Modelling the effects of benthic fauna on carbon, nitrogen and phosphorus dynamics in the Baltic Sea

[摘要] Even though the effects of benthic fauna on aquaticbiogeochemistry have been long recognized, few studies have addressed thecombined effects of animal bioturbation and metabolism on ecosystem–levelcarbon and nutrient dynamics. Here we merge a model of benthic fauna (BMM)into a physical–biogeochemical ecosystem model (BALTSEM) to study thelong-term and large-scale effects of benthic fauna on nutrient and carboncycling in the Baltic Sea. We include both the direct effects of faunalgrowth and metabolism and the indirect effects of its bioturbatingactivities on biogeochemical fluxes of and transformations between organicand inorganic forms of carbon (C), nitrogen (N), phosphorus (P) and oxygen(O). Analyses of simulation results from the Baltic Proper and Gulf of Rigaindicate that benthic fauna makes up a small portion of seafloor activeorganic stocks (on average 1 %–4 % in 2000–2020) but contributesconsiderably to benthic–pelagic fluxes of inorganic C (23 %–31 %), N(42 %–51 %) and P (25 %–34 %) through its metabolism. Results alsosuggest that the relative contribution of fauna to the mineralization ofsediment organic matter increases with increasing nutrient loads. Further,through enhanced sediment oxygenation, bioturbation decreases benthicdenitrification and increases P retention, the latter having far-reachingconsequences throughout the ecosystem. Reduced benthic–pelagic P fluxeslead to a reduction in N fixation and primary production, lower organicmatter sedimentation fluxes, and thereby generally lower benthic stocks andfluxes of C, N and P. This chain of effects through the ecosystem overridesthe local effects of faunal respiration, excretion and bioturbation. Due tolarge uncertainties related to the parameterization of benthic processes, weconsider this modelling study a first step towards disentangling the complexecosystem-scale effects of benthic fauna on biogeochemical cycling.

[学科分类] 大气科学