| 1. |
- Betterle, Andrea, et al.
(författare)
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Hyporheic exchange in recirculating flumes under heterogeneous bacterial and morphological conditions
- 2021
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Ingår i: Environmental Earth Sciences. - : Springer Science and Business Media LLC. - 1866-6280 .- 1866-6299. ; 80:6
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Tidskriftsartikel (refereegranskat)abstract
- Hyporheic exchange (HE) contributes to the biogeochemical turnover of macro- and micro-pollutants in rivers. However, the spatiotemporal complexity and variability of HE hinder understanding of its role in the overall functioning of riverine ecosystems. The present study focuses on investigating the role of bacterial diversity and sediment morphology on HE using a multi-flume experiment. A fully coupled surface–subsurface numerical model was used to highlight complex exchange patterns between surface water and the underlying flow field in the sediments. Under the experimental conditions, the surface water flow induced by bedforms has a prominent effect on both local trajectories and residence time distributions of hyporheic flow paths, whereas mean hyporheic retention times are mainly modulated by average surface flowrates. In case of complex bedform morphologies, the numerical model successfully reproduces the HE estimated by means of salt dilution tests. However, the 2D numerical representation of the system falls short in predicting HE in absence of bedforms, highlighting the intrinsic complexity of water circulation patterns in real scenarios. Finally, results show that higher bacterial diversities in the stream sediments can significantly reduce hyporheic fluxes. This work provides a framework to interpret micropollutants turnover in light of the underlying physical transport processes in the hyporheic zone. The study emphasizes the importance of better understanding the tradeoff between physically driven transport processes and bacterial dynamics in the hyporheic zone to quantify the fate of pollutants in streams and rivers.
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| 2. |
- Herzog, Skuyler P., et al.
(författare)
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Combined Surface-Subsurface Stream Restoration Structures Can Optimize Hyporheic Attenuation of Stream Water Contaminants
- 2023
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Ingår i: Environmental Science and Technology. - : American Chemical Society (ACS). - 0013-936X .- 1520-5851. ; 57:10, s. 4153-4166
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Tidskriftsartikel (refereegranskat)abstract
- There is a design-to-function knowledge gap regarding how engineered stream restoration structures can maximize hyporheic contaminant attenuation. Surface and subsurface structures have each been studied in isolation as techniques to restore hyporheic exchange, but surface-subsurface structures have not been investigated or optimized in an integrated manner. Here, we used a numerical model to systematically evaluate key design variables for combined surface (i.e., weir height and length) and subsurface (i.e., upstream and downstream baffle plate spacing) structures. We also compared performance metrics that place differing emphasis on hyporheic flux versus transit times. We found that surface structures tended to create higher flux, shorter transit time flowpaths, whereas subsurface structures promoted moderate-flux, longer transit time flowpaths. Optimal combined surface-subsurface structures could increase fluxes and transit times simultaneously, thus providing conditions for contaminant attenuation that were many times more effective than surface or subsurface structures alone. All performance metrics were improved by the presence of an upstream plate and the absence of a downstream plate. Increasing the weir length tended to improve all metrics, whereas the optimal weir height varied based on metrics. These findings may improve stream restoration by better aligning specific restoration goals with appropriate performance metrics and hyporheic structure designs.
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| 3. |
- Höhne, Anja, et al.
