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  • 551  (7)
  • Shear structure/flows  (2)
  • 2015-2019  (9)
  • 1945-1949
  • 1920-1924
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  • 1
    Publication Date: 2021-03-29
    Description: A qualitative and quantitative monitoring of groundwater discharge was conducted based on an airborne thermal campaign undertaken along the north-western coast of the Dead Sea in January 2011 to contribute to the relatively scarce information on groundwater discharge to date in the region. The application of airborne thermal data exploits thermal contrasts that exist between discharging groundwater and background sea surface temperatures of the Dead Sea. Using these contrasts, 72 discharge sites were identified from which only 42 were known from previous in situ measurements undertaken at terrestrial springs by the Israel Hydrological Service. Six of these sites represent submarine springs and at a further 24 locations groundwater appears to seep through the sediment. Although the abundance of groundwater seepage sites suggests a significant, but so far unknown groundwater source, the main contribution appears to originate from terrestrial springs. In an attempt to provide a quantitative approach for terrestrial springs, a linear bootstrap regression model between in situ spring discharge and respective thermal discharge plumes (r2 = 0.87 p 〈 0.001) is developed and presented here. While the results appear promising and could potentially be applied to derive discharge values at unmonitored sites, several influence factors need to be clarified before a robust and reliable model to efficiently derive a complete quantitative picture of groundwater discharge can be proposed.
    Keywords: thermal discharge plume; groundwater discharge; ; 551
    Language: English
    Type: article , publishedVersion
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  • 2
    Publication Date: 2021-03-29
    Description: Due to its extreme salinity and high Mg concentration the Dead Sea is characterized by a very low density of cells most of which are Archaea. We discovered several underwater fresh to brackish water springs in the Dead Sea harboring dense microbial communities. We provide the first characterization of these communities, discuss their possible origin, hydrochemical environment, energetic resources and the putative biogeochemical pathways they are mediating. Pyrosequencing of the 16S rRNA gene and community fingerprinting methods showed that the spring community originates from the Dead Sea sediments and not from the aquifer. Furthermore, it suggested that there is a dense Archaeal community in the shoreline pore water of the lake. Sequences of bacterial sulfate reducers, nitrifiers iron oxidizers and iron reducers were identified as well. Analysis of white and green biofilms suggested that sulfide oxidation through chemolitotrophy and phototrophy is highly significant. Hyperspectral analysis showed a tight association between abundant green sulfur bacteria and cyanobacteria in the green biofilms. Together, our findings show that the Dead Sea floor harbors diverse microbial communities, part of which is not known from other hypersaline environments. Analysis of the water’s chemistry shows evidence of microbial activity along the path and suggests that the springs supply nitrogen, phosphorus and organic matter to the microbial communities in the Dead Sea. The underwater springs are a newly recognized water source for the Dead Sea. Their input of microorganisms and nutrients needs to be considered in the assessment of possible impact of dilution events of the lake surface waters, such as those that will occur in the future due to the intended establishment of the Red Sea - Dead Sea water conduit.
    Keywords: Dead Sea; Archaeal community ; 551
    Language: English
    Type: article , publishedVersion
    Format: 21
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  • 3
    Publication Date: 2021-03-29
    Description: The objective of this work is the simulation of saturated and unsaturated flow in a karstified aquifer using a double continuum approach. The HydroGeoSphere code ( Therrien et al. , 2006 ) is employed to simulate spring dis- charge with the Richards equations and van Genuchten pa- rameters to represent flow in the (1) fractured matrix and (2) conduit continuum coupled by a linear exchange term. Rapid vertical small-scale flow processes in the unsaturated conduit continuum are accounted for by applying recharge boundary conditions at the bottom of the saturated model do- main. An extensive sensitivity analysis is performed on sin- gle parameters as well as parameter combinations. The tran- sient hydraulic response of the karst spring is strongly con- trolled by the matrix porosity as well as the van Genuchten parameters of the unsaturated matrix, which determine the head dependent inter-continuum water transfer when the con- duits are draining the matrix. Sensitivities of parameter com- binations partially reveal a non-linear dependence over the parameter space. This can be observed for parameters not belonging to the same continuum as well as combinations, which involve the exchange parameter, showing that results of the double continuum model may depict a certain de- gree of ambiguity. The application of van Genuchten pa- rameters for simulation of unsaturated flow in karst systems is critically discussed.
