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Heinz G. Stefan - One of the best experts on this subject based on the ideXlab platform.

  • Dissolved Oxygen Demand at the Sediment-Water Interface of a Stream: Near-Bed Turbulence and Pore Water Flow Effects
    Journal of Environmental Engineering, 2011
    Co-Authors: Makoto Higashino, Heinz G. Stefan
    Abstract:

    A microbial dissolved oxygen (DO) uptake model was developed for a stream bed, including the effect of turbulence in the flow over the bed and pore water flow in the porous bed. The fine-grained sediment bed has hydraulic conductivities 0.01≤k≤1  cm/s, i.e., sediment particle diameter 0.006≤ds≤0.06  cm. The pore water flow is driven by pressure fluctuations at the Sediment-Water Interface, mostly attributable to near-bed coherent motions in the turbulent boundary layer above the sediment bed. An effective mass transfer coefficient (De) coupled to a pore water flow model was used in the DO transport and DO uptake model. DO flux across the Sediment-Water Interface and into the sediment, i.e., sedimentary oxygen demand (SOD), was related to hydraulic conductivity and microbial oxygen uptake rate in the sediment and shear velocity at the Sediment-Water Interface. Simulated SOD values were validated against experimental data. For hydraulic conductivities of the sediment bed up to k≈0.01  cm/s, the pore water f...

  • Near-bed turbulence models : Significance for diffusional mass transfer at the sediment/water Interface
    Journal of Hydraulic Research, 2008
    Co-Authors: Makoto Higashino, Heinz G. Stefan
    Abstract:

    It is well-known that sediment/water interaction affects water quality in natural water bodies in a variety of ways. Diffusional mass transfer, across a sediment/water Interface can contribute significantly to the mass balances of dissolved substances such as oxygen, phosphorus, nitrogen and sulfate, especially in lakes, reservoirs, detention basins, navigation canals and estuaries. At low flow velocities above a sediment bed, diffusional mass transfer across a sediment/water Interface becomes limited by lack of turbulence in the boundary layer. In this paper, three boundary layer turbulence models are used to quantify the limiting effect of turbulence near a sediment bed on diffusional mass transfer across a sediment/water Interface: One is Dade's formula, the second is a model by Myong and Kasagi (MK model), and the third is a model by Nagano and Tagawa (NT model). The latter two are low-Reynolds number k–e turbulence models that have been successfully used for the prediction of turbulent heat transfer ...

  • Unsteady diffusional mass transfer at the sediment/water Interface: Theory and significance for SOD measurement.
    Water Research, 2003
    Co-Authors: Makoto Higashino, Charles J. Gantzer, Heinz G. Stefan
    Abstract:

    Abstract Dissolved oxygen uptake at a sediment/water Interface (SOD) is controlled by mass transport and/or biochemical reactions in two adjacent boundary layers: the diffusive boundary layer δ D in the water and the penetration depth δ in the sediment. Either one of those boundary layers or both can be controlling. The transition from sediment control to water control is a function of shear velocity at the sediment/water Interface ( U * ) and biochemical activity rate ( μ 0 ) in the sediment. A model was developed for the unsteady response of SOD and DO profiles near the sediment/water Interface. Michaelis-Menten kinetics were used initially, but zero order kinetics work just as well when the half saturation coefficient K O 2 is small as was suggested by field data. Beginning with zero DO in the sediments the times required to reach steady state DO profiles and SOD was on the order of minutes to hours, faster where biochemical activity is strong. The values of SOD estimated by the model were compared with experimental data to verify the reliability of the model. The model can reproduce observed penetration depths and diffusive boundary layer thickness. Values of SOD estimated by the model were of same magnitude as observed data. The unsteady DO uptake model can be used to provide guidance for field measurements of SOD. Placing a chamber (with a stirrer) into the sediments disturbs the DO equilibrium at the sediment/water Interface. A new equilibrium will be reached within a time that can be measured in terms of cumulative DO consumption in the chamber (SOD exerted). Upper bounds for (SOD exerted) are larger when biochemical activity in the sediments is smaller. Values of SOD exerted are less than 0.1 gm −2 when μ 0 is less than 50 mg l −1  d −1 and U * >0.1 cm/s. In other words, steady state conditions are easier to reach for high SOD values. Actual times required to reach steady state can be from minutes to hours. If flow conditions in the chamber and at the natural sediment/water Interface are much different, measured SOD values have to be adjusted. A procedure for the adjustments, which can be substantial, has been developed.

