Using 137Cs Resampling Method to Estimate Mean Soil Erosion Rates for Selected Time Windows

This chapter explains the reason for promoting the ¹³⁷Cs method, its advantages and disadvantages and the need for its standardization. It starts with brief introductory information on the importance of soil erosion problem for agriculture and food security, the role of ¹³⁷Cs method in soil erosion assessment and advantages and limitations of this method. Further it provides an overview of already existing ¹³⁷Cs resampling studies as well as the new case studies done by coauthors of these guidelines. Further it describes the content of individual chapters constituting this book and finally it explains the main results of reviewing the existing resampling studies, i.e. classifying the existing resampling approaches to two categories. There are emphasized four major limitations of ¹³⁷Cs method. Firstly, the time window to which the ¹³⁷Cs method refers (i.e. since the ¹³⁷Cs fallout in 1960s and the time of sampling) is becoming too long. In early 1990s when the ¹³⁷Cs-method became very popular it was just ca. 30 years, but for recent studies it is already ca. 60 years and that is too much for efficient studying the land use impacts and testing the efficiency of soil conservation measures. The second problem is the selection of conversion models, availability of some input parameters for conversion models and validation of models. Third problem is to distinguish Chernobyl ¹³⁷Cs from bomb ¹³⁷Cs in Chernobyl affected areas. Finally, the fourth limitation is the heterogeneity of ¹³⁷Cs spatial distribution, its microvariability and problems with representativeness of reference site. These limitations can be overcome if ¹³⁷Cs is resampled. In such case the investigated time window is much shorter, and its length can be chosen by researchers. Gaining data on input parameters is easier for shorter period. The older the past the lowest the probability that data (especially the land use, but also rainfall data) will be available. The ¹³⁷Cs resampling helps also partially reduce the problem with the ¹³⁷Cs spatial heterogeneity and reference value because there is a possibility to compare directly the ¹³⁷Cs activities from first and second sampling campaign at studied site, without the need of reference site. Overcoming these limitations makes the ¹³⁷Cs resampling method very attractive. It was used already in late 1980s but until presence it is used very rarely (just by few tens of study sites were investigated). These ¹³⁷Cs resampling studies used different approaches how to interpret the resampling results and this variability hinders the comparison of results presented in individual studies. Therefore, the resampling method needs some standardization, and this became one of the objectives of Coordinated research project (CRP) “Nuclear Techniques for a Better Understanding of the Impact of Climate Change on Soil Erosion in Upland Agro-ecosystems” (D1.50.17) launched by International Atomic Energy Agency (IAEA) in March 2016 and completed in December 2021. The research activities carried under this project resulted in formulating guidelines for the standardised implementation of ¹³⁷Cs resampling method. The first task towards any standardisation was to review the existing studies. In total 14 such studies were collected. The introductory chapter provides a table with their overview. Further step was to do own case studies testing the ¹³⁷Cs resampling. The review found that most studies use two major resampling approaches (1) traditional reference approach (TRA) and (2) spatial reference approach (SRA).

In this chapter, all studies on ¹³⁷Cs resampling collected from the literature as well as the recent contributions carried out by the authors of this guidelines are presented. The grouping of assembled studies was based on their geographical provenience. All discussed contributions were arranged into four subchapters: 2.1 North America and Australia (English speaking countries Canada, USA, and Australia), 2.2 Europe (represented by Italy and Spain), 2.3 Asia (represented by China) and 2.4 Africa (represented by Morocco). Each subchapter is further subdivided to countries and each country to individual studies (or groups of studies carried by one research team). The main purpose is to discuss and evaluate the reviewed studies and to classify the used ¹³⁷Cs resampling approaches.

This chapter presents a case study from Italy providing the validation of ¹³⁷Cs method versus the data from erosion plots. This is a unique study from site where the long-term erosion rates were measured at erosion plots and also ¹³⁷Cs sampling was done two times. It is the only one such study site worldwide. Therefore, it is presented here as a separate chapter. It should be understood as an example how should the ¹³⁷Cs resampling study be designed and how the ¹³⁷Cs method should be validated versus the data on soil erosion rates obtained by conventional erosion measurements. This resampling study was done in seven major methodological steps which were described in detail, each step separately. This is an example of optimal approach how to apply the ¹³⁷Cs resampling method. The resulting data are interpreted by both key resampling approaches (SRA and TRA). However, one such study cannot be sufficient for validation of ¹³⁷Cs resampling method. It rather should provide a guidance for other authors on the optimal direction of further research in future.

This chapter provides a step-by-step protocol to apply the ¹³⁷Cs resampling approach to assess soil erosion during chosen time periods, which is a final result of these guidelines. It is based on the results of Chapter 3, but the steps presented in that chapter are adjusted for an individual case of the Caratozzolo Study Site presented in Chapter 3. These steps were generalised to form of a universally applicable protocol of ¹³⁷Cs resampling procedure comprising of 7 steps but with two modifications, one for the traditional reference approach (TRA) and the second for the spatial reference approach (SRA). These steps are following: (1) Selecting and assessing study site and existing ¹³⁷Cs data, (2) Selecting the methodical approach (TRA versus SRA), (3) Second sampling campaign of selected study site, (4) Sample preparation and gamma spectroscopic analyses, (5) Determining the reference value (recalculating the earlier reference value for radioactive decay or new reference sampling), (6) Conversion of ¹³⁷Cs inventories from second sampling to soil redistribution rates, (7) Calculating soil redistribution rates for the time window since the first until the second sampling). These steps are characterized in a graphical scheme presenting also the two versions of this approach aimed on TRA and SRA. Finally, this chapter provides a discussion on the further research and proposes some possible objectives of next ¹³⁷Cs resampling studies.