Rate of soil formation in Arenosols of dunes on Spiekeroog Island (Germany)

Abstract

This study is concerned with the rate of soil formation in Arenosols of dunes on the barrier island Spiekeroog at the southern North Sea coast. It focuses on Fe dynamics in the soils in relation to slope aspect, as well as on the interaction between minerals and soil organic matter (SOM) in the course of soil formation. Ten quartz-rich (≈ 95 wt%) Arenosols on slopes with different aspects (north/south), low in primary carbonates (≈ 0.5 wt%) and total Fe (Fet, ≈ 0.15 wt%), were studied across a soil chronosequence with optically stimulated luminescence (OSL) ages between 43 ± 7 and 279 ± 26 years. During this period, pH (CaCl2) decreased from 7.1 in fresh sands to 3.1 in initially podzolized soils. SOM contents and the optical density of oxalate extracts (ODOE) increased with soil age. Differences in Fe stocks, vertical distribution of Fed, Feo and Fep and horizontation of equally old soils indicated an influence of microclimate on pedogenesis determined by slope aspect. Initial podzolization features occurred after 179 ± 17 years. Eluviation resulted in the formation of an E horizon free of amorphous and poorly crystalized Fe oxides (Feo-Fep), indicating that these oxides provided a source of Fe during podzolization. However, illuviation features were absent. Field findings, macroscopic examinations and carbon fractionations revealed, that SOM was exclusively present in free particulate form (free POM). This indicated, that prior to podzolization, mineral grains did not become enclosed by organic pigments during the formation of Ah horizons.