  • Periodic Diffusional Mass Transfer near Sediment/Water Interface: Theory
    Journal of Environmental Engineering, 2003
    Co-Authors: Makoto Higashino, Heinz G. Stefan, Charles J. Gantzer
    Abstract:

    Time-variable (periodic) flow over a lake bed, and the associated boundary layer development, have the potential to control or at least influence rates of mass transfer across the sediment/water Interface. An analysis for instantaneous and time averaged flux of a material across the sediment/water Interface for infinite supply in the water and infinite sink in the sediment is presented. The water flow above the Interface is characterized by the shear velocity (U*) which is a periodic function of time with a maximum amplitude of (U*0) as may be typical of an internal seiche (internal standing wave) motion in a density stratified lake. The relationship between the shear velocity on the lake bed and the wind shear on the lake surface is illustrated for an extremely simplified two-layered lake of constant depth. For a less restrictive analysis, shear velocities on a lake bed have to be obtained either from field measurements or from a three-dimensional lake circulation model driven by atmospheric forcing incl...

  • RESPONSE OF SOD TO TURBULENCE AND CHANGE IN DISSOLVED OXYGEN CONCENTRATION ABOVE THE SEDIMENT/WATER Interface
    Doboku Gakkai Ronbunshuu B, 2003
    Co-Authors: Makoto Higashino, Heinz G. Stefan
    Abstract:

    Sediment oxygen demand (SOD) is controlled by oxygen transfer in a diffusive boundary layer and by oxygen consumption due to microbial and chemical processes inside the sediment. SOD is a function of flow velocity above a sediment/water Interface, i.e. shear velocity, and biochemical activity rates. A model was presented for the unsteady response of SOD and the dissolved oxygen (DO) profile near the sediment/water Interface. The time required to reach a steady state DO profile and SOD for zero DO inside the sediment initially gets faster as biochemical activity becomes strong. The values of SOD estimated by the model were compared with experimental data. The model can reproduce observed diffusive boundary layer thicknesses. It is also found that values of SOD estimated by the model were of the same magnitude as the observed data.

Makoto Higashino - One of the best experts on this subject based on the ideXlab platform.

  • Dissolved Oxygen Demand at the Sediment-Water Interface of a Stream: Near-Bed Turbulence and Pore Water Flow Effects
    Journal of Environmental Engineering, 2011
    Co-Authors: Makoto Higashino, Heinz G. Stefan
    Abstract:

    A microbial dissolved oxygen (DO) uptake model was developed for a stream bed, including the effect of turbulence in the flow over the bed and pore water flow in the porous bed. The fine-grained sediment bed has hydraulic conductivities 0.01≤k≤1  cm/s, i.e., sediment particle diameter 0.006≤ds≤0.06  cm. The pore water flow is driven by pressure fluctuations at the Sediment-Water Interface, mostly attributable to near-bed coherent motions in the turbulent boundary layer above the sediment bed. An effective mass transfer coefficient (De) coupled to a pore water flow model was used in the DO transport and DO uptake model. DO flux across the Sediment-Water Interface and into the sediment, i.e., sedimentary oxygen demand (SOD), was related to hydraulic conductivity and microbial oxygen uptake rate in the sediment and shear velocity at the Sediment-Water Interface. Simulated SOD values were validated against experimental data. For hydraulic conductivities of the sediment bed up to k≈0.01  cm/s, the pore water f...

