Estimation of macropore flow characteristics in stony soils of a small mountain catchment

Abstract

The rapid movement of water in a complex system of preferential pathways in soils is a common natural phenomenon. However, quantification of the properties of this phenomenon is not easy and such results are not often found in the literature. The paper presents results of quantification of the number of macropores, their relative volume and the ratio of water infiltrating through the macropores for five study sites with stony soils located in a mountain catchment of northern Slovakia. These characteristics were calculated from the saturated and unsaturated soil hydraulic conductivities under the assumptions of the Poiseuille’s law. Saturated hydraulic conductivities were estimated by single ring infiltrometer measurements in the field and by falling head method in the laboratory. Unsaturated hydraulic conductivities were estimated by tension infiltration measurements in the field (using a minidisc infiltrometer, Decagon Devices). The largest amount of macropores (defined as the pores with radius larger than 1.5 mm) in the entire soil profile (7–5276 per 1 m2) was found at forest sites overgrown by spruce with high to extremely high stoniness. The number of macropores decreased with depth of the soil profile at all study sites. The contribution of macropore flow to water infiltration varied from approximately 63% to almost 100%. Although macropores can conduct a large proportion of water, their relative volume is small (0.001–0.9%). The relative volume of all macropores (active and non-active) estimated from the soil porosity and the water retention function was in the range 2–23%.