Diagnostics of gleyzation upon a low content of iron oxides (Using the example of tundra soils in the Kolyma Lowland)

Abstract

The matrix of iron (hydr)oxides exerts a decisive influence on the character of gleyzation. Upon a high content of iron (hydr)oxides, their reduction radically changes the horizon color from warm to cold hues, which is typical of soils on the Russian Plain. Upon the low content of iron (hydr)oxides, iron reduction takes place in phyllosilicates with minimal changes in the soil color. The cold hue of cryohydromorphic soils in the Kolyma Lowland is controlled by the color of the lithogenic matrix with a low content of iron (hydr)oxides. In this case, the soil color characteristics expressed in the Munsell notation or in the CIE-L*a*b* system are ineffective for diagnostic purposes. The colorimetric methods appear to be more efficient after the soil pretreatment with hydrogen peroxide, as the gleyed horizons turn green, while the nongleyed (and not overmoistened) horizons turn red. Physical methods (Mossbauer spectroscopy and magnetic susceptibility measurements) are more efficient for characterizing the properties of iron compounds in cryohydromorphic soils as compared with the methods of chemical extraction. Mossbauer spectroscopy proved to be highly efficient, as the iron oxidation index Fe3+/(Fe2++Fe3+) decreases in the gleyed horizons. Chemical reagents (Tamm’s and Mehra-Jackson’s reagents) dissolve Fe-phyllosilicates and are not selective in soils with a low content of iron (hydr)oxides.