Quick Search:    advanced search

GSW Home   GeoRef Home   My GSW Alerts   Contact GSW   About GSW   Journals List   Help

This Article Figures Only Full Text Full Text (PDF) Alert me when this article is cited Alert me if a correction is posted Citation Map Services Email this article to a friend Similar articles in this journal Similar articles in Web of Science Alert me to new issues of the journal Download to citation manager Citing Articles Citing Articles via Google Scholar Google Scholar Articles by EGLI, M. Articles by PLÖTZE, M. Search for Related Content GeoRef GeoRef Citation

Effect of slope aspect on transformation of clay minerals in Alpine soils

¹ Department of Geography, University of Zurich, Winterthurerstrasse 190, 8057 Zurich, Switzerland, ² Istituto Sperimentale per lo Studio e la Difesadel Suolo, PiazzaD’Azeglio 30, 50121 Firenze, Italy, ³ Museo Tridentino di Scienze Naturali, Via Calepina 14, 38100 Trento, Italy, and ⁴ ETH Zurich, Institute for Geotechnical Engineering, 8093 Zurich, Switzerland

^* E-mail: megli{at}geo.unizh.ch

(Received 2 January 2007; revised 21 June 2007)

Two soil profile sequences on paragneiss debris in the Val di Rabbi (Northern Italy) along an altitude gradient ranging from 1200 to 2400 m a.s.l. were studied to evaluate the effect of aspect on the weathering of clay minerals. All the soils had a coarse structure, a sandy texture and a low pH. Greater weathering intensities of clay-sized phyllosilicates (greater content of smectites) were observed in soils on the north-facing slope. On the south-facing slope, smectite was found only in the surface horizon of the soil profile at the highest altitude. Hot citrate treatment of north-facing soils revealed the presence of low-charged 2:1 clay minerals, the expansion of which was hindered in the untreated state by interlayered polymers. However, the hot citrate treatment encountered some problems with the samples of the south-facing soils: as confirmed by Fourier transform infrared spectroscopy, the hot citrate treatment was unable to remove all interlayer Al polymers. The 2:1 phyllosilicates were not expanded by ethylene glycol solvation in several samples, although thermogravimetric analyses indicated the presence of clay minerals with interlayer H₂O. At the same time, the collapse of clay minerals to 1.0 nm following K-saturation was evident. Theoretically, this should indicate that 2:1 phyllosilicates had no evident substitution of trioctahedral cations (Mg²⁺, Fe²⁺) by dioctahedral cations (Al³⁺ and Fe³⁺). X-ray diffraction analysis of the d₀₆₀ region and determination of the layer charge of clay minerals by the long-chain (C₁₈) alkylammonium ion, however, did not confirm this. A transformation from trioctahedral to dioctahedral species was observed and low-charge clay minerals ( ~0.30) were identified in the surface horizons of the south-facing sites. In the south-facing soils, the podzolization process was less pronounced because of a lower water flux through the soil and probably less complexing organic molecules that would remove the interlayer polymers. Besides the eluviation process, clay minerals underwent a process of ionic substitutions in the octahedral sheet that led to the reduction of the layer charge. This process was more obvious in the north-facing sites.

KEYWORDS: smectite, Na-citrate treatment, weathering, soils, microclimate, aspect