Snowmelt Infiltration into Alpine Soils Visualized by Dye Tracer Technique

Abstract

Snowmelt infiltration into alpine soils can be severely reduced and even impeded by soil frost. In order to learn more about the true nature of infiltration pathways into alpine soils, dye tracer experiments were set up at 2 locations in southern Switzerland: at Hannigalp (2100 m) and at Gd St Bernard. Over the course of two winters (2000–2001 and 2001–2002) we excavated vertical soil profiles during snowmelt to examine the distribution of a dye tracer (Brilliant Blue FCF) that had been applied on the surface of a 7-m2 plot at the beginning of the winter. Soil conditions varied between the winters, with the soils remaining unfrozen during the first and a significant frozen layer forming during the second. With this method the dominant infiltration processes at these 2 sites were identified. During the first winter the water infiltration at Hannigalp showed a pronounced preferential behavior, whereas at Gd St Bernard we found a more homogeneous front-like infiltration. During the second winter the impeding impact of the frozen soil was clearly seen at the Hannigalp site—however, only in the first stage of the snowmelt. More decisive for the formation of lateral surface runoff was the buildup of an ice layer on the soil surface due to melting and refreezing. Cold-chamber experiments, in which intact soil columns were irrigated with a dye tracer and a fluorescent tracer solution, confirmed our in situ observations with regard to heterogeneity and soil frost effect on the infiltration pattern. Our study showed that both tracers can be applied to frozen soil in the laboratory, whereas at the remote alpine locations only the dye tracer method was applicable.