The composition of groundwater discharging from perched aqui-
fers in the Azores results from the cumulative effect of several modi-
fying mechanisms, as marine airborne salts and seawater spraying,
the latter limited to the coastal fringe, CO2 dissolution and water–
rock interaction. It is possible to discriminate between aquifers
made of volcanic rocks of basic nature or more evolved lithological
terms regarding alkali and alkali-earth metal relationship (Cruz and
Amaral, 2004).