Relating Intensity of Soil Redistribution to Land Use Changes in Abandoned Pyrenean Fields Using Fallout Caesium‐137

Fallout caesium‐137 has been used to trace soil redistribution in abandoned fields located in the Central Spanish Pyrenees. A total of 28 fields with different lengths, slope angles and time since abandonment were selected on a representative south‐facing slope of the Estarrún valley. The local reference inventory and the magnitude and spatial distribution of ¹³⁷Cs inventories within these fields were documented and used as a basis for assessing patterns of soil redistribution. The local reference inventory was estimated to be 4,500 Bqm⁻². Within the fields, the average ¹³⁷Cs inventory at the top of the slope was 3,920 Bqm⁻², and accumulation of soil at the bottom of the slopes was demonstrated by an average ¹³⁷Cs inventory of 5,320 Bqm⁻². Deviations from the reference inventory were highest for fields with the longest slopes that had been abandoned for less than 30 years. Here, increases in the ¹³⁷Cs inventory, relative to the reference inventory, in excess of 20% were found at the bottom of the slopes. Considering all the fields and all geomorphic positions within the fields, the greatest ¹³⁷Cs losses and gains were found in the fields with the longest duration of abandonment, indicating more intense soil redistribution. Irrespective of the timing of abandonment, the ranges of ¹³⁷Cs inventories in the fields were found to be proportional to the water erosion index. The ¹³⁷Cs technique demonstrated that patterns of sediment redistribution were closely related to the topographic and physiographic characteristics of the slopes. Copyright © 2017 John Wiley & Sons, Ltd.