Fallout cesium‐137 (137Cs) measurements have been used in investigations of water‐induced soil erosion in a wide range of environments and in many different areas of the world over the past 20 yr. However, the existing calibration procedures commonly used for deriving quantitative estimates of soil redistribution rates from 137Cs measurements involve several limitations and uncertainties. Existing approaches to calibration and their associated limitations and uncertainties are briefly reviewed and improved models for converting 137Cs measurements to estimates of rates of water‐ and tillage‐induced soil redistribution, applicable to both cultivated and undisturbed soils, are proposed. Results obtained from existing field investigations and laboratory experiments indicate that redistribution of fallout 137Cs within the soil profile and across the land surface is influenced by several factors. These include time‐dependent fallout input, initial distribution within the surface layer, post‐depositional redistribution resulting from mechanical, physical, chemical, and biological processes operating in the soil system and the grain size selectivity associated with soil erosion and sediment transport processes. It is important to consider these factors when deriving estimates of soil redistribution rates using the 137Cs technique, and they have been incorporated into the improved models. The use of these models is demonstrated using data from a case study undertaken in a small catchment in Devon, UK, involving both cultivated and undisturbed soils.

No abstract

No abstract

No abstract

Abstract. Although 137Cs measurements have now been employed for assessing mediumterm (---45 years• rates of soil redistribution on cultivated land in many areas of the world, the potential of 'Be as a sediment tracer in soil erosion investigations has largely been neglected. Because of its much shorter half-life, 7Be measurements should provide a basis for documenting short-term (or event based) rates of soil loss. This paper presents some preliminary results from a detailed investigation of erosion and sediment delivery within a 6.7 ha cultivated field in Devon, England, using both 137Cs and ?Be. Measurements of both radionuclides have been employed to derive estimates of medium-and short-term rates of soil redistribution within the study field. The results obtained from the investigation confirm the potential for using 7Be measurements in soil erosion investigations, both in their own right and in conjunction with 137Cs measurements. IntroductionRecent concern for the on-site and off-site impacts of soil erosion [Clark, 1985] and recognition of the important role of soil erosion in the mobilization and transport of sedimentassociated nutrients and contaminants, including agricultural pesticides [Allan, 1986;Vaithiyanathan and Correll, 1992], has highlighted the need for improved information concerning rates of soil loss from agricultural land. Such information is required both to provide improved assessment and understanding of the problem and to guide the development of effective land management strategies. In responding to this need, there is a requirement for information regarding both gross and net rates of erosion. The former provides evidence of soil degradation, but the latter is of greater relevance to off-site problems, where it is important to know the proportion of the eroded sediment that is transported toward local watercourses rather than being deposited close to the eroded area. The ratio of net to gross erosion for a specific areal unit is frequently referred to as its sediment delivery ratio [Walling, 1983] grid for •37Cs analysis to document the spatial distribution of •37Cs inventories. Sampling was conducted using a motorized percussion corer equipped with a 6.9 cm diameter core tube. In addition to the grid-based sampling, additional soil cores were collected from areas characterized by marked topographic change to increase the resolution of the sampling network. Cores were collected to a depth of -60 cm, and a small sample was obtained from the base of each core for subsequent radionuclide assay to ensure that the core had penetrated to the full depth of the •37Cs profile. To provide additional information on the vertical distribution of 137Cs activity and the plough depth for the field, several soil cores were collected from flat ridge areas and depression areas near the bottom of the field for depth-incremental sectioning using a larger 12 cm diameter core tube. Both sectioned soil cores and bulk cores were also collected from undisturbed sites under permanent pasture adjacent to the ...