ABSTRACT
Hydrogeochemical processes were investigated in the Pateira de Fermentelos lagoon, a shallow freshwater body with important ecosystems. Besides rainwater, at least three main types of natural waters contribute to the water balance and water quality in the lagoon: (1) the Cértima River with a mineralised Ca-HCO3 water and circum-neutral pH; (2) the Cretaceous aquifers with a Na-Cl water and acidic pH; (3) the Triassic aquifers with a mixed water type, and slightly alkaline pH; (4) and, possibly, the Águeda River with a diluted Na-Cl water. The hyporheic and riparian sediments associated to the lagoon are rich in clays, iron oxyhydroxides and organic matter. Water-rock interactions play a major role in the hydrochemistry of water bodies, leading to a wide range of the mineralisation of natural waters and to the occurrence of trace elements such as arsenic, lead and manganese. Additionally, anthropogenic activities are deteriorating the water quality of surface and groundwater bodies.
