Ionic deposition and chemistry of soil solutions in a forested study area in the Chojnów Forest District in the years 2004-2007

Kowalska, Anna; Janek, Magdalena

doi:10.2478/v10025-010-0036-3

Cited by 1 publication

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“…A part of this study also involved the measurement of pore-water chemistry (including cation and anion concentrations, pH, DOC concentrations and soil gas CO 2 concentrations) in the upper two zones to elucidate weathering processes. Although a wide variety of studies have examined temporal changes in DOC with depth in soils (Andrews et al, 2011;Dalva and Moore, 1991;Lorieri and Elsenbeer, 1997;Tolpeshta and Sokolova, 2009), fewer studies have examined other constituents including Al, Fe, Mn and nitrate (Asano et al, 2006;Avila et al, 1995;Dalva and Moore, 1991;Kowalska and Janek, 2009;Lorieri and Elsenbeer, 1997;Tolpeshta and Sokolova, 2009) or the effects of preferential flow paths (Andrews et al, 2011;Asano et al, 2006;Bundt et al, 2001). We use these measurements, as well as measured soil pore-water chemistry, to understand the formation processes of this regolith profile.…”

Section: Introductionmentioning

confidence: 99%

Investigation of a diabase-derived regolith profile from Pennsylvania: Mineralogy, chemistry and Fe isotope fractionation

et al. 2016

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At Earth's surface, bedrock transforms to regolith in a process that has many implications for water storage, soil formation, and nutrient availability to ecosystems. To understand deep regolith formation, we investigate three zones demarcating changes in mineralogy, chemistry and Fe isotopic composition in a 4-m thick regolith profile developed at a ridge top in Pennsylvania (U.S.A.) that is underlain entirely by diabase. Zone 1, at the bottom, is characterized by major element depletion, abrupt oxidation of Fe(II), a rapid decrease in sulfur concentrations and the presence of short-range ordered (SRO) Fe with depleted δ 56 Fe values. We attribute many of the observations at this depth (which we refer to as the lithogenic zone) to the effects of spheroidal weathering, which may be releasing a flux of Fe(II) with low δ 56 Fe values as the mineral pyroxene is weathered. This Fe(II) is oxidized and likely precipitated as isotopically light SRO Fe phases, which then recrystallize with time. Crystallization in Zone 2 is inferred to result in loss of isotopically light SRO Fe. Finally, SRO Fe isotopic compositions become lighter again near the land surface in Zone 3, the zone of most intense biogenic weathering related to exudation of protons and organic acids by plant roots. In this zone, these acids solubilize and remove isotopically light SRO Fe. This pattern of SRO Fe isotopic variability, which has been observed in other deep regolith profiles on spheroidally weathering bedrock, may be explained best by a combination of lithogenic and biogenic processes. The effects of biota reach deeper than the dominantly biogenic zone due to high concentrations of carbon dioxide, trapped in the soil by the low-permeability Bt/BC interface. Dissolution based on modern pore fluids in the upper two meters of regolith is occurring at a rate that is within an order of magnitude of the time-integrated rate of dissolution constrained mineralogically in the upper two meters. This correspondence is consistent with the conclusion that the rate of regolith formation remains roughly constant over time. Constant rates of weathering are expected in zones where erosion rates and rainfall are also constant. In that case, the thickness of the diabase may be considered to be at steady state (i.e., the rate of weathering advance due to deep lithogenic processes is roughly equivalent to the rate of advance at shallow depths due to biogenic processes).

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