(författare)
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Fate of trace organic compounds in the hyporheic zone : Influence of microbial metabolism
- 2022
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Ingår i: Water Research. - : Elsevier BV. - 0043-1354 .- 1879-2448. ; 224
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Tidskriftsartikel (refereegranskat)abstract
- The hyporheic zone (HZ) is considered a hydrodynamically-driven bioreactor with significant pollutant removal capacities and can therefore not only improve wholestream water quality but also preserve human and ecosystem health. Microbial metabolism is hypothesized to play a key role in pollutant transformation in hyporheic sediments of natural streams. However, previous work investigating the influence of microbial metabolism on pollutant transformation has been predominantly laboratory studies. The key challenge for field studies is the appropriate determination of net microbial metabolism, i.e. information on the actual exposure times to specific microbial processes in the investigated system. The present study uses reactive fluorescent tracers to determine microbial metabolism and ultimately its influence on pollutant transformation, e.g. for trace organic compounds, in hyporheic sediments under natural conditions. In particular, the reactive fluorescent tracers resazurin and its main transformation product resorufin were used to determine the microbial metabolism of facultative or obligate aerobes. The influence of the derived microbial metabolism on the transformation of 20 trace organic compounds, such as pharmaceuticals, including 3 parent–daughter pairs, was examined. The present findings validate laboratory results on the microbially-mediated transformation of the anticonvulsant gabapentin to its main transformation product gabapentin lactam under natural conditions. All other TrOCs investigated did not show a clear link between TrOC reactivity to the microbial metabolism informed by the resazurin–resorufin-system. Overall, the present study not only demonstrates the use of the fluorescent tracer-system resazurin and resorufin for determining microbial metabolism of facultative or obligate aerobes but also generally highlights the potential of reactive fluorescent tracers to disentangle specific reactive properties and ultimately their influence on the fate of pollutants in natural HZs.
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| 4. |
- Jaeger, Anna, et al.
(författare)
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Spatial and Temporal Variability in Attenuation of Polar Organic Micropollutants in an Urban Lowland Stream
- 2019
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Ingår i: Environmental Science and Technology. - : American Chemical Society (ACS). - 0013-936X .- 1520-5851. ; 53:5, s. 2383-2395
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Tidskriftsartikel (refereegranskat)abstract
- Contamination of rivers by trace organic compounds (TrOCs) poses a risk for aquatic ecosystems and drinking water quality. Spatially- and temporally varying environmental conditions are expected to play a major role in controlling in-stream attenuation of TrOCs. This variability is rarely captured by in situ studies of TrOC attenuation. Instead, snap-shots or time-weighted average conditions and corresponding attenuation rates are reported. The present work sought to investigate this variability and factors controlling it by analysis of 24 TrOCs over a 4.7 km reach of the River Erpe (Berlin, Germany). The factors investigated included sunlight and water temperature as well as the presence of macrophytes. Attenuation rate constants in 48 consecutive hourly water parcels were tracked along two contiguous river sections of different characteristics. Section 1 was less shaded and more densely covered with submerged macrophytes compared to section 2. The sampling campaign was repeated after macrophyte removal from section 1. The findings show, that section 1 generally provided more favorable conditions for both photo- and biodegradation. Macrophyte removal enhanced photolysis of some compounds (e.g., hydrochlorothiazide and diclofenac) while reducing the biodegradation of metoprolol. The transformation products metoprolol acid and valsartan acid were formed along the reach under all conditions.
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| 5. |
- Jaeger, Anna, et al.
(författare)
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Time Series of Electrical Conductivity Fluctuations Give Insights Into Long-Term Solute Transport Dynamics of an Urban Stream
- 2023
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Ingår i: Water resources research. - : American Geophysical Union (AGU). - 0043-1397 .- 1944-7973. ; 59:7
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Tidskriftsartikel (refereegranskat)abstract
- Artificial tracers are often used for quantitative estimates of solute transport properties in rivers. However, single-injection tracer tests give insights in transport characteristics limited to the ecohydrological conditions at the testing time. Series of time-consuming and laborious tracer tests would be required to properly capture seasonal changes. The present study uses intrinsic diurnal fluctuations of electrical conductivity (EC) caused by discharge of treated wastewater as a tracer to evaluate solute transport processes along a 4.7-km reach of the River Erpe, Germany. By reproducing the fluctuations recorded along the river using the solute transport model one-dimensional transport with inflow and storage, this study investigated the long-term dynamics in solute transport properties. Individual 48-hr curves of EC were used in the steady state configuration of the model to gain 48-hr-integrated estimates of selected transport parameters. Using a sliding window approach in 1-hr steps along the 2,270-hr time series of EC the temporal variability of solute transport between April and June 2016 was assessed. To test the identifiability of parameters using the proposed method, sensitivity analyses and a breakthrough curve analysis of selected 48-hr windows were implemented. With time advancing into the summer, a significant rising trend (Mann-Kendall test p-value < 0.05) of the cross sectional area of the channel was observed and attributed to the growth of macrophytes and a significant slightly decreasing trend for the storage rate was found. The presented method is of high value for river management, as promoting transient storage enhances biogeochemical cycling and benefits water quality.
