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  • ddc:628.162  (1)
  • sediment-water interface  (1)
  • sinkhole  (1)
  • 1
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    High‐Resolution Integrated Transport Model for Studying Surface Water–Groundwater Interaction (2021)
    Blackwell Publishing Ltd | Malden, US
    Details
    Publication Date: 2021-06-27
    Description: Transport processes that lead to exchange of mass between surface water and groundwater play a significant role for the ecological functioning of aquatic systems, for hydrological processes and for biogeochemical transformations. In this study, we present a novel integral modeling approach for flow and transport at the sediment–water interface. The model allows us to simultaneously simulate turbulent surface and subsurface flow and transport with the same conceptual approach. For this purpose, a conservative transport equation was implemented to an existing approach that uses an extended version of the Navier–Stokes equations. Based on previous flume studies which investigated the spreading of a dye tracer under neutral, losing and gaining flow conditions the new solver is validated. Tracer distributions of the experiments are in close agreement with the simulations. The simulated flow paths are significantly affected by in‐ and outflowing groundwater flow. The highest velocities within the sediment are found for losing condition, which leads to shorter residence times compared to neutral and gaining conditions. The largest extent of the hyporheic exchange flow is observed under neutral condition. The new solver can be used for further examinations of cases that are not suitable for the conventional coupled models, for example, if Reynolds numbers are larger than 10. Moreover, results gained with the integral solver provide high‐resolution information on pressure and velocity distributions at the rippled streambed, which can be used to improve flow predictions. This includes the extent of hyporheic exchange under varying ambient groundwater flow conditions.
    Description: Technische Universität Berlin, Germany
    Description: German Research Foundation http://dx.doi.org/10.13039/501100001659
    Keywords: 551.4 ; aquatic systems ; sediment-water interface ; transport model
    Type: article
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  • 2
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    Seasonal Differences in the Attenuation of Polar Trace Organics in the Hyporheic Zone of an Urban Stream (2022)
    Details
    Publication Date: 2022-04-04
    Description: Attenuation of trace organic compounds (TrOCs) in a river occurs to a large extent in its hyporheic zone. A major part of the attenuation of polar TrOCs is of microbial origin. As microbial activity depends on temperature and redox conditions, seasonal differences in TrOC attenuation are likely. We investigated TrOC attenuation at a river influenced by treated wastewater during two sampling campaigns, one in summer and one in winter. In addition to redox conditions and temperature, we also determined residence times of porewater in sediment using three methods: (a) non‐parametric deconvolution of electrical conductivity time series, (b) the model VFLUX 2.0 based on temperature time series (only summer), and (c) applying Darcy's law to differences in hydraulic heads (only summer). Contrary to our expectations, we found higher attenuation for 12 out of 18 TrOCs in winter, while three TrOCs were better attenuated in summer. Sediment conditions varied between seasons as more of the top sandy layer with a higher hydraulic permeability accumulated on the river bed in summer. As a result, residence times in the sediment were shorter in summer. In winter, longer residence times, lower temperatures, and a steeper oxygen gradient in sediment coincided with higher TrOC attenuation. Further research is needed to understand our unexpected findings and underlying mechanisms.
    Description: Key Points: The attenuation of 12 out of 18 trace organic compounds (TrOCs) in the hyporheic zone was higher in winter while three TrOCs were attenuated better in summer. Residence times in sediment were longer and more diverse in winter. The extent of the oxic sediment was similar between seasons but the gradient from the oxic to anoxic zone was steeper in winter.
    Description: Deutsche Forschungsgemeinschaft (DFG) http://dx.doi.org/10.13039/501100001659
    Description: EC | H2020 | H2020 Priority Excellent Science | H2020 Marie Skłodowska‐Curie Actions (MSCA) http://dx.doi.org/10.13039/100010665
    Description: University of Western Australia ‐ University Postgraduate Award
    Description: Australian Government Research Training Program Scholarship
    Description: Bundesministerium für Bildung und Forschung (BMBF) http://dx.doi.org/10.13039/501100002347
    Description: https://doi.org/10.18728/igb-fred-578.0
    Keywords: ddc:628.162
    Language: English
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  • 3
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    Dynamics of Greenhouse Gases (CH4 and CO2) in Meromictic Lake Burgsee, Germany (2022)
    Details
    Publication Date: 2023-01-21
    Description: Extraordinary amounts of greenhouse gases can be stored within the monimolimnion of meromictic lakes, that is, in the water body which is excluded from mixing events. Lake Burgsee (Thuringia, Germany) is a shallow (depth 〈5 m) lake with a approximately 24 m deep sinkhole, which is fed by underground brine sources and has formed such a monimolimnion. We investigated the carbon dioxide and methane dynamics in this meromictic lake, from production potentials in the sediment via concentrations in the monimolimnion and mixolimnion to emissions to the atmosphere. In the monimolimnion, we found one of the highest methane concentrations (up to 〉5 mmol L−1) ever reported for a natural freshwater lake, while carbon dioxide concentrations in the water and methane production rates in the sediments were rather ordinary and within the range of holomictic eutrophic lakes. At the thermocline, gas concentrations accumulated to approximately 100 μmol L−1 CH4 and 80–230 μmol L−1 CO2. Estimated fluxes to the atmosphere reached considerable 3.5 mmol CH4 m−2 d−1 and 1.5 mmol CO2 m−2 d−1 above the sinkhole and 0.8 mmol CH4 m−2 d−1 and 0.4 mmol CO2 m−2 d−1 above the near‐by shallow lake center in 2018. Our results demonstrate that lakes in natural brine areas may provide significant storages and releases of greenhouse gases and require further investigation.
    Description: Plain Language Summary: In meromictic lakes, the deepest water layer, the monimolimnion, is stagnant and not included in seasonal water circulation. Organic matter continuously sinks down into the oxygen‐free monimolimnion, where it is decomposed into the final gaseous products carbon dioxide (CO2) and methane (CH4). Lake Burgsee is a meromictic shallow (depth 〈5 m), brine‐fed lake with a approximately 24 m deep sinkhole. At the bottom of the narrow sinkhole, salinities are as high as in brackish water and cause a chemical stratification of the water body—a monimolimnion—in approximately 18 m depth. CH4 concentrations above the sediment reach 〉5 mmol L−1, which is more than one order of magnitude higher than at the water surface and among the highest CH4 concentrations found in freshwater lakes worldwide. Further, emissions of CH4 and CO2 from the water to the atmosphere were considerable in 2018, and about four times higher above the sinkhole than above the shallow lake center. These results demonstrate, that lakes in natural brine areas may store and release significant amounts of greenhouse gases and require further investigation.
    Description: Key Points: In the urban meromictic Lake Burgsee, methane production potentials in the sediment are similar to eutrophic holomictic lakes. At its deepest site, it contains one of the highest methane concentrations (〉5 mmol L−1 CH4) ever reported for a natural freshwater lake. Lake Burgsee emits up to 〉3 mmol m−2 d−1 CH4 to the atmosphere above the sinkhole and 〈1 mmol m−2 d−1 CH4 at a near‐by shallow site.
    Keywords: ddc:551 ; meromictic lake ; sinkhole ; salinity ; greenhouse gases ; methane flux ; carbon dioxide
    Language: English
    Type: doc-type:article
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