Spatial variability of erosion and soil organic matter content estimated from 137Cs measurements and geostatistics

• Published in: Geoderma 2008-06, Vol.145 (3), p.245-251
• Main Authors: Mabit, L., Bernard, C., Makhlouf, M., Laverdière, M.R.
• Format: Article
• Language: English
• Subjects: 137Cs; Fallout radionuclides; Geostatistics; Kriging; Organic matter; Spatial variability
• ISSN: 0016-7061; 1872-6259
• DOI: 10.1016/j.geoderma.2008.03.013

The spatial variability of soil erosion was studied through the use of fallout radionuclides (FRNs) and geostatistics. The spatial correlation structures of radiocesium ( 137Cs), soil redistribution and organic matter (OM) content have been established in a 2.16 ha agricultural field located 30 km east of Quebec City, Canada. A significant relationship was found between 137Cs (Bq m − 2 ) and OM (%) in the 0–20 cm soil depth ( n = 42; r 2 = 0.63, p < 0.001), highlighting the relation between these two parameters. The conversion of the areal activities of 137Cs into soil redistribution (t ha − 1 yr − 1 ) was done using the Mass Balance Model 2 (MBM 2). The magnitude of soil redistribution, at the sampled points, ranged from an erosion rate of 62 t ha − 1 yr − 1 to a deposition of 17 t ha − 1 yr − 1 . Geostatistics coupled with a geographic information system (GIS) were used to create a map of soil redistribution, based on the spatial variability of FRNs, and to establish a sediment budget. Prior to mapping, semivariograms were produced, taking into account the autocorrelation present in the data. A significant autocorrelation and reliable variograms were obtained for the three tested parameters ( 137Cs, OM content and soil redistribution) (0.87 ≤ r 2 ≤ 0.95; 0.7 ≤ Scale/Sill ≤ 0.96 and 4% ≤ ‘nugget-to-sill’ < 20%). Using the Kriging interpolation and ‘area weighted mean’ of the soil redistribution map, a sediment budget was estimated for the whole field. A net sediment output was estimated as 16.6 t ha − 1 yr − 1 , for a sediment delivery ratio (SDR) of 99%. This high SDR is believed to reflect the joint impact of tillage, water and snowmelt erosion on the net sediment production. Approximately 85% of the agricultural field surface was estimated to be affected by erosion rates approaching or exceeding the suggested tolerance level of 6 t ha − 1 yr − 1 for most Canadian soils. The geostatistics concept is a powerful tool in soil science and especially for FRNs use in order to characterize the spatial variability of erosion and sedimentation processes.