Long‐Term Soil Redistribution in a Small French Watershed as Estimated from Cesium‐137 Data

Abstract

Changes initiated in the 1970s in the agricultural landscape of the north European plains have resulted in increased water erosion. The spatial redistribution of 137Cs was used to assess the magnitude of long‐term soil movements in a 180 ha watershed located in northern France. The 137Cs base level was estimated at 2000 ± 200 Bq m−2. The point data suggest annual soil movements ranging from a loss of 18 Mg ha−1 to a deposition of 19 Mg ha−1. After spatializing these data, it is concluded that 41% of the watershed area can be considered as stable. Some 45% of the watershed area suffered a net soil loss, with an average rate of 6 Mg ha−1 yr−1. Net deposition occurred over 14% of the area, with an average annual rate of 7 Mg ha−1. From these values, it was estimated that a net output of 1.9 Mg ha−1 yr−1 of eroded material would have left the watershed. This represents a sediment delivery ratio of 59%. These results are consistent with those of other European researchers under comparable environments. They also stress the point that redeposition is an important part of the global erosion process. Finally, these results highlight some of the advantages of the 137Cs technique, which makes possible the development of long‐term sediment budgets at the watershed scale.

Multi‐year tracking of sediment sources in a small agricultural watershed using rare earth elements

“…The enrichment ratio was greater than 1·0 for 73 per cent of the storms during the experimental period. This compares with a tracer enrichment ratio for 137 Cs reportedly ranging from 1·1 to 3·0 (Bernard et al, 1998;He and Walling, 1996). Several factors may have contributed to the enrichment ratio exceeding 1·0.…”

How to make 137Cs erosion estimation more useful: An uncertainty perspective

“…Besides without spatial variability sampler size should not have an effect. It was reported that the typical CV on reference sites was about 20% (e.g., Sutherland, 1996;Bernard et al, 1998;Basher, 2000;Fornes et al, 2005). For a 20% CV, at least 15 independent samples would be required to estimate 137 Cs reference mean with an allowable .…”

“…On reference sites, a 20% coefficient of variation (CV) of 137 Cs inventory was reported typical (Sutherland, 1996;Bernard et al, 1998;Basher, 2000;Fornes et al, 2005;Mabit et al, 2009). For a 20% CV, approximately 11 samples are needed to quantify the reference inventory with an allowable error of 10% at the 90% confidence.…”

Effects of field reorganisation on the spatial variability of runoff and erosion rates in vineyards of Northeastern Spain

“…The resulting cultivated soils consist of soils with altered soil profile, with different soil depths, very low organic matter content, very poor structure and low infiltration capacity, which favour erosion processes, and present spatial variability within the plots. All these aspects are not usually taken into account when land transformations are carried out (Bernard et al, 1998;Schoorl and Veldkamp, 2001). Some research carried out in the Mediterranean area points out the influence of these land transformations on changes in the hydrological processes (Alcaraz, 1997; Barthès et al, 1997;Dazzi, Fierotti and Raimondi, 1998;Misopolinos and Zalidis, 2000).…”