Changes in flow and transport patterns in fen peat following soil degradation

The preferential movement of water and transport of substances play an important role in soil, but they are not yet fully understood, especially in degraded peat soil. In this study, we aimed to deduce changes in flow and transport patterns with titanium dioxide (TiO2) as a dye tracer during the course of soil degradation resulting from peat drainage. The dye tracer experiments were carried out on columns of eight types of differently degraded peat soil from three sites taken in both vertical and horizontal directions. The titanium dioxide suspension (average particle size of 0.3 µm; 10 g l−1) was applied in a pulse of 40 mm to each soil core. The cores were subsequently cut into six slices, photographed and the images were analysed for the extent of dye cover and number of pores. In addition, the saturated hydraulic conductivity (Ks) was determined. Preferential flow occurred in all of the peat types investigated. From the stained soil structural elements, we concluded that undecomposed plant remains are the major preferential flow pathways in less degraded peat. For more strongly degraded peat, bio-pores, such as root and earthworm channels, operated as the major transport network. Results show that Ks and the effective pore network in less degraded peat soil are anisotropic. With increasing peat degradation, Ks and the cross-section of effective pores decreased in the predominant direction only and the anisotropy of both properties decreased. The Ks was closely related to the number of macropores and pore continuity. Therefore, we conclude that changes in flow and transport pathways and Ks with increasing peat degradation result from the disintegration of the peat-forming plant material and the decrease in number and continuity of macropores. Highlights We aimed to deduce changes in flow and transport patterns during peat degradation. TiO2 (dye tracer) was used to visualize the flow and transport patterns in degraded peat soil. The preferential flow paths, Ks and pore structures changed with peat degradation. Changes in flow and transport paths and Ks relate to peat-forming plant materials and pore structure.