Abstract

The spatial correlation of ¹³⁷Cs (Bq m^-2), soil texture, organic matter content (%) and soil erosion-sedimentation patterns was estimated in a 2.16 ha field using geostatistics coupled with a Geographic Information System (GIS). The studied field is localized in the southern part of the Boyer River watershed, in Eastern Canada. Semivariograms were produced to take into account the spatial structure present in the data. A good autocorrelation and reliable variograms were found for each parameter tested (0.87≤R²≤0.95 and 0.7≤Scale/Sill≤0.96). Soil organic matter spatial redistribution was correlated to soil erosion and sedimentation as shown by the significant relationship (R=0.8; p≤0.01; n=42) in the first 20 cm between 137Cs and organic matter. The spatial Fallout RadioNuclides (FRN) distribution was estimated by Ordinary Kriging and Inverse Distance Weighting (IDW) to design contour maps. Using the different interpolation methods and ‘area weighted mean’ of a ¹³⁷Cs redistribution map, a radioisotope budget was established. It was estimated that around 2x107 Bq of ¹³⁷Cs are missing (around 30% of the total fallout since 1954, the first major introduction of ¹³⁷Cs in the global environment) and were exported by physical processes (runoff and erosion process associated) from the area under investigation. The net sediment production was estimated for the whole field at 16.6 t ha^-1 yr^-1 with a sediment delivery ratio of 99%. These results show that due to erosion processes and especially snow melt erosion, most of the sediment mobilized was transported out of the field.

Keywords: ¹³⁷Cs, Organic Matter (OM), Sediment budget, Geostatistics, Ordinary Kriging (OK), Inverse Distance Weighting (IDW), Sediment Delivery Ratio (SDR)