    Keywords: saturated unsaturated flow; karst systems; catchment scale; double continuum ; 551
    Language: English
    Type: article , publishedVersion
    Format: 15
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  • 4
    Publication Date: 2021-03-29
    Description: Due to their heterogeneous nature, karst aquifers pose a major challenge for hydrogeological investigations. Important procedures like the delineation of catchment areas for springs are hindered by the unknown locations and hy- draulic properties of highly conductive karstic zones. In this work numerical modeling was employed as a tool in delineating catchment areas of several springs within a karst area in southwestern Germany. For this purpose, different distributive modeling approaches were implemented in the finite element simulation software Comsol Multiphysics ® . The investigation focuses on the question to which degree the effect of karstification has to be taken into account for accurately simulating the hydraulic head distribution and the observed spring discharges. The results reveal that the representation of heterogeneities has a large influence on the delineation of the catchment areas. Not only the location of highly conductive elements but also their geometries play a major role for the resulting hydraulic head distribution and thus for catchment area de- lineation. The size distribution of the karst conduits derived from the numerical models agrees with knowledge from karst genesis. It was thus shown that numerical modeling is a use- ful tool for catchment delineation in karst aquifers based on results from different field observations.
    Description: Open-Access-Publikationsfonds 2013
    Keywords: karst aquifer; hydraulics; ; 551
    Language: English
    Type: article , publishedVersion
    Format: 14
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  • 5
    Publication Date: 2021-03-29
    Description: Open-Access-Publikationsfonds 2014
    Keywords: karst aquifer; flow; Transport; catchment scale ; 551
    Language: English
    Type: article , publishedVersion
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  • 6
    Publication Date: 2021-03-29
    Description: Karst aquifers are characterized by highly conductive conduit flow paths embedded in a less conductive fissured and fractured matrix, resulting in strong permeability contrasts with structured heterogeneity and anisotropy. Groundwater storage occurs predominantly in the fissured matrix. Hence, most mathematical karst models assume quasi-steady-state flow in conduits neglecting conduitassociated drainable storage (CADS). The concept of CADS considers storage volumes, where karst water is not part of the active flow system but hydraulically connected to conduits (for example karstic voids and large fractures). The disregard of conduit storage can be inappropriate when direct water abstraction from karst conduits occurs, e.g., largescale pumping. In such cases, CADS may be relevant. Furthermore, the typical fixed-head boundary condition at the karst outlet can be inadequate for water abstraction scenarios because unhampered water inflow is possible. The objective of this work is to analyze the significance of CADS and flow-limited boundary conditions on the hydraulic behavior of karst aquifers in water abstraction scenarios. To this end, the numerical discrete-continuum model MODFLOW-2005 Conduit Flow Process Mode 1 (CFPM1) is enhanced to account for CADS. Additionally, a fixed-head limited-flow (FHLQ) boundary condition is added that limits inflow from constant head boundaries to a user-defined threshold. The effects and the proper functioning of these modifications are demonstrated by simplified model studies. Both enhancements, CADS and FHLQ boundary, are shown to be useful for water abstraction scenarios within karst aquifers. An idealized representation of a large-scale pumping test in a karst conduit is used to demonstrate that the enhanced CFPM1 is able to adequately represent water abstraction processes in both the conduits and the matrix of real karst systems, as illustrated by its application to the Cent Fonts karst system.
    Keywords: water abstraction; karst; ; 551
    Language: English
    Type: article , publishedVersion
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  • 7
    Publication Date: 2021-03-29
    Keywords: Landsat ETM+; Sea surface temperature; Submarine groundwater discharge; Groundwater resource ; 551 ; Earth Sciences; Geology
    Language: English
    Type: article , publishedVersion
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  • 8
    Publication Date: 2022-05-25
    Description: Author Posting. © American Meteorological Society, 2015. This article is posted here by permission of American Meteorological Society for personal use, not for redistribution. The definitive version was published in Journal of Physical Oceanography 45 (2015): 2773–2789, doi:10.1175/JPO-D-15-0031.1.
