Water chemistry and isotope study of streams and springs in northern Chile

Abstract

The relationship between the stable isotopic and chemical composition of rain, spring, and stream water was studied in the high Andes of northern Chile. The isotopic pattern of the springs is mainly a reflection of the altitude of their recharge areas; however, processes that occur during snow melting seem to play a major role in the high-altitude springs. The streams show patterns similar to the springs in the higher part of the basins, but their isotopic composition is modified along the river course, due mainly to evaporation. The difference in chemical composition between the springs at high and intermediate elevations reflects the duration of water-rock interaction. The best parameter to trace this length of travelling time is the Na + K + ratio, which increases as a result of removal of K + into alteration minerals (K-silicates). The Na + Cl − ratio increases with salinity in springs and decreases in stream water. This reflects the different sources of salt, whereas the main source of salts in spring water is the dissolution of silicate and sulfide minerals. Halite accumulations close to the surface is the main salt source in the streams. During floods the stream water chemical characteristics change, Na + Cl − increases with decreased salinity and Na + K + decreases.