Saturation, Reduction, and the Formation of Iron–Manganese Concretions in the Jackson‐Frazier Wetland, Oregon

Abstract

redoximorphic features is important for a clear understanding of reductimorphic processes. The Jackson-Frazier wetland is a rare, relatively undisturbed wet-The Jackson-Frazier wetland is a rare, relatively unland in the Willamette Valley of Oregon that experiences repetitive disturbed wetland in the Willamette Valley of Oregon annual flooding and drying cycles. Redoximorphic features formed that experiences repetitive annual flooding and drying by these wetting and drying cycles have not been calibrated with cycles and serves as a model for natural wetland condisaturation and reduction. Long-term measurements of soil saturation and soil redox potential (E H ) were combined with measurements tions in the area. The development of hydric soils in of Fe and Mn concentrations to understand the formation of these the wetland is driven by the annual flooding, prolonged redoximorphic features in the wetland soils. The Jackson-Frazier wetperiods of soil saturation, abundant organic carbon, and land is underlain by three stratigraphic units that control its hydrology: mild temperatures that facilitate reductive dissolution Holocene alluvium (A and Bss horizons), Malpass clay (2Bt horizon), and segregation of Fe and Mn into redoximorphic conand Irish Bend silts (3BC horizon). All three units are saturated for centrations and/or depletions (Somera, 1967; Cogger up to 9 mo each year, leading to E H values that fall below the Fe reand Kennedy, 1992; Lovely, 1993; Miller et al., 1993; Veduction threshold. Extractable Fe and Mn in nodules, concretions, praskas, 1994). Three distinct stratigraphic units within and soft masses document substantial depletions from the matrix soil the Jackson-Frazier wetland all contain Fe-Mn concenin all three units. In the 3BC, diffuse halos of Fe accumulation and trations in the form of macroscopic concretions and matrix chromas from two to four indicate a source of Fe that can be nodules (Stewart, 1997). Similar concentrations were reduced, translocated, and concentrated in nodular form. In the Bss identified as early as 1940 by Drosdoff and Nikiforoff and 3BC horizons, soft masses surrounding concentrations and higher ratios of oxalate to dithionite-citrate-bicarbonate Fe (Fe Ox /Fe DCB ) in the (1940), and more recent work by Somera (1967) and larger concentrations suggest that nodules and concretions are cur-Seter and Baham (1994) has shown that the greatest rently forming by accretion of Fe. In the 2Bt, virtually all of the Fe amount of nodules occur in the wettest (poorly drained) and Mn is gone from the matrix, and concretion boundaries are sharp.

Using ancient and recent soil properties to design a conceptual hydrological response model

“…Low chroma colours are associated with seasonal saturation while high chroma colours are an indication of minimal saturation (He et al, 2003;Ticehurst et al, 2007;Van Huyssteen et al, 2005;Van Tol et al, 2011). The Fe and Mn concretion contents are the highest in horizons with fluctuating water tables rather than in horizons that are more permanently saturated (D'amore et al, 2004;Le Roux, 1996). Hydrochemistry of Fe is highly dependent of wetland coverage and is negatively correlated with peak flow (Björkvald et al, 2008) as Fe is reduced in wetland soils (Van Huyssteen et al, 2005), while peak flow is commonly associated with overland flow (Björkvald et al, 2008).…”

Geochemistry of Alluvial Soils Composed of Metal-Enriched Sediments, Main Stem of the Coeur d'Alene River, Idaho

“…Only limited substitutioti of Mn iti Fe oxides such as goethite has been documented (Schwertmann, 1984). Hypothetically, cycling of these oxide minerals would begin in the spring as the saturated soils began to warm sufficiently to promote biological activity (D'Amore et al, 2004;Vepraskas, 1994). As Eh decreased, the Mn oxides would be dissolved first, followed by Fe oxides.…”

Evaluation of Continuous In Situ Monitoring of Soil Changes with Varying Flooding Regimes

“…Whereas redox potentials in the control channels were relatively constant over the course of the experimental period, with manual monitoring we detected a decline in redox potential during a time of heavy rainfall. Austin andHuddleston (1999) andD'Amore et al (2004) both described a rapid decline in redox potentials with saturation and a subsequent rise in redox potentials with desaturation and reaeration of the soil. In addition, D'Amore, Stewart, and Huddleston (2004) and Mansfeldt (2003) indicated that lower redox potentials were associated with longer periods of saturation.…”

“…Austin andHuddleston (1999) andD'Amore et al (2004) both described a rapid decline in redox potentials with saturation and a subsequent rise in redox potentials with desaturation and reaeration of the soil. In addition, D'Amore, Stewart, and Huddleston (2004) and Mansfeldt (2003) indicated that lower redox potentials were associated with longer periods of saturation. Similarly, a decline in redox potential with inundation and a rise in redox potentials with the dry-down of the channels were observed in this study.…”

“…Microsite variability may account for some of the differences between automated and manual redox potential readings (Patrick, Gambrell, and Faulkner 1996;Austin and Huddleson 1999;Vepraskas andFaulkner 2001, Eshel andBanin 2002;Mansfeldt 2003;D'Amore, Stewart, and Huddleston 2004). For example, placement of an electrode near organic matter that is actively undergoing microbial oxidation will result in observation of lower redox potentials (Vepraskas and Faulkner 2001).…”