Soil water repellency along elevation gradients: The role of climate, land use and soil chemistry

Abstract

The rate of water infiltration, surface runoff, and overland flow are all affected by soil water repellency (SWR), i.e., the reduced affinity for water caused by hydrophobic coatings on soil particles. SWR impacts water balance, which in turn affects ecosystem’s function and watersheds hydrology, but little is known about changes of these properties along elevation gradient. Here, we investigate variation in SWR along four elevation gradients in four Italian mountain peaks, encompassing different land use and vegetation types from Mediterranean to temperate and alpine ecosystems. A total of 240 soil samples were collected for 48 ecosystems, and SWR was determined using the molarity of an ethanol droplet test. Soil characteristics were assessed using texture, pH, organic matter content, and soil salinity. Climate data were obtained using WorldClim, and their relationship with SWR was examined. SWR showed a unimodal pattern along the four elevation levels and in all cases peaked at mid-elevations between 1000 and 2500 m a.s.l.. SWR was highest under coniferous and deciduous forests and lowest for arable and bare soil. Soil organic matter and pH were the main determinants of SWR, with a positive and negative correlation, respectively. As for climate, mean annual temperature showed a hump-shaped relationship with SWR. In detail, we found that soil was hydrophilic at the extremes of elevation gradient where mean annual temperatures are less than −3.4 °C for alpine bare soils and higher than 12.7 °C for arable soils. This study allowed us to show how land use, soil chemistry, and climate are related to SWR along an elevation gradient. Further research is needed to concretely evaluate the effect of SWR on erosion risk at the watershed scale in the context of climate change.