ESTIMATION OF SEDIMENT REDISTRIBUTION WITHIN AGRICULTURAL FIELDS USING CESIUM-137, CRYSTAL SPRINGS, SASKATCHEWAN, CANADA

Redistribution of the globally deposited artificial radionuclide caesium-137 was used to quantify the net sediment flux in two agricultural fields. Accelerated erosion within the near-level field (mean slope 1.3°) was assumed to be primarily controlled by aeolian processes and the net output of sediment was 1.5 t ha-1 yr-1. The sediment delivery ratio of this field was approximately 11 per cent, which indicates significant sediment redistribution and storage within the field. The medium-sloping field (mean slope 3.0°) differed significantly from the near-level site in terms of landform element distribution, gradient, profile curvature and sediment redistribution. Using a digital elevation model erosion was found to be concentrated in divergent shoulder elements in upslope areas of the field. Deposition was primarily concentrated in convergent footslope elements. The net sediment output was 6.6 t ha-1 yr-1, with a sediment delivery ratio of 22 per cent. Rill and interrill erosion were assumed to be the major processes active within the medium-sloping field since 81 per cent of the sample points had slopes in excess of 2°, which is considered to be the lower boundary for rill initiation on loamy soils. Accelerated erosion is ubiquitous on both fields with 54-75 per cent of the sample points experiencing net erosion in excess of the rate of soil formation (1.0 t ha-1yr-1). In addition, 30 per cent of the near-level sites and 64 per cent of the medium-sloping sites exceeded the upper boundary of soil loss tolerance (T-value), which is 11 t ha-1 yr-1. These data have significant implications for soil quality and sustainable agricultural development within the Canadian prairies. © 1990.