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Increased Stability of Organic Matter Sorbed to Ferrihydrite and Goethite on Aging

Soil Sciences, Martin Luther Univ. Halle-Wittenberg, Weidenplan 14, 06108 Halle (Saale), Germany

View larger version (75K): [in this window] [in a new window]   Fig. 1. High-resolution scanning electron microscope images of the ferrihydrite and goethite samples. Images result from detection of secondary electrons (Everhart–Thornley detector/in-lens detector).

View larger version (15K): [in this window] [in a new window]   Fig. 2. Sorption of organic matter to ferrihydrite and goethite. The sorption is given as the relation between organic C (OC) sorbed and the added mass of OC, both normalized to the initial surface area of the minerals. The error bars (standard errors for each three replicate treatments) were smaller than the symbols. Arrows indicate the samples selected for the aging experiment.

View larger version (22K): [in this window] [in a new window]   Fig. 3. Response of micropore (<2 nm) and mesopore (2–50 nm) volumes accessible to N2, CO2 (only micropores), or Hg (only mesopores) to increasing amounts of organic matter (OM) sorbed to ferrihydrite and goethite. The sorbed OM is given as organic C. For the mineral–OM complexes, the pore volumes are normalized to minerals therein. Bars are standard errors; n = 3.

View larger version (15K): [in this window] [in a new window]   Fig. 4. Concentrations of organic C (OC) in ferrihydrite and goethite samples, each with two different initial loadings of sorbed organic matter (OM), during the 1080-d aging. The initial OM loadings are given as OC concentrations in the mineral–OM complexes. Bars are standard errors; n = 3.

View larger version (16K): [in this window] [in a new window]   Fig. 5. Micropore (<2 nm) and mesopore (2–50 nm) volumes accessible to either N2 or CO2 (only micropores) of ferrihydrite and goethite without sorbed organic matter during the 1080-d aging. Bars are standard errors; n = 3. Horizontal lines indicate the initial micropore and mesopore volumes as determined by N2 sorption.

View larger version (30K): [in this window] [in a new window]   Fig. 6. Micropore (<2 nm) and mesopore (2–50 nm) volumes accessible to either N2 or CO2 (only micropores) of ferrihydrite and goethite, each with two different initial loadings of sorbed organic matter (OM), during the 1080-d aging. The initial OM loadings are given as organic C (OC) concentrations in the mineral–OM complexes; the pore volumes are normalized to minerals within the mineral–OM complexes. Bars are standard errors; n = 3. Horizontal lines indicate the initial micropore and mesopore volumes as determined by N2 sorption.

View larger version (16K): [in this window] [in a new window]   Fig. 7. Changes in the portion of sorbed organic C (OC) extractable by 0.1 M NaOH–0.4 M NaF in samples of ferrihydrite and goethite, with two different initial loadings of sorbed organic matter (OM), during the 1080-d aging. The initial OM loadings are given as concentrations of OC in the mineral–OM complexes. Bars are standard errors; n = 3.

View larger version (16K): [in this window] [in a new window]   Fig. 8. Changes in the portion of organic C (OC) removal by 0.1 M NaOCl (pH 7) in samples of ferrihydrite and goethite, each with two initial different loadings of sorbed organic matter (OM), during the 1080-d aging. The initial OM loadings are given as concentrations of OC in the mineral–OM complexes. Bars are standard errors; n = 3.

View larger version (19K): [in this window] [in a new window]   Fig. 9. Relation between the portions of organic C (OC) extractable by 0.1 M NaOH–0.4 M NaF and removable by 0.1 M NaOCl (pH 7) in samples of ferrihydrite and goethite, each with two initial different loadings of sorbed organic matter (OM), during the 1080-d aging. The initial OM loadings are given as concentrations of OC in the mineral–OM complexes. Bars are standard errors; n = 3.