    Description: Tidal oscillatory salt transport, induced by the correlation between tidal variations in salinity and velocity, is an important term for the subtidal salt balance under the commonly used Eulerian method of salt transport decomposition. In this paper, its mechanisms in a partially stratified estuary are investigated with a numerical model of the Hudson estuary. During neap tides, when the estuary is strongly stratified, the tidal oscillatory salt transport is mainly due to the hydraulic response of the halocline to the longitudinal variation of topography. This mechanism does not involve vertical mixing, so it should not be regarded as oscillatory shear dispersion, but instead it should be regarded as advective transport of salt, which results from the vertical distortion of exchange flow obtained in the Eulerian decomposition by vertical fluctuations of the halocline. During spring tides, the estuary is weakly stratified, and vertical mixing plays a significant role in the tidal variation of salinity. In the spring tide regime, the tidal oscillatory salt transport is mainly due to oscillatory shear dispersion. In addition, the transient lateral circulation near large channel curvature causes the transverse tilt of the halocline. This mechanism has little effect on the cross-sectionally integrated tidal oscillatory salt transport, but it results in an apparent left–right cross-channel asymmetry of tidal oscillatory salt transport. With the isohaline framework, tidal oscillatory salt transport can be regarded as a part of the net estuarine salt transport, and the Lagrangian advective mechanism and dispersive mechanism can be distinguished.
    Description: Tao Wang was supported by the Open Research Fund of State Key Laboratory of Estuarine and Coastal Research (Grant SKLEC-KF201509) and Chinese Scholarship Council. Geyer was supported by by NSF Grant OCE 0926427. Wensheng Jiang was supported by NSFC-Shandong Joint Fund for Marine Science Research Centers (Grant U1406401).
    Description: 2016-05-01
    Keywords: Geographic location/entity ; Estuaries ; Circulation/ Dynamics ; Baroclinic flows ; Dispersion ; Shear structure/flows ; Atm/Ocean Structure/ Phenomena ; Diapycnal mixing ; Models and modeling ; Regional models
    Repository Name: Woods Hole Open Access Server
    Type: Article
    Format: application/pdf
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  • 9
    Publication Date: 2022-05-26
    Description: Author Posting. © American Meteorological Society, 2016. This article is posted here by permission of American Meteorological Society for personal use, not for redistribution. The definitive version was published in Journal of Physical Oceanography 46 (2016): 1769-1783, doi:10.1175/JPO-D-15-0193.1.
    Description: High-resolution observations of velocity, salinity, and turbulence quantities were collected in a salt wedge estuary to quantify the efficiency of stratified mixing in a high-energy environment. During the ebb tide, a midwater column layer of strong shear and stratification developed, exhibiting near-critical gradient Richardson numbers and turbulent kinetic energy (TKE) dissipation rates greater than 10−4 m2 s−3, based on inertial subrange spectra. Collocated estimates of scalar variance dissipation from microconductivity sensors were used to estimate buoyancy flux and the flux Richardson number Rif. The majority of the samples were outside the boundary layer, based on the ratio of Ozmidov and boundary length scales, and had a mean Rif = 0.23 ± 0.01 (dissipation flux coefficient Γ = 0.30 ± 0.02) and a median gradient Richardson number Rig = 0.25. The boundary-influenced subset of the data had decreased efficiency, with Rif = 0.17 ± 0.02 (Γ = 0.20 ± 0.03) and median Rig = 0.16. The relationship between Rif and Rig was consistent with a turbulent Prandtl number of 1. Acoustic backscatter imagery revealed coherent braids in the mixing layer during the early ebb and a transition to more homogeneous turbulence in the midebb. A temporal trend in efficiency was also visible, with higher efficiency in the early ebb and lower efficiency in the late ebb when the bottom boundary layer had greater influence on the flow. These findings show that mixing efficiency of turbulence in a continuously forced, energetic, free shear layer can be significantly greater than the broadly cited upper bound from Osborn of 0.15–0.17.
    Description: Holleman was supported by the Devonshire Scholars program. The field study and the coauthors’ contributions were supported by NSF Grant OCE 0926427.
    Description: 2016-11-24
    Keywords: Circulation/ Dynamics ; Mixing ; Shear structure/flows ; Turbulence ; Observational techniques and algorithms ; Ship observations
    Repository Name: Woods Hole Open Access Server
    Type: Article
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