Applying the caesium-137 technique for studying sediment redistribution at basin scale

Identifying areas of the landscape that are mosi sensitive or susceptible to erosion stimulated lbestudy of within-basin variability or tbe sediment delivery processes and tbe use of spatiaUydistributed models coupled with Geograpltical Infonnation SYsterns.Tbe progress or distributed models is hindered by tbe lack or measurements able to establish thelink between tbe eroded soil leaving an area and tbe patterns or erosion and deposition occurringalong tbc hydrauIic path from tOO considered area to the nearest stream reach. Tmcer techniquesafforo an alternative lo the use of plots and a rneans of overcoming tbe problerns or measurementrepresentativeness and spatial variability.The tracer most widely used in soil erosion and sediment yield studies is caesiwn-137, an artificialradionucIide, whicb was released into the environment as a result of above·ground thermonuclearweapons testing. Fallout deposition on the Iand surface occurred main1y with precipitation. Whenfallout caesium-137 comes in contact Witb soil, il is readily fixed or adsorbed on tbe organic andclay particles and subsequent movement by natural chemica1 and processes is limited.In tltis paper caesium-137 measurements available for two basins with different crop covers. locatedin Sicily an<:t in Calabria, are used for validating the Sediment Delivery Oistributed (SEDO)approach based on the Revised Universal Soil Loss Equation and tbe sedirnent delivery ratio oreach morphological unit intò wltich the basin is divided.· For tbe Sicilian basin, whicb is used forwheat cropping, the predictive ability of the SEDD model is positivel)' tested comparing thecalculated sediment yield values with the measured ones obtained by the caesiographic map and theproportional method of Martz and de Jong. For the Calabrian basin, which is covered byEuca/yptus occidenta/is Engl., the testing of tbe SEDD approaçh is carried out by comparing thecalculated sediment yield and the caesium 1055 at tbe morpbological unit and basin scale.