| 1. |
- Ehrnsten, Eva, et al.
(författare)
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Modelling the effects of benthic fauna on carbon, nitrogen and phosphorus dynamics in the Baltic Sea
- 2022
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Ingår i: Biogeosciences. - : Copernicus GmbH. - 1726-4170 .- 1726-4189. ; 19:13, s. 3337-3367
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Tidskriftsartikel (refereegranskat)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 active organic stocks (on average 1 %–4 % in 2000–2020) but contributes considerably to benthic–pelagic fluxes of inorganic C (23 %–31 %), N (42 %–51 %) and P (25 %–34 %) through its metabolism. Results also suggest that the relative contribution of fauna to the mineralization of sediment organic matter increases with increasing nutrient loads. Further, through enhanced sediment oxygenation, bioturbation decreases benthic denitrification and increases P retention, the latter having far-reaching consequences throughout the ecosystem. Reduced benthic–pelagic P fluxes lead to a reduction in 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 effects through the ecosystem overrides the local effects of faunal respiration, excretion and bioturbation. Due to large uncertainties related to the parameterization of benthic processes, we consider this modelling study a first step towards disentangling the complex ecosystem-scale effects of benthic fauna on biogeochemical cycling.
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| 2. |
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| 3. |
- Kuliński, Karol, et al.
(författare)
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Biogeochemical functioning of the Baltic Sea
- 2022
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Ingår i: Earth System Dynamics. - : Copernicus GmbH. - 2190-4979 .- 2190-4987. ; 13, s. 633-685
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Forskningsöversikt (refereegranskat)abstract
- Location, specific topography, and hydrographic setting together with climate change and strong anthropogenic pressure are the main factors shaping the biogeochemical functioning and thus also the ecological status of the Baltic Sea. The recent decades have brought significant changes in the Baltic Sea. First, the rising nutrient loads from land in the second half of the 20th century led to eutrophication and spreading of hypoxic and anoxic areas, for which permanent stratification of the water column and limited ventilation of deep-water layers made favourable conditions. Since the 1980s the nutrient loads to the Baltic Sea have been continuously decreasing. This, however, has so far not resulted in significant improvements in oxygen availability in the deep regions, which has revealed a slow response time of the system to the reduction of the land-derived nutrient loads. Responsible for that is the low burial efficiency of phosphorus at anoxic conditions and its remobilization from sediments when conditions change from oxic to anoxic. This results in a stoichiometric excess of phosphorus available for organic-matter production, which promotes the growth of N2-fixing cyanobacteria and in turn supports eutrophication. This assessment reviews the available and published knowledge on the biogeochemical functioning of the Baltic Sea. In its content, the paper covers the aspects related to changes in carbon, nitrogen, and phosphorus (C, N, and P) external loads, their transformations in the coastal zone, changes in organic-matter production (eutrophication) and remineralization (oxygen availability), and the role of sediments in burial and turnover of C, N, and P. In addition to that, this paper focuses also on changes in the marine CO2 system, the structure and functioning of the microbial community, and the role of contaminants for biogeochemical processes. This comprehensive assessment allowed also for identifying knowledge gaps and future research needs in the field of marine biogeochemistry in the Baltic Sea. Copyright:
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| 4. |
- Savchuk, Oleg, 1948-, et al.
