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  • 1. Ahlgren, Joakim
    et al.
    Grimvall, Anders
    Omstedt, Anders
    Rolff, Carl
    Stockholm University, Faculty of Science, Stockholm University Baltic Sea Centre. Swedish Institute for the Marine Environment, Sweden.
    Wikner, Johan
    Temperature, DOC level and basin interactions explain the declining oxygen concentrations in the Bothnian Sea2017In: Journal of Marine Systems, ISSN 0924-7963, E-ISSN 1879-1573, Vol. 170, p. 22-30Article in journal (Refereed)
    Abstract [en]

    Hypoxia and oxygen deficient zones are expanding worldwide. To properly manage this deterioration of the marine environment, it is important to identify the causes of oxygen declines and the influence of anthropogenic activities. Here, we provide a study aiming to explain the declining oxygen levels in the deep waters of the Bothnian Sea over the past 20 years by investigating data from environmental monitoring programmes. The observed decline in oxygen concentrations in deep waters was found to be primarily a consequence of water temperature increase and partly caused by an increase in dissolved organic carbon (DOC) in the seawater (R-Adj(2). = 0.83) as well as inflow from the adjacent sea basin. As none of the tested eutrophication-related predictors were significant according to a stepwise multiple regression, a regional increase in nutrient inputs to the area is unlikely to explain a significant portion of the oxygen decline. Based on the findings of this study, preventing the development of anoxia in the deep water of the Bothnian Sea is dependent on the large-scale measures taken to reduce climate change. In addition, the reduction of the nutrient load to the Baltic Proper is required to counteract the development of hypoxic and phosphate-rich water in the Baltic Proper, which can form deep water in the Bothnian Sea. The relative importance of these sources to oxygen consumption is difficult to determine from the available data, but the results clearly demonstrate the importance of climate related factors such as temperature, DOC and inflow from adjacent basins for the oxygen status of the sea.

  • 2. Almroth-Rosell, Elin
    et al.
    Eilola, Kari
    Kuznetsov, Ivan
    Hall, Per O. J.
    Meier, H. E. Markus
    Stockholm University, Faculty of Science, Department of Meteorology . Swedish Meteorological and Hydrological Institute, Sweden.
    A new approach to model oxygen dependent benthic phosphate fluxes in the Baltic Sea2015In: Journal of Marine Systems, ISSN 0924-7963, E-ISSN 1879-1573, Vol. 144, p. 127-141Article in journal (Refereed)
    Abstract [en]

    The new approach to model the oxygen dependent phosphate release by implementing formulations of the oxygen penetration depths (OPD) and mineral bound inorganic phosphorus pools to the Swedish Coastal and Ocean Biogeochemical model (SCOBI) is described. The phosphorus dynamics and the oxygen concentrations in the Baltic proper sediment are studied during the period 1980-2008 using SCOBI coupled to the 3D-Rossby Centre Ocean model. Model data are compared to observations from monitoring stations and experiments. The impact from oxygen consumption on the determination of the OPD is found to be largest in the coastal zones where also the largest OPD are found. In the deep water the low oxygen concentrations mainly determine the OPD. Highest modelled release rate of phosphate from the sediment is about 59 x 10(3) t P year(-1) and is found on anoxic sediment at depths between 60-150 m, corresponding to 17% of the Baltic proper total area. The deposition of organic and inorganic phosphorus on sediments with oxic bottom water is larger than the release of phosphorus, about 43 x 10(3) t P year(-1). For anoxic bottoms the release of total phosphorus during the investigated period is larger than the deposition, about 19 x 10(3) t P year(-1). In total the net Baltic proper sediment sink is about 23.7 x 10(3) t P year(-1). The estimated phosphorus sink efficiency of the entire Baltic Sea is on average about 83% during the period.

  • 3. Björk, Göran
    et al.
    Nordberg, Kjell
    Arneborg, Lars
    Bornmalm, Lennart
    Harland, Rex
    Robijn, Ardo
    Ödalen, Malin
    Stockholm University, Faculty of Science, Department of Meteorology .
    Seasonal oxygen depletion in a shallow sill fjord on the Swedish west coast2017In: Journal of Marine Systems, ISSN 0924-7963, E-ISSN 1879-1573, Vol. 175, p. 1-14Article in journal (Refereed)
    Abstract [en]

    During the summer of 2008, oxygen depleted water, between 5 and 12 m depth, was discovered in Sannasfjord on the Swedish west coast. The resulting sediments were black, benthic macrofauna were absent and Beggiatoa bacterial mats were a characteristic feature. This phenomenon, which was observed several years in a row, appears to be a relatively new phenomenon starting in the mid-1980s. In this study we attempt to find the underlying causes by investigating climatic effects (temperature, wind and precipitation), the local supply of nutrients from land, ecosystem change and the supply of organic material from the open Skagerrak. An analysis of long meteorological time series indicates that climatic effects are contributory, but probably not a dominating factor leading to hypoxia. Results from an advection-diffusion model solving for oxygen show that the observed increase in the river supply of nutrients has a high potential to generate hypoxia. Although complex and more difficult to quantify, it appears that ecosystem changes, with higher abundance of filamentous algae, may have played an important role. It is also possible that an enhanced supply of organic material from the open Skagerrak has contributed.