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| 6. |
- Jaeger, Anna, et al.
(författare)
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Transformation of organic micropollutants along hyporheic flow in bedforms of river-simulating flumes
- 2021
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Ingår i: Scientific Reports. - : Springer Science and Business Media LLC. - 2045-2322. ; 11:1
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Tidskriftsartikel (refereegranskat)abstract
- Urban streams receive increasing loads of organic micropollutants from treated wastewaters. A comprehensive understanding of the in-stream fate of micropollutants is thus of high interest for water quality management. Bedforms induce pumping effects considerably contributing to whole stream hyporheic exchange and are hotspots of biogeochemical turnover processes. However, little is known about the transformation of micropollutants in such structures. In the present study, we set up recirculating flumes to examine the transformation of a set of micropollutants along single flowpaths in two triangular bedforms. We sampled porewater from four locations in the bedforms over 78 days and analysed the resulting concentration curves using the results of a hydrodynamic model in combination with a reactive transport model accounting for advection, dispersion, first-order removal and retardation. The four porewater sampling locations were positioned on individual flowpaths with median solute travel times ranging from 11.5 to 43.3 h as shown in a hydrodynamic model previously. Highest stability was estimated for hydrochlorothiazide on all flowpaths. Lowest detectable half-lives were estimated for sotalol (0.7 h) and sitagliptin (0.2 h) along the shortest flowpath. Also, venlafaxine, acesulfame, bezafibrate, irbesartan, valsartan, ibuprofen and naproxen displayed lower half-lives at shorter flowpaths in the first bedform. However, the behavior of many compounds in the second bedform deviated from expectations, where particularly transformation products, e.g. valsartan acid, showed high concentrations. Flowpath-specific behavior as observed for metformin or flume-specific behavior as observed for metoprolol acid, for instance, was attributed to potential small-scale or flume-scale heterogeneity of microbial community compositions, respectively. The results of the study indicate that the shallow hyporheic flow field and the small-scale heterogeneity of the microbial community are major controlling factors for the transformation of relevant micropollutants in river sediments.
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| 7. |
- Jaeger, Anna, et al.
(författare)
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Using recirculating flumes and a response surface model to investigate the role of hyporheic exchange and bacterial diversity on micropollutant half-lives
- 2019
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Ingår i: Environmental Science. - : Royal Society of Chemistry (RSC). - 2050-7887 .- 2050-7895. ; 21:12, s. 2093-2108
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Tidskriftsartikel (refereegranskat)abstract
- Enhancing the understanding of the fate of wastewater-derived organic micropollutants in rivers is crucial to improve risk assessment, regulatory decision making and river management. Hyporheic exchange and sediment bacterial diversity are two factors gaining increasing importance as drivers for micropollutant degradation, but are complex to study in field experiments and usually ignored in laboratory tests aimed to estimate environmental half-lives. Flume mesocosms are useful to investigate micropollutant degradation processes, bridging the gap between the field and batch experiments. However, few studies have used flumes in this context. We present a novel experimental setup using 20 recirculating flumes and a response surface model to study the influence of hyporheic exchange and sediment bacterial diversity on half-lives of the anti-epileptic drug carbamazepine (CBZ) and the artificial sweetener acesulfame (ACS). The effect of bedform-induced hyporheic exchange was tested by three treatment levels differing in number of bedforms (0, 3 and 6). Three levels of sediment bacterial diversity were obtained by diluting sediment from the River Erpe in Berlin, Germany, with sand (1 : 10, 1 : 1000 and 1 : 100 000). Our results show that ACS half-lives were significantly influenced by sediment dilution and number of bedforms. Half-lives of CBZ were higher than ACS, and were significantly affected only by the sediment dilution variable, and thus by bacterial diversity. Our results show that (1) the flume-setup is a useful tool to study the fate of micropollutants in rivers, and that (2) higher hyporheic exchange and bacterial diversity in the sediment can increase the degradation of micropollutants in rivers.
