scholarly journals Solute Transport and Transformation in an Intermittent, Headwater Mountain Stream with Diurnal Discharge Fluctuations

Water ◽  
2019 ◽  
Vol 11 (11) ◽  
pp. 2208 ◽  
Author(s):  
Ward ◽  
Kurz ◽  
Schmadel ◽  
Knapp ◽  
Blaen ◽  
...  
Keyword(s):  
Solute Transport ◽  
Time Variable ◽  
Mountain Stream ◽  
Selection Function ◽  
Transport And Transformation ◽  
Discharge Fluctuations ◽  
Single Discharge ◽  
Reaction Potential ◽  
Stream Control ◽  
Reactive Solutes

Time-variable discharge is known to control both transport and transformation of solutes in the river corridor. Still, few studies consider the interactions of transport and transformation together. Here, we consider how diurnal discharge fluctuations in an intermittent, headwater stream control reach-scale solute transport and transformation as measured with conservative and reactive tracers during a period of no precipitation. One common conceptual model is that extended contact times with hyporheic zones during low discharge conditions allows for increased transformation of reactive solutes. Instead, we found tracer timescales within the reach were related to discharge, described by a single discharge-variable StorAge Selection function. We found that Resazurin to Resorufin (Raz-to-Rru) transformation is static in time, and apparent differences in reactive tracer were due to interactions with different ages of storage, not with time-variable reactivity. Overall we found reactivity was highest in youngest storage locations, with minimal Raz-to-Rru conversion in waters older than about 20 h of storage in our study reach. Therefore, not all storage in the study reach has the same potential biogeochemical function and increasing residence time of solute storage does not necessarily increase reaction potential of that solute, contrary to prevailing expectations.

Changes in discharge affect more surface than subsurface breakdown of organic matter in a mountain stream

2016 ◽  
Vol 67 (12) ◽  
pp. 1826 ◽  
Author(s):  
Libe Solagaistua ◽  
Maite Arroita ◽  
Ibon Aristi ◽  
Aitor Larrañaga ◽  
Arturo Elosegi
Keyword(s):  
Organic Matter ◽  
Water Depth ◽  
Alnus Glutinosa ◽  
Mountain Stream ◽  
Litter Breakdown ◽  
Lotic Ecosystems ◽  
Leaf Litter Breakdown ◽  
Discharge Fluctuations ◽  
Breakdown Rates ◽  
Dry Out

Discharge fluctuations modify water depth and velocity in streams and this can affect leaf litter breakdown, which is an important ecosystem function. Both during droughts, when parts of the surface dry out, and during floods, which scour the benthic surface, macroinvertebrates can seek refuge in the subsurface. Therefore, as an important part of them depend on organic matter, the effects of discharge fluctuations on leaf breakdown might be greater on the surface than in the subsurface of lotic ecosystems. To test this hypothesis, we measured microbial and total breakdown rates of alder (Alnus glutinosa (L.) Gaertner) both on the surface and in the subsurface in two areas of a stream, namely, the permanently wet channel and the parafluvial areas. Reduced discharge dried out only the surface of the parafluvial areas, and thus, breakdown rates were reduced only in this habitat. In contrast, breakdown rates were similar in both habitats of the permanently wet channel, but also in the subsurface of the parafluvial area. The subsurface can mitigate the effects of discharge alterations on the breakdown of organic matter in streams, which might be critical for the productivity of these ecosystems under increased drought frequencies.

The Lagrangian Picture, Part I : Fundamentals of the Lagrangian Approach to Solute Transport

2003 ◽  
Author(s):  
Yoram Rubin
Keyword(s):  
Velocity Field ◽  
Solute Transport ◽  
Complex Geometry ◽  
Concentration Field ◽  
Breakthrough Curves ◽  
Lagrangian Approach ◽  
Travel Times ◽  
Solute Fluxes ◽  
Reactive Solutes ◽  
Solute Particle

This chapter explores the principles of the Lagrangian approach to solute transport, with an emphasis on the dispersive action of the spatial variability of the velocity field. We start by developing the tools for characterizing the displacement of a single, small solute particle that will subsequently be used for characterization of the concentration’s variability and uncertainty, and we continue with a discussion of the stochastic description of solute travel times and fluxes. The principles presented in this chapter will be employed in chapter 10 to derive tools for applications such as macrodispersion coefficients, solute travel time moments, the moments of the solute fluxes and breakthrough curves, and transport of reactive solutes. As has been observed in many field studies and numerical simulations, the motion of solute bodies in geological media is complex, making the geometry of the solute bodies hard to predict. Furthermore, the concentration varies erratically, sometimes by orders of magnitude, over very short distances. The variability of the velocity field plays a significant role in shaping this complex geometry, and makes it impossible to characterize the concentration field deterministically. The alternatives we will pursue include characterizing the concentration through its moments such as the expected value and variance, and other descriptors of transport such as solute fluxes and travel times. This line was pursued in chapter 8 using the Eulerian framework. In this chapter we pursue this line from the Lagrangian perspective. Applications of these concepts are presented in chapter 10. Let us consider the displacement of a marked solute particle over time.

scholarly journals Centrifugal Modeling and Validation of Solute Transport within Unsaturated Zone