  • 4.
    Dahlgren Strååt, Kim
    et al.
    Stockholm University, Faculty of Science, Department of Environmental Science and Analytical Chemistry.
    Mörth, Carl-Magnus
    Stockholm University, Faculty of Science, Department of Geological Sciences. Stockholm University, Faculty of Science, Stockholm University Baltic Sea Centre.
    Undeman, Emma
    Stockholm University, Faculty of Science, Department of Environmental Science and Analytical Chemistry. Stockholm University, Faculty of Science, Stockholm University Baltic Sea Centre.
    Future export of particulate and dissolved organic carbon from land to coastal zones of the Baltic Sea2018In: Journal of Marine Systems, ISSN 0924-7963, E-ISSN 1879-1573, Vol. 177, p. 8-20Article in journal (Refereed)
    Abstract [en]

    The Baltic Sea is a semi-enclosed brackish sea in Northern Europe with a drainage basin four times larger than the sea itself. Riverine organic carbon (Particulate Organic Carbon, POC and Dissolved Organic Carbon, DOC) dominates carbon input to the Baltic Sea and influences both land-to-sea transport of nutrients and contaminants, and hence the functioning of the coastal ecosystem. The potential impact of future climate change on loads of POC and DOC in the Baltic Sea drainage basin (BSDB) was assessed using a hydrological-biogeochemical model (CSIM). The changes in annual and seasonal concentrations and loads of both POC and DOC by the end of this century were predicted using three climate change scenarios and compared to the current state. In all scenarios, overall increasing DOC loads, but unchanged POC loads, were projected in the north. In the southern part of the BSDB, predicted DOC loads were not significantly changing over time, although POC loads decreased in all scenarios. The magnitude and significance of the trends varied with scenario but the sign (+ or -) of the projected trends for the entire simulation period never conflicted. Results were discussed in detail for the middle CO2 emission scenario (business as usual, a1b). On an annual and entire drainage basin scale, the total POC load was projected to decrease by ca 7% under this scenario, mainly due to reduced riverine primary production in the southern parts of the BSDB. The average total DOC load was not predicted to change significantly between years 2010 and 2100 due to counteracting decreasing and increasing trends of DOC loads to the six major sub-basins in the Baltic Sea. However, predicted seasonal total loads of POC and DOC increased significantly by ca 46% and 30% in winter and decreased by 8% and 21% in summer over time, respectively. For POC the change in winter loads was a consequence of increasing soil erosion and a shift in duration of snowfall and onset of the spring flood impacting the input of terrestrial litter, while reduced primary production mainly explained the differences predicted in summer. The simulations also showed that future changes in POC and DOC export can vary significantly across the different sub-basins of the Baltic Sea. These changes in organic carbon input may impact future coastal food web structures e.g. by influencing bacterial and phytoplankton production in coastal zones, which in turn may have consequences at higher trophic levels.

  • 5.
    Demina, Ludmila
    et al.
    P.P Shirshov Institute of Oceanology, Russian Academy of Sciences.
    Holm, Nils
    Stockholm University, Faculty of Science, Department of Geological Sciences.
    Galkin, Sergey
    P.P Shirshov Institute of Oceanology, Russian Academy of Sciences.
    Lein, Alla
    P.P. Shirshov Institute of Oceanology, Russian Academy of Sciences.
    Some features of the trace metal biogeochemistry in the deep-sea hydrothermal vent fields (Menez Gwen, Rainbow, Broken Spur at the MAR and 9°50'N at the EPR): A synthesis2013In: Journal of Marine Systems, ISSN 0924-7963, E-ISSN 1879-1573, Vol. 126, no SI, p. 94-105Article in journal (Refereed)
    Abstract [en]

    Along with summarizing the published literature and our own data some new results on properties of the trace metal biogeochemistry in the deep-sea hydrothermal ecosystems at the Mid-Atlantic Ridge (MAR) and East Pacific Rise (EPR) are shown. Differences in mean concentrations of big group of trace metals (Fe, Mn, Zn, Cu, Ni, Cr, Co, As, Pb, Cd, Ag, Hg) between the biotope water of the low- and high-temperature hydrothermal vent fields were firstly revealed. The same trace metals were studied in different groups of organisms within different temperature zones at one and the same vent field (9°50′N EPR), as well as in fauna inhabiting geochemically different vent sites. Distribution patterns of Fe, Mn, Zn, Cu, Cd, Pb, Ag, Ni, Cr, Co, As, Se, Sb, and Hg in different taxa gave an evidence of the influence of environmental and biological parameters on their bioaccumulation in organisms. Among the animals a particular “champion” with respect to the trace metal content was found to be a polychaeta Alvinella pompejana that inhabits the hottest places of the vent sulfide chimneys of the 9°50′N field, EPR. New data on the trace metal distribution between soft tissues and carbonate shell let us estimate a role of biomineralization in the accumulation of metals in the Bathimodiolus mussels. Contrasting geochemical behavior was revealed for Cu that is enriched in soft tissues of mussels and depleted in shells, on the one hand, and Mn that is accumulated almost totally in mussel shells, on the other hand.

    Deep-sea hydrothermal biological communities demonstrate a strong concentration function, and bioconcentration factors (BCF) of trace metals estimated for Bathimodiolus mussels collected at the four hydrothermal fields vary within the limits of n102–n105 and are similar to that of the littoral mussels. Due to this and to the high values of biomasses per square meter, the hydrothermal fauna may be considered as a newly discovered biological filter of the oceans.

