A Geobiological View of Weathering and Erosion

Brantley, Susan L.; Lebedeva, M. I.; Hausrath, Elisabeth M.

doi:10.1002/9781118280874.ch12

Cited by 19 publications

(15 citation statements)

References 124 publications

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“…Like all models of weathering, reactive transport codes are used to simulate simplified systems. In modeling the weathering of model rocks, for example, we have previously considered either one (Lebedeva et al ., , ; Brantley et al ., ; Bazilevskaya et al ., ; Lebedeva and Brantley, , ) or two weathering fronts (Lebedeva et al ., ; Brantley and Lebedeva, ; Brantley et al ., , ;). In effect, we reduce the complexity of the weathering problem to a model of alteration of four minerals to simulate the reaction of the bases (base oxides) and reductants (reducible metal oxides) in the rocks with a simplified set of acids (CO 2 + H 2 O) and oxidants (O 2 + H 2 O) in the meteoric fluids.…”

Section: Rationale For Our Approachmentioning

confidence: 99%

Exploring an ‘ideal hill': how lithology and transport mechanisms affect the possibility of a steady state during weathering and erosion

Lebedeva

Brantley

2020

Earth Surf Processes Landf

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We present a model of chemical reaction within hills to explore how evolving porosity (and by inference, permeability) affects flow pathways and weathering. The model consists of hydrologic and reactive‐transport equations that describe alteration of ferrous minerals and feldspar. These reactions were chosen because previous work emphasized that oxygen‐ and acid‐driven weathering affects porosity differently in felsic and mafic rocks. A parameter controlling the order of the fronts is presented. In the absence of erosion, the two reaction fronts move at different velocities and the relative depths depend on geochemical conditions and starting composition. In turn, the fronts and associated changes in porosity drastically affect both the vertical and lateral velocities of water flow. For these cases, estimates of weathering advance rates based on simple models that posit unidirectional constant‐velocity advection do not apply. In the model hills, weathering advance rates diminish with time as the Darcy velocities decrease with depth. The system can thus attain a dynamical steady state at any erosion rate where the regolith thickness is constant in time and velocities of both fronts become equal to one another and to the erosion rate. The slower the advection velocities in a system, the faster it attains a steady state. For example, a massive rock with relatively fast‐dissolving minerals such as diabase – where solute transport across the reaction front mainly occurs by diffusion – can reach a steady state more quickly than granitoid rocks in which advection contributes to solute transport. The attainment of a steady state is controlled by coupling between weathering and hydrologic processes that force water to flow horizontally above reaction fronts where permeability changes rapidly with depth and acts as a partial barrier to fluid flow. Published 2020. This article is a U.S. Government work and is in the public domain in the USA.

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Section: Rationale For Our Approachmentioning

confidence: 99%

Exploring an ‘ideal hill': how lithology and transport mechanisms affect the possibility of a steady state during weathering and erosion

Lebedeva

Brantley

2020

Earth Surf Processes Landf

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“…Variation with depth in allocation of distinct photosynthetic compounds may be a strategy for forests possessing deep, well-networked root systems. Organic acid exudation may be an important strategy for deriving mineral nutrition in deep horizons where reactive mineral surface area is greater and geogenic nutrients are relatively more available (Brantley et al, 2012). In contrast, sugar exudation fueling microbially-mediated organic matter decay and microbially-derived carbonic acid may offer more nutrition in shallower horizons, where organic matter concentrations and heterotrophic microbe abundances tend to be greater (Fierer et al, 2007).…”

Section: Well-developed Rooting Systems Pump Photosynthate Deep Into mentioning

confidence: 99%

Loss of deep roots limits biogenic agents of soil development that are only partially restored by decades of forest regeneration

