Using 137Cs and 210Pbex measurements and conventional surveys to investigate the relative contributions of interrill/rill and gully erosion to soil loss from a small cultivated catchment in Sicily

In many cultivated areas in semiarid Mediterranean regions, soil erosion is responsible for problems related to both on-site and off-site impacts, including reduced crop productivity, water quality, and degradation of freshwater ecosystems. In some areas of Sicily, where intense short duration rainfall events are common, soil erosion is a very serious problem, especially on land subjected to continuous tillage operations. The rates of soil loss in these areas and their impact differ according to the dominant type of erosion. Several existing studies have focused on the impacts of either linear (gully- or ephemeral gully-erosion) or interrill–rill erosion, but to date the relative magnitude of these two different types of erosion, has rarely been assessed. This paper reports the results of a study aimed at comparing the relative contribution of interrill–rill erosion and gully erosion to soil loss from a small cultivated catchment located in Sicily (Italy). Surveys of ephemeral gullies (EG) in the study catchment carried out at the event scale since 1999 are used to quantify soil loss attributable to EG erosion. 137Cs and 210Pbex measurements are used to quantify the net soil loss from the catchment attributable to interrill–rill (IRR) erosion. The study demonstrates that EG formation occurred 7 years out of 10, with a mean soil loss averaged over a 10-year period equal to 26.5 t/ha/yr. The rates of IRR erosion estimated using 137Cs and 210Pbex measurements provided values of mean annual net soil loss of 38.8 t/ha/yr and 34.2 t/ha/yr, respectively. The resulting ratios of soil loss attributable to EG to total soil loss (IRR + EG) were 0.41 and 0.44 for the 137Cs and 210Pbex measurements, respectively. The results suggest that the contributions of EG and IRR erosion are of a similar magnitude in semiarid regions of Sicily, although the precise value of the ratio is likely to vary both spatially and temporally in response to catchment morphology, soil erodibility and land use and inter-annual variability of rainfall magnitude and erosivity. The findings are consistent with those of other studies that have attempted to compare the relative efficacy of the two erosion types. The use of 137Cs and 210Pbex measurements in the study area provided important insights into the relative importance of IRR and EG erosion and the same approach could be employed in other locations where both forms of erosion occur and there is a need to quantify their relative importance.