  • 6.
    Ehrnsten, Eva
    et al.
    Stockholm University, Faculty of Science, Stockholm University Baltic Sea Centre. University of Helsinki, Finland.
    Norkko, Alf
    Stockholm University, Faculty of Science, Stockholm University Baltic Sea Centre. University of Helsinki, Finland.
    Timmermann, Karen
    Gustafsson, Bo G.
    Stockholm University, Faculty of Science, Stockholm University Baltic Sea Centre. University of Helsinki, Finland.
    Benthic-pelagic coupling in coastal seas - Modelling macrofaunal biomass and carbon processing in response to organic matter supply2019In: Journal of Marine Systems, ISSN 0924-7963, E-ISSN 1879-1573, Vol. 196, p. 36-47Article in journal (Refereed)
    Abstract [en]

    Benthic macrofauna is an important component linking pelagic and benthic ecosystems, especially in productive coastal areas. Through their metabolism and behaviour, benthic animals affect biogeochemical fluxes between the sediment and water column. Mechanistic models that quantify these benthic-pelagic links are imperative to understand the functioning of coastal ecosystems. In this study, we develop a dynamic model of benthic macrofauna to quantify the relationship between organic matter input and benthic macrofaunal biomass in the coastal zone. The model simulates the carbon dynamics of three functional groups of benthic macrofauna and their sediment food sources and is forced by a hydrodynamic-biogeochemical model simulating pelagic physical and biological dynamics. The model reproduces measured time-series of macrofaunal biomass from two coastal sites with contrasting sedimentation in the Baltic Sea in 1993-2005 with comparatively high accuracy, including a major increase at one of the sites dominated by the bivalve Limecola (Macoma) balthica. This shift in community composition suggests altered pathways of organic matter degradation: 39% of simulated sedimentation was mineralised by macrofauna in 2005 compared to 10% in 1995. From the early 2000s onward macrofaunal biomass seems to be food-limited, as ca 80% of organic carbon sedimentation was processed by the deposit-feeding macrofauna at both sites. This model is a first step to help quantify the role of macrofauna in marine coastal ecosystem functioning and biogeochemical cycles and build predictive capacity of the effects of anthropogenic stressors, such as eutrophication and climate change, on coastal ecosystems.

  • 7. Eilola, K.
    et al.
    Gustafsson, Bo G.
    Stockholm University, Stockholm Resilience Centre, Baltic Nest Institute.
    Kuznetsov, I.
    Meier, H. E. M.
    Neumann, T.
    Savchuk, O. P.
    Stockholm University, Stockholm Resilience Centre, Baltic Nest Institute.
    Evaluation of biogeochemical cycles in an ensemble of three state-of-the-art numerical models of the Baltic Sea2011In: Journal of Marine Systems, ISSN 0924-7963, E-ISSN 1879-1573, Vol. 88, no 2, p. 267-284Article in journal (Refereed)
    Abstract [en]

    Three state-of-the-art coupled physical-biogeochemical models, the BAltic sea Long-Term large-Scale Eutrophication Model (BALTSEM), the Ecological Regional Ocean Model (ERGOM), and the Swedish Coastal arid Ocean Biogeochemical model coupled to the Rossby Centre Ocean circulation model (RCO-SCOBI), are used to calculate changing nutrient and oxygen dynamics in the Baltic Sea. The models are different in that ERGOM and RCO-SCOBI are three-dimensional (3D) circulation models while BALTSEM resolves the Baltic Sea into 13 dynamically interconnected and horizontally integrated sub-basins. The aim is to assess the simulated long-term dynamics and to discuss the response of the coupled physical-biogeochemical models to changing physical conditions and nutrient loadings during the period 1970-2005. We compared the long-term seasonal and annual statistics of inorganic nitrogen, phosphorus, and oxygen from hindcast simulations with those estimated from observations. We also studied the extension of hypoxic bottom areas covered by waters with O(2)<2 ml O(2) l(-1) and cod reproductive volumes comprising waters with salinity >11 and O(2)>2 ml O(2) l(-1). The models reproduce much of the nutrient biogeochemical cycling in the Baltic proper. However, biases are larger in the Bothnian Sea and Bothnian Bay. No model shows outstanding performance in all aspects but instead the ensemble mean results are better than or as good as the results of any of the individual models. Uncertainties are primarily related to differences in the bioavailable fractions of nutrient loadings from land and parameterizations of key processes like sediment fluxes that are presently not well known. Also the uncertainty related to the initialization of the models in the early 1960s influence the modeled biogeochemical cycles during the investigated period.

  • 8.
    Ekeroth, Nils
    et al.
    Stockholm University, Faculty of Science, Department of Ecology, Environment and Plant Sciences.
    Kononets, Mikhail
    Walve, Jakob
    Stockholm University, Faculty of Science, Department of Ecology, Environment and Plant Sciences.
    Blomqvist, Sven
    Stockholm University, Faculty of Science, Department of Ecology, Environment and Plant Sciences.
    Hall, Per O. J.
    Effects of oxygen on recycling of biogenic elements from sediments of a stratified coastal Baltic Sea basin2016In: Journal of Marine Systems, ISSN 0924-7963, E-ISSN 1879-1573, Vol. 154, p. 206-219Article in journal (Refereed)
    Abstract [en]

    Benthic nutrient dynamics in the coastal basin Kanholmsfjarden, NW Baltic proper, were studied by in situ flux measurements and sediment samplings in 2010-2013. The benthic release of NH4 and DIP from anoxic sediments in Kanholmsfjarden were calculated to renew the standing stock inventories of DIN and DIP in the overlying water in roughly 1 year. Starting in summer 2012, mixing of oxygen-rich water into the deep part of the basin temporarily improved the oxygen conditions in the deep water. During the 1 year oxygenated period, the total phosphorus inventory in the surficial sediment increased by 0.4 g P m(-2) or 65%. This was most likely due to stimulated bacterial P assimilation under oxygenated conditions. By July 2013, the bottom water had again turned anoxic, and DIP and DSi fluxes were even higher than earlier in the study period. These high fluxes are attributed to degradation of sedimentary pools of P and Si that had accumulated during the bottom water oxygenation in 2012. The strong correlation between DIP and DSi fluxes and the similar dynamics of DIP and DSi in the sediment pore water and near bottom water, suggest a similar redox dependency of benthic-pelagic exchange for these nutrients.

