The use of environmental isotopes in groundwater studies with hydrogeoethics: essential or dispensable?

Groundwaters are the primary source of drinking water for half of the world’s population. They represent about 97% of the world’s available freshwater resources, being extensively abstracted and contaminated in many parts of the world. Among groundwaters are the thermal waters, a source of health, well-being, and a major touristic attraction (geoheritage), also providing a link to the natural environment. Therefore, it is strongly important to manage such type of groundwaters in a sustainable way, according to the Sustainable Development Goals (SDGs) of the United Nations 2030 Development Agenda. In this context, geoethics plays an important role to raise in geoscientist’s community their awareness of ethical, social, and cultural responsibilities in conducting scientific Earth Sciences activities, and their possibility to influence decision-makers concerning groundwater sustainable management (hydrogeoethics). This paper aims to highlight the role of environmental isotopes in hydrogeoethics. A brief review of two case studies is presented, showing that nuclear techniques (Isotope Hydrology), combined with other tools of Geosciences (e.g., Geology and Geochemistry), have demonstrated to be essential in the sustainable management of different types of groundwater resources: (i) the Caldas da Rainha thermal waters, where conventional geochemical and isotopic techniques (e.g., δ²H, δ¹⁸O, ³H, δ³⁴S_(SO4) and δ¹⁸O_(SO4)), showed that the thermal waters are “geologically protected” from anthropogenic contamination, and (ii) the Santa Margarida Military Camp case study, where δ²H and δ¹⁸O data clearly showed no mixing between the Mediterranean temporary pond waters (projectile impact zones associated with real fire training) and the groundwaters of the region, used for agriculture and human consumption.