Scale effect on the time dependence of mineral dissolution rates in physically heterogeneous porous media

Jung, Heewon; Navarre‐Sitchler, Alexis

doi:10.1016/j.gca.2018.05.009

Cited by 33 publications

(18 citation statements)

References 40 publications

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“…For example, the value of reaction rate k used in the base case may be substantially larger than that required to reproduce hillslope‐scale processes. Recent work (Jung and Navarre‐sitchler, , ) has demonstrated that fine‐scale heterogeneity in permeability can have significant effects on apparent values of effective weathering reaction rates k , perhaps accounting for well‐documented reduction in reaction rates over time. Weathering proceeds first along fast flow paths where the small effective porosity means weathering products can be rapidly removed by advection.…”

Section: Discussionmentioning

confidence: 99%

A low‐dimensional model of bedrock weathering and lateral flow coevolution in hillslopes: 2. Controls on weathering and permeability profiles, drainage hydraulics, and solute export pathways

Harman

Cosans

2019

Hydrological Processes

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The advance of a chemical weathering front into the bedrock of a hillslope is often limited by the rate weathering products that can be carried away, maintaining chemical disequilibrium.If the weathering front is within the saturated zone, groundwater flow downslope may affect the rate of transport and weathering-however, weathering also modifies the rock permeability and the subsurface potential gradient that drives lateral groundwater flow. This feedback may help explain why there tends to be neither ''runaway weathering'' to great depth nor exposed bedrock covering much of the earth and may provide a mechanism for weathering front advance to keep pace with incision of adjacent streams into bedrock. This is the second of a two-part paper exploring the coevolution of bedrock weathering and lateral flow in hillslopes using a simple low-dimensional model based on hydraulic groundwater theory. Here, we show how a simplified kinetic model of 1-D rock weathering can be extended to consider lateral flow in a 2-D hillslope. Exact and approximate analytical solutions for the location and thickness of weathering within the hillslope are obtained for a number of cases. A location for the weathering front can be found such that lateral flow is able to export weathering products at the rate required to keep pace with stream incision at steady state. Three pathways of solute export are identified: ''diffusing up,'' where solutes diffuse up and away from the weathering front into the laterally flowing aquifer; ''draining down,'' where solutes are advected primarily downward into the unweathered bedrock; and ''draining along,'' where solutes travel laterally within the weathering zone. For each pathway, a different subsurface topography and overall relief of unweathered bedrock within the hillslope is needed to remove solutes at steady state. The relief each pathway requires depends on the rate of stream incision raised to a different power, such that at a given incision rate, one pathway requires minimal relief and, therefore, likely determines the steady-state hillslope profile.

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Section: Discussionmentioning

confidence: 99%

A low‐dimensional model of bedrock weathering and lateral flow coevolution in hillslopes: 2. Controls on weathering and permeability profiles, drainage hydraulics, and solute export pathways

Harman

Cosans

2019

Hydrological Processes

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“…It is likely that heterogeneity in hydraulic conductivity has important effects on effective weathering rates at the hillslope scale (see e.g., Jung and Navarre‐sitchler, , ), which may in turn have important implications for the internal organization of weathering and flow paths in hillslopes. However, it may be useful to consider those effects in the context of the overall hillslope‐scale concepts being developed here.…”

Section: Discussionmentioning

confidence: 99%

A low‐dimensional model of bedrock weathering and lateral flow coevolution in hillslopes: 1. Hydraulic theory of reactive transport

Harman

Kim

2019

Hydrological Processes

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This is the first of a two-part paper exploring the coevolution of bedrock weathering and lateral flow in hillslopes using a simple low-dimensional model based on hydraulic groundwater theory (also known as Dupuit or Boussinesq theory). Here, we examine the effect of lateral flow on the downward fluxes of water and solutes through perched groundwater at steady state. We derive analytical expressions describing the decline in the downward flux rate with depth. Using these, we obtain analytical expressions for water age in a number of cases. The results show that when the permeability field is homogeneous, the spatial structure of water age depends qualitatively on a single dimensionless number, Hi. This number captures the relative contributions to the lateral hydraulic potential gradient of the relief of the lower-most impermeable boundary (which may be below the weathering front within permeable or incipiently weathered bedrock) and the water table. A ''scaled lateral symmetry'' exists when Hi is low: age varies primarily in the vertical dimension, and variations in the horizontal dimension x almost disappear when the vertical dimension z is expressed as a fraction z∕H(x) of the laterally flowing system thickness H(x). Taking advantage of this symmetry, we show how the lateral dimension of the advection-diffusion-reaction equation can be collapsed, yielding a 1-D vertical equation in which the advective flux downward declines with depth. The equation holds even when the permeability field is not homogeneous, as long as the variations in permeability have the same scaled lateral symmetry structure. This new 1-D approximation is used in the accompanying paper to extend chemical weathering models derived for 1-D columns to hillslope domains.

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“…This study aims to investigate the role of chemical heterogeneity on reactive transport in porous media and to provide a high-resolution dataset, obtained under well-controlled conditions, which can be used as a benchmark for validation of reactive transport simulators. The latter are fundamental tools to understand complex geochemical reactions in subsurface porous media and for the quantitative upscaling of important biogeochemical processes such as mineral precipitation and dissolution in field scale reactive transport scenarios (e.g., Jung and Navarre-Sitchler, 2018;Wen and Li, 2018). We performed a detailed investigation of pyrite oxidation in saturated porous media by carrying out laboratory experiments in different setups including batch, 1-D column, and 2-D flow-through systems.…”

Section: Accepted Manuscriptmentioning

confidence: 99%

Reactive fronts in chemically heterogeneous porous media: Experimental and modeling investigation of pyrite oxidation

Battistel

Muniruzzaman

Onses

et al. 2019

Applied Geochemistry

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Scale effect on the time dependence of mineral dissolution rates in physically heterogeneous porous media

Cited by 33 publications

References 40 publications

A low‐dimensional model of bedrock weathering and lateral flow coevolution in hillslopes: 2. Controls on weathering and permeability profiles, drainage hydraulics, and solute export pathways

A low‐dimensional model of bedrock weathering and lateral flow coevolution in hillslopes: 2. Controls on weathering and permeability profiles, drainage hydraulics, and solute export pathways

A low‐dimensional model of bedrock weathering and lateral flow coevolution in hillslopes: 1. Hydraulic theory of reactive transport

Reactive fronts in chemically heterogeneous porous media: Experimental and modeling investigation of pyrite oxidation

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