  • 9.
    Gustafsson, Erik
    et al.
    Stockholm University, Faculty of Science, Stockholm University Baltic Sea Centre, Baltic Nest Institute.
    Deutsch, Barbara
    Stockholm University, Faculty of Science, Department of Applied Environmental Science (ITM). Stockholm University, Faculty of Science, Stockholm University Baltic Sea Centre, Baltic Nest Institute.
    Gustafsson, Bo G.
    Stockholm University, Faculty of Science, Stockholm University Baltic Sea Centre, Baltic Nest Institute.
    Humborg, Christoph
    Stockholm University, Faculty of Science, Department of Applied Environmental Science (ITM). Stockholm University, Faculty of Science, Stockholm University Baltic Sea Centre, Baltic Nest Institute.
    Mörth, Carl-Magnus
    Stockholm University, Faculty of Science, Department of Geological Sciences. Stockholm University, Faculty of Science, Stockholm University Baltic Sea Centre, Baltic Nest Institute.
    Carbon cycling in the Baltic Sea - The fate of allochthonous organic carbon and its impact on air-sea CO2 exchange2014In: Journal of Marine Systems, ISSN 0924-7963, E-ISSN 1879-1573, Vol. 129, p. 289-302Article in journal (Refereed)
    Abstract [en]

    A coupled physical-biogeochemical model (BALTSEM) is used to estimate carbon fluxes in the Baltic Sea over the 1980-2006 period. Budget calculations for organic carbon indicate that of the total allochthonous organic carbon (TOCT) supplied to the system, on average 56% is mineralized, 36% is exported out of the system, and the remainder is buried. River discharge is the main source of dissolved inorganic carbon (DIC) to the Baltic Sea. However, model results indicate that in the Gulf of Bothnia (northern Baltic Sea), the contribution to the DIC stock by TOCT mineralization is of the same order as direct river input of DIC In the Kattegat and Danish Straits (southwestern Baltic Sea) on the other hand, net uptake of atmospheric CO2 comprises the major DIC source. Despite large variations within the system, with net outgassing from some sub-basins and net absorption in others, the Baltic Sea as a whole was estimated to be a net sink for atmospheric CO2. Mineralization of allochthonous dissolved organic carbon (DOCT) influences air-sea CO2 exchange. A sensitivity study indicates that depending on the labile fraction of DOCT, the contribution from CO2 absorption to total external DIC sources can amount to 10-25%.

  • 10.
    Gustafsson, Erik
    et al.
    Stockholm University, Faculty of Science, Stockholm University Baltic Sea Centre, Baltic Nest Institute.
    Mörth, Carl-Magnus
    Stockholm University, Faculty of Science, Stockholm University Baltic Sea Centre, Baltic Nest Institute. Stockholm University, Faculty of Science, Department of Geological Sciences.
    Humborg, Christoph
    Stockholm University, Faculty of Science, Stockholm University Baltic Sea Centre, Baltic Nest Institute. Stockholm University, Faculty of Science, Department of Applied Environmental Science (ITM).
    Gustafsson, Bo G.
    Stockholm University, Faculty of Science, Stockholm University Baltic Sea Centre, Baltic Nest Institute.
    Modelling the C-13 and C-12 isotopes of inorganic and organic carbon in the Baltic Sea2015In: Journal of Marine Systems, ISSN 0924-7963, E-ISSN 1879-1573, Vol. 148, p. 122-130Article in journal (Refereed)
    Abstract [en]

    In this study, C-12 and C-13 contents of all carbon containing state variables (dissolved inorganic and organic carbon, detrital carbon, and the carbon content of autotrophs and heterotrophs) have for the first time been explicitly included in a coupled physical-biogeochemical Baltic Sea model. Different processes in the carbon cycling have distinct fractionation values, resulting in specific isotopic fingerprints. Thus, in addition to simulating concentrations of different tracers, our new model formulation improves the possibility to constrain the rates of processes such as CO2 assimilation, mineralization, and air-sea exchange. We demonstrate that phytoplankton production and respiration, and the related air-sea CO2 fluxes, are to a large degree controlling the isotopic composition of organic and inorganic carbon in the system. The isotopic composition is further, but to a lesser extent, influenced by river loads and deep water inflows as well as transformation of terrestrial organic carbon within the system. Changes in the isotopic composition over the 20th century have been dominated by two processes the preferential release of C-12 to the atmosphere in association with fossil fuel burning, and the eutrophication of the Baltic Sea related to increased nutrient loads under the second half of the century.

