Accounting for the Decreasing Reaction Potential of Heterogeneous Aquifers in a Stochastic Framework of Aquifer‐Scale Reactive Transport

Loschko, Matthias; Wöhling, Thomas; Rudolph, David L.; Cirpka, Olaf A.

doi:10.1002/2017wr021645

Cited by 15 publications

(17 citation statements)

References 78 publications

(101 reference statements)

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“…Water transit times have been increasingly recognized as representing the key connections between water flow and biogeochemical transformation at the catchment scale (Abbott et al, 2016; Hrachowitz et al, 2016; Oehler, Durand, Bordenave, Saadi, & Salmon‐Monviola, 2009; Pinay et al, 2015) and growing evidence has alluded the connection between transit time and nitrate removal (Abbott et al, 2016; Pinay et al, 2015; van der Velde, de Rooij, Rozemeijer, van Geer, & Broers, 2010). The extent of denitrification in heterogeneous aquifers hinges upon the cumulative exposure time, or the total time water has been in contact with nitrate and organic carbon (Loschko, Wöhling, Rudolph, & Cirpka, 2016, 2018; Sanz‐Prat et al, 2016). van der Velde et al (2010) used process‐based modelling and compared Cl as a non‐reactive tracer and NO 3 as a reactive solute.…”

Section: Introductionmentioning

confidence: 99%

Nitrate removal and young stream water fractions at the catchment scale

Benettin

Fovet

2020

Hydrological Processes

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Despite extensive research on nitrate export and removal, nutrient contamination remains a major threat to water bodies worldwide. At the local scale, nitrate removal is governed by biogeochemical conditions that vary in space and time, making integration to entire landscapes critical. Water transit times have often been used to describe solute transport, but the relation between water age and nitrate removal at the catchment scale is still poorly understood. We test the hypothesis that nitrate removal peaks when the fraction of young water in discharge is at its minimum, because nitrate removal occurs mostly under dry conditions where deeper, older groundwater dominates streamflow. We tested this hypothesis by exploring a detailed water quality record from the Kervidy-Naizin catchment (FR) and comparing the dynamics of nitrate to those of a conservative solute (chloride). We find that estimates of nitrate removal are consistent with previous estimates at the site and they show a good (inverse) correlation with the fraction of streamflow that is younger than 2.5 months. However, this young water fraction cannot be used to predict nitrate removal in the winter-spring period, when no removal is observed regardless of streamflow age. While this leads us to reject our hypothesis during the winter period, it also suggests that water age distributions and their correlation with nitrate removal can possibly reveal distinct sources of stream water at different hydrologic regimes and relevant biogeochemical reactions. K E Y W O R D Sagricultural catchment, chloride transport, denitrification, Naizin, nitrate removal, SAS function, water age, young water fraction

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Section: Introductionmentioning

confidence: 99%

Nitrate removal and young stream water fractions at the catchment scale

Benettin

Fovet

2020

Hydrological Processes

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“…These rate laws are derived from theories derived considering only chemistry with with parameters measured typically in well-mixed systems without mass transport limitation. Natural systems are almost never wellmixed (Dentz et al 2011;Loschko et al 2018). In particular, at the watershed scale, hydrological processes, often shaped by both external forcing and internal structure characteristics, influence reactant concentrations, distance to equilibrium, and redox state.…”

