Spatial scales of 137Cs-derived soil flux by wind in a 25 km2 arable area of eastern England

The area effected by wind erosion in England is estimated to be small, but the magnitude of the problem within this area is unknown. Direct measurement of the process is difficult because of very high spatial and temporal variability, selectivity and its slow, insidious nature. The artificial radionuclide caesium-137 ((137)Cs), offers an alternative method. It was used here to estimate the net (ca. 35 year) soil flux (erosion and deposition) in a 5 X 5 km area (ca. 19 km(2) area sampled) of East Anglia. It is the first study in the UK to investigate the continuous spatial variation of (137)Cs over an area of such a size and one of only a few in the world to focus specifically on the redistribution of soil by wind. A two-stage, nested sampling frame captured approximately 50% of the variation that occurred between and within fields. A total of 148 samples were taken and their analysis was used to produce a variogram of the spatial variation. A spherical model was fitted to the experimental variogram using a weighted least-squares procedure. Simulations of sampling configurations on a regular grid did not provide a practical improvement to the nested sampling frame within the specified tolerance. Instead, the parameters were used in ordinary kriging to map (137)Cs every 50 in at unsampled locations across the area. A tentative value for the newly established (137)Cs reference inventory for the region was 2068 +/- 130 Bq m(-2). Owens' mass-balance model of the relationship between (137)Cs movement and soil redistribution was modified to the spatially distributed situation and also so that it could account better for the factors that control wind erosion and deposition (Towards improved interpretation of caesium-137 measurements in soil erosion studies. Unpublished PhD thesis, Exter University). A calibration relationship for each field was used to calculate the net soil flux at every 50 m. The sample region was found to approximately balance with a net soil loss of 0.6 t ha(-1) year(-1); the range was -32.6 to +37.5 t ha(-1) year(-1). Soil from the high-loss fields was accumulating in field boundaries. Despite little of the material leaving the region, the effect of soil nutrient loss on the fields may be considerable. It appears that wind erosion may have as great or greater impact in the areas where it is active than does water erosion. Net soil flux was inferred to be the result of wind erosion, but soil loss on harvested crops (primarily sugar beet), and perhaps losses during tillage (pulverizing erosion) may be other contributors, and this requires future study. Moreover, the quantity of soil lost may not be as important as its quality. Future work is therefore also required to investigate the mass-balance of soil nutrient enrichment and depletion as a consequence of soil erosion and fertiliser application. (C) 2003 Elsevier Science B.V All rights reserved.