Comparison of different types of peat corers in volumetric sampling.

As part of an investigation of the long-term effects of ditch-draining on peat deposits, we cored peat samples altogether from 51 peatland sites that had been earlier inventoried by volumetric coring by the Geological Survey of Finland (GTK) during the 1980s. In most cases, it proved possible to match the old and new profiles cored of the same site, especially concerning their lower parts, in which typically no big changes seem to have taken place. However, comparison of the results revealed a recurring, albeit not systematic bias: the dry bulk density values of the GTK data tended to be somewhat smaller than our corresponding results. In cases where peat compression can be ruled out, a plausible explanation is that the piston corer did not function properly. This paper describes a test series in which we compared the GTK piston corer, a 1-m box corer and a Russian peat corer in quantitative sampling of peat strata. The piston corer proved to have a slight tendency to underperform, particularly with peats rich in sedge, cottongrass or wood remains. Implications of the variable sampler performance on quantitative peat inventories are discussed.