TY - JOUR

T1 - Stable Cu isotope fractionation in soils during oxic weathering and podzolization

AU - Bigalke, Moritz

AU - Weyer, Stefan

AU - Wilcke, Wolfgang

N1 - Funding information: We thank the Earth System Science Research Center (“Geocycles”) of the Johannes Gutenberg University Mainz for funding, Stefan Stückrad for sampling and description of the Skeletic Cambisol and Ingo Lobe for supplying soil samples and related information. Furthermore we thank Sylvia Bondzio, Michael Kersten, Dieter Mertz and the group of Nicolas H. Bings for various support and the DFG Graduate School 826 for helpful discussions. We also thank the associate editor Dr. Mark Rehkämper, Dr. Jan G. Wiederhold and two anonymous reviewers for helpful and constructive comments and questions.

PY - 2011/6/1

Y1 - 2011/6/1

N2 - Copper stable isotope ratios are fractionated during various biogeochemical processes and may trace the fate of Cu during long-term pedogenetic processes. We assessed the effects of oxic weathering (formation of Cambisols) and podzolization on Cu isotope ratios (δ65Cu). Two Cambisols (oxic weathered soils without strong vertical translocations of soil constituents) and two Podzols (soils showing vertical translocation of organic matter, Fe and Al) were analyzed for Cu concentrations, partitioning of Cu in seven fractions of a sequential extraction and δ65Cu values in bulk soil. Cu concentrations in the studied soils were low (1.4-27.6μgg-1) and Cu was mainly associated with strongly bound Fe oxide- and silicate-associated forms. Bulk δ65Cu values varied between -0.57‰ and 0.44‰ in all studied horizons. The O horizons had on average significantly lighter Cu isotope compositions (-0.21‰) than the A horizons (0.13‰) which can either be explained by Cu isotope fractionation during cycling through the plants or deposition of isotopically light Cu from the atmosphere. Oxic weathering without pronounced podzolization in both Cambisols and a weakly developed Podzol (Haplic Podzol 2) caused no significant isotope fractionation in the single profiles, while a slight tendency to lower δ65Cu values with depth was visible in all four profiles. This is the opposite depth distribution of δ65Cu values to that we observed in hydromorphic soils (soils which show indication of redox changes because of the influence of water saturation) in a previous study. In a more pronounced Podzol (Haplic Podzol 1), δ65Cu values and Cu concentrations decreased from Ah to E horizons and increased again deeper in the soil. Humus-rich sections of the Bhs horizon had higher Cu concentrations (2.8μgg-1) and a higher δ65Cu value (-0.18‰) than oxide-rich sections (1.9μgg-1, -0.35‰) suggesting Cu translocation between E and B horizons as organo-Cu complexes. The different depth distributions in oxic weathered and hydromorphic soils and the pronounced vertical differences in δ65Cu values in Haplic Podzol 1 indicate a promising potential of δ65Cu values to improve our knowledge of the fate of Cu during long-term pedogenetic processes.

AB - Copper stable isotope ratios are fractionated during various biogeochemical processes and may trace the fate of Cu during long-term pedogenetic processes. We assessed the effects of oxic weathering (formation of Cambisols) and podzolization on Cu isotope ratios (δ65Cu). Two Cambisols (oxic weathered soils without strong vertical translocations of soil constituents) and two Podzols (soils showing vertical translocation of organic matter, Fe and Al) were analyzed for Cu concentrations, partitioning of Cu in seven fractions of a sequential extraction and δ65Cu values in bulk soil. Cu concentrations in the studied soils were low (1.4-27.6μgg-1) and Cu was mainly associated with strongly bound Fe oxide- and silicate-associated forms. Bulk δ65Cu values varied between -0.57‰ and 0.44‰ in all studied horizons. The O horizons had on average significantly lighter Cu isotope compositions (-0.21‰) than the A horizons (0.13‰) which can either be explained by Cu isotope fractionation during cycling through the plants or deposition of isotopically light Cu from the atmosphere. Oxic weathering without pronounced podzolization in both Cambisols and a weakly developed Podzol (Haplic Podzol 2) caused no significant isotope fractionation in the single profiles, while a slight tendency to lower δ65Cu values with depth was visible in all four profiles. This is the opposite depth distribution of δ65Cu values to that we observed in hydromorphic soils (soils which show indication of redox changes because of the influence of water saturation) in a previous study. In a more pronounced Podzol (Haplic Podzol 1), δ65Cu values and Cu concentrations decreased from Ah to E horizons and increased again deeper in the soil. Humus-rich sections of the Bhs horizon had higher Cu concentrations (2.8μgg-1) and a higher δ65Cu value (-0.18‰) than oxide-rich sections (1.9μgg-1, -0.35‰) suggesting Cu translocation between E and B horizons as organo-Cu complexes. The different depth distributions in oxic weathered and hydromorphic soils and the pronounced vertical differences in δ65Cu values in Haplic Podzol 1 indicate a promising potential of δ65Cu values to improve our knowledge of the fate of Cu during long-term pedogenetic processes.

UR - http://www.scopus.com/inward/record.url?scp=79955469836&partnerID=8YFLogxK

U2 - 10.1016/j.gca.2011.03.005

DO - 10.1016/j.gca.2011.03.005

M3 - Article

AN - SCOPUS:79955469836

VL - 75

SP - 3119

EP - 3134

JO - Geochimica et cosmochimica acta

JF - Geochimica et cosmochimica acta

SN - 0016-7037

IS - 11

ER -