Share Stelvio - Case Study 3

Bei Laghetti

Many lakes within the Stelvio National Park have been sampled and analyzed for water chemical composition. Two of these, however, deserve a special mention. These lakes, nicknamed “beautiful lakes”, are the Lower Bei Laghetti (FROD68 – 2719 m a.s.l.) and the Upper Bei Laghetti (FROD77 – 2738 m a.s.l.), in the Sobretta Valley. The lakes showed remarkably different chemical composition: the Lower lake was affected by extremely high concentrations of sulphate and magnesium. Among the lakes studied within the Park, this lake was that affected by the highest solute content (mean conductivity 250 µs cm^-1). The lake has also low pH (5.5-5.8) and alkalinity (5-12 µeq L^-1) values, indicating a high sensitivity to acidification. The most striking result is the sharp difference with respect the Upper lake, where sulphate and magnesium prevailed among ions, but with distinctly lower concentrations, and significantly higher pH and alkalinity (7.3 e 230 µeq L^-1, respectively).

A further interesting result of this study is the presence of trace metals in the Lower lake, especially nickel, aluminium and zinc. Concentrations of these metals are markedly higher than those usually reported for high altitude lakes. Both trace metals, and sulphate and magnesium ions in the lakes are of natural origin due to the dissolution of some types of rocks in the catchment causing lake waters acidification and presence of dissolved metals. Moreover, the Lower lake is characterized by a sharp light blue water colour. The same colour can be seen in the Upper lake, but just in a limited portion, close to the lake shore. Therefore, the two lakes, even if very close one to the other, are fed by distinct water sources. In addition, the whole area is certainly characterized by a highly heterogeneous geo-lithological cover.