Subsurface flow and large-scale lateral saturated soil hydraulic conductivity in a Mediterranean hillslope with contrasting land uses

The lateral saturated hydraulic conductivity, K_s,l, is the soil property that mostly governs subsurface flow in hillslopes. Determinations of K_s,l at the hillslope scale are expected to yield valuable information for interpreting and modeling hydrological processes since soil heterogeneities are functionally averaged in this case. However, these data are rare since the experiments are quite difficult and costly. In this investigation, that was carried out in Sardinia (Italy), large-scale determinations of K_s,l were done in two adjacent hillslopes covered by a Mediterranean maquis and grass, respectively, with the following objectives: i) to evaluate the effect of land use change on K_s,l, and ii) to compare estimates of K_s,l obtained under natural and artificial rainfall conditions. Higher K_s,l values were obtained under the maquis than in the grassed soil since the soil macropore network was better connected in the maquis soil. The lateral conductivity increased sharply close to the soil surface. The sharp increase of K_s,l started at a larger depth for the maquis soil than the grassed one. The K_s,l values estimated during artificial rainfall experiments agreed with those obtained during the natural rainfall periods. For the grassed site, it was possible to detect a stabilization of K_s,l in the upper soil layer, suggesting that flow transport capacity of the soil pore system did not increase indefinitely. This study highlighted the importance of the experimental determination of K_s,l at the hillslope scale for subsurface modeling, and also as a benchmark for developing appropriate sampling methodologies based on near-point estimation of K_s,l.