4. Future directions for the 137CS, approach
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Although the 137Cs approach towards assessing the rates and patterns of soil erosion has been applied in an increasing number of studies in recent years, considerable scope remains to refine the technique employed and to exploit its potential more fully. To date, most of the studies employing this approach have been concerned with soil erosion by water and tillage, but there is clearly potential for extending its application to wind erosion [37]. Where it is possible to envisage longer term investigations, it should also be feasible to extend the approach to include resampling of soil inventories to permit comparison of values for known dates and thus estimate the erosion rates for the associated intervening periods. Care would, however, be needed to ensure that the period between measurements was sufficiently long to produce significant differences in recorded inventories, bearing in mind the precision errors typically associated with gamma assays. This strategy has the attraction of removing the need to establish the reference inventory for a site, but it no longer exploits the potential for the approach to provide retrospective estimates. Several other areas worthy of further investigation, including a global scale assessment of reference inventories, experimental investigations of radiocaesium behaviour in agricultural soils, and improvement of calibration relationships, have been highlighted above. Additional aspects meriting further attention include improvement of sampling strategies to optimize the return from sample analysis, and incorporation of more rigorously defined precision confidence limits into the establishment of reference inventories and into calibration procedures. Most work to date has focused on applying radiocaesium measurements within small areas, commonly individual fields, since the approach is well suited to generating detailed information on spatial patterns of erosion and deposition at this scale, but scope clearly exists for using caesium measurements to provide a number of individual point estimates of erosion rates within a larger area to serve as ground truth for the calibration and verification of deterministic and statistical prediction procedures capable of synthesizing the general pattern of soil loss across the area. The potential for coupling 137Cs measurements with information derived from satellite remote sensing imagery to provide a basis for erosion hazard assessment over larger areas has also been demonstrated by several workers [23, 38].
Considerable potential also exists to exploit the essentially unique nature of the data provided by the caesium technique. It affords one of the few viable means of assessing the impact of tillage on soil redistribution [39, 40] and the spatially distributed data generated are ideally suited to coupling with GIS and spatial statistics [41] and for use in verifying distributed erosion and soil loss models [42]. Scope also clearly exists for using radiocaesium derived estimates of soil loss as a basis for investigating medium term soil loss/crop productivity relationships. In addition, there is considerable potential for extending the use of 137Cs, as a sediment tracer from consideration of soil redistribution within individual fields to investigation of the movement and storage of sediment within a drainage basin. Walling and Bradley [43] have, for example, shown how 137Cs measurements can provide the basis for establishing the sediment budget for a small drainage basin, and the successful application of 137Cs measurements in fingerprinting suspended sediment sources and in estimating the rates of overbank floodplain accretion has been demonstrated by a number of studies [44-48].
