Landscape evolution and changes in soil hydraulic properties at the decadal, centennial and millennial scale: A case study from the Campine area, northern Belgium

Soil hydraulic properties evolve over time as a result of soil formation processes. We investigated the rate and circumstances of change in soil hydraulic properties as a result of soil and landscape evolution that took place over a period of a few decades to several thousands of years. To this end, a sediment-soil sequence in which different sandy landscapes and associated soils are preserved was studied with respect to its geomorphological and pedohydrological characteristics. Three stages of soil development corresponding to specific landscapes were observed within a 2-m deep profile: 1) a stabilisation surface within an active drift sand landscape, 2) an A-horizon that developed on a stabilised drift sand landscape and 3) a pronounced podzol that developed in a stabilised landscape from the last glacial. Measurement of soil physical properties was conducted including grain size analysis, organic carbon content, soil water retention characteristic and hydraulic conductivity using constant head and air permeability analyses. Age control of soil horizons and vegetation history were obtained from optically stimulated luminescence (OSL) dating, radiocarbon (14C) dating, pollen analysis and historical archives. The results suggest a strong relationship between landscape evolution, soil development and hydraulic properties. Small changes in hydraulic properties may already be observed on a decadal and centennial scale, while long-term podzolisation processes may decrease the hydraulic conductivity of parent material up to three orders of magnitude in several thousands of years. It is concluded that combination of geomorphological and pedohydrological analyses of sediment-soil archives may provide a unique means to gain insight into the rate and extent of past changes in soil hydraulic properties and the consequences of future hydrological changes as a result of these evolving properties.