogs were computed and a database of gradient results was generated for each profile. This involved the identification of generic slope features within the profile of the bogs. An attempt to identify characteristic values associated with generic profiles was then made.
A simple data model has been derived, which is indicative of gradient thresholds between characteristic groups. Significant values for hydraulic gradient of between 0.0063-0.0082 across the raised bog dome, and 0.02 for the Rand or steeper shoulders of the bog are suggested for thresholds between relatively intact and damaged systems. These results may
be used to compute target water levels at the edges of a mire, and to predict where in the surrounding land this needs to be achieved in order to help sustain the raised water table of the core peat dome. Following a verification process the indicative model was used to predict a preferred hydrological boundary at a further raised bog site (Swarth Moor in North Yorkshire; SD806695).
Whilst the results relate to raised n-iires within the UK, and it would be useful therefore to now carry out a comparative study elsewhere, the results of this thesis strongly suggest that quantified gradient data provide a surrogate for judging where the hydrology of peripheral land may influence the condition of the core site. This may offer advantages to conservation agencies in their attempts to maximise the potential for sustainable restoration of this rare and valued habitat.