Derivation of functional layers in a podzol toposequence for simulating cadmium transport

Abstract Subdivided horizons of three Spodosols along a toposequence are analysed for total cadmium concentration, organic carbon content, pH, water retention parameters and saturated hydraulic conductivity. A functional property, cadmium travel time, is used to identify functional layers. Different pedological horizons are pooled into functional layers after testing significance of difference between cadmium travel times using a non-parameterc Mann Whitney U-test. For a Humod profile the number of layers reduces from 7 to 3, while for an Aquod profile a reduction from 6 to 2 layers is obtained. Spodosols conceptualised as layered soils show lower mean cadmium travel times, compared to Spodosols having random physical and chemical properties. The required sampling effort to estimate the true mean cadmium travel time is lower for Spodosols described by functional layers than for Spodosols described by pedogenic horizons.