Studies on calcium, magnesium & sulphate in the Mandovi &Zuari River systems (Goa)

Abstract

Distribution of calcium, magnesium and sulphate have been examined in the tide-dominated Mandovi and Zuari river systems. Calcium and magnesium appear to take some part in the bio-geochemical cycles of the rivers and behave as semi-conservative parameters. Sulphate, however behaves in a purely conservative manner and remains in a steady state in the rivers. A 'Simple mixture' relationship is applied to calculate the dilution and mixing processes in the rivers using calcium, magnesium and sulphate as indicators, it has been observed that the percentage of sea water in the estuarine region of Mandovi vary from 88-92 during premonsoon,12-23 during monsoon and 78-79 during postmonsoon. Similar figures for Zuari are 94-99, 27-43 and 79-91 during the 3 seasons. The possibility of loss of calcium and magnesium due to precipitation as their insoluble phosphates in the upper reaches of the rivers is discussed.