Exposure-time based modeling of nonlinear reactive transport in porous media subject to physical and geochemical heterogeneity

Sanz-Prat, Alicia; Lu, Chuanhe; Amos, Richard T.; Finkel, Michael; Blowes, David W.; Cirpka, Olaf A.

doi:10.1016/j.jconhyd.2016.06.002

Cited by 28 publications

(33 citation statements)

References 51 publications

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“…During high discharge conditions, the transport of surface water into the streambed accelerates (Gu et al, ; Malcolm et al, ), hence leading to increased accumulation of solutes deeper into the streambed. Previous research has demonstrated that the nutrient cycling at the river‐aquifer system is strongly controlled by, and often proportional to the residence times of surface water in the HZ (McCallum & Shanafield, ; Wondzell & Swanson, ; Zarnetske et al, , ) and are good indicators of biogeochemical processes (Sanz‐Prat et al, , ). Our results indicate that peak flow event characteristics like magnitude, skewness of peaks, and duration of the event can have a considerable impact on HEF and the mean residence time of water in the HZ.…”

Section: Discussionmentioning

confidence: 99%

Dynamic Hyporheic Zones: Exploring the Role of Peak Flow Events on Bedform‐Induced Hyporheic Exchange

Singh

Gomez‐Velez

et al. 2019

Water Resources Research

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Discharge varies in space and time, driving hyporheic exchange processes in river corridors that affect biogeochemical cycling and ultimately control the dynamics of biogeochemical hot spots and hot moments. Herein, we use a reduced‐order model to conduct the systematic analysis of the interplay between discharge variability (peak flow intensities, duration, and skewness) and streambed topography (bedform aspect ratios and channel slopes) and their role in the flow and transport characteristics of hyporheic zones (HZs). We use a simple and robust conceptualization of single peak flow events for a series of periodic sinusoidal bedforms. Using the model, we estimate the spatial extent of the HZ, the total amount of exchange, and the residence time of water and solutes within the reactive environment and its duration relative to typical time scales for oxygen consumption (i.e., a measure of the denitrification potential). Our results demonstrate that HZ expansion and contraction is controlled by events yet modulated by ambient groundwater flow. Even though the change in hyporheic exchange flux (%) relative to baseflow conditions is invariant for different values of channel slopes, absolute magnitudes varied substantially. Primarily, peak flow events cause more discharge of older water for the higher aspect ratios (i.e., for dunes and ripples) and lower channel slopes. Variations in residence times during peak flow events lead to the development of larger areas of potential nitrification and denitrification in the HZ for longer durations. These findings have potential implications for river management and restoration, particularly the need for (re)consideration of the importance of hyporheic exchange under dynamic flow conditions.

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Section: Discussionmentioning

confidence: 99%

Dynamic Hyporheic Zones: Exploring the Role of Peak Flow Events on Bedform‐Induced Hyporheic Exchange

Singh

Gomez‐Velez

et al. 2019

Water Resources Research

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“…Evidence that residence‐time in phase can serve as a fundamental variable controlling effective kinetics is available from research ranging from diffusive mass transfer in soils [ Rao et al ., ] to colloid filtration [ Dabros and Van de Ven , ] to mineralogical [ Glassley et al ., ] or biochemical [ Sanz‐Prat et al ., ] heterogeneity. The exposure‐time approach [ Ginn , ] provides one avenue toward the development of models to account for these effects.…”

Section: Resultsmentioning

confidence: 99%

“…Both methods are spatially local, testable by batch experiments on mass exchange without advective‐dispersive transport, mathematically relatively straightforward requiring only calculus and differential equations, and linear, allowing for superposition of reaction kinetics in either mobile or immobile phases. Therefore, both serve as a potential upscaling basis for reactive transport [e.g., Ma et al ., ; Soler‐Sagarra et al ., , and references cited therein; Sanz‐Prat et al ., ]. The transport operator is unrelated to the mass exchange models and so can be independently specified as Fickian or non‐Fickian.…”

