Spectroscopic (XANES/XRF) characterization of contaminant manganese cycling in a temperate watershed

• Published in: Biogeochemistry 2014-12, Vol.121 (3), p.505-517
• Main Authors: Herndon, Elizabeth M, Martínez, Carmen E, Brantley, Susan L
• Format: Article
• Language: English
• Subjects: absorption; Animal and plant ecology; Animal, plant and microbial ecology; anthropogenic activities; Anthropogenic factors; atmospheric deposition; atmospheric precipitation; Biogeosciences; Biological and medical sciences; Contaminants; Contamination; Decomposition; Earth and Environmental Science; Earth Sciences; Earth, ocean, space; Ecosystems; Engineering and environment geology. Geothermics; Environmental Chemistry; Exact sciences and technology; fluorescence; Forest soils; Fundamental and applied biological sciences. Psychology; Leaves; Life Sciences; Manganese; Manganese compounds; Mineral soils; Organic matter; Organic soils; Oxidation; Oxides; Plant species; Pollution, environment geology; River systems; rivers; Roots; shale; Shales; Soil depth; Soil pollution; Soils; Spatial distribution; Speciation; spectroscopy; Spectrum analysis; stems; Surficial geology; Synecology; Temperature effects; Terrestrial ecosystems; toxicity; Vegetation; Watersheds; X-radiation; X-ray fluorescence
• ISSN: 0168-2563; 1573-515X
• DOI: 10.1007/s10533-014-0018-7

Many soils around the globe are contaminated with metals due to inputs from anthropogenic activities; however, the long-term processes that retain these metals in soils or flush them into river systems remain unclear. Soils at the Susquehanna/Shale Hills Critical Zone Observatory, a headwater catchment in central Pennsylvania, USA, are enriched in manganese due to past atmospheric deposition from industrial sources. To investigate how Mn is retained in the catchment, we evaluated the spatial distribution and speciation of Mn in the soil–plant system using X-ray fluorescence and X-ray Absorption Near Edge Structure spectroscopies. Weathered soils near the land surface were enriched in both amorphous and crystalline Mn(III/IV)-oxides, presumably derived from biogenic precipitation and atmospheric deposition, respectively. In contrast, mineral soils near the soil–bedrock interface contained Mn(II) in clays and crystalline Mn(III/IV)-oxides that formed as Mn(II) was leached from the parent shale and oxidized. Roots, stems, and foliar tissue were dominated by organic-bound and aqueous Mn(II); however, a small portion of foliar Mn was concentrated as organic-bound Mn(III) in dark spots that denote Mn toxicity. During decomposition of leaves and roots, soluble Mn(II) stored in vegetation was rapidly oxidized and immobilized as mixed-valence Mn-oxides. We propose that considerable uptake of Mn by certain plant species combined with rapid oxidation of Mn during organic matter decomposition contributes to long-term retention in soils and may slow removal of Mn contamination from watersheds.