Oxalate‐fluoride anion exchange in alpine tundra soil: Impact on aluminium transport

• Published in: European Journal of Soil Science
• Main Authors: Evans, Andrew, Jacobs, Michael B.
• Format: Article in Journal/Newspaper
• Language: English
• Published: Wiley 2020
• Subjects: Tundra
• Online Access: http://dx.doi.org/10.1111/ejss.13020; https://api.wiley.com/onlinelibrary/tdm/v1/articles/10.1111%2Fejss.13020; https://onlinelibrary.wiley.com/doi/pdf/10.1111/ejss.13020; https://onlinelibrary.wiley.com/doi/full-xml/10.1111/ejss.13020

Abstract Anion exchange between ubiquitous low‐molecular‐weight organic acids (LMWOA), such as oxalate, and surface‐retained inorganic anions, such as F − , SO 4 2− and OH − , can play a critical role in Al bioavailability and transport in acidic alpine tundra soil. A series of batch equilibration and composite soil column leaching studies were conducted to examine anion exchange reactions between F − , oxalate and OH − , and the impact of increased soil solution F − concentration on Al transport. The addition of either F − or oxalate to soil suspensions resulted in significantly higher solution pH, suggesting F − and oxalate exchange with surface –OH groups. Distinct stages of OH − release were observed for all soil horizons leached with 1.32 × 10 −3 mol l −1 F − , with OH − release decreasing in the order O/A1 ~ A2> > Bw. A similar OH − release pattern was observed in the O/A1 horizon for the 7.81 × 10 −4 mol l −1 oxalate treatment, suggesting that both F − and oxalate may be competing for common exchange sites in the O/A1 horizon. Fluoride displacement by oxalate, in batch equilibration experiments, was observed for both the 2.84 × 10 −4 mol l −1 and 7.81 × 10 −4 mol l −1 oxalate treatment. Individual soil horizons leached with 7.81 × 10 −4 mol l −1 oxalate exhibited increased F − leaching in the order O/A1 > A2 ~ Bw, with pulsed F − movement being observed in the O/A1 horizon. Soil columns eluted with 1.32 × 10 −3 mol l −1 F − exhibited increased Al solubilization and transport, with Al leaching increasing in the order Bw > A2 > O/A1. Sequential leaching of soil columns in the order D. I. H 2 O → 1.32 × 10 −3 mol l −1 F − → D.I. H 2 O → 7.81 × 10 −4 mol l −1 oxalate indicated that previously adsorbed F − was displaced by oxalate. Displacement of F − by oxalate increased in the order O/A1 > A2 > Bw. Hydroxyl displacement by both F − and oxalate may be an important source of acid neutralization in a soil wetting front, affecting Al speciation and transport. Highlights Oxalate and F − ...