  • 11.
    Humborg, Christoph
    et al.
    Stockholm University, Faculty of Science, Department of Applied Environmental Science (ITM).
    Rahm, Lars
    Conley, Daniel J.
    Tamminen, Timo
    von Bodungen, Bodo
    Silicon and the Baltic Sea: Long-term Si decrease in the Baltic Sea - A conceivable ecological risk?2008In: Journal of Marine Systems, ISSN 0924-7963, E-ISSN 1879-1573, Vol. 73, no 3-4, p. 221-222Article in journal (Refereed)
  • 12.
    Humborg, Christoph
    et al.
    Stockholm University, Faculty of Science, Department of Applied Environmental Science (ITM).
    Smedberg, Erik
    Stockholm University, Faculty of Science, Department of Applied Environmental Science (ITM).
    Rodriguez Medina, Miguel
    Stockholm University, Faculty of Science, Department of Systems Ecology.
    Mörth, Carl-Magnus
    Stockholm University, Faculty of Science, Department of Geology and Geochemistry.
    Changes in dissolved silicate loads to the Baltic Sea: The effects of lakes and reservoirs2008In: Journal of Marine Systems, ISSN 0924-7963, E-ISSN 1879-1573, Vol. 73, no 3-4, p. 223-235Article in journal (Refereed)
    Abstract [en]

    We tested the hypothesis that dissolved silicate (DSi) yields [kg km− 2 yr− 1] of 82 major watersheds of the Baltic Sea can be expressed as a function of the hydraulic load (HL) as a measure of water residence time and the total organic carbon (TOC) concentration, both variables potentially increasing the DSi yield. Most boreal rivers fitted a linear regression model using HL as an independent variable to explain the DSi yield. Rivers with high HL, i.e., shortest residence times, showed highest DSi yields up to 2300 kg km− 2 yr− 1. This is most likely caused by an excess supply of DSi, i.e., the geochemical sources prevail over biological sinks in these boreal watersheds. The DSi yield for regulated and unregulated larger rivers of the boreal watersheds constituting about 40% of the total water discharge and of the total DSi load to the Baltic Sea, respectively, can be expressed as: DSi yield = 190 + 49.5 HL[m yr− 1] + 0.346 TOC [µM] (R2 = 0.80). Since both HL and TOC concentrations have decreased after damming, the DSi yields have decreased significantly in the regulated boreal watersheds, for the River Luleälven we estimated more than 30%. The larger eutrophic watersheds draining cultivated landscape of the southern catchment of the Baltic Sea and representing about 50% of the annual water discharge to the Baltic Sea, deviated from this pattern and showed lower DSi yields between 60–580 kg km− 2 yr− 1. DSi yields showed saturation curve like relationship to HL and it appears that DSi is retained in the watersheds efficiently through biogenic silica (BSi) production and subsequent sedimentation along the entire river network. The relationship between HL and DSi yields for all larger cultivated watersheds was best fitted by a Freundlich isotherm (DSi = 115.7HL109; R2 = 0.73), because once lake and reservoir area exceeds 10% of the watershed area, minimum DSi yields were reached. To estimate an uperturbed DSi yield for the larger eutrophic southeastern watersheds is still difficult, since no unperturbed watersheds for comparison were available. However, a rough estimate indicate that the DSi flux from the cultivated watersheds to the Baltic Sea is nowadays only half the uperturbed flux. Overall, the riverine DSi loads to the Baltic Sea might have dropped with 30–40% during the last century.

  • 13. Isaev, A. V.
    et al.
    Eremina, T. R.
    Ryabchenko, V. A.
    Savchuk, Oleg P.
    Stockholm University, Faculty of Science, Stockholm University Baltic Sea Centre, Baltic Nest Institute. St. Petersburg State University, Russia.
    Model estimates of the impact of bioirrigation activity of Marenzelleria spp. on the Gulf of Finland ecosystem in a changing climate2017In: Journal of Marine Systems, ISSN 0924-7963, E-ISSN 1879-1573, Vol. 171, p. 81-88Article in journal (Refereed)
    Abstract [en]

    Drastic changes have occurred in the Eastern Gulf of Finland ecosystem after recent invasion and establishment of polychaete Marenzelleria spp. Possible mechanisms of these changes are explored with the help of three-dimensional ecosystem model SPBEM. Relative significance of bioirrigation activity is studied by comparison of two climate change scenario simulations, which include or disregard Marenzelleria effects. The novel results obtained with this approach demonstrate that on a system level biogeochemical consequences of both implemented climate changes scenario and polychaete activity are equivalent to a weakening of vicious circle of the Baltic Sea eutrophication. The eutrophication-mitigating effects of the Marenzelleria invasion into the Eastern Gulf of Finland, revealed by the long-term field measurements, are explained by simulation-based considerations.

  • 14.
    Jönsson, Anders
    et al.
    Stockholm University, Faculty of Science, Department of Geology and Geochemistry. Stockholm University, Faculty of Science, Department of Applied Environmental Science (ITM).
    Lindström, Martin
    Carman, Rolf
    Stockholm University, Faculty of Science, Department of Geology and Geochemistry.
    Mörth, Carl-Magnus
    Stockholm University, Faculty of Science, Department of Geology and Geochemistry.
    Meili, Markus
    Stockholm University, Faculty of Science, Department of Applied Environmental Science (ITM).
    Gustafsson, Örjan
    Stockholm University, Faculty of Science, Department of Applied Environmental Science (ITM).
    Evaluation of the Stockholm archipelago, northwestern Baltic Sea proper, as a trap for freshwater-runoff organic carbon2005In: Journal of Marine Systems, ISSN 0924-7963, E-ISSN 1879-1573, Vol. 56, no 1-2, p. 167-178Article in journal (Refereed)
    Abstract [en]

    Time-series data on the freshwater inflow of total organic carbon (TOC) to the Stockholm Archipelago, Baltic Sea, covering four full years, showed a distinct seasonal pattern with six times higher monthly flow in winter–spring than in the summer with an annual freshwater TOC input of 28 Gg year−1. Estimation of burial flux and source apportionment of sedimentary OC in the Inner Archipelago (IA) was based on extensive sediment sampling of seismically surveyed accumulation bottom areas. The resulting IA-averaged OC content was 56±16 mg g dw−1 sediment, yielding an IA-wide bottom sediment deposition for the 1992–1995 period of 3.1 Gg year−1.

