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

Aquands are soils derived from holocenic volcanic ashes located in southern Chile. Due to the presence of very high levels of organic matter (30 %), these soils present a high total porosity (80 %) but at the same time, a limited water storage capacity due to their shallow soil depths. The aim of this work was to analyze the influence of land use change of a Duric Histic Placaquand (Nadi) soil on soil physical properties and their consequences on water and temperature dynamics. The volumetric water content (qField) and soil temperature (T) were registered at different depths in a Nadi soil under a secondary native forest (sNF) and naturalized grassland (NG). Undisturbed soil samples were collected to analyze the water retention curve, saturated (Ks) and unsaturated (Ku) hydraulic conductivity and water repellency. The dynamics of rainfall and water table depth (WT) were registered using a rain gauge and groundwater wells. The land use change of a Nadi soil from sNF to NG induced soil structural changes in the first 15 cm of soil reducing the amount of macropores under NG and affecting the hydraulic conductivity function as well as qField and T dynamics, i.e. while the WT in winter reached the soil surface in the NG, under sNF the air-filled pores were still present. Similarly, the T gradients increased as qField decreased, being more intensive under NG. A nonhomogeneous soil wetting and water infiltration was assessed, which can be related to an increased spatial water repellency, soil hydraulic properties and rainfalls.