Soil water repellency under dry and wet antecedent weather conditions for selected land-cover types in the coastal zone of central Portugal

Abstract

This paper reports on the first systematic inventory of soil water repellency in Portuguese coastal dune sand areas. Since water repellency is widely associated with certain vegetation types or individual plant species, this inventory concerned arable land as well as 6 natural and semi-natural land-cover types representative for the vegetation zonation in the study area. Since water repellency further is a feature that commonly varies through time, disappearing when soils become wet, initial sampling was carried out during late summer 2000 and later repeated, at 1 of the 2 sites per land-cover type, during early spring 2001. Water repellency was principally measured in the field using the Molarity of an Ethanol Droplet (MED) test. Under the dry summer conditions, water repellency was a widespread phenomenon at and immediately below, the soil surface and numerous significant differences in ethanol classes existed between the land-cover types. The transient nature of water repellency was confirmed by many instances of significantly lower spring than summer ethanol classes. These significant differences were in general accompanied by a significant negative correlation of the summer and spring ethanol classes with volumetric soil moisture content. The sites’ overall repellency levels under dry antecedent weather conditions were significantly correlated with their overall levels of soil organic matter.

Molecular characterization of wildfire impacts on organic matter in eroded sediments and topsoil in Mediterranean eucalypt stands

“…The hydrophobic nature of charcoal residues might have contributed to the comparatively high erosion rates at the EB site (Malvar et al, 2013;Prats et al, 2014;Shakesby and Doerr, 2006). Not only long unburnt but also recently burnt eucalyptus plantations in the study region have been found to exhibit extreme topsoil water repellency, especially during dry antecedent weather conditions (Keizer et al, 2005(Keizer et al, , 2008. Phenols and alkylphenols were found in all samples, probably originating from phenolic precursors compounds such as lignin, tannin, proteinaceous biomass, and carbohydrates (Tegelaar et al, 1995) or derived from the heat-transformed products of such constituents .…”

The role of soil water repellency in overland flow generation in pine and eucalypt forest stands in coastal Portugal

“…The approach involves a series of comparisons. A pine and a eucalypt forest stand were selected for study because they had been found to differ substantially in repellency conditions during late summer 2000 (Keizer et al 2005, this issue), with the eucalypt stand presenting a higher overall repellency level as well as a more homogeneous spatial pattern. Within each stand, 2 slopes were selected with contrasting aspects and, in association, somewhat different slope angles.…”

Surface and subsurface flow in eucalyptus plantations in north-central Portugal

“…In the study area, following dry spells and with presence of strong soil water repellency, rainfall events produced negligible amounts of OLF as well-illustrated by the dry events. It is well-established that soil water repellency and its high spatial variability (Keizer et al, 2005a;Leighton-Boyce, 2003;Santos et al, 2013) promote spatially localized infiltration or percolation, with the development of fingered or preferential flow paths, which can explained the observed low production of OLF. Nevertheless, during the dry period, SSF came exclusively from the soil matrix, therefore, the water that infiltrated by preferential paths was reabsorbed by soil matrix.…”

“…Also saturation-excess OLF can be expected to play an important role in streamflow generation in the study region, especially during the wet winter seasons when soil water repellency tends to be less pronounced Keizer et al, 2005a). Namely, rainfall is rather high in the upper Caramulo Mountains in particular, amounting to over 1400 mm per year, and soils tend to be shallow (Malvar et al, 2013;Shakesby et al, 1996).…”

“…Second, many Eucalyptus plantations in the Caramulo Mountains have a low ground cover of vegetation and litter and a high cover of stones, especially when they are recently planted, and infiltration-excess OLF is often associated with areas having sparse vegetation and/or a very stony soil surface (Ruiz-Sinoga et al, 2010). Third, the Eucalypt plantations in the study region are well-known for their strong to extreme soil water repellency, especially after dry spells Keizer et al, 2005a;Santos et al, 2013), and soil water repellency is widely regarded to induce infiltration-excess OLF (Ferreira et al, 2000;Keizer et al, 2005b;Leighton-Boyce et al, 2005;Malvar et al, 2013).…”