Numerical analysis of soil development in a chronosequence on Fraser Island, southeastern Queensland

Abstract

Analytical data for K, Na, Ca, Mg, Al and Fe on acid extracts of samples from 52 profiles from Fraser Island, south-eastern Queensland, were used to investigate soil development in a chronosequence of podzol soils on sand, dating from mid-Pleistocene to the present. The variation observed could be accounted for by two factors, one associated with K, Fe and Al, and the other with Na, Ca and Mg. The first was most closely associated with the podzolisation process involving the weathering of minerals and the removal of the products by leaching and the deposition of Fe and A1 in the B horizon (a katamorphic factor). The second was seen as a biotic factor related to surface accumulation by the present-day vegetation. In the A horizon, both factors were related to age, implying that the soils become more impoverished with increasing age. The biotic factor, which was strongly related to the C and N contents, was also related to depth, decreasing exponentially to approximately 1.5 m, implying that this was the limit of the effect of the modern plant cover on the soil. In the B horizon, factor scores for the katamorphic factor increased markedly, indicating an increase, but not necessarily an accumulation, of K, Fe and Al. There was no relationship, however, with depth, age or carbon content. Factor scores related to the biotic factor showed a significant relationship with age, with Ca and Mg accumulating to a lesser degree in older B horizons. Several lines of evidence indicate that spodic horizons at depths greater than 1.5 m are not now in equilibrium with the surface horizons.