| 1. |
- Lewandowski, Jörg, et al.
(author)
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Is the Hyporheic Zone Relevant beyond the Scientific Community?
- 2019
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In: Water. - : MDPI AG. - 2073-4441. ; 11:11
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Journal article (peer-reviewed)abstract
- Rivers are important ecosystems under continuous anthropogenic stresses. The hyporheic zone is a ubiquitous, reactive interface between the main channel and its surrounding sediments along the river network. We elaborate on the main physical, biological, and biogeochemical drivers and processes within the hyporheic zone that have been studied by multiple scientific disciplines for almost half a century. These previous efforts have shown that the hyporheic zone is a modulator for most metabolic stream processes and serves as a refuge and habitat for a diverse range of aquatic organisms. It also exerts a major control on river water quality by increasing the contact time with reactive environments, which in turn results in retention and transformation of nutrients, trace organic compounds, fine suspended particles, and microplastics, among others. The paper showcases the critical importance of hyporheic zones, both from a scientific and an applied perspective, and their role in ecosystem services to answer the question of the manuscript title. It identifies major research gaps in our understanding of hyporheic processes. In conclusion, we highlight the potential of hyporheic restoration to efficiently manage and reactivate ecosystem functions and services in river corridors.
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| 2. |
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| 3. |
- Mojarrad, Babak Brian
(author)
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Multi-Scale Surface Water-Groundwater Interaction : Implications for GroundwaterDischarge Patterns
- 2021
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Doctoral thesis (other academic/artistic)abstract
- Rivers and aquifers are continuously exchanging water, driven by processes that occur on various temporal and spatial scales, ranging from small streambed features to large geological structures. The interaction between these two components occurs in permeable sediments below the stream channel, called the hyporheic zone. This zone is an important ecotone in which water, energy, and solutes originating from groundwater and stream water mix. The exchange fluxes through the hyporheic zone are controlled by a distribution of hierarchically nested flow cells of different sizes that are generated by a spectrum of spatial scales of the hydraulic head condition. Thus, a multiscale mathematical approach is required to reach a comprehensive understanding of the hyporheic exchange processes. Therefore, this thesis investigates the roles of regional groundwater flow and hyporheic fluxes in a nested flow system within the streambed sediment. Next, the study assesses the importance of regional and local parameters in generalizing the surface water and groundwater interaction. This division of the top-boundary condition in two scale-intervals of the sub-surface flow is arbitrary but facilitates the analytical procedure. The regional groundwater flow field is evaluated using numerical modeling, accounting for the site-specific landscape morphology and geological heterogeneity of a Swedish boreal catchment. An exact spectral solution is applied to the hyporheic flow with account taken to local streambed topography fluctuation. Combinatorial sampling of the modeled flow data and a Monte Carlo simulation are used in a sensitivity analysis to address the uncertainty in hydrostatic and dynamic head contributions to the hyporheic flow field. Then, the impact of the regional groundwater and the hyporheic flows on the nested flow system in aquatic sediment are studied through superpositioning of the flow fields. This is an efficient approach to analyze the nested flow system because the impact on individual scale intervals can be evaluated separately. Additionally, the impacts of streamflow discharge intensity on hyporheic exchange flow fields are investigated through field investigation. In this study, the hyporheic fluxes velocity at the streambed interface were generally at least one order of magnitude higher than groundwater flow velocity. This reflects the domination of hyporheic fluxes at the streambed interface, leading to significant impacts on the discharge of deeper groundwater through the hyporheic zone. Significant effects were found in flow travel time, direction and discharge areas at the streambed sediment. Thus, the upward groundwater flow contracted near the streambed surface and discharged in a fragmented pinhole pattern at the sediment–water interface. The results also indicated that the magnitude of groundwater flow and the heterogeneity of the subsurface sediment (i.e., the depth decaying hydraulic conductivity of streambed sediment) controlled the depth of hyporheic exchange flow in aquatic sediment. Furthermore, the increased stream flow intensity led to a wide range of hyporheic flow residence times in which temperature was used to evaluate stream segments with gaining and losing conditions.
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| 4. |
- Mojarrad, Babak Brian, et al.
(author)
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The Effect of Stream Discharge on Hyporheic Exchange
- 2019
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In: Water. - : MDPI. - 2073-4441. ; 11:7
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Journal article (peer-reviewed)abstract
- Streambed morphology, streamflow dynamics, and the heterogeneity of streambed sediments critically controls the interaction between surface water and groundwater. The present study investigated the impact of different flow regimes on hyporheic exchange in a boreal stream in northern Sweden using experimental and numerical approaches. Low-, base-, and high-flow discharges were simulated by regulating the streamflow upstream in the study area, and temperature was used as the natural tracer to monitor the impact of the different flow discharges on hyporheic exchange fluxes in stretches of stream featuring gaining and losing conditions. A numerical model was developed using geomorphological and hydrological properties of the stream and was then used to perform a detailed analysis of the subsurface water flow. Additionally, the impact of heterogeneity in sediment permeability on hyporheic exchange fluxes was investigated. Both the experimental and modelling results show that temporally increasing flow resulted in a larger (deeper) extent of the hyporheic zone as well as longer hyporheic flow residence times. However, the result of the numerical analysis is strongly controlled by heterogeneity in sediment permeability. In particular, for homogeneous sediments, the fragmentation of upwelling length substantially varies with streamflow dynamics due to the contribution of deeper fluxes.