    The sediments in the eastern Lake Mälaren (LM), IA, and Outer Archipelago (OA) were geochemically distinguishable based on their stable carbon isotope signatures (δ13C). The δ13C values were −28.2±0.6, −25.4±1.0, and −23.6±0.3, respectively, for LM (n=15), IA (n=17), and OA (n=31). These spatial trends were consistent with the C:N ratios, which were 9.96±1.2, 9.29±0.73, and 9.13±0.22 for the same subsystems. Using a simple isotopic mass balance model, it was deduced that about one-third (39%) of the OC burial in the IA sediments was of Lake Mälaren runoff origin.

    Hence, a low archipelago-trapping efficiency of only 4% for the runoff TOC was found to be accumulating in the sediments underlying the approximately 30 km transect through the IA eastward of Stockholm. This scenario suggests that the organic matter and associated substances added by the Lake Mälaren outflow, passing through urban Stockholm, are largely either remineralised and released to the IA water column, or transported with the currents to more pristine offshore Baltic ecosystems.

  • 15.
    Kari, Elina
    et al.
    Stockholm University, Faculty of Science, Department of Ecology, Environment and Plant Sciences.
    Merkouriadi, Ioanna
    Walve, Jakob
    Stockholm University, Faculty of Science, Department of Ecology, Environment and Plant Sciences.
    Leppäranta, Matti
    Kratzer, Susanne
    Stockholm University, Faculty of Science, Department of Ecology, Environment and Plant Sciences.
    Development of under-ice stratification in Himmerfjärden bay, north-western Baltic proper, and their effect on the phytoplankton spring bloom2018In: Journal of Marine Systems, ISSN 0924-7963, E-ISSN 1879-1573, Vol. 186, p. 85-95Article in journal (Refereed)
    Abstract [en]

    Seasonal sea ice cover reduces wind-driven mixing and allows for under-ice stratification to develop. These under-ice plumes are a common phenomenon in the seasonal sea ice zone. They stabilize stratification and concentrate terrestrial runoff in the top layer, transporting it further offshore than during ice-free seasons. In this study, the effect of sea ice on spring stratification is investigated in Himmerfjärden bay in the NW Baltic Sea. Distinct under-ice plumes were detected during long ice seasons. The preconditions for the development of the under-ice plumes are described as well as the typical spatial and temporal dimensions of the resulting stratification patterns. Furthermore, the effect of the under-ice plume on the timing of the onset and the maximum of the phytoplankton spring bloom were investigated, in terms of chlorophyll-a (Chl-a) concentrations. At the head of the bay, bloom onset was delayed on average by 18 days in the event of an under-ice plume. However, neither the maximum concentration of Chl-a nor the timing of the Chl-a maximum were affected, implying that the growth period was shorter with a higher daily productivity. During this period from spring bloom onset to maximum Chl-a, the diatom biomass was higher and Mesodinium rubrum biomass was lower in years with under-ice plumes compared to years without under-ice plumes. Our results thus suggest that the projected shorter ice seasons in the future will reduce the probability of under-ice plume development, creating more dynamic spring bloom conditions. These dynamic conditions and the earlier onset of the spring bloom seem to favor the M. rubrum rather than diatoms.

  • 16. Lehtoranta, Jouni
    et al.
    Savchuk, Oleg P.
    Stockholm University, Faculty of Science, Stockholm University Baltic Sea Centre, Baltic Nest Institute.
    Elken, Juri
    Dahlbo, Kim
    Kuosa, Harri
    Raateoja, Mika
    Kauppila, Pirkko
    Raike, Antti
    Pitkanen, Heikki
    Atmospheric forcing controlling inter-annual nutrient dynamics in the open Gulf of Finland2017In: Journal of Marine Systems, ISSN 0924-7963, E-ISSN 1879-1573, Vol. 171, p. 4-20Article in journal (Refereed)
    Abstract [en]

    The loading of P into the Gulf of Finland has decreased markedly, but no overall trend in the concentration of P has been observed in the open Gulf, where the concentrations of both inorganic N and P still have a pronounced inter annual variability. Our main aim was to study whether the internal processes driven by atmospheric forcing can explain the variation in the nutrient conditions in the Gulf during the period 1992-2014. We observed that the long-term salinity variation of the bottom water in the northern Baltic Proper controls that in the Gulf, and that the deep-water concentrations of oxygen and nutrients are significantly correlated between the basins. This imposes preconditions regarding how atmospheric forcing may influence deep water flows and stratification in the Gulf on a long-term scale. We found that over short timescales, winter winds in particular can control the in- and outflows of water and the vertical stratification and mixing, which to a large extent explained the inter-annual variation in the DIN and TP pools in the Gulf. We conclude that the inter-annual variation in the amounts, ratios, and spatial distribution of nutrients sets variable preconditions for the spring and potential blue-green algae blooms, and that internal processes were able to mask the effects of the P load reductions implemented across the whole Gulf. The transportation of P along the bottom from the northern Baltic Proper and its evident uplift in the Gulf highlights the fact that the nutrient reductions are also needed in the entire catchment of the Baltic Sea to improve the trophic status of the open Gulf.

