Introduction

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).