An experimental tracer study of the role of macropores in infiltration in grassland soils

Abstract

Abstract:Water flow in macropores is an important mechanism of infiltration in natural soils and, as such, is crucial for the prediction of runoff generation. The major flow processes controlling macropore flow are the initiation of macropore flow (water supply into macropores) and the water transfer from the macropores into the surrounding soil matrix (interaction). The water movement during infiltration and the resulting flow paths were studied with combined sprinkling and dye tracer experiments under different rainfall intensities and initial soil moisture conditions. The dye tracer was continuously applied with the sprinkling water on 1 m 2 plots. After the sprinkling, horizontal and vertical soil sections were prepared for surveying dye patterns, which showed the cumulated flow pathways in the soils. These experiments were carried out on four hillslope sites covered with grassland, where earthworms mainly built the macropore system. The evaluation of the flow processes in the soil was based on classified dye patterns and measurements of water content and matric potential. The results illustrate how flow in earthworm channels influences general hydrological flow processes during extreme rainfall events. Macropore flow was initiated from the soil surface or from a saturated or partially saturated soil layer. Transfer of water from the macropores into the soil matrix was mainly influenced by the soil properties and soil water content. The permeability of the underlying bedrock in combination with this transfer of water controlled the drainage of the macropores. Finally, major effects of macropore flow processes on the hydrological response were extracted. Infiltration excess overland flow was reduced if water bypassed the less permeable layer through macropores, saturation excess overland flow was less affected by macropores, and subsurface flow was activated very rapidly because the infiltrated water bypassed the soil matrix. This study highlights the most important processes that have to be considered in order to understand better and to model infiltration in natural soils in the future.

What can flux tracking teach us about water age distribution patterns and their temporal dynamics?

“…However, the overall proportion of older water released can potentially increase due to higher percolation rates from water stored in the matrix (Eq. 15), which is broadly consistent with observations reported by Weiler and Naef (2003). Dynamic partial mixing was only considered where significant changes in soil moisture content below FC occur, i.e.…”

Field investigation of preferential fissure flow paths with hydrochemical analysis of small-scale sprinkling experiments

“…McDonnell, 1990;Uchida et al, 2001). Furthermore, our results support the concept that antecedent water storage influences the initiation of preferential flow, as found, for example, in Trojan and Linden (1992), Zehe and Fluhler (2001) and Weiler and Naef (2003).…”

“…Allaire-Leung et al, 2000;Larsbo and Jarvis, 2006) to field experiments at different scales (e.g. Collins et al, 2002;Weiler and Naef, 2003;Mali et al, 2007;Kienzler and Naef, 2008). However, there are no plot-scale field measurements dedicated to monitoring and quantifying preferential fissure flow, being a special case of macropores with apertures up to tens of centimetres.…”

Threshold behaviour in hydrological systems as (human) geo-ecosystems: manifestations, controls, implications

“…Several authors have suggested that threshold behaviour is of key importance for understanding and predicting the dynamics and stability of our climate system (Claussen, 1999;Pitman and Stouffer, 2006), the dynamics and resilience of geo-ecosystems (With and Crist, 1995;Wilcox et al, 2003a;Schröder, 2006;Emanuel et al, 2007;Saco et al, 2007), and the dynamics of fluxes in hydrologic systems (Beven and Germann, 1981;Woods and Sivapalan, 1999;Uhlenbrook and Leibundgut, 2002;Weiler and Naef, 2003a;Zehe et al, 2007). As suggested by Thom (Thom, 1977(Thom, , 1989 in the context of catastrophe theory, and as will be discussed below, threshold behaviour drastically reduces our ability to make predictions at the level of (a) an individual process, (b) the response of larger units (e.g., hillslopes or catchments) that involve interactions of many processes, and (c) the long-term hydrologic functioning of complete geoecosystems.…”