The assessment of soil redistribution on agricultural land using the environmental isotope of Caesium-137

Environmental radionuclides have the potential to be used to trace sediment movements. Caesium-137 (137Cs), a radionuclide released during nuclear weapon tests from 1950s to 1960s is strongly adsorbed on to clay. It enters the Malaysian environment through cold continental polar (cPk) air mass circulation and Hadley cell effects from the higher latitude regions, converged during Inter-tropical Convergence Zones (ITCZ) oscillation and deposited through precipitation on to the soil as fallouts. Its content in the soil profile has been used to estimate soil loss due to water erosion in agricultural land. Two soil sampling methods, incremental and bulk sampling, were adopted to collect samples from the erosion plot and reference sites to a depth of 40 cm for the determination of 137Cs inventories. The soil depth-profile of 137Cs inventory at an undisturbed site exhibits an exponential function with most of the contents are accumulated within the upper 12 cm portion of the soil profile whereas in the disturbed sites the 137Cs content were partially mixed within the plough layer. The average 137Cs reference inventory from two different locations was 580.7 Bq/ m2 while local 137Cs reference inventory was 551.9 Bq/ m2. The USLE, Ritchie equation and three mathematical models were used to estimate the rate of soil loss. The Proportional Model was found suitable to be used in this environment. Net soil loss from the study slope was estimated by the USLE of 4.34 ton/ ha/ yr. The soil redistribution patterns show that the upper and middle slopes had been eroded while deposition was observed at the foot slope. The maximum land form evolutions of the eroded areas was 4.5 mm/ yr and 0.5 mm/ yr for the depositional areas. The long-term erosion rate of the study area was considered low. (author)