A new method to measure copper binding affinity of DOM and its application to soil solutions with DOM of varying quality

摘要

Copper (Cu) complexation by dissolved organic matter (DOM) mobilises Cu in soils, but the role of DOM quality in this process is still not clarified. Differences in DOM quantity and quality (aromaticity, total DOM acidity and Cu mobilising potential, CuMP) were analysed in the soil solutions of thirteen uncontaminated topsoils. Solutions were obtained using different extraction methods, from soils incubated for different times. A one-step resin exchange method was developed to measure the CuMP (mmol Cu/kg DOC) of DOM at pCu 11.3 and pH 7.0, representative for conditions in neutral-pH uncontaminated soils. The CuMP varied tenfold and followed the order water extract >0. 01M CaCl<,2> extract > pore water. Soil solutions from soils kept dry for a long time or subjected to drying-wetting cycles had high dissolved organic carbon (DOC) concentrations with low DOM aromaticity and CuMP. Prolonged incubations decreased DOC concentrations and increased aromaticity and Cu affinity of DOM. A significant positive correlation between the specific UV-absorption (SUVA), indicating aromaticity, and CuMP was found for all DOM samples (R<'2>=0.58). For one soil, soil samples were taken from different depths and pore water was immediately extracted. The CuMP and SUVA of DOM was smallest for the solution of the deepest soil layer (40-60cm). It was concluded that both quantity and quality of DOM has to be taken into account when predicting Cu mobilisation in soils.