Hidrogeoquímica de un sistema de la región semiárida; el río Suquía, Córdoba, Argentina:

DIEGO M. GAIERO 53 (2): 167-186

Revista asociacion argentina de geologia

asociacion argentina de geologia

Año: 1998 p. 167 - 186

Hidrogeochemistry of a semiarid system, Suquía River, Córdoba, Argentina: I. Sources of  major ions. The Suquía River occupies a medium size drainage basin (7,700 km2), in the semiarid (800 mm of rainfall per year) region of central Argentina. The Suquía system has been studied in detail with the purpose of probing into aspects of the geochemistry of semiarid rivers. Over 130 water samples have been analyzed, collected in different sectors and during different seasons. The functioning of the studied riverine system was investigated by means of different aproaches, e.g., seasonal and temporal variability; R-mode factor analysis; mass balance and termodinamic. The sampling stations located in the upper catchment and those located in the south central region of the Punilla Valley, are dilute sources totally developed over igneous and metamorphic rocks, in steep slopes. The rivers draining the northern portions of the Punilla Valley, show marked differences with those draining the south central sector, which are attributed to a variable geochemical control. In the oriental slope, downstream from the San Roque reservoir, the river maintains the chemical signature of the upper drainage (bicarbonate-calcium/sodium), only locally modified. The chemical composition of the dissolved solids obeys to the control exerted by the igneous-metamorphic complex. In the lowermost portion, the natural sources are masked by man-made ones (city of Córdoba). Salty groundwater seems to limit its influence to the Mar Chiquita depression. Mass balance calculations clearly showed that atmospheric precipitation is the main source of Cl- in the upper catchment. Close to urban centers, its concentrations are likely related to partly treated effluents. SO- concentrations could be related to several sources: a) groundwater circulating through sedimentary rocks; b) pyrite oxydation; and c) man-controlled sources. Plagioclase is the mineral phase which contributes significantly to the dissolved load, supplying Na+, Ca2+, HCO and SiO2.  An important fraction of the total Na+, and to a lesser extent of Ca2+, enters the system through the atmosphere. The restricted presence of marble, amphibolites and calcretes -along with erosion processes-, would be an important source of Ca2+, HCO and Mg2+, contributing a proportionally larger fraction than the weathering of silicates. The relief is, undoubtly, the most significant variable which controls the geochemistry of the system.  Through results and conclusions arising from this work, it has been possible to formulate a conceptual model which identifies the major geochemical characteristics of a typical semiarid riverine system.