  • Near-bed turbulence models : Significance for diffusional mass transfer at the sediment/water Interface
    Journal of Hydraulic Research, 2008
    Co-Authors: Makoto Higashino, Heinz G. Stefan
    Abstract:

    It is well-known that sediment/water interaction affects water quality in natural water bodies in a variety of ways. Diffusional mass transfer, across a sediment/water Interface can contribute significantly to the mass balances of dissolved substances such as oxygen, phosphorus, nitrogen and sulfate, especially in lakes, reservoirs, detention basins, navigation canals and estuaries. At low flow velocities above a sediment bed, diffusional mass transfer across a sediment/water Interface becomes limited by lack of turbulence in the boundary layer. In this paper, three boundary layer turbulence models are used to quantify the limiting effect of turbulence near a sediment bed on diffusional mass transfer across a sediment/water Interface: One is Dade's formula, the second is a model by Myong and Kasagi (MK model), and the third is a model by Nagano and Tagawa (NT model). The latter two are low-Reynolds number k–e turbulence models that have been successfully used for the prediction of turbulent heat transfer ...

  • Unsteady diffusional mass transfer at the sediment/water Interface: Theory and significance for SOD measurement.
    Water Research, 2003
    Co-Authors: Makoto Higashino, Charles J. Gantzer, Heinz G. Stefan
    Abstract:

    Abstract Dissolved oxygen uptake at a sediment/water Interface (SOD) is controlled by mass transport and/or biochemical reactions in two adjacent boundary layers: the diffusive boundary layer δ D in the water and the penetration depth δ in the sediment. Either one of those boundary layers or both can be controlling. The transition from sediment control to water control is a function of shear velocity at the sediment/water Interface ( U * ) and biochemical activity rate ( μ 0 ) in the sediment. A model was developed for the unsteady response of SOD and DO profiles near the sediment/water Interface. Michaelis-Menten kinetics were used initially, but zero order kinetics work just as well when the half saturation coefficient K O 2 is small as was suggested by field data. Beginning with zero DO in the sediments the times required to reach steady state DO profiles and SOD was on the order of minutes to hours, faster where biochemical activity is strong. The values of SOD estimated by the model were compared with experimental data to verify the reliability of the model. The model can reproduce observed penetration depths and diffusive boundary layer thickness. Values of SOD estimated by the model were of same magnitude as observed data. The unsteady DO uptake model can be used to provide guidance for field measurements of SOD. Placing a chamber (with a stirrer) into the sediments disturbs the DO equilibrium at the sediment/water Interface. A new equilibrium will be reached within a time that can be measured in terms of cumulative DO consumption in the chamber (SOD exerted). Upper bounds for (SOD exerted) are larger when biochemical activity in the sediments is smaller. Values of SOD exerted are less than 0.1 gm −2 when μ 0 is less than 50 mg l −1  d −1 and U * >0.1 cm/s. In other words, steady state conditions are easier to reach for high SOD values. Actual times required to reach steady state can be from minutes to hours. If flow conditions in the chamber and at the natural sediment/water Interface are much different, measured SOD values have to be adjusted. A procedure for the adjustments, which can be substantial, has been developed.

  • Periodic Diffusional Mass Transfer near Sediment/Water Interface: Theory
    Journal of Environmental Engineering, 2003
    Co-Authors: Makoto Higashino, Heinz G. Stefan, Charles J. Gantzer
    Abstract:

    Time-variable (periodic) flow over a lake bed, and the associated boundary layer development, have the potential to control or at least influence rates of mass transfer across the sediment/water Interface. An analysis for instantaneous and time averaged flux of a material across the sediment/water Interface for infinite supply in the water and infinite sink in the sediment is presented. The water flow above the Interface is characterized by the shear velocity (U*) which is a periodic function of time with a maximum amplitude of (U*0) as may be typical of an internal seiche (internal standing wave) motion in a density stratified lake. The relationship between the shear velocity on the lake bed and the wind shear on the lake surface is illustrated for an extremely simplified two-layered lake of constant depth. For a less restrictive analysis, shear velocities on a lake bed have to be obtained either from field measurements or from a three-dimensional lake circulation model driven by atmospheric forcing incl...

