Distribution and behaviour of fluoride in Mandovi and Zuari estuaries, central west coast of India

Abstract

Fluoride concentrations in Mandovi and Zuari estuaries are regulated largely by salt water intrusion. Highest concentrations are observed during the premonsoon season, when the salt water intrusion is also the highest, the concentration increasing from fresh water-end to the sea-end. During monsoon, however, fluoride concentrations are the lowest and the estuaries show freshwater characteristics at the surface while at the bottom higher fluoride concentrations are observed near the mouth as a result of salt wedge formation. Postmonsoon season shows a recovery period when the fluoride concentration has values lying between those during premonsoon and monsoon. F-Cl relationship is linear during monsoon and postmonsoon indicating that fluoride behaves conservatively during these 2 seasons. During the premonsoon, however, the F-Cl relationship is not linear but exponential of the type Y = abx which is curve concave to the fluoride-axis indicating that fluoride is lost in estuaries in this season (28 and 25% in Mandovi and Zuari respectively)