Water content dynamics in a volcanic ash soil slope in southern Chile

Abstract

Andisols present exceptional physical properties, making up < 1% of the world's soils. While there is a lot of information about non-volcanic soil properties, research about soils of volcanic origin is limited. Specifically, no major studies have been carried out to improve our knowledge of these soils' hydrological behavior, which is relevant due to the impact of climate change on water resources and to the soil's role in the hydrological cycle. Thus, the aim of this work was to analyze the water content dynamics of a soil slope derived from volcanic ashes under different land covers. We hypothesized that land cover, rainfall, and air temperature, in addition to the hydraulic properties of the volcanic ash soil, regulate the slope's water content dynamics. Our study was conducted in S Chile, in a fluvial terrace covered by pastures in the uplands, a native forest in the adjacent slope, and a hygrophilous forest in the floodplain at the base of the slope, surrounding a stream. Soil physical properties, such as bulk density (Db), volume of macropores (wCP), plant available water (PAW) and saturated hydraulic conductivity (Ks) were studied. Rainfall, air temperature, volumetric water content ( Field ) and soil temperature were continuously measured with data loggers. The groundwater level was also measured. Water content dynamics reflect the behavior of rainfall and air/soil temperatures under different land covers, as well as, revealing the specific behavior of volcanic soil's pore system (e.g., Db < 0.9 Mg m -3 ). Soil depths exposed to more intensive and dynamic wetting and drying cycles presented well-defined water release ranges as compared to the pore system of deeper soil horizons. Soils present large water holding capacities (PAW > 24%), however, during summer they can reach volumetric water contents near to the permanent wilting point quickly at a depth of 5 cm. The water table altitude was directly related to the temporal changes of Field measured at a depth of 50 cm, highlighting the fact that the saturated and unsaturated zones are connected.

Spatial and temporal variability of physical properties of Aquands under different land uses in southern Chile

“…To compare two contrasting conditions, the measurements were conducted in winter (26 June 2013) and spring (09 December 2014). Before each measurement, the WET Sensor was calibrated using undisturbed soil samples (765 cm 3 ) collected from the studied soils (Dörner et al ., ).…”

“…The sensors (two per depth at each site) recorded both volumetric water content and temperature every 10 min (Em50, Decagon Devices, USA), and data for the dates of field measurements in June and December are reported. The 5TM sensors were also calibrated (Dörner et al ., ). Rainfall events at sNF and NG sites were registered using an ECRN Rain Gauge (Decagon Devices, Pullman, Washington, USA).…”

“…The effect of the land use change on the soil physical quality has been well documented for Andisols in southern Chile (e.g. Dörner et al ., ). However, this does not hold true for Ñadi soils (Ellies, ).…”

“…The restricted depth of Ñadi soil profiles suggests that the impact of the land use change on physical functions (e.g. water storage capacity due to a significant decrease in soil depth) should be greater than those observed for the deep Andisols (Dörner et al ., ). While the land use change implies mechanical stresses that induce space‐dependent soil deformations, the implementation of drainage increases hydraulic stresses, and, consequently, a secondary soil settlement by soil shrinkage may occur (Gebhardt et al ., ).…”

Water and temperature dynamics of Aquands under different uses in southern Chile

“…Indorante et al, 2013) and is well known for Typic Hapludands (locally called Trumaos) in southern Chile (Ellies et al, 1996;Dörner et al, 2009Dörner et al, , 2010Dörner et al, , 2015. However, little research has been carried out on Ñadi (Aquands) soils (Ellies, 2001;Thiers et al, 2007;Dörner et al, 2016).…”