Abstract
Estimates of peat depth are required to inform understanding of peatland development, functioning, and ecosystem services such as carbon storage. However, there is a considerable lack of peat depth data at local, national, and global scales. Recent studies have attempted to address this knowledge deficit by using manual probing and ground-penetrating radar (GPR) to estimate depth. Despite increasing application, little consideration has been given to the accuracy of either of these techniques. This study examines the accuracy of probing and GPR for measuring peat depth. Corresponding GPR and probing surveys were carried out at a catchment scale in a blanket peatland. GPR depth estimations, calibrated using common midpoint (CMP) surveys, were found to be on average 35% greater than probe measurements. The source of disagreement was found to be predominantly caused by depth probes becoming obstructed by artifacts within the peat body, although occasionally probing rods also penetrated sediments underlying the peat. Using the Complex Refractive Index Model, it was found that applying a single velocity of 0.036 m ns−1 across a single site may also result in −8 to +17% error in estimation of peat depth due to spatial variability in water content and porosity. It is suggested that GPR calibrated at each site using CMP surveys may provide a more accurate method for measuring peat depth.
Highlights
Many of the ecosystem services provided by peatlands are delivered due to processes which occur beneath the surface and extend throughout the whole peat profile [Parry et al, 2012]
The mean velocity resulting from the common midpoint (CMP) (0.036 m nsÀ1, εr = 69.4) was used to calculate the corresponding ground-penetrating radar (GPR) depth at each of the 162 manually probed depth points
In 9% of the sampling points, the depth obtained from using a probe was over 1 m shallower than the depth derived from using the GPR (Figure 3)
Summary
Many of the ecosystem services provided by peatlands are delivered due to processes which occur beneath the surface and extend throughout the whole peat profile [Parry et al, 2012]. Peat depth data sets are an essential component of carbon accumulation calculations [Gorham, 1991; Loisel et al, 2013; van Bellen et al, 2011] and in developing carbon inventories and maps of carbon distribution [Beilman et al, 2008; Sheng et al, 2004; Parry and Charman, 2013]. These data are subsequently used in global climate change models [Charman et al, 2012] and to justify land management decisions [Frogbrook et al, 2009]. Two techniques are commonly applied to measure the depth of peat: (1) manual probing with metal rods, which records depth at intervals across a peatland, and (2) ground-penetrating radar (GPR), a geophysical technique which can semicontinuously image the base of peat
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