The convenient fiction of steady-state soil thickness

Phillips, Jonathan D.

doi:10.1016/j.geoderma.2010.03.008

Cited by 74 publications

(49 citation statements)

References 80 publications

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“…Likewise, the assumption of a steady-state may also be problematic for many conditions (McFadden, 2013;Phillips, 2010).…”

Section: Discussionmentioning

confidence: 99%

“…Dixon et al, 2009;Heimsath, 2006), but the aggrading or degrading phases usually cannot be measured. Steady-state regolith or soil thickness, whereby surface removals approximately balance the production of new soil by bedrock weathering, is a common assumption of most models of hillslope and landscape evolution (Phillips, 2010). According to Phillips (2010), the assumption of steady-state conditions for soil, regolith, or weathering profile development may lead to unrealistic representations of the dynamics of pedogenesis and weathering profile evolution.…”

Section: Techniques For the Determination Of Soil Formation Ratesmentioning

confidence: 99%

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Soil formation rates on silicate parent material in alpine environments: Different approaches–different results?

2014

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High-mountain soils develop in particularly sensitive environments. Consequently, deciphering and predicting what drives the rates of soil formation in such environments are a major challenge. In terms of soil production or formation from chemical weathering, the predominating perception for highmountain soils and cold environments is often that the chemical weathering 'portion' of soil development is temperature-inhibited, often to the point of non-occurrence. Several concepts exist to determine longterm rates of soil formation and development. We present three different approaches: (1) quantification of soil formation from minimally eroded soils of known age using chronosequences (known surface age and soil thickness -SAST), (2) determination of soil residence times (SRT) and production rates through chemical weathering using (un)stable isotopes (e.g. 230Th/234U activity ratios), and (3) a steady state approach using cosmogenic isotopes (e.g. 10Be). For each method, data from different climate zones, and particularly from high-mountains (alpine environment), are compared. The SAST and steady state approach give quite similar results for alpine environments (European Alps and the Wind River Range (Rocky Mountains, USA)). Using the SRT approach, soil formation rates in mountain areas (but having a temperate climate) do not differ greatly from the SAST and steady state approaches. Independent of the chosen approach, the results seem moderately comparable. Soil formation rates in high-mountain areas (alpine climate) range from very low to extremely high values and show a clear decreasing tendency with time. Very young soils have up to 3-4 orders of magnitude higher rates of development than old soils (105 to 106 yr). This apparently is a result of kinetic limits on weathering in regions having young surfaces and supply limits to weathering on old surfaces. Due to the requirement for chemical weathering to occur, soil production rates cannot be infinitely high. Consequently, a speed limit must exist. In the literature, this limit has been set at about 320 to 450 t/km2/a. Our results from the SAST approach show, however, that in alpine areas soil formation easily reaches rates of up to 800-2000 t/km2/a. These data are consistent with previous studies in mountain regions demonstrating that particularly young soils intensively weather, even under continuous seasonal snowpack and, thus, that the concept of 'temperature-controlled' soil development (soil-forming intervals) in alpine regions must be reconsidered. High-mountain soils develop in particularly sensitive environments. Consequently, deciphering and predicting what drives the rates of soil formation in such environments are a major challenge. In terms of soil production or formation from chemical weathering, the predominating perception for high-mountain soils and cold environments is often that the chemical weathering 'portion' of soil development is temperature-inhibited, often to the point of non-occurrence. Several concepts exist to determine long...

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“…Likewise, the assumption of a steady-state may also be problematic for many conditions (McFadden, 2013;Phillips, 2010).…”

Section: Discussionmentioning

confidence: 99%

Section: Techniques For the Determination Of Soil Formation Ratesmentioning

confidence: 99%

Soil formation rates on silicate parent material in alpine environments: Different approaches–different results?

2014

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“…In others, soils can develop or degrade, sometimes disappearing altogether ('regolith stripping; ' Phillips 2005) and at other times involving biological activity and weathering profiles to 100 m depth (Stone and Comerford 1994). Phillips (2010) sees the concept of steady-state soil thickness (and presumably composition) as 'a convenient fiction,' i.e. not true, but occasionally useful.…”

