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Soil Science Society of America Journal Abstract - Soil Physics & Hydrology

Insights into the Formation Process and Environmental Fingerprints of Iron–Manganese Nodules in Subtropical Soils of China

 

This article in SSSAJ

  1. Vol. 79 No. 4, p. 1101-1114
     
    Received: Jan 31, 2015
    Accepted: June 04, 2015
    Published: July 10, 2015


    * Corresponding author(s): lusg@zju.edu.cn
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doi:10.2136/sssaj2015.01.0049
  1. Xiu-Ling Yua,
  2. Ya-Nan Fub and
  3. Philip C. Brookes Sheng-Gao Lu *c
  1. a College of Environmental and Resource Sciences Zhejiang Univ.Hangzhou 310058 China
    b X-ray Imaging and Biomedical Application Beamline Shanghai Synchrotron Radiation Facility Shanghai Institute of Applied Physics Chinese Academy of Sciences Shanghai 201204 China
    c College of Environmental and Resource Sciences Zhejiang Univ. Hangzhou 310058 China

Abstract

In this work, we collected different size Fe–Mn nodules from a Plinthudult in the subtropical region of China and studied their internal structure and the distribution of trace elements by three synchrotron-based X-ray microprobe techniques: X-ray micro-computed tomography (SR-mCT), X-ray micro-fluorescence (μ-XRF), and micro X-ray absorption near edge structures (μ-XANES). The SR-mCT images reveal that the large nodules (2–3, 3–5, and 5–8 mm in diameter) have distinct Fe and Mn concentric ring structure, while the small nodule (1–2 mm) exhibits a homogeneous fabric. The μ-XRF maps show that Mn is concentrated near the nucleus of the nodule, while Fe is more concentrated in the exterior of the nodule. The 1- to 2-mm nodule has significantly higher total porosity than the >2-mm nodules; however, the spatial distribution of pores within the nodules indicates that the >2-mm nodules have smaller >30-μm pores and show more anisotropy in the outer part than in the inner part. The porosity and pore anisotropy of the nodules were considered to affect the size and shape of Fe–Mn nodules in soil. Quantification of the ring structure for the 3- to 5-mm nodule reconstructed the formation process of the nodule, showing that the nodule was formed through two growth stages, with each stage consisting of two and five redox processes. The internal structure of Fe–Mn nodules not only records pedo-environmental changes during the formation process but also provides ample opportunity for the adsorption and sequestration of trace elements from the soil.

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Copyright © 2015. Copyright © by the Soil Science Society of America, Inc.