X-Ray CT Scanning Reveals Long-Term Copper Pollution Effects On Functional Soil Structure.

Soil structure plays the main role in the ability of the soil to fulfill essential soil functions such as the root growth, rate of water infiltration and retention, transport of gaseous and chemicals/pollutants through the soil. Soil structure is a dynamic soil property and affected by various factors such as soil type, land use, and soil contamination. In this study, we quantified the soil structure using X-ray CT scanning and revealed the effect of a long history of Copper (Cu) pollution on it. A fallow field at Hygum Denmark provides this opportunity as it had a long history of Copper sulphate contamination in a gradient with Cu content varies from 21 mg kg-1 to 3837 mg kg-1. Total 20 intact soil columns (diameter of 10 cm and height of 8 cm) were sampled at five locations along the Cu-gradient from a depth of 5 to 15 cm below surface level. The soil columns were scanned at a voxel resolution of 0.21 mm x 0.21 mm x 0.21 mm. Images were analyzed using the Image-J software. Three-dimensional visualization of macropores showed that biopores (pores formed by organisms and plant roots) are present in abundance in this field at a Cu level of 21 mg kg-1 and decreased as the Cu content increases, and at Cu level of 3837 mg kg-1 hardly any biopore was observed. Macroporosity decreased from 0.07 to 0.01 cm3 cm-3, macropore length density from 4.14 to 1.10 cm cm-3 and macropore connectivity from 0.60 to 0.20 as Cu content in the field increased from 21 to 3837 mg kg-1. For all the soil columns, macroporosity showed a significant decrease along the column depth. The results suggest that Cu contamination has a strong impact on soil structure and hence on all soil physical and biological processes.