## 2 Materials and Methods
#### 2.1.2 The FRN Technique for Assessing Soil and Water Resources' Degradation  
Currently, techniques using environmental radionuclides such as FRN, including \({}^{7}\)Be, \({}^{137}\)Cs, and \({}^{210}\)Pbex, are used worldwide to determine soil erosion/deposition rates in the landscape and surface water bodies. These isotopic techniques are accessible and affordable tools to evaluate spatial and temporal patterns of soil erosion [45; 46]. The use of FRN continues to be developed worldwide, evidenced by the observation of dissimilar investigations where \({}^{7}\)Be, \({}^{137}\)Cs, \({}^{210}\)Pbex, and \({}^{239+240}\)Pu are applied in many parts of the world, depending on the study's time scale. From all available FRNs, \({}^{7}\)Be is the only soil tracer that can obtain short-term soil redistribution information. Among many other investigations conducted, research by [PERSON] in 2018 [47] in Haiti to document soil redistribution rates associated with traditional farming practices can be mentioned. In 2018 [45], [PERSON] developed important work integrating CSSI and FRN to track land-use type-specific net erosion rates in a small tropical watershed. Mabit in 2018 [29] showed the IAEA/FAO support and intention to develop joint methodologies to combat soil degradation and exhibited FRN and CSSI techniques as efficient assessment tools. In 2019 [48], [PERSON] used the FRN nuclear technique to document soil redistribution in the landscape and used CSSI to identify sedimentary sources in central Argentina. [PERSON] in 2019 [49], to reduce the loss of fertile soil from rainfed croplands on steep slopes, used \({}^{137}\)Cs and \({}^{210}\)Pb\({}_{\text{ex}}\) measurements to evaluate the effectiveness of soil conservation practices in controlling soil erosion in Kouhin, Qazvin province of Iran. This naturally occurring cosmogenic isotope was first used in the late 1990s, and advances in recent decades now allow investigation of erosion processes not only during extreme weather events of short duration but also over prolonged periods of up to several months [50]. La Manna in 2019 [51] used FRN (\({}^{137}\)Cs) to study the medium-term erosion processes in volcanic soils of Andean Patagonia; the results confirmed the potential of this technique for assessing erosion processes. [PERSON], in 2019 and 2020 [52; 53], studied the spatial variability of soil nutrients in Mediterranean mountain agroecosystems combining complex land uses and steep topography to assess the nutrient fate, understand the potential impact of soil erosion on nutrient redistribution across landscapes, and also characterize the lateral mobilization of soil organic and inorganic carbon along topographically driven transects over four decades in a sub-humular karst area of northern Spain. The spatial distribution of the fallout radionuclides was assessed by [PERSON] in 2021 [54] to determine the mass activities of fallout (\({}^{137}\)Cs, \({}^{210}\)Pbex) and lithogenic radionuclides (\({}^{238}\)U, \({}^{226}\)Ra, \({}^{232}\)Th, and \({}^{40}\)K) and to evaluate the main controls affecting their spatial variations in the catchment of northeastern Spain. A work developed by [PERSON] in 2020 [55] in western Iran and southern Italy to assess the potential of using \({}^{7}\)Be measurements to estimate soil erosion on short time scales exposed the need for further work to evaluate the feasibility of using \({}^{7}\)Be in different areas and under different land uses or vegetation covers. [PERSON], in 2020 [56], applied the \({}^{137}\)Cs nuclear technique to estimate soil redistribution rates for deforestation-induced land uses in Golestan province, Iran. In northern Spain, [PERSON], in 2020 [53; 57], used \({}^{137}\)Cs inventories to characterize organic and inorganic lateral carbon mobilization and its influence on water erosion. [PERSON], in 2021 [35], estimated soil erosion and sedimentation on steeply sloping agricultural land, enabling action for soil conservation.