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| 8. |
- Lewandowski, Jörg, et al.
(författare)
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Is the Hyporheic Zone Relevant beyond the Scientific Community?
- 2019
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Ingår i: Water. - : MDPI AG. - 2073-4441. ; 11:11
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Tidskriftsartikel (refereegranskat)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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| 9. |
- McCallum, James L., et al.
(författare)
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A Numerical Stream Transport Modeling Approach Including Multiple Conceptualizations of Hyporheic Exchange and Spatial Variability to Assess Contaminant Removal
- 2020
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Ingår i: Water resources research. - 0043-1397 .- 1944-7973. ; 56:3
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Tidskriftsartikel (refereegranskat)abstract
- Understanding the mechanisms and controls on contaminant removal in streams is essential in managing human and ecosystem health. The hyporheic zone (HZ) plays a key role in the removal of contaminants from streams. Often, tracer tests are implemented in conjunction with measurements of compounds to assess the removal rates of contaminants in streams. The predicted removal rates largely rely on the estimated hyporheic residence time, and hence, the chosen conceptual model of hyporheic exchange flows (HEFs) will influence the predicted removal rate. Despite this, different HEF models are generally not considered when assessing contaminant removal rates. In this paper, we present a numerical modeling approach for interpreting tracer tests to determine contaminant removal rates that allows for multiple conceptual models of HEF to be considered. We demonstrate this method by interpreting data from a conservative tracer test in conjunction with grab samples of trace organic compounds using two commonly used models of HEF: one that assumes first-order exchange between the stream and the HZ and one that considers a power law weighting of first-order exchange coefficients. For the three degrading compounds measured, guanylurea, valsartan, and diclofenac, we observed that the power law model consistently predicted higher removal rates in the stream compared to the first-order model. Variations were also observed between the removal rates estimated in the HZ. Our results highlight the importance of considering multiple conceptualizations of the HEF when assessing contaminant removal rates.
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| 10. |
- Peralta-Maraver, Ignacio, et al.
(författare)
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Environmental filtering and community delineation in the streambed ecotone
- 2018
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Ingår i: Scientific Reports. - : Springer Science and Business Media LLC. - 2045-2322. ; 8
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Tidskriftsartikel (refereegranskat)abstract
- A current controversy in ecology is whether biological communities are discrete biological entities or simply study units created for convenience; a debate that becomes even more heated when delimiting communities along ecotones. Here, we report an interdisciplinary study designed to address the interplay between environmental drivers and community ecology in a typical ecotone ecosystem: the streambed. Environmental filtering at a micro-scale determined how diversity, productivity and composition of the whole streambed assemblage varied with depth and with the direction of vertical water exchange. Biomass and production decreased with increasing depth, and were lower under upwelling than downwelling conditions. However, the rate at which biomass and production decreased with increasing depth differed significantly for different taxonomic groups. Using quantitative biocenosis analysis, we also showed that benthic and hyporheic zone assemblages (assemblages in close juxtaposition) could be clearly distinguished as discrete communities with individual integrity. Vertical hydrodynamic conditions also influenced the demarcation between both communities; the benthic community reached greater depths in downwelling than in upwelling zones.
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