Sulfur and strontium isotope composition of the Llobregat river (NE Spain): Tracers of natural and anthropogenic chemicals in stream waters

Abstract

The use of sulfur and strontium isotopes as tracers forthe source/s of water contaminants have been applied to thewater of the Llobregat River system (NE Spain). Surfacewater samples from June 1997 were collected from theLlobregat River and its main tributaries and creeks. Thechemistry of most stream waters are controlled mainly bythe weathering of Tertiary chemical sediments within thedrainage basin. The largest variation in δ34Svalues were found in the small creeks with values rangingfrom –9.9 to 15‰, whilst in the main river channels valuesranged from 6.3 to 12.4‰. The 87Sr/86Sr ratio fordissolved strontium ranged from 0.70795 for a non-pollutedsite to 0.70882 for a polluted one. Most of the waters withhigh NO3 and low Ca/Na ratio converge to the same87Sr/86Sr value, pointing to dominant pollutantend member contribution or a mixing of pollutants with anisotopic composition around 0.7083–0.7085. Although theconcentration of the natural inputs in the river forsulfate and strontium are high, as a result of the sulfateoutcrops within the geology of the basin, their isotopiccharacteristics suggest that they can be used as adiscriminating device in water pollution problems. Howeverto establish the detailed characteristics of the isotopesas geochemical tools, specific high-resolution case studiesare necessary in small areas, where the inputs are well known.