01 Feb 2022
01 Feb 2022
Status: a revised version of this preprint is currently under review for the journal BG.

Large-scale effects of benthic fauna on carbon, nitrogen, and phosphorus dynamics in the Baltic Sea

Eva Ehrnsten1, Oleg Pavlovitch Savchuk1, and Bo Gustav Gustafsson1,2 Eva Ehrnsten et al.
  • 1Baltic Nest Institute, Baltic Sea Centre, Stockholm University, Stockholm, 10691, Sweden
  • 2Tvärminne Zoological Station, University of Helsinki, Hanko, 10900, Finland

Abstract. Even though the effects of benthic fauna on aquatic biogeochemistry have been long recognized, few studies have addressed the combined effects of animal bioturbation and metabolism on ecosystem–level carbon and nutrient dynamics. Here we merge a model of benthic fauna (BMM) into a physical–biogeochemical ecosystem model (BALTSEM) to study the long–term and large–scale effects of benthic fauna on nutrient and carbon cycling in the Baltic Sea. We include both the direct effects of faunal growth and metabolism and the indirect effects of its bioturbating activities on biogeochemical fluxes of and transformations between organic and inorganic forms of carbon (C), nitrogen (N), phosphorus (P) and oxygen (O). Analyses of simulation results from the Baltic Proper and Gulf of Riga indicate that benthic fauna makes up a small portion of seafloor organic stocks, but contributes considerably to benthic–pelagic fluxes of inorganic C, N and P through its metabolism. Results also suggest that the relative contribution of fauna to mineralisation of sediment organic matter increases with increasing nutrient loads. Further, bioturbation decreases benthic denitrification and increases P retention in sediments, the latter having far–reaching consequences throughout the ecosystem. Reduced benthic–pelagic P fluxes lead to a reduction of N fixation and primary production, lower organic matter sedimentation fluxes and thereby generally lower benthic stocks and fluxes of C, N and P. This chain of indirect effects overrides the direct effects of faunal respiration, excretion and bioturbation. Due to large uncertainties related to parameterization of benthic processes, we consider this modelling study a first step towards disentangling the complex large–scale effects of benthic fauna on biogeochemical cycling.

Eva Ehrnsten et al.

Status: final response (author comments only)

Comment types: AC – author | RC – referee | CC – community | EC – editor | CEC – chief editor | : Report abuse
  • RC1: 'Comment on bg-2022-31', Anonymous Referee #1, 01 Mar 2022
    • AC1: 'Reply on RC1', Eva Ehrnsten, 14 Apr 2022
    • AC4: 'Reply on RC1', Eva Ehrnsten, 14 Apr 2022
  • RC2: 'Comment on bg-2022-31', Hans Cederwall, 07 Mar 2022
  • RC3: 'Comment on bg-2022-31', Anonymous Referee #3, 14 Mar 2022
    • AC3: 'Reply on RC3', Eva Ehrnsten, 14 Apr 2022
    • AC4: 'Reply on RC1', Eva Ehrnsten, 14 Apr 2022

Eva Ehrnsten et al.

Eva Ehrnsten et al.


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Short summary
We studied the effects of benthic fauna, animals living on or in the seafloor, on the biogeochemical cycles of carbon, nitrogen and phosphorus using a model of the Baltic Sea ecosystem. By eating and excreting, the animals transform a large part of organic matter sinking to the seafloor into inorganic forms, which fuel plankton blooms. Simultaneously, when they move around (bioturbate), phosphorus is bound in the sediments. This reduces nitrogen-fixing plankton blooms and oxygen depletion.