Intensity and persistence of water repellency in relation to vegetation types and soil parameters in Mediterranean SW Spain

The objectives of this research are the following: [1] to study the persistence and intensity of water repellency in soil samples (0–5 cm deep) collected under different plant species, [2] to analyze the relationships between soil water repellency and environmental factors including soil organic matter content, soil acidity, and texture, and [3] to study the variations of soil water repellency measured on soil samples collected in winter (2007) and summer (2008) in the studied area. Soil water repellency has been studied in Mediterranean coniferous and eucalyptus forests, particularly after burning, but the number of studies concerning other Mediterranean forest systems is still very low. In this paper, soil water repellency was measured by using the water drop penetration time test and the ethanol percentage test on samples collected during the winter of 2007 and the summer of 2008 under different land uses (pines, cork oaks, eucalyptus, heathland and olive trees) in a Mediterranean subhumid forested area (Los Alcornocales Natural Park, Cádiz and Málaga, Spain). Most of the soil samples collected under heathland showed extreme water repellency, whereas soils under olive trees showed low or inexistent water repellency. The organic matter content and acidity were highly correlated with water repellency in soils under pines, cork oaks and eucalyptus, while soils under heathland or olive trees showed poorer correlations. The average soil moisture content of samples collected during winter (2007) was 20.7± 7.9%, and it decreased in samples collected during summer (2008) to 1.1± 0.6%. The persistence and intensity of water repellency varied slightly between samples collected in winter and summer in soils under all species except under heathland. Water repellency persisted in most cases during the wet and dry season, and many soils showed strong water repellency even during winter. The patchy patterns of persistence and intensity of soil water repellency are conditioned by the spatial distribution of the studied land uses, which dictate the intensity and persistence of soil water repellency, and modulated by other environmental factors. The vegetation effects on soil hydrology should be considered for afforestation work and flooding control.