The physical significance of soil mottling in a Wisconsin toposequence

Veneman, P. L. M.; Vepraskas, M. J.; Bouma, J.

doi:10.1016/0016-7061(76)90081-1

Cited by 95 publications

(45 citation statements)

References 8 publications

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“…Indeed, several studies have documented Fe reduction in subsoils (0.5 -1.5 m) using 90 morphological observations and geochemical analyses (Veneman et al 1976 with tortuous diffusion paths allows anaerobic processes to occur in close spatial proximity to 98 macropores with near-atmospheric O2 concentrations (Sexstone et al 1985). As a consequence, 99 measurements of O2 in soil macropores (defined here as "bulk O2") do not necessarily reflect the 100 prevalence of anaerobic microsites at small (mm -cm) spatial scales, despite their utility when 101 comparing among sites over larger (m -km) spatial scales Hall and Silver 102 2015; Liptzin and Silver 2015).…”

mentioning

confidence: 99%

Drivers and patterns of iron redox cycling from surface to bedrock in a deep tropical forest soil: a new conceptual model

et al. 2016

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Iron (Fe) reduction and oxidation are important biogeochemical processes coupled to decomposition, nutrient cycling, and mineral weathering, but factors controlling their rates and spatial distribution with depth are poorly understood in terrestrial soils. In aquatic ecosystems, Fe reduction often occurs below a zone of oxic sediments. We tested an alternative conceptual model for Fe redox cycling in terrestrial soils using a deep humid tropical forest soil profile. We hypothesized that Fe reduction in anaerobic microsites scales with depth variation in labile C and Fe availability, as opposed to bulk oxygen (O2). We measured bulk O2 at multiple depths from 0.1 to 5 m quasi-continuously over 18 months and sampled soils from surface to bedrock (~7 m). Median O2 mixing ratios declined from 19.8 ± 1.2 % at 0.25 m to 16.1 ± 1.0 % at 1 m, but did not consistently decrease below 1 m, challenging a recent model of regolith development. Reduced Fe (Fe(II)) extractable in 0.5 M hydrochloric acid was greatest in 0-0.1 m soil and declined precipitously with depth, and did not correspond with visible gleying in B horizons. We observed similar depth trends in potential Fe reduction under anaerobic conditions. Depth trends in Fe(II) also closely mirrored short-term soil respiration and bulk soil C. Labile C stimulated Fe reduction at 0-0.1 m depth, whereas addition of short-range-ordered Fe oxides had no effect. Cultivable Fe-reducing bacterial abundance was four orders of magnitude greater in surface soil (0-0.1 m) than below 1 m. Although cultivable Fe oxidizing bacteria were typically also more abundant in surface soil, addition of labile C and nitrate stimulated Fe oxidizers in deep soil by two orders of magnitude under anaerobic conditions. This implies that infiltration of nitrate (and possibly C) from shallow soil water could potentially promote biotic Fe oxidation, a critical step in bedrock weathering, 7 m below. Together, these data suggest that C, Fe, and nutrient availability increase microbial Fe reduction and oxidation in surface (vs deeper) soil microsites despite high bulk O2, in contrast to the depth segregation of electron accepting processes often observed in aquatic ecosystems. Furthermore, the greatest capacity for Fe redox cycling can occur in A horizons that do not display gleying or mottling. decomposition, nutrient cycling, and mineral weathering, but factors controlling their rates and 21 spatial distribution with depth are poorly understood in terrestrial soils. In aquatic ecosystems, Fe 22 reduction often occurs below a zone of oxic sediments. We tested an alternative conceptual 23 model for Fe redox cycling in terrestrial soils using a deep humid tropical forest soil profile. We 24 hypothesized that Fe reduction in anaerobic microsites scales with depth variation in labile C and 25Fe availability, as opposed to bulk oxygen (O2). We measured bulk O2 at multiple depths from 26 0.1-5 m quasi-continuously over 18 months and sampled soils from surface to bedrock (~7 m). 27Median O2 mixing rati...

