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  • 1
    ISSN: 1365-2427
    Source: Blackwell Publishing Journal Backfiles 1879-2005
    Topics: Biology
    Notes: 1. The development of a population of Thiocystis minor (formerly Chromatium minus) in the deepest, anoxic layers of Moncortès Lake (Lleida, Spain) was studied by means of an in situ, laser particle analyser. Particle size distribution was measured at hourly and monthly time intervals.2. The population was located between the redoxcline (∼3 m below the mean population depth) and the oxycline (∼6 m above the mean population depth) with a seasonal vertical displacement (SVD) of up to 6 m (from April to October).3. Diel vertical migration of the population was followed in three field campaigns, when the population was most abundant. The largest vertical displacement was 2.8 m (in 11.5 h) and the fastest vertical displacement was 0.6 m h−1. Sudden changes in the irradiance reaching the bacterial population were detected by the cells, which moved up or down, rapidly modifying the mean vertical position of the population.4. There was positive phototaxis with an ascent during the morning and a descent during the afternoon/night. The whole population was active while migrating upwards (towards higher light intensity) or downwards (towards lower redox concentration).
    Type of Medium: Electronic Resource
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  • 2
    ISSN: 1365-3091
    Source: Blackwell Publishing Journal Backfiles 1879-2005
    Topics: Geosciences
    Notes: A hydrothermal plume forms in Lake Banyoles, NE Spain, as a result of convection above a springwater-fed suspension cloud ponded on the lake floor. The plume propagates upwards reaching a level of neutral buoyancy from where a turbidity current spreads out laterally. Two-dimensional temperature and particle concentration measurements show the fate of the hydrothermal plume and its associated turbidity current and reveal its seasonal development. Silt particles transported by the plume have been used as tracers to determine the maximum and equilibrium heights of the plume. When the lake is stratified, the vertical transport of sediment is confined to the lake hypolimnion, as the thermocline limits the vertical propagation of the plume. In contrast, when the lake water column is mixed, the plume reaches the surface of the lake. The field measurements have been compared with models for thermal convection from finite isolated sources. Measurements of the flow velocity at the source of the hydrothermal plume (i.e. the rim current velocity) indicate that cold hypolimnetic water is entrained by the plume. Sedimentation rates measured from sediment traps at the zone where the turbidity current develops vary between 10 and 25 g m−2 day−1, and result from continuous silt particle sedimentation from the turbidity current. Sedimentation rates in traps are higher for stations situated close to the source than those further away (〈5 g m−2 day−1). Moreover, the results demonstrate that double diffusive sedimentation from the turbidity current was dominant over grain-by-grain settling, causing a mixed distribution of sediments in the region where the turbidity current spreads. The deposition of silt particles could explain the occurrence of silt layers interbedded with biocalcarenites in the littoral zones of the lake and the stratigraphy identified by seismic profiles and cores taken from the lake floor.
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  • 3
    Electronic Resource
    Electronic Resource
    Springer
    Aquatic sciences 58 (1996), S. 367-377 
    ISSN: 1420-9055
    Keywords: Gravity current ; differential cooling ; geostrophy ; entrainment ; Lake Banyoles
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology
    Notes: Abstract Extensive field data of a density current driven by the differences in the cooling rates between the two lobes of a small lake are presented. These data illustrate the fact that this gravitational motion affects the whole system and dominates its lakewide circulation. Moreover, data are used to evaluate the entrainment into the density current and also to discuss the regime of the flow from a scaling analysis of the horizontal momentum equations. This analysis is specifically applied to the central area of the lake, where the density current flows from one lobe to the other. Results of this study show that in the longitudinal direction there is a balance between the pressure gradient and the turbulent viscous term. Further, it is found that geostrophy correctly describes the transversal pattern of the passage of the gravity current from the northern lobe to the southern, where it flows confined to the western shoreline.
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  • 4
    Electronic Resource
    Electronic Resource
    Springer
    Aquatic sciences 60 (1998), S. 338-358 
    ISSN: 1420-9055
    Keywords: Key words: Sediment, lutocline, groundwater, jet, Lake Banyoles.
