An environmental hazard defined as a situation or a substance that potentially can threaten nature, environment and human health. Environmental hazards such as flood, drought, soil and water pollution, soil erosion etc may lead to adverse effects on ecosystem services, food security, and sustainable development, in addition to threatening animal and society health. Therefore, it is necessary to extend our knowledge about environmental hazard by discovering new information about these risks using new techniques, to mitigate the adverse impacts of environmental hazards as well as to manage natural resources in a sustainable way. In recent century, natural isotopes frequently used to understand possible source of pollutants, quantify water cycle components, trace water and sediment flow paths as well as assess soil erosion processes, nutrients movement and substance circle in food chain. Isotopes, atoms of the same element, might be in both stable and radioactive forms. Radioisotope, having a non-stable nucleus and emits radiation spontaneously, and stable isotope, without any radiation emission, are frequently used for tracing the sources and pathways of pollutants, water, soil and nutrients in an ecosystems. Because of higher time and effort saving, specificity, accuracy and quantitative and qualitative analysis, nuclear techniques provide unique information especially in complex environment. Integrated tracing of stable isotopes, for instance 18O, deuterium (2H) and 15N, in dissolved components, water bodies, soil and sediment provide precious data to quantify the extent of and the source pollutants, soil erosion, nutrients and water fluxes within an ecosystem. In this manuscript, several examples of application of environmental stable isotopes in hydrometeorology issues, water and soil pollution and soil erosion were discussed. In many cases, stable isotope analyses enable us to better calibrate and validate usual hydrological, hydrochemical and soil erosion studies techniques by providing exact and detailed data. Numerous researchers have used stable isotope in hydro-metrology. One of the interesting area of research using stable isotope is paleoclimatology and paleohydrology. Sediment and ice cores as well as tree-ring studies have been used to reconstruct past hydrometeorological events, climatic conditions and climate changes over time. Stable isotope can also help to quantify water cycle components in a watershed and related aquifer, to determine baseflow amounts and groundwater-surface water interaction, to understand possible interconnection between aquifers, to measure recharge and seepage rate and to identify water flow paths within a watershed/aquifer. It is also applicable to • clarify the origin of the water in new springs • check dam leakage • study flow path in a complex karst areas • monitor seawater intrusion in coastal aquifer • identify contaminants source and dynamics in surface and ground water bodies • and trace specific substances in food chain. Stable isotope can act as tracers and fingerprint water, soil and pollutants. These data facilitate to characterize the main sources and transport path of pollutant, sediments and nutrients in a watershed (basin). It enhances our knowledge about interaction between soil-water-plant and other ecosystem components and provides priceless data regarding hot spots of land degradation, main pollution sources, potential flood prone areas and other environmental hazards. Unique information obtained from stable isotope analysis in understanding potential natural hazards will help decision-maker and stakeholder to choose proper management practices and strategies in order to minimize adverse effects of environmental hazards and improve ecosystem resilience. At the end of this presentation, potential and limitations of stable isotopes application in Iran were discussed.