  • 17.
    Müller-Karulis, Bärbel
    et al.
    Stockholm University, Stockholm Resilience Centre, Baltic Nest Institute.
    Aigars, Juris
    Latvian Institute of Aquatic Ecology, 8 Daugavgrivas, LV-1048 Riga, Latvia.
    Modeling the long-term dynamics of nutrients and phytoplankton in the Gulf of Riga2011In: Journal of Marine Systems, ISSN 0924-7963, E-ISSN 1879-1573, Vol. 87, no 3-4, p. 161-176Article in journal (Refereed)
    Abstract [en]

    The long term dynamics of nitrogen, phosphorus, and phytoplankton in the Gulf of Riga were simulated with a biogeochemical box model that resolved seasonal cycles. The model was calibrated using a numerical optimization procedure that adjusted 37 parameters to maximize the model data fit for field observations from 1973 to 2000 and validated with an independent dataset covering 2001-2007. Both the long-term increase and subsequent decline in winter nitrogen concentrations, as well as the continuous increase in winter phosphate levels were well reproduced by the model, which also gave reasonable representations of the seasonal dynamics of nutrients and phytoplankton. Starting from the mid-1990s, the model simulated an increase in cyanobacteria growth sustained by internal phosphorus loading. While nitrogen was efficiently removed by denitrification from the Gulf of Riga, comparatively slow export to the Baltic Proper was the main removal pathway of phosphorus. Modeled residence times were 5.4 years for nitrogen and 38 years for phosphorus. Scenario simulations indicated that the Gulf of Riga responds to phosphorus load reductions with a gradual decrease in primary production and cyanobacteria growth, while the effect of nitrogen load reductions is largely offset by nitrogen fixation.

  • 18. Pastuszak, Marianna
    et al.
    Conley, Daniel J.
    Humborg, Christoph
    Stockholm University, Faculty of Science, Department of Applied Environmental Science (ITM).
    Witek, Zbigniew
    Sitek, Stanislaw
    Silicon dynamics in the Oder estuary, Baltic Sea2008In: Journal of Marine Systems, ISSN 0924-7963, E-ISSN 1879-1573, Vol. 73, no 3-4, p. 250-262Article in journal (Refereed)
    Abstract [en]

    Studies on dissolved silicate (DSi) and biogenic silica (BSi) dynamics were carried out in the Oder estuary, Baltic Sea in 2000-2005. The Oder estuary proved to be an important component of the Oder River-Baltic Sea continuum where very intensive seasonal DSi uptake during spring and autumn, but also BSi regeneration during summer take place. Owing to the regeneration process annual DSi patterns in the river and the estuary distinctly differed; the annual patterns of DSi in the estuary showed two maxima and two minima in contrast to one maximum- and one minimum-pattern in the Oder River. F)Si concentrations in the river and in the estuary were highest in winter (200-250 mu mol dm(-3)) and lowest (often less than 1 mu mol dm(-3)) in spring, concomitant with diatom growth; such low values are known to be limiting for new diatom growth. Secondary DSi summer peaks at the estuary exit exceeded 100 mu mol dm(-3), and these maxima were followed by autumn minima coinciding with the autumn diatom bloom. Seasonal peaks in BSi concentrations (ca. 100 mu mol dm(-3)) occurred during the spring diatom bloom in die Oder River. Mass balance calculations of DSi and BSi showed that DSi + BSi import to the estuary over a two year period was 103.2 kt and that can be compared with the DSi export of 98.5 kt. The difference between these numbers gives room for ca. 2.5 kt BSi to be annually exported to the Baltic Sea. Sediment cores studies point to BSi annual accumulation on the level of 2.5 kt BSi. BSi import to the estuary is on the level of ca. 10.5 kt, thus ca. 5 kt of BSi is annually converted into the DSi, increasing the pool of DSi that leaves the system. BSi concentrations being ca. 2 times higher at the estuary entrance than at its exit remain in a good agreement with the DSi and BSi budgeting presented in the paper.

  • 19.
    Sanchez-Garcia, Laura
    et al.
    Stockholm University, Faculty of Science, Department of Applied Environmental Science (ITM).
    de Andres, J. -Ramon
    Martin-Rubi, J. -Antonio
    Geochemical signature in off-shore sediments from the Gulf of Cadiz inner shelf Sources and spatial variability of major and trace elements2010In: Journal of Marine Systems, ISSN 0924-7963, E-ISSN 1879-1573, Vol. 80, no 04-mar, p. 191-202Article in journal (Refereed)
    Abstract [en]