(författare)
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Three-Dimensional Hindcast of Nitrogen and Phosphorus Biogeochemical Dynamics in Lake Onego Ecosystem, 1985–2015. Part II: Seasonal Dynamics and Spatial Features; Integral Fluxes : [Трехмерная ретроспективная оценка биогеохимической динамики азота и фосфора в экосистеме Онежского озера за период с 1985 по 2015 гг. Часть II: Сезонная динамика и пространственные особенности; интегральные потоки]
- 2022
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Ingår i: Fundamental and Applied Hydrophysics. - 2073-6673. ; 15:2, s. 98-109
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Tidskriftsartikel (refereegranskat)abstract
- A three-dimensional coupled hydrodynamical biogeochemical model of the nitrogen and phosphorus cycles has been used for a long-term reanalysis of the Lake Onego ecosystem. The comparison between simulation and sparse irregular observations, presented in the first part of this paper, demonstrated plausibility of the reconstructed temporal and spatial features of biogeochemical dynamics at a long-term scale, while seasonal dynamics of variables and fluxes are presented here. As new regional phenological knowledge, the reanalysis quantifies that the spring phytoplankton bloom, previously overlooked, reaches a maximum of 500 ± ± 128 mg C m-2 d-1 in May, contributes to approximately half of the lake's annual primary production of 17.0-20.6 g C m-2 yr-1, and is triggered by increasing light availability rather than by an insignificant rise in water temperature. Coherent nutrient budgets provide reliable estimates of phosphorus and nitrogen residence times of 47 and 17 years, respectively. The shorter nitrogen residence time is explained by sediment denitrification, which in Lake Onego removes over 90 % of the bioavailable nitrogen input, but is often ignored in studies of other large lakes. An overall assessment of the model performance allows us considering the model a necessary and reliable tool for scenario simulations of possible changes in the Lake Onego ecosystem at the requested spatial and temporal scales.
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| 5. |
- Svedäng, Henrik, et al.
(författare)
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On the decline of eastern Baltic cod : we need to take more holistic views into account. Reply to Brander (2022) comment on Svedäng et al. (2022)
- 2022
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Ingår i: ICES Journal of Marine Science. - : Oxford University Press (OUP). - 1054-3139 .- 1095-9289. ; 79:7, s. 2157-2158
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Tidskriftsartikel (refereegranskat)abstract
- Explaining the recent decline of eastern Baltic cod (EBC) remains scientifically challenging. Brander proposes in a comment to Svedäng et al.that the observed trend in oxygen in SD 25 supports the idea that juvenile cod are balancing the physiological cost of living under mild hypoxiaby offsetting the risk of being eaten by diving seals and cormorants in shallower water with more oxygen. There are a number of objections tothis conjecture, besides the fact that supporting observations are missing. Hence, it is difficult to reconcile the long-term development of EBCunder varying oxygen conditions with the hypothesis that a small reduction in oxygen content can explain the current strong and uniform declinein growth observed in the entire southern Baltic Sea.
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| 6. |
- Svedäng, Henrik, et al.
(författare)
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Re-thinking the “ecological envelope” of Eastern Baltic cod (Gadus morhua) : conditions for productivity, reproduction, and feeding over time
- 2022
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Ingår i: ICES Journal of Marine Science. - : Oxford University Press (OUP). - 1054-3139 .- 1095-9289. ; 79:3, s. 689-708
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Tidskriftsartikel (refereegranskat)abstract
- Hypoxia is presently seen as the principal driver behind the decline of the former dominating Eastern Baltic cod stock (EBC; Gadus morhua). It has been proposed that both worsening conditions for reproduction and lower individual growth, condition, and survival are linked to hypoxia. Here, we elucidate the ecological envelope of EBC in terms of salinity stratification, oxygen content, and benthic animal biomasses, and how it has affected EBC productivity over time. The spawning conditions started deteriorating in the Gotland Deep in the 1950s due to oxygen depletion. In contrast, in the Bornholm Basin, hydrographic conditions have remained unchanged over the last 60 years. Indeed, the current extent of both well-oxygenated areas and the frequency of hypoxia events do not differ substantially from periods with high EBC productivity in the 1970s–1980s. Furthermore, oxygenated and therefore potentially suitable feeding areas are abundant in all parts of the Baltic Sea, and our novel analysis provides no evidence of a reduction in benthic food sources for EBC over the last 30 years. We find that while reproduction failure is intricately linked to hydrographic dynamics, a relationship between the spread of hypoxia and the decline in EBC productivity during the last decades cannot be substantiated.
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