  • RESPONSE OF SOD TO TURBULENCE AND CHANGE IN DISSOLVED OXYGEN CONCENTRATION ABOVE THE SEDIMENT/WATER Interface
    Doboku Gakkai Ronbunshuu B, 2003
    Co-Authors: Makoto Higashino, Heinz G. Stefan
    Abstract:

    Sediment oxygen demand (SOD) is controlled by oxygen transfer in a diffusive boundary layer and by oxygen consumption due to microbial and chemical processes inside the sediment. SOD is a function of flow velocity above a sediment/water Interface, i.e. shear velocity, and biochemical activity rates. A model was presented for the unsteady response of SOD and the dissolved oxygen (DO) profile near the sediment/water Interface. The time required to reach a steady state DO profile and SOD for zero DO inside the sediment initially gets faster as biochemical activity becomes strong. The values of SOD estimated by the model were compared with experimental data. The model can reproduce observed diffusive boundary layer thicknesses. It is also found that values of SOD estimated by the model were of the same magnitude as the observed data.

Charles J. Gantzer - One of the best experts on this subject based on the ideXlab platform.

  • Unsteady diffusional mass transfer at the sediment/water Interface: Theory and significance for SOD measurement.
    Water Research, 2003
    Co-Authors: Makoto Higashino, Charles J. Gantzer, Heinz G. Stefan
    Abstract:

    Abstract Dissolved oxygen uptake at a sediment/water Interface (SOD) is controlled by mass transport and/or biochemical reactions in two adjacent boundary layers: the diffusive boundary layer δ D in the water and the penetration depth δ in the sediment. Either one of those boundary layers or both can be controlling. The transition from sediment control to water control is a function of shear velocity at the sediment/water Interface ( U * ) and biochemical activity rate ( μ 0 ) in the sediment. A model was developed for the unsteady response of SOD and DO profiles near the sediment/water Interface. Michaelis-Menten kinetics were used initially, but zero order kinetics work just as well when the half saturation coefficient K O 2 is small as was suggested by field data. Beginning with zero DO in the sediments the times required to reach steady state DO profiles and SOD was on the order of minutes to hours, faster where biochemical activity is strong. The values of SOD estimated by the model were compared with experimental data to verify the reliability of the model. The model can reproduce observed penetration depths and diffusive boundary layer thickness. Values of SOD estimated by the model were of same magnitude as observed data. The unsteady DO uptake model can be used to provide guidance for field measurements of SOD. Placing a chamber (with a stirrer) into the sediments disturbs the DO equilibrium at the sediment/water Interface. A new equilibrium will be reached within a time that can be measured in terms of cumulative DO consumption in the chamber (SOD exerted). Upper bounds for (SOD exerted) are larger when biochemical activity in the sediments is smaller. Values of SOD exerted are less than 0.1 gm −2 when μ 0 is less than 50 mg l −1  d −1 and U * >0.1 cm/s. In other words, steady state conditions are easier to reach for high SOD values. Actual times required to reach steady state can be from minutes to hours. If flow conditions in the chamber and at the natural sediment/water Interface are much different, measured SOD values have to be adjusted. A procedure for the adjustments, which can be substantial, has been developed.

  • Periodic Diffusional Mass Transfer near Sediment/Water Interface: Theory
    Journal of Environmental Engineering, 2003
    Co-Authors: Makoto Higashino, Heinz G. Stefan, Charles J. Gantzer
    Abstract:

    Time-variable (periodic) flow over a lake bed, and the associated boundary layer development, have the potential to control or at least influence rates of mass transfer across the sediment/water Interface. An analysis for instantaneous and time averaged flux of a material across the sediment/water Interface for infinite supply in the water and infinite sink in the sediment is presented. The water flow above the Interface is characterized by the shear velocity (U*) which is a periodic function of time with a maximum amplitude of (U*0) as may be typical of an internal seiche (internal standing wave) motion in a density stratified lake. The relationship between the shear velocity on the lake bed and the wind shear on the lake surface is illustrated for an extremely simplified two-layered lake of constant depth. For a less restrictive analysis, shear velocities on a lake bed have to be obtained either from field measurements or from a three-dimensional lake circulation model driven by atmospheric forcing incl...

