Hydraulic properties of fen peat soils in Poland

The hydraulic properties of fen peat soils from the Biebrza River Valley in the north-east of Poland were investigated. 87 soil samples were collected from nine typical peat-moorsh soil profiles representing three types of peat: moss with fibrous structure, herbaceous and wooden peat characterised by amorphous structure with high humus content. The multi-step outflow method was used to determine the parameters of the Mualem-van Genuchten model (MVG) that describes soil moisture retention characteristics and the unsaturated hydraulic conductivity function of each soil sample. The agglomerative hierarchical cluster analysis of the parameters of MVG model was applied in order to obtain typical hydraulic functions for the three types of peat considered. As a result of the analysis, the hydraulic properties of the fen peat soils were agglomerated into five clusters. The MVG model parameters as well as hydraulic functions were analysed for distinguished clusters. The parameters of the moss peats with low degree of decomposition and fibric structure were different from those of the herbaceous and wooden decomposed peats with high humus content. The largest values of the hydraulically active pore space (difference between saturated and residual moisture content) were observed for moss peat samples, while the lowest values were observed for wooden peat samples. The empirical parameters describing the shape of the unsaturated hydraulic conductivity function were depended on the type of the peat and therefore the degree of decomposition. The L parameter values of the herbaceous and wooden peats were generally greater than 0, whereas for the moss peat samples they were ranging from − 5 to 5. The unsaturated hydraulic conductivity of the herbaceous and wooden peat soils was close to that of very fine-textured mineral soils.