Water extractable concentrations of Fe, Mn, Ni, Co, Mo, Pb and Cd under different land uses of Danube basin in Croatia

Abstract

Water extraction of trace elements can simulate the concentration of elements in the soil solution from where the plant takes up the elements. The objective of this investigation was to determine the water extractable concentration of seven trace elements (Fe, Mn, Ni, Co, Mo, Pb and Cd) and to assess their relationship with soil properties of the Danube basin in Croatia. Soil samples from the surface layer (0–25 cm) of 74 sites, having different land uses (forest and agricultural land), were collected. Samples were analysed for total and water extractable trace elements as well as for pH, DOC, SOC and CEC. The concentrations of water extractable fraction of trace elements were on average: 20.14 mg kg−1 for Fe, 3.61 mg kg−1 for Mn, 0.07 mg kg−1 for Ni, 0.016 mg kg−1 for Co, 0.01 mg kg−1 for Mo, 0.01 mg kg−1 for Pb and 0.0009 mg kg−1 for Cd. Soil properties were in the following range: pH 4.3–8 (Avg: 6.35), DOC 6.1–73 mg l−1 (Avg: 26 mg l−1), CEC 1.3–24 cmol kg−1 (Avg: 9 cmol kg−1) and SOC 0.5–5% (Avg: 1.7%). The concentration of water extractable fraction of trace elements was significantly correlated with pH (p <0.001), DOC (p <0.001 – p <0.05) and CEC (p <0.001) but their relationship with total content of trace element and SOC was rather weak, suggesting that total metal alone cannot be an indicator of toxicity or deficiency. Results show that pH, DOC and CEC are important soil quality parameters taking part in the solubility control of trace metals in the soil rather than their total concentration. The difference between land uses has been observed as well, suggesting that a change in land use can cause a change in trace element solubility.