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Drivers and patterns of iron redox cycling from surface to bedrock in a deep tropical forest soil: a new conceptual model

et al. 2016

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“…Grey, yellow, red and black mottles occur with decreasing distance from a macropore. The position of either black or grey mottles closest to the macropore, is indicative upon the oxidising or reducing role of the pore, respectively (Veneman et al, 1976;Veprakas & Bouma, 1976).…”

Section: Micromorphological Evidence Of Redox Activity In the Soft Plmentioning

confidence: 99%

Micromorphological evidence of redox activity in the soft plinthic B horizon of a soil of the Bainsvlei form in an arid bioclimate

Roux

Preez

2008

South African Journal of Plant and Soil

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“…There is also a marked correlation between water tables and morphological features such as depth to faint and distinct mottling, matrix hue, value and chroma. Veneman, Vepraskas & Bouma (1976) reported that the occurrence of high chroma colours inside peds and few Mn or Fe cutans or nodules was associated with short periods (one day or less) of water saturation. They also stated that a soil colour chroma of two inside peds, the occurrence of ped ferrans and neoferrans and few Mn cutans or nodules are associated with short periods of saturation not exceeding several days.…”

Section: Introductionmentioning

confidence: 99%

The relationship between subsoil colour and degree of wetness in a suite of soils in the Grabouw district, Western Cape II. Predicting duration of water saturation and evaluation of colour definitions for colour-defined horizons

Huyssteen

Ellis

Lambrechts

1997

South African Journal of Plant and Soil

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Existing colour indices were evaluated to determine their correlation with duration of water saturation, for a hydrosequence in the Grabouw district, Western Cape. Correlation coefficients ranged between 0.31 and 0.63. More simple colour indices were developed. Dry soil colour is a relatively good indicator (r = 0.77) of duration of free water. For this study the equation: Duration of free water = 2.35 x Huedry + 5.79 x Value dry -7.31 Chromadry -27.89 can be used to predict duration of free water in diagnostic red apedal B, yellOW-brown apedal B, yellow E and grey E horizons. It seems that the present colour definitions for diagnostic horizons in the South African soil classification system are sufficiently accurate to distinguish meaningfully between these horizons with respect to duration of free water.Bestaande kleurindekse is geevalueer om die korrelasie daarvan met tydperk van waterversadiging vir 'n hidrologiese katena in die Grabouw distrik, Wes-Kaap te bepaal. Korrelasiekoeffisiente hiervoor wissel tussen 0.31 en 0.63. Meer eenvoudige k/eurindekse is ontwikke/. Droe grondk/eur is 'n re/atief goeie indikator van tydperk van vrywaterversadiging (r= 0.77). Vir hierdie studie kan die vergelyking: Tydperk van vrywater = 2.35 x Skakeringdroog + 5.7~x Waardedroog -7.31 Chromadroog -27.89 gebruik word om tydperk van vrywaterversadiging in diagnostiese rooi apedale B, geell:lruin apedale B, geel E en grys E horisonte te voorspel. Dit blyk dat die huidige kleurdefinisies vir hierdie diagnostiese horisonte in die Suid-Afrikaanse grondklassifikasiesisteem akkuraat genoeg is om sinvo/ tussen hierdie horisonte te onderskei betreffende die verskil in tydperk van vrywaterversadiging.

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The physical significance of soil mottling in a Wisconsin toposequence

Cited by 95 publications

References 8 publications

Drivers and patterns of iron redox cycling from surface to bedrock in a deep tropical forest soil: a new conceptual model

Drivers and patterns of iron redox cycling from surface to bedrock in a deep tropical forest soil: a new conceptual model

Micromorphological evidence of redox activity in the soft plinthic B horizon of a soil of the Bainsvlei form in an arid bioclimate

The relationship between subsoil colour and degree of wetness in a suite of soils in the Grabouw district, Western Cape II. Predicting duration of water saturation and evaluation of colour definitions for colour-defined horizons

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