## 2 Materials and Methods
#### 2.1.4 The IH Technique to Evaluate Soil and Water Resources' Degradation
Stable isotopes in water (18O and 2H) are suitable for assessing groundwater sources and quantifying their recharge rates, as each source has a unique and constant isotopic composition (if it does not change phase in flow) [116]. Stable and radioactive isotopes provide relevant information on the age of groundwater and its flow direction, as well as the recharge and discharge zones of the aquifer. In addition, isotopic, piezometric, and geological data are used to build conceptual groundwater flow models. Natural variation in stable isotope ratios of water is a tool for measuring and partitioning water fluxes between different systems [117]. Application of IH as a Scientific-Technical Tool to Support the Sustainability of Water Resources  
A detailed analysis of the use of IH allowed us to identify some characteristics of the techniques applied, the radionuclides used, and the main representative scopes implemented in these studies. From the review of 25 recent articles on the application of IH in different parts of the world, we found that the main isotopes used in the studies are the traditional water isotopes (\({}^{18}\)O and \({}^{2}\)H), which are included in all studies to evaluate water dynamics. The review of these studies shows that isotope hydrological techniques are an essential source of information on hydrological processes and directly support improving water resource management. All the studies presented demonstrate the effectiveness of using water isotopes as a relevant tool for characterizing and assessing water dynamics to support sustainable management. Additional radioactive isotopes were incorporated as supported in IH applications: \({}^{3}\)H [118,119], \(\delta^{15}\)N [120], 222 Rn [119,121], \(\delta^{37}\)Cl and \(\delta^{13}\)C [122], \({}^{14}\)C [123], and the stable carbon applied in one paper [124]. The reviewed research using IH covers several areas. The most common is the characterization and investigation of groundwater sustainability [112,118,125,126,127,128,129,130,131,132]. Some studies are related to assessing human disturbance [6,120,123] and assessing human risk exposure through ingestion [117]. There are papers focused on supporting archaeological studies [124], characterizing geothermal resources [133], and improving hydrological modeling [134]. Other contributions focus on studying atmospheric processes and moisture contribution at the regional scale [135] and assessing water behavior and absorption depths in tropical forests [136]. In terms of the locations of IH study sites, Asia is the most represented region, with works from China, Japan, South Korea, India, and Australia [6,112,118,119,120,121,123,127,128,133,136,132]. There are also contributions from Africa: Ethiopia and Madagascar [126,129,130,137]; from the Middle East: Iran [117,122,134,137,138]; from Europe: Spain and Croatia [124]; and from Latin America: Mexico and Argentina [135,131,135,139]. Analysis of Trends in the Use of Isotopic and Nuclear Techniques in Water and Land Degradation Research  
A traditional literature review was conducted to gain the most comprehensive understanding of the current state of isotopic and nuclear techniques and to propose a hypothesis that integrates the synergistic convergence of these techniques to evaluate soil degradation. The investigative works by various specialists encompass a range of topics related to soil and water degradation. Additionally, they include an assessment of the feasibility of utilizing isotopic and nuclear techniques for characterizing and evaluating the impacts of these forms of degradation. These works have been referenced and comprise 140 papers published from 2017 to 2024. The 140 publications include 31 works on the current global situation in soil and water degradation and 109 works on the technical application of isotopic and nuclear techniques. The research results provided by this detailed review of the materials allow us to conclude that, currently, these techniques are applied individually and not in an integrated manner.