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| 5. |
- Morén, Ida, et al.
(author)
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Geographic and hydromorphologic controls on interactions between hyporheic flow and discharging deep groundwater
- 2023
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In: Hydrogeology Journal. - : Springer Nature. - 1431-2174 .- 1435-0157. ; 31:3, s. 537-555
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Journal article (peer-reviewed)abstract
- Hyporheic exchange flow (HEF) at the streambed–water interface (SWI) has been shown to impact the pattern and rate of discharging groundwater flow (GWF) and the consequential transport of heat, solutes and contaminants from the subsurface into streams. However, the control of geographic and hydromorphological catchment characteristics on GWF–HEF interactions is still not fully understood. Here, the spatial variability in flow characteristics in discharge zones was investigated and averaged over three spatial scales in five geographically different catchments in Sweden. Specifically, the deep GWF discharge velocity at the SWI was estimated using steady-state numerical models, accounting for the real multiscale topography and heterogeneous geology, while an analytical model, based on power spectral analysis of the streambed topography and statistical assessments of the stream hydraulics, was used to estimate the HEF. The modeling resulted in large variability in deep GWF and HEF velocities, both within and between catchments, and a regression analysis was performed to explain this observed variability by using a set of independent variables representing catchment topography and geology as well as local stream hydromorphology. Moreover, the HEF velocity was approximately two orders of magnitude larger than the deep GWF velocity in most of the investigated stream reaches, indicating significant potential to accelerate the deep GWF velocity and reduce the discharge areas. The greatest impact occurred in catchments with low average slope and in reaches close to the catchment outlet, where the deep GWF discharge velocity was generally low.
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| 7. |
- Wörman, Anders, et al.
(author)
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Fragmentation of the Hyporheic Zone Due to Regional Groundwater Circulation
- 2019
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In: Water resources research. - : American Geophysical Union (AGU). - 0043-1397 .- 1944-7973. ; 55:2, s. 1-21
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Journal article (peer-reviewed)abstract
- By use of numerical modeling and field observations, this work quantified the effects of catchment-scale upwelling groundwater on the hyporheic (below stream) fluxes over a wide range of spatial scales. A groundwater flow model was developed that specifically accounted for the hydrostatic and dynamic head fluctuations induced by the streambed topography. Although the magnitudes and relative importance of these streambed-induced fluxes were found to be highly sensitive to site-specific hydromorphological properties, we showed that streambed topographic structures exert a predominant control on the magnitude of hyporheic exchange fluxes in a Swedish boreal catchment. The magnitude of the exchange intensity evaluated at the streambed interface was found to be dominated by the streambed-induced hydraulic head across stream order. However, the catchment-scale groundwater flow field substantially affected the distribution of groundwater discharge points and thus decreased the fragmentation of the hyporheic zone, specifically by shifting the cumulative density function toward larger areas of coherent upwelling at the streambed interface. This work highlights the spectrum of spatial scales affecting the surface water-groundwater exchange patterns and resolves the roles of key mechanisms in controlling the fragmentation of the hyporheic zone.
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| 8. |
- Wörman, Anders, et al.
(author)
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Parameterizing water fluxes in the geosphere-biosphere interface zone : For use in biosphere modelling as part of the long-term safety assessment
- 2019
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In: International High-Level Radioactive Waste Management 2019, IHLRWM 2019. - : American Nuclear Society. ; , s. 554-558
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Conference paper (peer-reviewed)abstract
- The post-closure safety assessment of the disposal system for high-level nuclear waste should reflect a sufficient understanding of the natural environment surrounding the engineered barriers and future effects of releases of contaminants on human health and the environment. A critical part of radiological models for the biosphere is due to the transport of deep groundwater and subsequent mixing with surface waters when it emerges instreams and wetlands. These processes are highly influenced by the so-called hyporheic flow; the small-scale flow field in the sediments below the stream caused by local pressure gradients at the streambed interface, which contributes to a fragmentation of the upwelling groundwater. The present work addresses the effects of catchment-scale upwelling groundwater on the hyporheic fluxes over a wide range of spatial scales in boreal, glacial landscapes. In such landscapes, the groundwater surface generally follows the topography and soil layers are relatively thin. A model framework was developed to account for both the effects of the regional (groundwater) and locally (streambed) induced flow fields on the hyporheic exchange, specifically accounting for the hydrostatic and dynamic head fluctuations induced by the streambed topography. We show that the hyporheic flow field substantially affected the distribution of deep groundwater discharge points in streams and thus increased the fragmentation of the upwelling, here defined as the size of coherent up- or downwelling areas at the streambed interface. Due to the inverse relationship between the rate coefficient and the groundwater discharge areas, this fragmentation implies a considerable increase in both the flow velocities and rate coefficients through the upper part of the GBI, which are crucial components in dose assessments. Furthermore, the groundwater-surface water interactions were studied in several sub-watersheds to provide a basis for understanding the importance of different topographic and geographic factors and for statistical derivation of general relationships for mass transfer rate coefficients to be used to parameterize water fluxes in radiological dose models for the biosphere. It was found that site specific conditions were difficult to generalize in the form of proxy factors with high confidence, but the most essential factors were found to be stream-order, landscape slope, thickness of Quaternary deposits and indices representing the fractal nature of the landscape topography.
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