| 1. |
- Johansson, H., et al.
(författare)
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Retention of conservative and sorptive solutes in streams - simultaneous tracer experiments
- 2001
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Ingår i: Science of the Total Environment. - 0048-9697 .- 1879-1026. ; 266:03-jan, s. 229-238
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Tidskriftsartikel (refereegranskat)abstract
- The effective transport velocity of solutes in rivers and streams is governed by transient storage in hyporheic zones in which the longitudinal advection velocity is small relative to the main stream flow velocity. Results from a simultaneous tracer experiment using a non-reactive (tritium, (H2O)-H-3) and a sorptive tracer [chromium, Cr-51(III)] have formed the basis of a more accurate interpretation of the retention characteristics of solutes in streams than previously has been possible. By using a simultaneous injection of these two tracers, it was possible to distinguish between their different behaviours. Based on estimations of fluxes, the retained mass of chromium in the storage zones along the 30-km-long study-reach was 76% after 150 h. Independent observations in the bed sediment indicated that the loss of chromium observed in the water was mainly a result of uptake into the bed sediment. To describe the transport in the stream, a model concept including solute sorption kinetics in the bed sediment was proposed. Evaluation of parameters in the model, indicated that the uptake of chromium in the bed sediment is controlled by sorption kinetics.
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| 2. |
- Jonsson, K., et al.
(författare)
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Hyporheic exchange of reactive and conservative solutes in streams - tracer methodology and model interpretation
- 2003
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Ingår i: Journal of Hydrology. - : Elsevier BV. - 0022-1694 .- 1879-2707. ; 278:04-jan, s. 153-171
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Tidskriftsartikel (refereegranskat)abstract
- A transient storage model is evaluated using results from a tracer experiment, where a conservative and a reactive tracer (H-3 and Cr-51(III)) were injected simultaneously and monitored in stream water and bed sediment. About 76% of the chromium was lost from the stream water on the reach 30 km downstream of the injection point directly after the passage of the pulse in the flowing water. The bed sediment hosted the main part of the retained chromium. The time to washout 75% of the maximum solute uptake in the sediment was similar to 85 times longer for chromium than for tritium (i.e. similar to 45 days). It was possible to describe the sediment-water exchange with a diffusive flux formulation that could be evaluated using tritium breakthrough curves in the stream water or the tritium inventory breakthrough curves in the sediment. This experiment revealed further that observations of chromium concentrations in the sediment were essential for the quantifying of sorption properties, as it was not possible to catch accurately the time scale of sorption within the duration of the breakthrough curves in the stream water. There was a clear need for a rate-limited description of the sorption of chromium in the sediment. We found that a first-order kinetic description of the sorption process could acceptably describe the breakthrough curves in both the stream water and the bed sediment.
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| 3. |
- Jonsson, K., et al.
(författare)
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Sorption behavior and long-term retention of reactive solutes in the hyporheic zone of streams
- 2004
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Ingår i: Journal of environmental engineering. - : American Society of Civil Engineers (ASCE). - 0733-9372 .- 1943-7870. ; 130:5, s. 573-584
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Tidskriftsartikel (refereegranskat)abstract
- This paper analyzes the transport of sorbing solutes by extending the advective storage path model developed for longitudinal transport of inert solutes in streams coupled with flow-induced uptake in the hyporheic zone. Independent observations of a conservative (H-3) and a reactive (Cr-51) tracer in both the stream water and the hyporheic zone were used to differentiate between hydraulic and sorption processes. The method of temporal moments was found to be inadequate for parameter determination, whereas fitting versus the entire tracer breakthrough curves with special emphasis on the tail indicates that the proposed model could be used to represent both conservative and reactive transport. Information on the tracer inventory of the conservative tracer in the hyporheic zone was found to be of vital importance to the evaluation of the hydraulic exchange. A model evaluation based on stream water data alone can yield predictions of a wash-out in the hyporheic zone that deviates markedly from the observed wash-out. This prohibits long-term predictions of the wash-out from the hyporheic zone as well as the evaluation of sorption properties. The sorption in the hyporheic zone was found to follow a two-step model, where the first step is instantaneous and the second kinetic. A model with a single-step sorption process could not reproduce the observed breakthrough curves. An evaluation of the relative importance of including sorption kinetics in solute stream transport models is elucidated by means of the analytical expressions for the temporal moments. The omission of the kinetics in the second sorption step in the hyporheic zone will result in relative errors in the moments of second order or higher. The error will increase with decreasing residence time in the hyporheic zone. Especially, long-term predictions of the wash-out from the hyporheic zone require consideration of the rate-limited sorption.
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| 4. |
- Wörman, Anders, et al.
(författare)
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Effect of flow-induced exchange in hyporheic zones on longitudinal transport of solutes in streams and rivers
- 2002
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Ingår i: Water resources research. - : American Geophysical Union (AGU). - 0043-1397 .- 1944-7973. ; 38:1
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Tidskriftsartikel (refereegranskat)abstract
- [1] Temporary storage of solutes in streams is often controlled by flow-induced uptake in hyporheic zones. This phenomenon accounts for the tails that are generally observed following the passage of a solute pulse, and such exchange is particularly important for the transport of reactive substances that can be subject to various biogeochemical processes in the subsurface. Advective pumping, induced by streamflow over an irregular permeable bed, leads to a distribution of pore water flow paths in the streambed and a corresponding distribution of subsurface solute residence times. This paper describes a modeling framework that couples longitudinal solute transport in streams with solute advection along a continuous distribution of hyporheic flow paths. Moment methods are used to calculate the shape of solute breakthrough curves in the stream based on various representations of hypotheic exchange, including both advective pumping and several idealized formulations. Basic hydrodynamic principles are used to derive the distribution of solute residence times due to pumping. The model provides an accurate representation of the breakthrough curves of tritium along a 30 km reach of Sava Brook in Uppland County in Sweden. Both hydrodynamic theory for pumping exchange and pore water samples obtained from the bed during the tracer experiment suggest that the residence time for solutes in the hyporheic zone is characterized by a log normal probability density function. Closed-form solutions of the central temporal moments of solute breakthrough curves in the stream reveal a significant similarity between this new model and existing models of hyporheic exchange, including the Transient Storage Model. The new model is advantageous because its fundamentally derived exchange parameters can be expressed as functions of basic hydrodynamic quantities, which allows the model results to be generalized to conditions beyond those directly observed during tracer experiments. The utility of this approach is demonstrated by using the pumping theory to relate the spatial variation of hyporheic exchange rate along Sava Brook with the local Froude number, hydraulic conductivity and water depth.
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