Chemical composition and water quality of the Casta？o river, Calingasta, San Juan province, Argentina

the province of san juan, in arid centralwest argentina, is irrigated by two fluvial systems: the jachal and san juan river basins. the casta？o river is one of the two main tributaries to the latter. it crosses the casta？o viejo mining district, which was a producer of lead, zinc and copper. to investigate the water quality and the possible hydrochemical variations given rise by the mining activity, a sampling net was devised along the river course for determining concentrations of calcium, magnesium, sodium, carbonates, bicarbonates, sulphates, cadmium, copper, chrome, lead, zinc, aluminium, ph, dissolved solids and electric conductivity. the results obtained indicate that some chemical parameter of the river water vary in the different seasons of the year. the salinity, dissolved oxygen and biochemical demand of oxygen were found to be low, no toxic substances were detected in significant amounts, and the water quality has not been affected by the mining activity.