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 (7700 km(2)) river system located in central Argentina. Its mountainous upper catchment includes pristine areas as well as a variety of human settlements and a reservoir lake. A large city (Cordoba, ca. 1.3 million inhabitants) and a terminal hypersaline lake are included in the middle 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 seasons (spring and autumn), seeking to establish the factors which control the temporal and spatial variability. The major findings were: a) concentrations of TNR metals were, in general, higher during springtime than during autumn, particularly downstream from the city of Cordoba; 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., downstream the city) and more pronounced reducing conditions could be the causes for the increased Fe concentration, probably precipitated as sulfides; d) organic matter exhibited a closer correlation with some TNR metals in autumn, probably caused by a larger capacity for complexation in the biologically-processed organic debris; and, e) the existence of pristine areas in the drainage basin allowed for the calculation of enrichment factors (EF) which show the significance of several environmental impacts in the Suquia system.