Impact of Low Pressure Grazing on the Hydrological and Sediment Connectivity in Hillslopes under Contrasted Mediterranean Climatic Conditions (South of Spain).

Abstract

Many areas from the Mediterranean region are characterised by steep slope gradient, patchy vegetation cover and soil surface conditionsprone to overland flow generation and sediment transport. This study evaluated the hydrological and sediment connectivity betweensections (top, middle and bottom-channel) from three low pressure grazed hillslopes located under contrasted Mediterranean climaticconditions in southern Spain. The aim was performed by installing rain-gauge stations and opened-plots in order to register overland flowand sediment concentration from February 2008 to January 2010. The results indicated that (i) major volumes of overland flow andsediment transport occurred more frequently in the humid and semiarid; (ii) the more frequent hydrological connectivity was observedbetween the middle and bottom-channel sections, although the major values of overland flow and sediment concentration were registeredin the upper sections; (iii) it was found very frequent those rainfall events in which all sections contributed with overland flow and sedi-ment to the channel; (iv) the factors controlling hydrological and sediment connectivity varied from one site to another depending on therainfall regime and vegetation cover, although the soil surface conditions (rock fragment cover either embedded or not embedded, crusts,annual plants, among others) were found as a key factor in all of them. In summary, the grazing activity, even being of low pressure,contributes to distance the hydrological and sediment connectivity from the response expected in the field sites, especially in that of humidMediterranean climate: more overland flow and less sediment concentration and, vice versa, when becomes arid