Controls of land use and soil structure on water movement: Lessons for pollutant transfer through the unsaturated zone

Abstract. The mean transit time (MTT) of water in a catchment gives information about storage, flow paths, sources of water and thus also about retention and release of solutes in a catchment. To our knowledge there are only a few catchment studies on the influence of vegetation cover changes on base flow MTTs. The main changes in vegetation cover in the Swiss Alps are massive shrub encroachment and forest expansion into formerly open habitats. Four small and relatively steep headwater catchments in the Swiss Alps (Ursern Valley) were investigated to relate different vegetation cover to water transit times.Time series of water stable isotopes were used to calculate MTTs. The high temporal variation of the stable isotope signals in precipitation was strongly dampened in stream base flow samples. MTTs of the four catchments were 70 to 102 weeks. The strong dampening of the stable isotope input signal as well as stream water geochemistry points to deeper flow paths and mixing of waters of different ages at the catchments' outlets. MTTs were neither related to topographic indices nor vegetation cover. The major part of the quickly infiltrating precipitation likely percolates through fractured and partially karstified deeper rock zones, which increases the control of bedrock flow paths on MTT. Snow accumulation and the timing of its melt play an important role for stable isotope dynamics during spring and early summer.We conclude that, in mountainous headwater catchments with relatively shallow soil layers, the hydrogeological and geochemical patterns (i.e. geochemistry, porosity and hydraulic conductivity of rocks) and snow dynamics influence storage, mixing and release of water in a stronger way than vegetation cover or topography do.

Section: Introductionmentioning

confidence: 80%

Importance of vegetation, topography and flow paths for water transit times of base flow in alpine headwater catchments

Mueller

Weingartner

Alewell

2013

“…The experimental area was kept shaded and sheltered from rain in all weather conditions to minimize evaporation and uncontrolled water input during the experiments. Brilliant Blue FCF was diluted in water of local origin to a concentration of 4 g L −1 and was sprayed with a backpack nozzle sprayer for even distribution (Bachmair et al, 2009). For an overall application amount of 20, 40 and 60 mm, each sub-area was sprinkled with an intensity of 20 mm h −1 .…”

Section: Dye Tracer Experimentsmentioning

confidence: 99%

Does drought alter hydrological functions in forest soils?

Gimbel¹,

Puhlmann²,

Weiler³

2016

Self Cite

Abstract. Climate change is expected to impact the water cycle and severely affect precipitation patterns across central Europe and in other parts of the world, leading to more frequent and severe droughts. Usually when projecting drought impacts on hydrological systems, it is assumed that system properties, like soil properties, remain stable and will not be affected by drought events. To study if this assumption is appropriate, we address the effects of drought on the infiltration behavior of forest soils using dye tracer experiments on six sites in three regions across Germany, which were forced into drought conditions. The sites cover clayey-, loamy-and sandy-textured soils. In each region, we compared a deciduous and a coniferous forest stand to address differences between the main tree species. The results of the dye tracer experiments show clear evidence for changes in infiltration behavior at the sites. The infiltration changed at the clayey plots from regular and homogeneous flow to fast preferential flow. Similar behavior was observed at the loamy plots, where large areas in the upper layers remained dry, displaying signs of strong water repellency. This was confirmed by water drop penetration time (WDPT) tests, which revealed, in all except one plot, moderate to severe water repellency. Water repellency was also accountable for the change of regular infiltration to fingered flow in the sandy soils. The results of this study suggest that the drought history or, more generally, the climatic conditions of a soil in the past are more important than the actual antecedent soil moisture status regarding hydrophobicity and infiltration behavior; furthermore, drought effects on infiltration need to be considered in hydrological models to obtain realistic predictions concerning water quality and quantity in runoff and groundwater recharge.

“…Our instrumentation with fully filtered monitoring wells, which is widespread in many research catchmentse.g., Maimai in New Zealand (Brammer and McDonnell, 1996;McGlynn et al, 2002), Tanakami Mountain Hillslope in Japan (Asano et al, 2002), Panola Mountain Research Catchment in the USA McDonnell, 2006), Black Forest Foothill Research Hillslope, Germany (Bachmair andWeiler, 2012) -was not able to attribute groundwater dynamics to the runoff formation processes of individual soil layers (Figs. 4,5,and 8).…”

Section: Groundwater Responsementioning

confidence: 99%

“…Brilliant blue dye experiments are typically conducted to identify soil structures that influence or enhance infiltration processes at the plot scale in rather flat terrain (Bachmair et al, 2009;Flury et al, 1994;Forrer et al, 2000;Weiler, 2001). Weiler and Flühler (2004) studied preferential infiltration with brilliant blue and focused on macropore flow initiation at four grassland sites under dry and wet antecedent soil moisture conditions.…”

Section: Introductionmentioning

confidence: 99%

“…Weiler and Flühler (2004) studied preferential infiltration with brilliant blue and focused on macropore flow initiation at four grassland sites under dry and wet antecedent soil moisture conditions. Bachmair et al (2009) studied the control of land use and related soil structures on preferential infiltration. Anderson et al (2009) used brilliant blue to stain a lateral preferential flow network, and focused on how preferential flow structures connect hydrologically at the hillslope scale.…”

Section: Introductionmentioning

confidence: 99%

See 1 more Smart Citation

True colors – experimental identification of hydrological processes at a hillslope prone to slide

Schneider

Pool

Strouhal

et al. 2014

Abstract. This study investigated runoff formation processes of a pre-alpine hillslope prone to slide. The experimental pasture plot (40 m × 60 m) is located in the northern front range of the Swiss Alps on a 30 • steep hillslope (1180 m a.s.l., 1500 + mm annual precipitation). A gleysol (H-Go-Gr) overlies weathered marlstone and conglomerate of subalpine molasse. We conducted sprinkling experiments on a subplot (10 m × 10 m) with variable rainfall intensities. During both experiments fluorescein line-tracer injections into the topsoil, and sodium chloride (NaCl) injections into the sprinkling water were used to monitor flow velocities in the soil. The observed flow velocities for fluorescein in the soil were 1.2 and 1.4 × 10 −3 m s −1 . The NaCl breakthrough occurred almost simultaneously in all monitored discharge levels (0.05, 0.25 and 1.0 m depth), indicating a high-infiltration capacity and efficient drainage of the soil. These initial observations suggested "transmissivity feedback", a form of subsurface stormflow, as the dominant runoff process. However, the results of a brilliant blue dye tracer experiment completely changed our perceptions of the hillslope's hydrological processes. Excavation of the dye-stained soils highlighted the dominance of "organic layer interflow", a form of shallow subsurface stormflow. The dye stained the entire H horizon, vertical soil fractures, and macropores (mostly worm burrows) up to 0.5 m depth. Lateral drainage in the subsoil or at the soil-bedrock interface was not observed, and thus was limited to the organic topsoil. In the context of shallow landslides, the subsoil (Go/Gr) acted as an infiltration and exfiltration barrier, which produced significant lateral saturated drainage in the topsoil (H) and possibly a confined aquifer in the bedrock.