USE OF FALLOUT RADIONUCLIDE MEASUREMENTS IN SOIL EROSION INVESTIGATIONS.
Accelerated erosion and associated soil degradation currently represent a serious global problem. Against this background, there is an increasing need to assemble reliable information on the rates of soil loss. Existing techniques for monitoring soil loss possess many limitations and a number of workers have explored the potential for using fallout radionuclides, and particularly 137Cs, to obtain estimates of the rates of soil erosion and deposition on agricultural land. In essence, the caesium technique provides a means of assembling retrospective information on medium term (about 35 year) rates of soil loss for an area and the spatial pattern of erosion and deposition involved, based on a single site visit. An example of the application of this approach to a cultivated field at Rufford Forest Farm, Nottinghamshire, United Kingdom, is provided to illustrate its value, and its potential for wider application is discussed. Further developments of the approach are also considered. Although, to date, few attempts have been made to exploit the potential for using other fallout radionuclides in soil erosion investigations, unsupported 210Pb and 7Be would appear to offer considerable promise. An example of the use of unsupported 210Pb measurements in a study of soil redistribution within a small field at Butsford Barton, Devon, UK, is presented and possible applications of 7Be measurements are considered.
Although much of the recent concern for the problems facing the global environment has focused on global warming and climatic change, there is also increasing evidence that accelerated erosion and associated soil degradation represent a major problem for the sustainable development of agricultural production in a world characterized by a rapidly expanding population. Brown [1], for example, has estimated that the world's croplands are currently losing 23 x 109 tonnes of soil in excess of new soil formation each year. This is equivalent to a depletion of
the global soil resource by 7 % each decade. Buringh [2] has also estimated that the global loss of agricultural land due to soil erosion amounts to 3 x 10(6) ha/a, and the recent International Soil Reference and Information Centre (ISRIC)/United Nations Environment Programme (UNEP) global survey of human induced soil degradation [31 indicates that nearly 10% of the total land surface of the globe is currently adversely affected by water erosion. Soil erosion has serious implications for agricultural productivity, but there are also many other important off-farm or downstream problems associated with increased sediment loads in rivers, including reservoir sedimentation and siltation of irrigation networks, waterways and harbours [4].
Against this background, there is an increasing need to assemble reliable information on recent rates of soil loss. Such data are required to assess the magnitude of the problem in particular areas, to obtain a better understanding of the environmental controls involved, to validate existing and new prediction models and to provide a basis for developing conservation measures and improved land management strategies. Existing techniques for monitoring soil erosion do, however, possess a number of important limitations in terms of the representativeness of the data obtained, their spatial resolution, their potential for providing information on longer term rates of soil loss and associated spatial patterns over extended areas, and the costs involved [5, 6]. Furthermore, it is something of a paradox that the data availability is frequently most limited in those countries, particularly developing countries, where the need is greatest. Because of these limitations and deficiencies, a number of workers have explored the potential for using fallout radionuclides, and more particularly 137Cs to obtain estimates of the rates of soil erosion and deposition on agricultural land. In essence, the 137Cs technique provides a means of assembling retrospective information on long term (about 35 year) rates of soil loss for an area and the spatial pattern of erosion and deposition involved, based on a single site visit [7]. This contribution attempts to provide an assessment of the potential for wider application of this approach in soil erosion investigations, including the use of other fallout radionuclides in addition to 137Cs.