Chemical Weathering of Crystalline Rocks in the Catchment Area of Acidic Ticino Lakes, Switzerland

Abstract

A~traet--Atmospheric acidic deposition introduces hydrogen ions to terrestrial and aquatic ecosystems, which become partially neutralized by chemical weathering. In the southern Alps of Switzerland, small catchments containing little or no soil and lacking carbonate minerals represent sensitive hydrological settings in which the relationship between alteration of granitic gneiss by acid deposition and the resulting composition of lake waters can be studied. Transmission and scanning electron microscopy, coupled with X-ray powder diffraction of lake sediments from such areas showed mainly unaltered minerals from parent rocks and no secondary silicate minerals. Element mapping indicated noncrystalline aluminum hydroxide as a product of the chemical weathering of silicates. Noncrystalline iron hydroxide was also observed. Mass balance calculations and the stoichiometry of suitable chemical reactions representing the weathering processes were used to derive a plausible reaction sequence on the interaction of the predominant reactive rock minerals with acid precipitation that accounted for the measured chemical composition of the acid lakes.

The role of trace minerals in chemical weathering in a high-elevation granitic watershed (Estibère, France): chemical and mineralogical evidence

“…However, there are relatively few studies of chemical weathering of granitic rocks in high mountains at the small watershed scale from areas really free of anthropogenic influences (e.g., acid rains). We can note the studies of Owens and Watson (1979) in Rhodesia, Giovanoli et al (1988), followed by Drever and Zobrist (1992), who studied chemical weathering in the Southern Swiss Alps and Blum et al (1998), Dalai et al (2002a,b), and Jacobson et al (2002) in Himalayas.…”

“…The influence of atmospheric input, particularly the role of dry deposition, may also be important in the watersheds we studied (Giovanoli et al, 1988;Drever and Finley, 1993;Delmas et al, 1996). Indeed, many studies are documented the 3 ϫ 10 4 1.45 ϫ 10 4 -0.97 ϫ 10 4 2 ϫ 10 4 2.23 ϫ 10 4 38 ϫ 10 2 75.9 ϫ 10 2 3.99 ϫ 10 4 Output fluxes (mol/km 2 /yr) 13.25 ϫ 10 4 4.17 ϫ 10 4 7.56 ϫ 10 4 0.97 ϫ 10 4 0.62 ϫ 10 4 1.23 ϫ 10 4 45.5 ϫ 10 2 38.2 ϫ 10 2 27.9 ϫ 10 4 Weathering fluxes (mol/km 2 /yr) 10.25 ϫ 10 4 2.72 ϫ 10 4 7.56 ϫ 10 4 -(Ϫ) 1.38 ϫ 10 4 (Ϫ) 1 ϫ 10 4 7.5 ϫ 10 2 (Ϫ) 37.7 ϫ 10 4 23.91 ϫ 10 4 Camarero and Catalan (1996).…”

Strontium as a tracer of weathering processes in a silicate catchment polluted by acid atmospheric inputs, Strengbach, France

“…Rock weathering rates in catchments have been estimated by considering either a steady-state mass balance approach or the stoichiometry of weathering reactions according to field or experimental data ŽVelbel, 1985;Colman and Dethier, 1986;Giovanoli et al, 1988;Mast et al, 1990;Kirkwood and Nesbitt, 1991;Drever and Zobrist, 1992;Casey et al, 1993;Swoboda-Colberg and Drever, 1993;Blum et . al., 1994 .…”

Acidification and weathering processes in high mountain lakes in Southern Alps

“…The Maggia Valley is one of the most acid-sensitive areas in the Alps, so these lakes are not representative of the whole set of lakes studied, lying as they do mainly on granitic bedrock: their alkalinity is below 50 peq 1-, with a median value of 2 eq 1-. Table 5 shows a comparison between lake chemistry and atmospheric deposition, corrected for evapotranspiration by multiplying for the factor precipitation/runoff of 1.4 proposed for this area by Giovanoli et al (1988).…”