Water Chemistry of Swiss Alpine Rivers

Abstract

Average concentrations of dissolved nutrients (NO₃, DRP, K) in the large alpine rivers Rhine, Rhône, Ticino, and Inn, and in small alpine streams and glacier streams, are low compared to those in midland rivers. Concentrations of NO₃ in the large rivers clearly exceed background concentrations. In spite of limited anthropogenic activities in alpine catchments, DRP concentrations in large rivers exhibited a downward trend over the last 30 years. Time series of NO₃ concentrations were first increasing and then leveled off. Export coefficients of NO₃ and DRP in alpine streams fall in the range of those estimated for nonagricultural lands and forests on the Swiss Plateau.

The chemical weathering rate of rock-forming minerals in alpine catchments is about 165 ± 45 g m⁻² y⁻¹, corresponding to an ablation rate of about 0.06 mm y⁻¹. Rates are dominated by the reaction of carbonate-containing rocks with CO₂ and the dissolution of anhydrite, whereas the weathering of silicate minerals contributes little. Total chemical weathering rates are in the same range as the export rate of fine sediments, as part of physical weathering products. In this respect, alpine rivers differ distinctly from lowland running waters. Long-term observations also revealed small changes in concentrations and loads of geochemical constituents. An increase in water temperature may be one driver for these changes, although other factors also play a role.