Effects of soil and vegetation development on surface hydrological properties of moraines in the Swiss Alps

Abstract

The near-surface saturated hydraulic conductivity (Ksat) is an important hydrological characteristic because it determines surface infiltration rates and the vertical and lateral redistribution of water in the soil. However, there is comparatively little knowledge about the changes in Ksat during landscape development and how the co-evolution of biological, pedological and hydrological characteristics affect the movement of water through the soil. On the one hand, increasing vegetation cover is expected to increase macroporosity and thus Ksat. On the other hand, clay formation is expected to decrease Ksat. To investigate how hillslope aging affects Ksat, we used a space-for-time approach and conducted comprehensive measurements of vegetation, soil and topography on a chronosequence of moraines in a proglacial area of the Swiss Alps. On four moraines, ranging from about ten thousand to ~30 years in age, we measured for three plots the near-surface soil characteristics. Surface and near-surface Ksat were high and decreased with depth on all moraines. Surface Ksat was highest on the youngest moraine (median: 4320 mm hr−1) and lowest (540 mm hr−1) on the oldest moraine. Ksat was significantly positive correlated with soil texture and the gravel content in the surface soil layer. The correlation analyses and Structural Equation Model suggested that the larger fraction of small particles for the older moraines had a bigger effect on Ksat than the denser root network. Even though the variability in measured Ksat-values within the moraines was high and water movement is thus likely very heterogeneous, the measured Ksat values suggest that infiltration-excess overland flow is very unlikely on these hillslopes but (lateral) near surface flow likely increases with the age of the hillslope. This information is important for understanding differences in runoff generation mechanisms in alpine areas with moraines of different ages, as well as landscape evolution models.