CHEMICAL-COMPOSITION CONTROL IN THE MEDINA RIVER, TUCUMAN, ARGENTINA

The Medina River, Tucuman, Argentina, shows seasonal and spatial chang es in the concentration of metal ions (Ca2+, Mg2+, Na+ and K+) and hyd rogencarbonate that reflect the rate of formation of carbon dioxide by oxidation of organic matter, partly compensated by the rate of releas e to the atmosphere, and by the rate of dissolution of sediments. The balance of these rates also determines the pH values. The organic matt er load in the river arises mainly from the sugar cane processing; sew age contribution is minor. Nitrate levels are rather constant along th e river.