Tritium and Carbon-14 Content as a Diagnostic Approach in Groundwater Resources Management and Protection

Abstract

Groundwater isotopic composition is widely used nowadays in the management and protection of water resources. This work will focus not only on the temporal and spatial variations of tritium content in precipitation and their relationships with groundwater active recharge, but also on the radiocarbon groundwater dating. The ³H levels determined in groundwater can be used as a complement to the carbon-14 dating of aquifer systems and in the identification of mixing between different water units or in the dynamics of water resources (transit time, definition of the main flow lines, for instance). Regional variations between the coast and the inlands of Continental Portugal will be analysed considering the influence of climatic and regional parameters in the isotopic composition of the groundwater. Two case studies will be discussed: (i) the study of Melgaço–Messagães aquifer, located in the NW of Portugal (granitic region), will be based on an isotopic approach that allowed the identification of the main origin of the dissolved carbon in the aqueous system; (ii) the Moura-Ficalho aquifer system, situated in SE of Portugal, where ³H and ¹⁴C measurements were applied to identify the active recharge of the system and in the characterization of two main flow paths with completely different velocities and apparent ages (2 and 17 ka BP).