Organic fermentative‐humic soil subhorizon (Ofh) as a ‘natural sponge’ of selected trace elements: Does this feature make it a potential geoindicator of temperate soil quality?

Abstract In a temperate climate zone, the outermost part of forest soil forms the organic‐O horizon. It consists of subhorizons of varying thickness, including the organic fermentative‐humic subhorizon (Ofh), which resembles a tobacco tangled mat. The scientific novelty of this project is to evaluate whether the specific structure of the subhorizon‐Ofh makes it a ‘natural sponge’ for trace elements such as Cd, Hg, Pb and Zn, and whether it can be used as a potential geoindicator of soil quality. To test this hypothesis, 110 soil samples (55 from the subhorizon‐Ofh and 55 from the underlying soil horizons‐A [humic] or AE [humic‐eluvial]) were collected from five forest areas located in the south‐central Poland (Świętokrzyskie province). All samples were analysed for Ba, Ca, Cd, Cu, Fe, Hg, K, Mn, Pb, S, Ti and Zn. pH, EC, soil organic matter, total C and N were also measured. Our results confirm that the subhorizon‐Ofh acts like the sponge in relation to Cd, Hg and Zn. Concentrations of these elements are two to four times higher than in the A and AE horizons. Such a relationship is not observed for Pb which predominates in the A horizon. This feature means that analyses of samples from different (sub)horizons can lead to misleading conclusions about soil quality and contamination levels, which have been verified by geochemical factors. Our results can be a starting point for further research into the possible use of the subhorizon‐Ofh as a geoindicator of temperate soil quality in relation to selected trace elements.