Section: Resultsmentioning

confidence: 99%

Phase exposure‐dependent exchange

Ginn

Schreyer

Zamani³

2017

Water Resources Research

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Solutes and suspended material often experience delays during exchange between phases one of which may be moving. Consequently transport often exhibits combined effects of advection/dispersion, and delays associated with exchange between phases. Such processes are ubiquitous and include transport in porous/fractured media, watersheds, rivers, forest canopies, urban infrastructure systems, and networks. Upscaling approaches often treat the transport and delay mechanisms together, yielding macroscopic “anomalous transport” models. When interaction with the immobile phase is responsible for the delays, it is not the transport that is anomalous, but the lack of it, due to delays. We model such exchanges with a simple generalization of first‐order kinetics completely independent of transport. Specifically, we introduce a remobilization rate coefficient that depends on the time in immobile phase. Memory‐function formulations of exchange (with or without transport) can be cast in this framework, and can represent practically all time‐nonlocal mass balance models including multirate mass transfer and its equivalent counterparts in the continuous time random walk and time‐fractional advection dispersion formalisms, as well as equilibrium exchange. Our model can address delayed single‐/multievent remobilizations as in delay‐differential equations and periodic remobilizations that may be useful in sediment transport modeling. It is also possible to link delay mechanisms with transport if so desired, or to superpose an additional source of nonlocality through the transport operator. This approach allows for mechanistic characterization of the mass transfer process with measurable parameters, and the full set of processes representable by these generalized kinetics is a new open question.

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“…In preceding studies, we have intensively analyzed under which conditions dispersive mixing can be neglected in reactive transport calculations, which is a prerequisite for transport formulations using travel times, exposure times, or the cumulative relative reactivity (Sanz‐Prat et al , ; Loschko et al , ). From these preceding studies we conclude that restricting physical transport to advection is permissible if the dissolved reactants are introduced over large areas and long times and if they react with components of the aquifer matrix.…”

Section: Introductionmentioning

confidence: 99%

An Electron‐Balance Based Approach to Predict the Decreasing Denitrification Potential of an Aquifer

et al. 2019

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Numerical models for reactive transport can be used to estimate the breakthrough of a contaminant in a pumping well or at other receptors. However, as natural aquifers are highly heterogeneous with unknown spatial details, reactive transport predictions on the aquifer scale require a stochastic framework for uncertainty analysis. The high computational demand of spatially explicit reactive‐transport models hampers such analysis, thus motivating the search for simplified estimation tools. We suggest performing an electron balance between the reactants in the infiltrating solution and in the aquifer matrix to obtain the hypothetical time of dissolved‐reactant breakthrough at a receptor if the reaction with the matrix was instantaneous. This time we denote as the advective breakthrough time for instantaneous reaction (τinst). It depends on the amount of the reaction partner present in the matrix, the mass flux of the dissolved reactant, and the stoichiometry. While the shape of the reactive‐species breakthrough curve depends on various kinetic parameters, the overall timing scales with τinst. We calculate the latter by particle tracking. The effort of computing τinst is so low that stochastic calculations become feasible. We apply the concept to a two‐dimensional test case of aerobic respiration and denitrification. A detailed spatially explicit reactive‐transport model includes microbial dynamics. Scaling the time of local breakthrough curves observed at individual points by τinst decreased the variability of electron‐donor breakthrough curves significantly. We conclude that the advective breakthrough time for instantaneous reaction is efficient in estimating the time over which an aquifer retains its degradation potential.

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Exposure-time based modeling of nonlinear reactive transport in porous media subject to physical and geochemical heterogeneity

Cited by 28 publications

References 51 publications

Dynamic Hyporheic Zones: Exploring the Role of Peak Flow Events on Bedform‐Induced Hyporheic Exchange

Dynamic Hyporheic Zones: Exploring the Role of Peak Flow Events on Bedform‐Induced Hyporheic Exchange

Phase exposure‐dependent exchange

An Electron‐Balance Based Approach to Predict the Decreasing Denitrification Potential of an Aquifer

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