|Maguffin, Scott - Cornell University - New York|
|Abu-ali, Lena - Cornell University - New York|
|Woll, Arthur - Cornell University - New York|
|Smleska, Louisa - Cornell University - New York|
|Reid, Matthew - Cornell University - New York|
Submitted to: International Soil Science Society Conference Proceedings
Publication Type: Abstract Only
Publication Acceptance Date: 12/29/2018
Publication Date: 1/7/2019
Citation: Maguffin, S., Abu-Ali, L., Woll, A., Smleska, L., Rohila, J.S., McClung, A.M., Reid, M.C. 2019. The role of manganese redox dynamics in controlling arsenic mobility in paddy soils. International Soil Science Society Conference Proceedings. Available: https://scisoc.confex.com/scisoc/2019sssa/meetingapp.cgi/Paper/116394.
Technical Abstract: Arsenic (As) mobilization in soil environments is typically considered to be controlled by reductive dissolution of iron (Fe) oxide minerals. This conceptual model overlooks the role of manganese (Mn) oxides in As fate and transport, despite the ubiquity of Mn oxides in soils, the role of Mn oxides as redox buffers, and their well-known ability to oxidize arsenite to arsenate and then act as a sorbent for arsenate. This contribution explores the role of Mn oxides in governing the timing of As release into the soil solution, and seeks to disentangle the effect of Mn oxides as a redox buffer from their role as the host mineral for As release. We present results from synchrotron-based micro X-ray fluorescence (µXRF) analysis of rice paddy soils collected from Arkansas, USA, evaluating As-Fe-Mn co-localization. In the upper 10 cm of the soil column, the Mn/Fe ratio was 0.06 and As hot spots were more strongly correlated with Mn than with Fe. Mn/Fe ratios decreased with depth in the soil column to 0.003 between 24 and 32 cm, with Fe emerging as the dominant spatial correlate of arsenic as depth increases. The role of Mn versus Fe oxide mineral dissolution in controlling As release into the soil solution of an Arkansas paddy soil is evaluated by combining in situ monitoring of soil solution chemistry with measurements of soil physical parameters, including redox potential, via a distributed sensor network. Special attention is paid to As mobility and Fe:Mn redox dynamics during periodic drying and re-wetting of the soil column. Finally, laboratory soil microcosms were prepared from Arkansas paddy soil and amended with synthetic birnessite to yield a range of Mn/Fe ratios, and well-controlled experiments were used to quantify the role of the Mn/Fe ratio in controlling the timing of As release into the soil solution.