The use of Mini Disk Infiltrometer (MDI) for testing infiltration, sorptivity and water repellence on slopes affected by fire

Abstract

Wildfires degrade the vegetation cover that protects the soil from the rain¿s aggressiveness and erosion processes. Fire consumes litter layer and small bushes, leading to important changes in vegetation and topsoil structures. Peak rainfall after fire, generates runoff, and less water is incorporated into the soil, resulting in reduced infiltration. Mediterranean soils under shrubland vegetation are often shallow and are located on slopes prone to erosion. In these conditions, the post-fire environment of the surface horizons is a determining factor in establishing the amount of mineral soil exposed to raindrop splash, overland flow, and the development of water repellent soil conditions. Physical and chemical changes in the upper soil horizons, induced by fires, greatly affect other properties influencing water infiltration. The combustion process also turns the litter and duff layers into ash and charcoal, which can seal soil pores and therefore decrease hydraulic conductivity and soil infiltration capacity (DeBano et al., 1998). Soil water infiltration in semi-arid areas is highly dependent on the dynamic soil characteristics such as organic matter, root systems, macropores, vegetation cover, soil crust formation, soil aggregation, soil water content (Bergkam and Cammeraat, 1996), soil texture, rock fragment size, percentage and geometry. The spatial and temporal variability of these soil properties are subjected to the discontinuous distribution of vegetation and the complex interactions between plant and soil surface. As a result, the plant environment influences soil surface properties and hence, soil water infiltration and redistribution. Thus, the characteristics of the surface horizons are determinant in the evolution of the soil water infiltration and, therefore, changes induced by fire on them are relevant to understand the variation of soil hydrological processes on burned slopes. The aim of this research is to apply the mini disk infiltrometer (MDI) methodology to quantify variations in soil hydrological parameters (infiltration rate and capacity, sorptivity and water repellence) under natural field conditions, after a repeated fire, and to consider the effect of the previous presence or absence of vegetation cover on the soil surface hydrological properties.