## 2 Materials and Methods
#### 2.1.4 The IH Technique to Evaluate Soil and Water Resources' Degradation
The selection of research works was based on the timing of their completion. A comprehensive search was conducted for relevant scientific papers across various databases, including the Web of Science, Scopus, the Scientific Electronic Library Online (SciELO), ResearchGate, and Google Scholar. The search for current studies covered the period 2017-2024 and was limited to Spanish- (4) and English-language (136) papers. The objective was to establish research trends by reviewing publications on how researchers approach assessments of the degradation of soil and water sources by applying three nuclear and isotope techniques: FRN, FP, and IH, and related research published in high-impact journalsat a global level. The search terms (keywords) were associated with using isotopic and nuclear techniques and environmental phenomena in the landscape. These included isotope hydrology, \({}^{18}\)O, \({}^{2}\)H (deuterium), fallout radionuclide, \({}^{137}\)Cs, \({}^{210}\)Pb, \({}^{7}\)Be, FP, CSSI, water erosion, integration, sedimentation, land degradation, and other relevant factors. The search and selection of the analyzed publications were dedicated to obtaining the best representation of the research developed in recent years and covering a wide range of technical and geographical scenarios. This approach was taken for a detailed analysis of the current trends in using nuclear techniques. A total of 109 papers are summarized in Table 1, which shows the distribution of the three techniques analyzed (FRN, FP, and IH) according to the development of their application and their integrative link with other methods. Because erosion and sedimentation phenomena are intricate processes occurring in the landscape that result in the degradation of both soil and water resources, there is an apparent necessity for the integrated or combined use of the techniques that have been analyzed to gain a deeper understanding of these phenomena and to contribute to developing integrated solutions that will help minimize these forms of degradation. However, as evidenced in Table 1, the integrated application of these techniques is notably limited and they are predominantly used individually. These techniques characterize and address specific forms of degradation, whether soil-related or water-related. A mere seven research papers demonstrate the joint utilization of the FRN and FP techniques (with CSSI employed as a tracer), two papers illustrate the combination of FRN and IH, and five papers exhibit the comprehensive integration of the three techniques under examination (FRN, FP, and IH). The use of the universal soil loss equations was also examined, with particular attention paid to the necessary modifications that must be made to ensure the fulfillment of current requirements regarding the results that are produced. This review confirmed that the universal equations continue to be applied on a global scale, and three papers demonstrate the use of these equations in combination with the FRN (utilizing the \({}^{137}\)Cs tracer to assess soil redistribution in the landscape). Figure 1 depicts the timings of the selected research works, which were conducted entirely within the period spanning 2017 to 2024. These works are collectively focused on soil and water degradation and the development of three isotopic and nuclear techniques that are instrumental in assessing the sustainable development of these resources. A total of 140 papers are referenced, of which 1 was published in 2017, 14 in 2018, 23 in 2019, 29 in 2020, 31 in 2021, 22 in 2022, 19 in 2023, and 2 in 2024.