Section: Evidence For Continental Dsi Retention From River Geochemistrymentioning

confidence: 99%

Lack of steady-state in the global biogeochemical Si cycle: emerging evidence from lake Si sequestration

et al. 2014

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Weathering of silicate minerals releases dissolved silicate (DSi) to the soil-vegetation system. Accumulation and recycling of this DSi by terrestrial ecosystems creates a pool of reactive Si on the continents that buffers DSi export to the ocean. Human perturbations to the functioning of the buffer have been a recent research focus, yet a common assumption is that the continental Si cycle is at steadystate. However, we have no good idea of the timescales of ecosystem Si pool equilibration with their environments. A review of modelling and geochemical considerations suggests the modern continental Si cycle is in fact characterised in the longterm by an active accumulation of reactive Si, at least partially attributable to lakes and reservoirs. These lentic systems accumulate Si via biological conversion of DSi to biogenic silica (BSi). An analysis of new and published data for nearly 700 systems is presented to assess their contribution to the accumulating continental pool. Surface sediment BSi concentrations (n = 692) vary between zero and [60 % SiO 2 by weight, apparently independently of lake size, location or water chemistry. Using sediment core BSi accumulation rates (n = 109), still no relationships are found with lake or catchment parameters. However, issues associated with single-core accumulation rates should in any case preclude their use in elemental accumulation calculations. Based on lake/reservoir mass-balances (n = 34), our best global-scale estimate of combined lake and reservoir Si retention is 1.53 TMol year -1 , or 21-27 % of river DSi export. Again, no scalable relationships are apparent, suggesting Si retention is a complex process that varies from catchment to catchment. The lake Si sink has implications for estimation of weathering flux generation from river chemistry. The size of the total continental Si pool is poorly constrained, as is its accumulation rate, but lakes clearly contribute substantially. A corollary to this emerging understanding is that the flux and isotopic composition of DSi delivered to the ocean has likely varied over time, partly mediated by a fluctuating continental pool, including in lakes.

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“…If the theory of steady-state thickness holds true, this implies that within an area of constant or minimally variable climate and geology, thickness should be closely related to topography, and soil taxonomical units should be formed in homogeneous large patches closely related to major topographical forms. Even now, "Gilbert's humped soil production function" has supporters (see Small et al, 1999;Anderson 2002) as well as critics, and its validity is much discussed (Gabet and Mudd, 2010;Phillips, 2010). Carson and Kirkby (1972) concluded that "Gilbert's steady-state soils" are actually metastable and the model does not operate at the landscape scale.…”

Section: P šAmonil Et Al: Disturbances Can Control Fine-scale Pedodmentioning

confidence: 99%

Disturbances can control fine-scale pedodiversity in old-growth forests: is the soil evolution theory disturbed as well?

et al. 2014

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Abstract. Biota–soil interactions in natural ecosystems are the subject of considerable research. Our hypothesis is that individual trees play a significant role through biomechanical and biochemical disturbances affecting soil formation in temperate forests, resulting in a complex spatial pattern of disturbance regimes and a close relationship between disturbance histories and soil units. In Žofínský Prales (Czech Republic) – the fourth oldest, continuously protected reserve in Europe and the first site of global research network SIGEO (Smithsonian Institution Global Earth Observatories) in continental Europe – we compared extensive dendrochronological, soil and pit–mound microtopography data both temporally and spatially from an area of anthropogenically unaffected 42 ha collected from 2008–2012. These data sets differ in terms of information complexity and length of memory: tree cores contain complex information about the disturbance history of the past 350 years, footprints of disturbances from the uprooting of a specific tree can persist 1700 years, and soils represent an extensive composite phenotype that has been developing for at least the entire postglacial period (10 500 years). On average, 6.18–13.41% of the canopy on individual soil units was disturbed per decade. Even though the "backbone" of key events in the development of the forest ecosystem remained the same (e.g. the 1870s, 1880s and 1980s), the internal structure of disturbance history often differed among soil units; the most exceptional were Gleysols and Histosols, where important feedback from soil to trees was expected. However, the characteristics of treethrow dynamics as well as the frequencies of stronger releases in core series also significantly differed along a gradient of terrestrial soil weathering and leaching (Haplic Cambisols – Dystric Cambisols – Entic Podzols – Albic Podzols). These results suggest the existence of several disturbance regimes within the forest, controlling fine-scale pedodiversity.

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The convenient fiction of steady-state soil thickness

Cited by 74 publications

References 80 publications

Soil formation rates on silicate parent material in alpine environments: Different approaches–different results?

Soil formation rates on silicate parent material in alpine environments: Different approaches–different results?

Lack of steady-state in the global biogeochemical Si cycle: emerging evidence from lake Si sequestration

Disturbances can control fine-scale pedodiversity in old-growth forests: is the soil evolution theory disturbed as well?

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