Section: Drivers Of Chemical Weathering In Natural Systemsmentioning

confidence: 99%

Watershed Reactive Transport

2019

Reviews in Mineralogy and Geochemistry

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A watershed (also drainage basin, river basin, or catchment) is defined as "… the area that topographically appears to contribute all the water that passes through a specified cross section of a stream (the outlet)" (Dingman 2015). In this chapter, I choose to use the term "watershed" as it is a broadly used one; it should be understood more as small watersheds or catchments. Watersheds are the fundamental units that support river networks, the blood vessels at Earth's surface ultimately draining into the ocean. Watersheds are complex hydro-biogeochemical reactors. They receive water, mass, and energy, transport them to distinct compartments, and transform them into various forms (Fig.1). Hydrological processes partition precipitation to the atmosphere, to the ground surface, and to the subsurface, eventually entering streams. Similarly, plants translate sunlight, water, CO 2 , and nutrients into organic matters (leaves, stems, roots) that fall and deposit in soil. As water routes through soils, it interacts with roots, microbes, and reactive gases (i.e., CO 2 and O 2), releases solutes, and ultimately transporting them out of watersheds. The water flow (discharge) and solute concentrations measured at stream outlets therefore reflect convoluted signature of ecohydrological and biogeochemical coupling. The process interactions and feedbacks are dictated not only by hydroclimatic forcing but also the architecture of watersheds, in particular the above-ground characteristics such as land cover and surface topography, as well as the below-ground structure including soil depth, soil type, geology, and root architecture. The external forcing and internal idiosyncrasies dictate the magnitude, timing, and spatial distribution of water flow and chemistry (Chorover et al. 2011; Brooks et al. 2015), giving rise to non-linear emergent behaviors that are unique of watershed reactive transport processes. Understanding feedbacks and non-linearity requires process-based models that integrate multiple interacting processes. Such integration however does not come easily with traditional boundaries of hydrology versus biogeochemistry relevant disciplines. As will be discussed later in this chapter, relevant model development has been advancing along two separate lines: hydrology models that solve for water storage and fluxes at the watershed scale and beyond (Fatichi et al. 2016), and reactive transport models (RTMs) that center on aqueous and solid concentration changes arising from transport and multi-component biogeochemical reactions typically in "closed" groundwater systems without much interactions with "open" watersheds directly receiving precipitation and sun light (Steefel et al. 2015; Li et al. 2017b). This comes along with a history of hydrologists often trained as physicists studying fluid mechanics, and biogeochemists typically grow up as geologists, chemists, or environmental engineers. There are however considerable needs to reach beyond disciplinary boundaries and integrate the two lines to develop watershed reacti...

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“…In advection-dominated transport, Lagrangian methods based on random walk particle tracking are an attractive alternative and have repeatedly been used to compute travel times in engineering practice and to analyze the impact of the spatial hydraulic conductivity distribution on solute spreading [5,26,44], among others. Particle tracking has also been used to construct streamlines, on which efficient one-dimensional Eulerian transport schemes using a travel time discretization can be applied [2,13,19,28].…”

Section: Introductionmentioning

confidence: 99%

Postprocessing of standard finite element velocity fields for accurate particle tracking applied to groundwater flow

Selzer

Cirpka

2020

Comput Geosci

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Particle tracking is a computationally advantageous and fast scheme to determine travel times and trajectories in subsurface hydrology. Accurate particle tracking requires element-wise mass-conservative, conforming velocity fields. This condition is not fulfilled by the standard linear Galerkin finite element method (FEM). We present a projection, which maps a non-conforming, element-wise given velocity field, computed on triangles and tetrahedra, onto a conforming velocity field in lowest-order Raviart-Thomas-Nédélec ($\mathcal {RTN}_{0}$ R T N 0 ) space, which meets the requirements of accurate particle tracking. The projection is based on minimizing the difference in the hydraulic gradients at the element centroids between the standard FEM solution and the hydraulic gradients consistent with the $\mathcal {RTN}_{0}$ R T N 0 velocity field imposing element-wise mass conservation. Using the conforming velocity field in $\mathcal {RTN}_{0}$ R T N 0 space on triangles and tetrahedra, we present semi-analytical particle tracking methods for divergent and non-divergent flow. We compare the results with those obtained by a cell-centered finite volume method defined for the same elements, and a test case considering hydraulic anisotropy to an analytical solution. The velocity fields and associated particle trajectories based on the projection of the standard FEM solution are comparable to those resulting from the finite volume method, but the projected fields are smoother within zones of piecewise uniform hydraulic conductivity. While the $\mathcal {RTN}_{0}$ R T N 0 -projected standard FEM solution is thus more accurate, the computational costs of the cell-centered finite volume approach are considerably smaller.

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Accounting for the Decreasing Reaction Potential of Heterogeneous Aquifers in a Stochastic Framework of Aquifer‐Scale Reactive Transport

Cited by 15 publications

References 78 publications

Nitrate removal and young stream water fractions at the catchment scale

Nitrate removal and young stream water fractions at the catchment scale

Watershed Reactive Transport

Postprocessing of standard finite element velocity fields for accurate particle tracking applied to groundwater flow

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