Water ◽  
2019 ◽  
Vol 11 (3) ◽  
pp. 610
Author(s):  
Huanhuan Qin
Keyword(s):  
Numerical Modeling ◽  
Numerical Model ◽  
Solute Transport ◽  
Chemical Reactions ◽  
Unsaturated Zone ◽  
Poor Quality ◽  
Physical Processes ◽  
Transport Simulation ◽  
Reactive Solutes

Numerical modeling has been adopted to assess the feasibility of centrifugal simulation of solute transport within the unsaturated zone. A numerical model was developed to study the centrifugal simulation of nonreactive, adsorption, radionuclide, and reactive solutes. The results showed that it is feasible to conduct centrifugal experiments for nonreactive solute transport. For the solute transport containing physical processes or chemical reactions, if the reaction is very rapid or slow, it is feasible to conduct centrifugal experiments. For the solute transport with a product B generated, if the reaction is relatively slow, the centrifugal prediction of solute is suitable. The centrifugal prediction of solute A matches the prototype quite well, but the prediction of B is in poor quality. If B is the focus, it is not feasible to conduct centrifugal experiments; but if B is not important, the centrifugal modeling is suitable. This has significant implications for the centrifugal modeling application to solute transport simulation within the unsaturated zone.

scholarly journals Time‐Variable Transit Time Distributions in the Hyporheic Zone of a Headwater Mountain Stream

2018 ◽  
Vol 54 (3) ◽  
pp. 2017-2036 ◽  
Author(s):  
Adam S. Ward ◽  
Noah M. Schmadel ◽  
Steven M. Wondzell
Keyword(s):  
Transit Time ◽  
Hyporheic Zone ◽  
Time Variable ◽  
Mountain Stream

scholarly journals Saturated and unsaturated salt transport in peat from a constructed fen

SOIL ◽  
2018 ◽  
Vol 4 (1) ◽  
pp. 63-81 ◽  
Author(s):  
Reuven B. Simhayov ◽  
Tobias K. D. Weber ◽  
Jonathan S. Price
Keyword(s):  
Solute Transport ◽  
Pressure Head ◽  
Salt Transport ◽  
Good Prediction ◽  
Adsorption Model ◽  
Transport Models ◽  
Unsaturated Transport ◽  
Reactive Solutes ◽  
Breakthrough Experiments ◽  
Non Equilibrium

Abstract. The underlying processes governing solute transport in peat from an experimentally constructed fen peatland were analyzed by performing saturated and unsaturated solute breakthrough experiments using Na+ and Cl− as reactive and non-reactive solutes, respectively. We tested the performance of three solute transport models, including the classical equilibrium convection–dispersion equation (CDE), a chemical non-equilibrium one-site adsorption model (OSA) and a model to account for physical non-equilibrium, the mobile–immobile (MIM) phases. The selection was motivated by the fact that the applicability of the MIM in peat soils finds a wide consensus. However, results from inverse modeling and a robust statistical evaluation of this peat provide evidence that the measured breakthrough of the conservative tracer, Cl−, could be simulated well using the CDE. Furthermore, the very high Damköhler number (which approaches infinity) suggests instantaneous equilibration between the mobile and immobile phases underscoring the redundancy of the MIM approach for this particular peat. Scanning electron microscope images of the peat show the typical multi-pore size distribution structures have been homogenized sufficiently by decomposition, such that physical non-equilibrium solute transport no longer governs the transport process. This result is corroborated by the fact the soil hydraulic properties were adequately described using a unimodal van Genuchten–Mualem model between saturation and a pressure head of ∼-1000 cm of water. Hence, MIM was not the most suitable choice, and the long tailing of the Na+ breakthrough curve was caused by chemical non-equilibrium. Successful description was possible using the OSA model. To test our results for the unsaturated case, we conducted an unsaturated steady-state evaporation experiment to drive Na+ and Cl− transport. Using the parameterized transport models from the saturated experiments, we could numerically simulate the unsaturated transport using Hydrus-1-D. The simulation showed a good prediction of observed values, confirming the suitability of the parameters for use in a slightly unsaturated transport simulation. The findings improve the understanding of solute redistribution in the constructed fen and imply that MIM should not be automatically assumed for solute transport in peat but rather should be evidence based.

Jacobi Spectral Collocation Method for the Time Variable-Order Fractional Mobile-Immobile Advection-Dispersion Solute Transport Model

2016 ◽  
Vol 6 (3) ◽  
pp. 337-352 ◽  
Author(s):  
Heping Ma ◽  
Yubo Yang
Keyword(s):  
Fractional Derivative ◽  
Solute Transport ◽  
Collocation Method ◽  
Dispersion Model ◽  
Time Variable ◽  
Spectral Collocation Method ◽  
Variable Order ◽  
Spectral Collocation ◽  
Advection Dispersion ◽  
Variable Order Fractional Derivative

AbstractAn efficient high order numerical method is presented to solve the mobile-immobile advection-dispersion model with the Coimbra time variable-order fractional derivative, which is used to simulate solute transport in watershed catchments and rivers. On establishing an efficient recursive algorithm based on the properties of Jacobi polynomials to approximate the Coimbra variable-order fractional derivative operator, we use spectral collocation method with both temporal and spatial discretisation to solve the time variable-order fractional mobile-immobile advection-dispersion model. Numerical examples then illustrate the effectiveness and high order convergence of our approach.

Sign in / Sign up

Export Citation Format

Share Document