Nature and genesis of spodic horizons characterized by inverted color and organic content in a subalpine podzolic soil (Pyrenees Mountains, France)

Abstract

Podzolic soils showing an inverted sequence between Bh and Bs horizons have been recently described in the French Pyrenees. This paper deals with the spodic characters of two inverted podzol profiles found in the granitic Estibère valley. Taking into consideration a coherent genesis of these soils, we perform this study through a multidisciplinary approach (e.g., pedology, mineralogy). We describe the evolution of the different forms of free iron and aluminum in relation to organic constituents and the mineralogical characteristics of the soil. Spodic criteria indicate that those soils could be classified as podzolic soils. The study of the spodic horizons show the existence of an ochrous horizon “BP1”, rich in immobilized forms of iron (i.e., amorphous and partially crystallized forms). It overlies a darker chocolate colored horizon “BP2” rich in organic-complexed aluminum, aluminosilicate gels and humic constituents, particularly humic acids. We explain the organic accumulation in the deep “BP2” as the result of particular seasonal hydrologic processes related to the geomorphologic and climatogenic situations of the soils profiles.

Podzolization over ophiolitic materials in the western Alps (Natural Park of Mont Avic, Aosta Valley, Italy)

“…Similar trends were found by Remaury et al (2002) under P. uncinata in the French Pyrenees. The total organic carbon content (TOC) is higher in some strongly bleached E than in Bs horizons (i.e., P6); this may be due to fine roots accidentally included in the samples.…”

“…According to Remaury et al (2002), the crystalline Fe oxides (Fe dFe o ) in Bs horizons are the product of in situ weathering of Fe-bearing primary minerals. In the studied profiles, high Fe d values in the Bs horizons are related to large amounts of Fe tot , associated with much lower values in the overlying E and in the underlying C horizons; the hypothesis of the above-mentioned authors therefore does not fit the observed situation in the study area.…”

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

“…1A). Soils in the Estibère watershed have been the subject of previous studies (Remaury, 1999(Remaury, , 2002.…”

“…Rocky crests are covered by heath and pine whereas depressions are more or less colonized by hydromorphic vegetation. Two types of soil develop over the granitic units: ranker type soils under grassland and podzolic type soils mainly located on slopes and rocky zones more or less colonized by open forest and ericaceae (Remaury et al, 1999(Remaury et al, , 2002. Both are thin, acid, and have a high organic matter content.…”

“…The clay fraction (Ͻ2 m) in the podzolic soils from the Estibère watershed represents 4 to 20% of the Ͻ2 mm fraction (Remaury, 1999(Remaury, , 2002. XRD analysis of the clay fraction indicated the presence of smectite (showing X-ray characteristics of a Na-smectite: occurrence of 12.5 Å peak on the air-dried pattern, a 17 Å peak on the ethylene glycoled pattern and their disappearance in the heated pattern), illite (10 Å ), mixed layer illite-smectite (intermediate peaks between 10 Å and 12.5 Å ), and chlorite, and to a lesser extent vermiculite (14 Å ) and kaolinite (7 Å ) in the clay fraction.…”