Cation exchange processes and human activities in unconfined aquifers

Abstract

During the 1999–2002 water years, a hydrogeological research project was carried out on the unconfined aquifer of Trifilia in the Peloponnese. Seawater intrusion due to overpumping, and intensive use of fertilizers caused the groundwater quality degradation that is a typical case for the coastal aquifers in Greece. Isopiezometric maps along with ion distribution balances, ion distribution maps and factor analysis indicate the existence of three zones of groundwater quality. In the first zone of saline water, a cation exchange process between the Ca²⁺ of sediments and the Na⁺ of groundwater contribute to the formation of the water type Na⁺-Ca²⁺-Cl⁻. In the second zone, which is considered as a transition zone, dominate the Ca²⁺-Na⁺-HCO₃ ⁻-Cl⁻ water type. In the third zone of Ca²⁺-HCO₃ ⁻-SO₄ ²⁻ water type, relationships among Ca²⁺, SO₄ ²⁻, NO₃ ⁻ and NH₄ can be attributed to the dissociation of ammonium nitrate and sulfate fertilizers on one hand, and Ca²⁺ derivation from cation exchange processes between water, rocks and clay minerals, such as smectite and illite, on the other.