Photo: Modelled extent of freshened groundwater offshore of the Maltese Islands (shown in light blue). In grey is the model extent.
An international team of scientists has estimated the volume of freshened groundwater resources offshore of the Maltese Islands at 1 km3, which could potentially provide an alternative supply of potable water for 75 years.
Offshore freshened groundwater is groundwater with a salinity below that of seawater that is stored in sediments and rocks below the seafloor.
To reach this estimate, the scientists first developed a detailed 3D geological model of the Maltese Islands and the adjacent seafloor. They then used advanced numerical models to simulate how the groundwater system of the archipelago would evolve in time.
The simulation results showed how 18,000 years ago, during the Ice Age, the groundwater system extended across the entire continental shelf of the Maltese Islands, which was exposed at the time. As a result of ensuing sea-level rise, the continental shelf was drowned, and only a quarter of the original groundwater volume has been preserved.
At present, offshore freshened groundwater is expected to predominantly occur between Malta and Gozo, and along the coast between Cirkewwa and Valletta, with the largest extensions offshore of St Paul's Bay, Salini and St Julian's. The groundwater body is up to 100 m thick and 3 km from the coast.
There are two issues with the potential exploitation of these offshore freshened groundwater resources. First, most of the groundwater appears to be hosted in low permeability layers, which would mean that its extraction could be complicated and expensive. Second, a decrease in precipitation predicted for the coming 100 years, as a result of regional climate change, is expected to diminish offshore freshened groundwater extent by 40%.
The study is a product of the project, which is led by Prof. Aaron Micallef from the Department of Geosciences of the University of Malta. It has just been published in the international journal . The team involved in this study includes scientists from Italy, USA and Finland.
