MODELING MOISTURE RETENTION IN PEAT SOILS

Soil moisture governs many biogeochemical processes in peatlands. Mode ling of those processes relative to climate and anthropogenic influenc es requires knowledge of the basic hydraulic properties of different p eat soils in a function form. Water retention of undisturbed surface p eat samples, collected at four depths at each of 38 undrained and drai ned pine (Pinus sylvestris L.) mire sites, was measured for suction pr essures of -0.98, -3.10, -6.19, -9.81, -98.1, and -1554.25 kPa, The ob tained data were used to test several well-known water retention model s commonly applied to mineral soils, The most suitable model was found to be van Genuchten's model if the residual water content was omitted . Feat characteristics were used to explain the variation in the model 's shape parameters. Accounting for the remains of Sphagnum, Carer, Er iophorum, and lignin and the distinction between shallow and deep peat layers considerably improved the moisture retention predictions compa red with using bulk density only. The different behavior of the shallo w vs. the deep peat layers was mainly attributed to the Sphagnum and l ignin residues, but not to the Carer residues. We developed a semiempi rical model with only one shape parameter, which was clearly better ex plained by the peat characteristics than the two shape parameters of t he van Genuchten model, We recommend that for statistical investigatio ns or investigations requiring a robust model. the semiempirical model be used. The van Genuchten model is to be preferred in predicting the moisture conditions near saturation.