Peat soils are typically rich in organic matter and subject to drainage; thus, secondary transformations depend greatly on drainage intensity. As a result, peat soils may exhibit different physicochemical properties, including different amounts of bound water, different kinds and contents of humic substances, and different sorption and exchangeable properties. Transformations in peat soils are accompanied by (i) changes in the geometrical and energetic characteristics of the soil particle surface, which can be revealed by evaluating soil porosity from mercury porosimetry data, and (ii) energetic and geometric heterogeneity, which can be evaluated from water vapor and N2 adsorption isotherms [44, 106-108, 123]. Weakly transformed peats exhibited significantly smaller Ds values (about 2.4) than extensively transformed ones (Ds > 2.6.). The Ds values obtained from mercury porosimetry data were usually smaller than those derived from N2 adsorption data fitted in the FHH isotherm. These results indicated that secondary transformation of peat soils caused an increased surface roughness. Further studies carried out on peat samples that were thermally treated at 50, 100 and 150°C, showed that the surface roughness of most transformed samples diminished with an increase in temperature [44, 107]. For some samples, however, the temperature effect was opposite. In general, it was difficult to relate these changes to other physicochemical characteristics of the peat soils investigated.

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