『Abstract
Two soil sequences in northern Italy (Val di Fiemme and Val Genova)
along an elevational gradient ranging from moderate (950 m a.s.l.)
to high alpine (2440 m a.s.l.) climate zones were investigated
with respect to element losses (Ca, Mg, K, Na, Fe, Al, Si, Mn)
and development of clay minerals. Soils formed on paleo-rhyolitic
parent material in Val di Fiemme and on tonalitic-granodioritic
morainic material in Val Genova. All the soils have a similar
age (〜12,000 y) and have been classified as Podzols. The soils
are very acid and the pH values tend to increase with decreasing
altitude. Podzolization processes were most intense in the range
of the subalpine forest up to the timberline (1400 - 1900 m above
sea-level (a.s.l.)). Element leaching was greatest in this range
and weathering rates decrease with both higher and lower altitudes.
Due to the different lithologies and precipitations between the
two valleys, the total amount of chemical weathering was slightly
different, although the same trends with altitude could be observed.
Imogolite-type materials (ITM) are generally of minor importance.
Greater concentrations of ITM were observed in the Bhs or Bs horizons
of the Episkeleti-Entic Podzols at the lower altitudes. Iron eluviation
was similar in all Podzols while larger amounts of eluviated Al
were detected in Val Genova. The pattern of smectite distribution
along the climosequences had similarities to the trend of cation
losses. The largest amount of low-charge expandable minerals seems
to exist in the range of the subalpine forest up to the timberline.
The development of clay minerals with a smaller layer charge was
more advanced in Podzols on rhyolitic material where smectite
could be detected in the Bhs and Bs horizon. Parent material influenced
chemical weathering in the soils along the two climosequences
and essentially determined the degree of weathering and the formation
of clay minerals.
Keywords: Alps; Climosequence; Parent material; Podzol; Smectite;
Weathering』
Introduction
Investigation area
Material and methods
Soil sampling
Soil chemistry
Soil mineralogy
Calculation of weathering rates
Results
Soil chemistry
Chemical weathering
Clay minerals
Discussion and conclusions
Acknowledgments
References