Billings

Hirmas

Sullivan

et al. 2018

Elementa: Science of the Anthropocene

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“…Other long-term studies that relate biogeochemistry to climate have also been used to argue that tree-CZ interactions may be central to our understanding of global change (Berner et al, 2003;Taylor et al, 2009). It is also well known that trees use many mechanisms that modulate CZ processes and development (Amundson, 2004;Brantley et al, 2012). To be specific, trees have the ability to alter bedrock chemically and physically as well as influence the style and pace of transport (Kelly et al, 1998;Gabet et al, 2003;Pawlik et al, 2016).…”

Section: Architectural Layering Of the Critical Zonementioning

confidence: 99%

“…Trees have thus been characterized as engines of weathering and erosion (Gabet and Mudd, 2010;Roering et al, 2010). It is unclear whether trees are more important as hillslope and soil stabilizers or as catalysts of bedrock erosion and soil formation globally (Brantley et al, 2012).…”

Section: Architectural Layering Of the Critical Zonementioning

confidence: 99%

“…As such, a specific focus is on trees -the most successful terrestrial entities transforming solar energy into the chemical energy of biomass. While many researchers have investigated the effect of vegetation on soils and weathering (e.g., Berner et al, 2003;Brantley et al, 2012), the emphasis of CZ science on deeper processes demands a focus on organisms such as trees that impact regolith over greater depths. In this paper, we highlight some puzzles about the nature of trees' effect on the CZ and the CZ's effect on trees.…”

Section: Introductionmentioning

confidence: 99%

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Reviews and syntheses: on the roles trees play in building and plumbing the critical zone

et al. 2017

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Abstract. Trees, the most successful biological power plants on earth, build and plumb the critical zone (CZ) in ways that we do not yet understand. To encourage exploration of the character and implications of interactions between trees and soil in the CZ, we propose nine hypotheses that can be tested at diverse settings. The hypotheses are roughly divided into those about the architecture (building) and those about the water (plumbing) in the CZ, but the two functions are intertwined. Depending upon one's disciplinary background, many of the nine hypotheses listed below may appear obviously true or obviously false. (1) Tree roots can only physically penetrate and biogeochemically comminute the immobile substrate underlying mobile soil where that underlying substrate is fractured or pre-weathered. (2) In settings where the thickness of weathered material, H , is large, trees primarily shape the CZ through biogeochemical reactions within the rooting zone. (3) In forested uplands, the thickness of mobile soil, h, can evolve toward a steady state because of feedbacks related to root disruption and tree throw. (4) In settings where h H and the rates of uplift and erosion are low, the uptake of phosphorus into trees is buffered by the fine-grained fraction of the soil, and the ultimate source of this phosphorus is dust. (5) In settings of limited water availability, trees maintain the highest length density of functional roots at depths where water can be extracted over most of the growing season with the least amount of energy expenditure. (6) Trees grow the majority of their roots in the zone where the most growth-limiting resource is abundant, but they also grow roots at other depths to forage for other resources and to hydraulically redistribute those resources to depths where they can be taken up more efficiently. (7) Trees rely on matrix water in the unsaturated zone that at times may have anPublished by Copernicus Publications on behalf of the European Geosciences Union. 5116 S. L. Brantley et al.: Reviews and syntheses: on the roles trees play in building and plumbing the critical zone isotopic composition distinct from the gravity-drained water that transits from the hillslope to groundwater and streamflow. (8) Mycorrhizal fungi can use matrix water directly, but trees can only use this water by accessing it indirectly through the fungi. (9) Even trees growing well above the valley floor of a catchment can directly affect stream chemistry where changes in permeability near the rooting zone promote intermittent zones of water saturation and downslope flow of water to the stream. By testing these nine hypotheses, we will generate important new cross-disciplinary insights that advance CZ science.

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A Geobiological View of Weathering and Erosion

Cited by 19 publications

References 124 publications

Exploring an ‘ideal hill': how lithology and transport mechanisms affect the possibility of a steady state during weathering and erosion

Exploring an ‘ideal hill': how lithology and transport mechanisms affect the possibility of a steady state during weathering and erosion

Loss of deep roots limits biogenic agents of soil development that are only partially restored by decades of forest regeneration

Reviews and syntheses: on the roles trees play in building and plumbing the critical zone

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