Composition characteristics of magnesium isotopes in groundwater and their application prospects in water cycle processes

In addition to traditional isotopes, non-traditional isotopes have gradually been applied in the hydrosphere, such as lithium, strontium, magnesium, etc. Magnesium is one of the main elements in the earth’s crust and participates in most geophysical and chemical processes. In seawater, the δ²⁶Mg value is -0.82‰ and relatively constant, which determines that the magnesium isotope composition of terrestrial water from seawater recharge is relatively consistent. This provides a constant initial isotope scale for studying water cycle processes and can be used as an ideal tracer element for groundwater research. Through comparative analysis of magnesium isotope composition characteristics and water cycle processes it is shown that the fractionation range of magnesium isotopes can reach 3.5‰, and they have different compositional characteristics in surface water and groundwater. In the process of groundwater rock interaction, magnesium isotopes undergo fractionation, providing valuable information for identifying mineral phase evolution. Magnesium isotopes follow the law of mass dependent fractionation. Therefore, in the process of groundwater infiltration and runoff, magnesium isotope fractionation caused by ion exchange and cohesive soil formation is easier for lighter magnesium isotopes to migrate to heavier magnesium isotopes. This provides the potential for magnesium isotopes to be used to study salt transport and the formation process of clay minerals.