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-m 2 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.

The influence of seasonally frozen soil on the snowmelt runoff at two Alpine sites in southern Switzerland

“…After that date the soil temperature stayed close to the freezing point. As shown by a nearby dye tracer experiment (Stähli et al, 2004), the soil remained frozen over the entire profile until the end of the snowmelt period. This tracer experiment allowed us also to detect an approximately 3 cm-thick basal ice sheet.…”

Effects of Frozen Soil on the Groundwater Recharge in Alpine Areas

“…The digital images (Figure 7.5) were processed with the following method (details in Stähli et al 2004). The average level of the color channels was standardized to a reference common for all profiles.…”

Effects of Frozen Soil on Snowmelt Runoff and Soil Water Storage at a Continental Scale

“…Lindstrom et al (2002) also concluded that there were no clear effects of frozen soil on the timing and magnitude of runoff from an analysis of 16-yr data in a 0.5-km 2 watershed in northern Sweden. Researchers (Stadler et al 1997;Stähli et al 1999;Nyberg et al 2001) have demonstrated that soil structure, air-filled porosity, ice content, and the number of freezing and thawing cycles are the governing factors affecting the infiltration capacity of frozen soil. Even at very local scales, recent laboratory and field studies using dye tracer techniques (Flury et al 1994;Stadler et al 2000;Stähli et al 2004) revealed that water can infiltrate into deeper soil through preferential pathways where air-filled macropores exist at the time of freezing.…”

“…One-dimensional numerical models using the fully coupled heat and mass balance equations (Flerchinger and Saxton 1989;Zhao and Gray 1997;Cox et al 1999;Koren et al 1999;Stähli et al 2001;Cherkauer and Lettenmaier 2003;Hansson et al 2004) showed a variety of ways to parameterize the hydraulic properties of frozen soil. Most of these models introduced the concept of supercooled soil water, which is the liquid water that coexists with ice over a wide range of temperatures below 0°C, by applying the freezing-point depression equation.…”

“…However, other modelers (Zhao and Gray 1997;Koren et al 1999;Stähli et al 2001;Cherkauer and Lettenmaier 2003) proposed quite different schemes to compute hydraulic properties as a means to produce greater infiltration rates. Stähli et al (2001) proposed two separate domains for the water infiltration into frozen soil: the low-flow domain where water flows through the liquid water film absorbed by the soil particles and the high-flow domain where water flows through the air-filled macropores. Koren et al (1999) assumed that frozen soil is permeable due to soil structural aggregates, cracks, dead root passages, and worm holes, and used the total water content (frozen and unfrozen) in the Clapp-Hornberger relationships in a land model for use in a weather prediction model.…”