Stable Copper Isotopes: A Novel Tool to Trace Copper Behavior in Hydromorphic Soils

• Published in: Soil Science Society of America journal Vol. 74; no. 1; pp. 60 - 73
• Main Authors: Bigalke, Moritz, Weyer, Stefan, Wilcke, Wolfgang
• Format: Journal Article
• Language: English
• Published: Madison Soil Science Society 01.01.2010; Soil Science Society of America; American Society of Agronomy
• Subjects: Agronomy. Soil science and plant productions; Binding sites; Biogeochemical cycles; Biogeochemistry; Biological and medical sciences; Copper; Defense mechanisms; Earth sciences; Earth, ocean, space; Exact sciences and technology; Fractionation; Fundamental and applied biological sciences. Psychology; groundwater; hydromorphic soils; Isotope fractionation; Isotopes; Mass spectrometry; mineral soils; Nanoparticles; organic horizons; quantitative analysis; Ratios; redox potential; soil chemistry; soil fertility; soil pollution; Soil properties; Soil science; soil water; soil-plant interactions; Soils; Stable isotopes; Stagnant water; Surficial geology; Vertical distribution; Group IB metal; Stable isotopes; copper; Soil science; Earth science; soils; behavior; Hydromorphic soils; tracks
• ISSN: 0361-5995; 1435-0661
• DOI: 10.2136/sssaj2008.0377

Copper is an essential micronutrient for all organisms but may also be a pollutant. We studied the natural abundance of stable Cu isotope ratios in four soils to test whether 65Cu values can be used as a tracer for biogeochemical processes in hydromorphic soils. Two of the soils were affected by stagnant water and the other two by groundwater. We determined standard soil properties and Cu partitioning into seven fractions of a sequential extraction. Copper stable isotope ratios were measured in total soil digests with multicollector inductively coupled plasma mass spectrometry. Copper concentrations in the study soils were low to average (5–34 mg kg–1). The variation in Cu isotope ratios was up to 0.6 in an individual soil. The organic layers of two of the profiles had lighter 65Cu values than the mineral soil, indicating isotopic fractionation of Cu during soil–plant–soil transfer. In the mineral soil, Cu isotopes showed distinguishable variations of up to 0.45. The vertical distribution of the 65Cu values, which paralleled that of the poorly crystalline to crystalline Fe oxide ratios, offers the first hints that Cu isotope ratios in soils may be influenced by alternating redox conditions. We conclude that variations in 65Cu in soils are large enough to be distinguished and may be indicative of biogeochemical cycling and geochemical processes. In particular, Cu isotope ratios might be helpful to trace long-term processes such as element transport and redox conditions, which are difficult to assess otherwise.