Quantifying interrill and ephemeral gully erosion in a small sicilian basin.

In many semiarid regions of the Mediterranean basin, soil erosion has become a serious environmental problem affecting land productivity, nutrient loss, water quality, and freshwater ecosystems. In some areas of Sicily, rates of soil loss differ according to erosion type and land degradation processes. To date, these differences, although evocated by several scientists and confifi rmed by visual inspections over the most vulnerable areas subjected to soil erosion processes, have been poorly quantififi ed. In this paper, measurements of ephemeral gullies (EG) carried out at event scale since 1999, in a small basin located in Sicily (Italy), have been used to quantify soil loss attributed to EG erosion. In addition, the sediment delivery distributed (SEDD) model, which was calibrated and validated in similar physiographic and land use conditions, was applied to document the contribution of rill-interrill erosion over the same area. Ephemeral gully formation occurred seven hydrologic years out of ten, with a frequency corresponding to 70 % of the years covered by the survey and to a return period of almost 1.4 years. The mean soil loss in the seven years when EG was active was equal to 37.88 t ha–1 year–1. The ratio between soil loss attributable to EG and total soil loss (SEDD + EG) resulted quite variable between erosion events accounting for 23 % to 98 % of total soil lost. The overall results indicate that there are signififi cant and important differences between these two types of degradation processes elucidating the importance of EG erosion in semiarid regions. Also, the contribution due to EG erosion emphasizes the need to extend the existing data set of soil loss by appropriate measurements and fifi eld campaigns.