Geochemical and magnetic properties of sediments as pollution indicators. Case study: río Suquía, Córdoba, Argentina

Abstract

The Suquía river basin (area ~6300 km²) is a medium-sized hydrological system located in the province of Córdoba, in the central region of Argentine. The Suquía river derives from the San Roque lake. This river flows through mountainous areas, crosses a densely populated city (Córdoba: 1.5 million inhabitants) and continues its course through the Chaco-Pampean plain, where agriculture and livestock farming are typical anthropic activities. The Suquía river receives along its course diverse polluting contributions. The degree of contamination of this natural system was evaluated through geochemical and magnetic analyses. For this purpose, sediment samples were collected from the river bed. The environmental magnetism methods (magnetic susceptibility and anhysteretic remanent magnetization) were carried out in order to determine and quantify the magnetic minerals. Major oxides and trace elements were determined in the < 62.5 mm fraction. The sediments show a low degree of mineralogical maturity and are equivalent to shales and Fe-shales. Diverse contamination indices showed the highest values in the mountainous area where the most elevated measurements of magnetic susceptibility were also registered. This is interpreted as consequence of natural factors enhanced by quarries exploitation. The lowest levels of pollution were recorded in the urban area, while in the rural area, a moderate to high degree of pollution associated with agricultural activities was determined. Thus, the processes that originate the geochemical and magnetic characteristics of these sediments are spatially differentiated throughout the basin and are due to the effect of both natural and anthropogenic factors. In addition, metal concentrations have increased in the last decade throughout the basin. A significant correlation between geochemical variables and magnetic parameters was determined, proving the potential of combined studies as a methodology for environmental monitoring in hydrological systems.