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology
    Notes: Abstract: In this paper, the suspension of sediments induced by groundwater jets in two basins of a karst lake (basin I and II of lake Banyoles, Catalonia) is studied. Field experiments were carried out during the period 1989-1994 to investigate the sediment dynamics within the basins. During this period, the sediment in basin I (B1) was found to be permanently in suspension while the sediment in basin II (B2) remained at the bottom of the basin, except on two occasions when the ground water discharge increased and caused resuspension. A two-dimensional k-ɛ turbulence model was used to simulate the suspension of the sediment and the formation of the lutocline (the interface of the suspended sediment). The model predicts a reduction of the turbulent kinetic energy at the lutocline due to the buoyancy flux. This is used to estimate the inflow into the basins and the maximum height that the lutocline can rise, which is found to depend on the settling velocity, the mean inflow rate and the geometry of the basin. Also, the model is used to predict the water circulation below the sediment interface.
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  • 5
    ISSN: 1420-9055
    Keywords: Key words: Lutocline, fluidized bed, suspended sediments, vertical jet.
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology
    Notes: Abstract: An experimental study was carried out to investigate the resuspension of particles by a momentum jet discharging from below into a conical basin. The work was motivated by its relevance to Lake Banyoles, where sediments are suspended in different conical basins by bottom jets fed by a groundwater karstic system. Two different flow regimes were identified: a "Jet Flow" regime (JF) and a "Lutocline Flow" regime (LF). In the LF regime, the particles were resuspended, forming a well-established interface along the entire cross-sectional ara of the cone. This regime occurs when the particle Reynolds number $ {\bf Re_p = (u-w_s)d_p/ \nu} $ where u is the mean velocity of the flow at the jet entry, w s is the settling velocity of particles, d p is the diameter of that particles and $ {\bf \nu} $ is the kinematic viscosity of water) is below a critical number Re c that depends on the slope of the basin. The maximum height to which particles rise in the LF regime was also determined as a function of four non-dimensional variables: D 1 = h o /(M o 1/2 /w s ), D 2 = h o /d p , Re p and $ {\bf tan \, \beta} $ (where h o is the height of the particle bed, M o is the kinematic momentum flux of the jet and $ {\bf tan \, \beta} $ is the slope of the basin). Application of the results to the basins of Lake Banyoles showed a good agreement provided that the aggregate properties of the suspensions are used. It is also shown that, in the LF regime, inflows to the basins can be estimated by a simple technique based on a balance between the sedimentation flux and the upward advection of sediments by the mean flow.
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  • 6
    Electronic Resource
    Electronic Resource
    Springer
    Flow, turbulence and combustion 59 (1997), S. 229-242 
    ISSN: 1573-1987
    Keywords: particle ; resuspension ; sedimentation ; turbulence ; karst lake
    Source: Springer Online Journal Archives 1860-2000
    Topics: Mechanical Engineering, Materials Science, Production Engineering, Mining and Metallurgy, Traffic Engineering, Precision Mechanics
    Notes: Abstract An experimental study was carried out to investigate the resuspension of heavy particles of a sediment bed by axi-symmetric turbulent jets issuing from below. The case of point jets and loosely-held monodispersed particles was considered, in particular, the cases of a single jet and an array of jets located in the intersection points of a square grid. The aim was to map the flow field and the nature of sediment distribution as a function of governing parameters and to parameterize salient observables such as the maximum height of rise of sediments. The results were extrapolated to study sediment resuspension in karstic lakes, especially lake Banyoles located in Catalonia, northeastern Spain.
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  • 7
    Publication Date: 2005-08-01
    Print ISSN: 0043-1354
    Electronic ISSN: 1879-2448
    Topics: Energy, Environment Protection, Nuclear Power Engineering
    Published by Elsevier
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  • 8
    Publication Date: 2002-10-01
    Print ISSN: 0043-1354
    Electronic ISSN: 1879-2448
    Topics: Energy, Environment Protection, Nuclear Power Engineering
    Published by Elsevier
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  • 9
    Publication Date: 2011-07-31
    Print ISSN: 1015-1621
    Electronic ISSN: 1420-9055
    Topics: Biology
    Published by Springer
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  • 10
    Publication Date: 1998-01-01
    Print ISSN: 1015-1621
    Electronic ISSN: 1420-9055
    Topics: Biology
    Published by Springer
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