SPATIAL AND TEMPORAL VARIABILITY OF TOTAL NON-RESIDUAL HEAVY-METALS CONTENT IN STREAM SEDIMENTS FROM THE SUQUIA RIVER SYSTEM, CORDOBA, ARGENTINA

The Suquia is a semiarid (rainfall, 700-900 mm y(-1)), medium-size (77 00 km(2)) river system located in central Argentina. Its mountainous u pper catchment includes pristine areas as well as a variety of human s ettlements and a reservoir lake. A large city (Cordoba, ca. 1.3 millio n inhabitants) and a terminal hypersaline lake are included in the mid dle and lower basin. Total non-residual (TNR) heavy metals (Pb, Cu, Ni , Zn, Mn, and Fe) have been determined in river bed sediments in two s easons (spring and autumn), seeking to establish the factors which con trol the temporal and spatial variability. The major findings were: a) concentrations of TNR metals were, in general, higher during springti me than during autumn, particularly downstream from the city of Cordob a; b) organic matter played a significant role as a controlling factor wherever it defined reducing conditions, lowering the concentrations of Mn and Fe hydrous oxides; c) a higher organic load (e.g., downstrea m the city) and more pronounced reducing conditions could be the cause s for the increased Fe concentration, probably precipitated as sulfide s; d) organic matter exhibited a closer correlation with some TNR meta ls in autumn, probably caused by a larger capacity for complexation in the biologically-processed organic debris; and, e) the existence of p ristine areas in the drainage basin allowed for the calculation of enr ichment factors (EF) which show the significance of several environmen tal impacts in the Suquia system.