engleski

Adsorption properties of loess and overlying topsoil of the continental loess sections in northwestern Croatia

Four loess sections situated in northwestern Croatia (Gušćerovec, Rovišće, Ludina and Kloštar Ivanić), approximately 10 m in depth, were investigated for their adsorption properties. In each section the samples were collected at three horizons: topsoil excluding the uppermost 15 cm, intermediate zone (soil- loess transition) being 40-50 cm in depth, and loess horizon at various depths. A change in bulk mineralogical composition, iron and manganese oxyhydroxides and organic matter content was monitored and compared to a change in cation exchange capacity throughout the investigated sections. Granulometric analysis of the loess samples showed that the silt fraction predominated ranging 55-75%. Clay fraction ranged between 24-43%. The sediment can be classified as very fine grained silt. Bulk mineral composition was determined by X- ray diffraction, and clay minerals were mutually differentiated upon saturation with ethylene glycol, and heating at 400 and 550°C. Content of iron and manganese oxyhydroxides was determined by oxalate method (in darkness), and that of organic matter by heating at 375 °C overnight. Cation exchange capacity (CEC) was determined by copper ethylenediamine complex at pH 7. Mineral composition of topsoil, intermediate zone and loess comprises quartz and illite-muscovite as main constituents with subordinate plagioclase, chlorite, kaolinite and, in some cases, vermiculite. In the investigated profiles the mineral composition does not vary significantly with only illite- muscovite being slightly more abundant in loess than in topsoil. Iron and manganese oxyhydroxides, with iron compounds being more abundant (1.12-7.02% Fe2O3), decrease with depth. Their higher content in topsoil can be related to mineral weathering and pedogenesis. Organic matter content changes irregularly through the sections. CEC values range from 7 to 21 mEq/100 g, and generally increase with depth. Topsoil CEC values range 7-11 mEq/100 g, those in intermediate zone 8-14 mEq/100 g and in loess 14-21 mEq/100 g. The observed trends of CEC value distribution throughout the investigated loess sections indicate its predominant relation to the phyllosilicate content, especially illite-muscovite. Also, the CEC values correspond well to the mean CEC values of phyllosilicate minerals determined in both topsoil and loess horizons.

loess ; soil ; clay ; CEC

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