The effects of changing land use on soil erosion and sediment mobilisation in two small catchments in Southern Italy.

Soil erosion is a major concern for the sustainable management of agricultural land because it reducessoil productivity, degrades stream water quality and increases water pollution risk for humans andaquatic ecosystems. In Southern Italy, where soil loss can exceed 100-150 t ha-1 year-1, there is adrive to minimize erosion by implementing improved management practices and erosion controlmeasures. Among these practices, a change in land use involving reafforestation of large areas aimed atproviding increased protection of the soil from rainfall and runoff has proved to be highly effective interms of reducing erosion risk. In order to devise meaningful land-use policies and to select effectivesoil conservation practices, it is important to evaluate the importance of forest cover in reducing soilerosion. In this context, the use of environmental radionuclides, and particularly 137Cs and excess210Pb, to estimate soil erosion has proved to possess several important advantages over traditionaltechniques, if reliable conversion models are available for estimating soil redistribution rates. The studyreported focuses on two small catchments (W2 and W3) located in Calabria, Southern Italy, for whichmeasurements of suspended sediment yield are available. Both the catchments originally supported arangeland vegetation cover and they are subsequently reafforested with Eucalyptus trees in 1968.Currently, only catchment W3 shows a continuous forest cover whereas catchment W2 shows somebare areas that preserve the natural vegetation. Within catchment W2 two additional erosion plots wereestablished in 1994 in order to explore the effect of the tree cover on soil erosion. Measurements ofsediment yield from the two catchments and the plots for several storm events and associatedinformation on the 137Cs and excess 210Pb of the sediment have been used to evaluate the effects ofthe conversion from rangeland to forest cover on sediment mobilisation and soil loss. The analysisshowed that the areas with the highest soil loss are associated with the slopes where the tree cover isdiscontinuous, emphasizing the importance of vegetation cover in influencing rates of soil loss in thestudy catchments. The results have also been used to validate some of the basic assumptionscommonly associated with the use of mass balance models for estimating rates of soil loss fromradionuclide measurements.