Biomixing generated by benthic filterfeeders: A diffusion model for near-bottom phytoplankton depletion

Poul Scheel Larsen, H.U. Riisgård

    Research output: Contribution to journalJournal articleResearchpeer-review

    Abstract

    Transient concentration distributions of flagellate cells (Rhodomonas sp.) measured in laboratory experiments (Riisgård et al., 1996 a,b) have been examined to develop a diffusion model for the process of phytoplankton depletion in stagnant seawater above populations of benthic filter-feeders, the polychaete Nereis diversicolor and the ascidian Ciona intestinalis, respectively. The model is based on sinks located at inhalant openings and Fick's law with an effective diffusivity that decreases with distance above the bottom due to the biomixing generated by exhalant and inhalant feeding currents. For N. diversicolor, having inhalant and exhalant openings flush with the sediment surface and a moderate exhalant jet velocity of about 0.01 m s-1, concentration boundary layer growth is retarded and limited by the low values of diffusivity prevailing at heights greater than about 0.05 m above the bottom. For C. intestinalis, having inhalant and exhalant openings situated about 0.05-0.1 m above the bottom and a higher and inclined exhalant jet velocity of about 0.1-0.2 m s-1, the concentration distributions show a nearly uniform depletion over a layer reaching a thickness of 0.2-0.3 m above the bottom due to high biomixing in this layer. Numerical predictions of concentration distributions reproduce essential features of experiments, and suggest near-bottom values of effective diffusivity of 0.3 x 10-6 and 150 x 10-6 m2 s-1, respectively, for N. diversicolor and C. intestinalis. It is suggested that the latter value is so large that the induced mixing should be accounted for in modelling benthic concentration boundary layers under flow conditions.
    Original languageEnglish
    JournalJournal of Sea Research
    Volume37
    Pages (from-to)81-90
    ISSN1385-1101
    Publication statusPublished - 1997

    Cite this

    @article{25906262a4f74d6aa9840773ffaaf30e,
    title = "Biomixing generated by benthic filterfeeders: A diffusion model for near-bottom phytoplankton depletion",
    abstract = "Transient concentration distributions of flagellate cells (Rhodomonas sp.) measured in laboratory experiments (Riisg{\aa}rd et al., 1996 a,b) have been examined to develop a diffusion model for the process of phytoplankton depletion in stagnant seawater above populations of benthic filter-feeders, the polychaete Nereis diversicolor and the ascidian Ciona intestinalis, respectively. The model is based on sinks located at inhalant openings and Fick's law with an effective diffusivity that decreases with distance above the bottom due to the biomixing generated by exhalant and inhalant feeding currents. For N. diversicolor, having inhalant and exhalant openings flush with the sediment surface and a moderate exhalant jet velocity of about 0.01 m s-1, concentration boundary layer growth is retarded and limited by the low values of diffusivity prevailing at heights greater than about 0.05 m above the bottom. For C. intestinalis, having inhalant and exhalant openings situated about 0.05-0.1 m above the bottom and a higher and inclined exhalant jet velocity of about 0.1-0.2 m s-1, the concentration distributions show a nearly uniform depletion over a layer reaching a thickness of 0.2-0.3 m above the bottom due to high biomixing in this layer. Numerical predictions of concentration distributions reproduce essential features of experiments, and suggest near-bottom values of effective diffusivity of 0.3 x 10-6 and 150 x 10-6 m2 s-1, respectively, for N. diversicolor and C. intestinalis. It is suggested that the latter value is so large that the induced mixing should be accounted for in modelling benthic concentration boundary layers under flow conditions.",
    author = "{Scheel Larsen}, Poul and H.U. Riisg{\aa}rd",
    year = "1997",
    language = "English",
    volume = "37",
    pages = "81--90",
    journal = "Journal of Sea Research",
    issn = "1385-1101",
    publisher = "Elsevier",

    }

    Biomixing generated by benthic filterfeeders: A diffusion model for near-bottom phytoplankton depletion. / Scheel Larsen, Poul; Riisgård, H.U.

    In: Journal of Sea Research, Vol. 37, 1997, p. 81-90.

    Research output: Contribution to journalJournal articleResearchpeer-review

    TY - JOUR

    T1 - Biomixing generated by benthic filterfeeders: A diffusion model for near-bottom phytoplankton depletion

    AU - Scheel Larsen, Poul

    AU - Riisgård, H.U.

    PY - 1997

    Y1 - 1997

    N2 - Transient concentration distributions of flagellate cells (Rhodomonas sp.) measured in laboratory experiments (Riisgård et al., 1996 a,b) have been examined to develop a diffusion model for the process of phytoplankton depletion in stagnant seawater above populations of benthic filter-feeders, the polychaete Nereis diversicolor and the ascidian Ciona intestinalis, respectively. The model is based on sinks located at inhalant openings and Fick's law with an effective diffusivity that decreases with distance above the bottom due to the biomixing generated by exhalant and inhalant feeding currents. For N. diversicolor, having inhalant and exhalant openings flush with the sediment surface and a moderate exhalant jet velocity of about 0.01 m s-1, concentration boundary layer growth is retarded and limited by the low values of diffusivity prevailing at heights greater than about 0.05 m above the bottom. For C. intestinalis, having inhalant and exhalant openings situated about 0.05-0.1 m above the bottom and a higher and inclined exhalant jet velocity of about 0.1-0.2 m s-1, the concentration distributions show a nearly uniform depletion over a layer reaching a thickness of 0.2-0.3 m above the bottom due to high biomixing in this layer. Numerical predictions of concentration distributions reproduce essential features of experiments, and suggest near-bottom values of effective diffusivity of 0.3 x 10-6 and 150 x 10-6 m2 s-1, respectively, for N. diversicolor and C. intestinalis. It is suggested that the latter value is so large that the induced mixing should be accounted for in modelling benthic concentration boundary layers under flow conditions.

    AB - Transient concentration distributions of flagellate cells (Rhodomonas sp.) measured in laboratory experiments (Riisgård et al., 1996 a,b) have been examined to develop a diffusion model for the process of phytoplankton depletion in stagnant seawater above populations of benthic filter-feeders, the polychaete Nereis diversicolor and the ascidian Ciona intestinalis, respectively. The model is based on sinks located at inhalant openings and Fick's law with an effective diffusivity that decreases with distance above the bottom due to the biomixing generated by exhalant and inhalant feeding currents. For N. diversicolor, having inhalant and exhalant openings flush with the sediment surface and a moderate exhalant jet velocity of about 0.01 m s-1, concentration boundary layer growth is retarded and limited by the low values of diffusivity prevailing at heights greater than about 0.05 m above the bottom. For C. intestinalis, having inhalant and exhalant openings situated about 0.05-0.1 m above the bottom and a higher and inclined exhalant jet velocity of about 0.1-0.2 m s-1, the concentration distributions show a nearly uniform depletion over a layer reaching a thickness of 0.2-0.3 m above the bottom due to high biomixing in this layer. Numerical predictions of concentration distributions reproduce essential features of experiments, and suggest near-bottom values of effective diffusivity of 0.3 x 10-6 and 150 x 10-6 m2 s-1, respectively, for N. diversicolor and C. intestinalis. It is suggested that the latter value is so large that the induced mixing should be accounted for in modelling benthic concentration boundary layers under flow conditions.

    M3 - Journal article

    VL - 37

    SP - 81

    EP - 90

    JO - Journal of Sea Research

    JF - Journal of Sea Research

    SN - 1385-1101

    ER -