Sulphur isotopes as tracers of the influence of potash mining in groundwater salinisation in the Llobregat Basin (NE Spain).

Conventional chemical data for spring and river waters are presented together with sulphur isotopic data for dissolved sulphate to elucidate the source of water salinisation in the middle section of the Llobregat River. As dilution processes do not affect sulphur isotopic composition, the analysis of delta34S of dissolved sulphate in waters provides an excellent tool for quantifying the environmental impact caused by the mining activity existing in the area. The delta34S of dissolved sulphate from mining effluents and saline springs unrelated to mining activity was analysed. The results obtained range from + 18 per thousand to + 20 per thousand (VCDT) for mining effluents and from + 10 per thousand to + 14 per thousand (VCDT) for natural saline springs. These values are in accordance with the pattern of sulphur isotopic composition of sulphates from the evaporite materials of this area. This distinctive isotopic composition has allowed us to determine the origin of salinity in those cases in which chemical features are not conclusive. In addition, two fertilisers widely used in the studied area are chemically and isotopically characterised and their contribution to groundwater salinisation is assessed.