Stuart G Wakeham - One of the best experts on this subject based on the ideXlab platform.

  • a study of oxic anoxic effects on degradation of sterols at the simulated sediment water Interface of coastal sediments
    Organic Geochemistry, 1998
    Co-Authors: Stuart G Wakeham
    Abstract:

    Laboratory incubation experiments were conducted to determine the behavior of sterols at the sediment–water Interface in oxic and anoxic sediments. Both plankton and 4-14C-cholesterol were used as tracers. Cholesterol was rapidly degraded at the sediment–water Interface: 55% of 14C-cholesterol was lost from sediments under anoxic conditions and 78% under oxic conditions over three and one-half months. About 3% of initially-added free radiolabel was incorporated into a bound pool that was released only by saponification of solvent-extracted sediment. Less than 1% of initially-added radiolabel remained in pore waters after three and one-half months. Rate constants for degradation of cholesterol in oxic and anoxic surficial sediments were estimated by tracking variations in radioactivity and sterol concentration as a function of time. We discuss our results in terms of factors affecting sterol degradation in coastal marine sediments, including molecular structure, sediment matrix effect, and redox conditions.

  • A study of oxic/anoxic effects on degradation of sterols at the simulated sediment–water Interface of coastal sediments
    Organic Geochemistry, 1998
    Co-Authors: Ming-yi Sun, Stuart G Wakeham
    Abstract:

    Laboratory incubation experiments were conducted to determine the behavior of sterols at the sediment–water Interface in oxic and anoxic sediments. Both plankton and 4-14C-cholesterol were used as tracers. Cholesterol was rapidly degraded at the sediment–water Interface: 55% of 14C-cholesterol was lost from sediments under anoxic conditions and 78% under oxic conditions over three and one-half months. About 3% of initially-added free radiolabel was incorporated into a bound pool that was released only by saponification of solvent-extracted sediment. Less than 1% of initially-added radiolabel remained in pore waters after three and one-half months. Rate constants for degradation of cholesterol in oxic and anoxic surficial sediments were estimated by tracking variations in radioactivity and sterol concentration as a function of time. We discuss our results in terms of factors affecting sterol degradation in coastal marine sediments, including molecular structure, sediment matrix effect, and redox conditions.

Jacques Grall - One of the best experts on this subject based on the ideXlab platform.

  • Transfer of metallic contaminants at the Sediment-Water Interface in a coastal lagoon: Role of the biological and microbial activity
    Journal De Physique. IV : JP, 2003
    Co-Authors: David Amouroux, Gilles Bareille, Laurent Chauvaud, Gerard Thouzeau, David Point, Emmanuel Tessier, Mathilde Monperrus, F Jean, Olivier F X Donard, Jacques Grall
    Abstract:

    Sediment-Water exchanges of trace metals and organometals in coastal environments are of primary concern for their cycling and environmental impact in these ecosystems. A multidisciplinary approach has been carried out in the Thau Lagoon on the French Mediterranean coast in order to investigate the role of the benthic ecology on trace metals and organometals cycling at the sediment water-Interface (Hg, Cd, Pb, Cu, Ni, MeHg+, Bu3Sn+). Incubation experiments have been performed at the sediment water-Interface at different stations using benthic chambers. Both hydrological parameters and trace metals and organometals have been sampled during these incubations in order to obtain an estimation of the Sediment-Water exchange fluxes. Benthic macrofauna and microbial populations have been examined to determined the major biological processes driving the benthic ecology at the different stations. The results indicate that the heterotrophic versus autotrophic benthic characteristics, as well as macrobenthic population, are driving factors for the Sediment-Water exchanges of trace metals and organometals.