    The geochemical characterization of 15 surficial sediments from the Gulf of Cadiz (GoC) inner shelf was assessed by examining their granulometric, mineralogic and major-minor elemental composition, in order to evaluate the sources of contaminants and describe environmental conditions. The study involved the comparison of the geochemical signature of the shelf sediments with that of surficial sediments from the main fluvial systems of the region: Guadiana, Piedras, Tinto and Odiel. Although the major supply of sedimentary material in this area is discharged by the Guadiana River, the high absolute concentration of elements associated to sulphide deposits (P, As, Cu, Hg, Pb and Zn) observed in some sediments indicated the important influence of the historically polluted Tinto-Odiel fluvial system in certain locations. The significant levels (>99%) of positive correlation observed between Al, Fe, K, Ni, V and, in a lesser extent, Na and Ba, suggested the association of these elements in the form of aluminous clay minerals. No correlation was observed between Al and Si (0.20), in contrast to the strong positive correlation found for the latter and Ti (0.91). On the other hand, an inverse relationship occurred between terrigenous-detrital sources and carbonate fractions, presumably related to biogenic origins, according to the significant negative correlations (> 99%) observed for Si, respect to Ca (-0.82), Mg (-0.96) and total inorganic carbon (-0.81). The general enrichment of As, Cu, Hg, Pb and Zn detected in the shelf sediments, together with strong and moderate positive correlations observed among these metals and P, Suggested a common origin for all these elements, potentially related to pollutant-anthropogenic activities developed in the industrial area of Huelva city. Those sediments situated closer to the Tinto-Odiel mouth displayed enrichment factors (EF) equal or higher than 2 for As, Cu, Hg, Pb and Zn, particularly evident in one sample (S7), which showed EF of 2.7, 18.7, 8.7, 4.0 and 5.7, respectively. Cluster and Principal Components Analyses allowed us to differentiate four groups of shelf sediments governed by similar geochemical patterns: (i) a first group including the sediments under the Guadiana river influence, formed by coarser siliclastic sediments, with dominant terrigenous-detrital signatures and enrichment of Co and Mn: (ii) a second group of off-shore muddy sediments. Ni-associated, showing moderate enrichment of Cu, Hg, Pb and Zn, as well as important contribution of carbonate forms, which represent the transition towards a dominant marine source; (iii) sample S7, formed by muddy materials and enriched in sulphide associated-heavy metals and phosphorous, according to its proximity to the Tinto-Odiel fluvial system; and (iv) the coarsest sample S13, with high concentration of carbonates and moderate enrichment of heavy metals, which reflects a mixed signature between the detritic influence from Guadiana and Piedras rivers and marine-biogenic sources.

  • 20.
    Sandman, Antonia
    et al.
    Stockholm University, Faculty of Science, Department of Systems Ecology.
    Isaeus, Martin
    AquaBiota Water Research, Stockholm.
    Bergström, Ulf
    Institute of Coastal Research, Swedish Board of Fisheries, Öregrund.
    Kautsky, Hans
    Stockholm University, Faculty of Science, Department of Systems Ecology.
    Spatial predictions of Baltic phytobenthic communities: Measuring robustness of generalized additive models based on transect data2008In: Journal of Marine Systems, ISSN 0924-7963, E-ISSN 1879-1573, Vol. 74, no Supplement 1, p. S86-S96Article in journal (Refereed)
    Abstract [en]

    The spatial distributions of benthic surface sediments and phytobenthic plant species were modelled at a high spatial resolution using generalized additive models together with field data from diving transects. The efficiency of different modelling options was validated using independent datasets, and model fit versus predictive power was analysed. For rock/boulder, sand and mud/clay increasing complexity of the model resulted in higher Reciever Operating Characteristics (ROC) values for the model fit, but lower ROC values for the independent validation. The same pattern was found for hard substrate algae species, whereas it was not true for the rooted plant species. As high model ROC values were often found to be connected to low predictive power of the models, this implies that internal model validation results should be treated cautiously. In general, the models should be kept simple, as the performance of the explanation model increases with increasing complexity, while the predictive power of the model generally decreases. Only by using external validation datasets, the true predictive capacity of an explanation model can be reliably measured, as internal validation schemes tend to over-estimate model performance. Our results also indicate that the Akaike Information Criterion is a more reliable model selection method than Cross-selection when there are few predictor variables.

  • 21. Schneider, Bernd
    et al.
    Gustafsson, Erik
    Stockholm University, Faculty of Science, Stockholm University Baltic Sea Centre, Baltic Nest Institute.
    Sadkowiak, Bernd
    Control of the mid-summer net community production and nitrogen fixation in the central Baltic Sea: An approach based on pCO2 measurements on a cargo ship2014In: Journal of Marine Systems, ISSN 0924-7963, E-ISSN 1879-1573, Vol. 136, p. 1-9Article in journal (Refereed)
    Abstract [en]

    Automated measurements of the surface CO2 partial pressure, pCO2, were performed since 2003 on a cargo ship along a transect between Helsinki in the Gulf of Finland and Lübeck/Gdynia in the southwest of the Baltic Sea. The temporal and spatial resolution of the measurements amounted to 2–4 days and about 2 nautical miles, respectively. Based on temperature and salinity records and on the mean alkalinity, the total CO2 concentrations, CT, were calculated from the mean pCO2 in the northeastern Gotland Sea. The CT data were used to establish a CO2 mass balance for the period from mid-June to the beginning of August in 2005, 2008, 2009 and 2011. Taking into account the air–sea CO2 gas exchange, the mass balance yielded the net organic matter (Corg) production which is fuelled by nitrogen fixation at this time of the year. Several production events were detected with rates up to 8 μmol-C L− 1 d− 1. The production rates were not related to temperature, but showed a distinct correlation with the rate of the temperature increase. This led to the conclusion that the exposure of nitrogen fixing cyanobacteria to irradiance is the dominating control for the Corg production. Therefore, we suggest using the ratio of irradiance to the mixed layer depth as a variable for the parameterization of nitrogen fixation in biogeochemical models. The Corg production and thus the nitrogen fixation rates remained almost constant as long as continuous rising temperatures indicated favorable irradiation conditions. A limitation of the rates by phosphate or any other factor could not be detected. Based on the C/N ratio of particulate organic matter during a cyanobacteria bloom, the Corg production was used to estimate the mid-summer nitrogen fixation. The values varied from 102 mmol m− 2 to 214 mmol m− 2 (mean: 138 mmol m− 2) for the different years and did not show any correlation with the phosphate excess after the spring nitrate depletion.

  • 22. Sferratore, Agata
    et al.
    Billen, Gilles
    Garnier, Josette
    Smedberg, Erik
    Stockholm University, Faculty of Science, Department of Applied Environmental Science (ITM).
    Humborg, Christoph
    Stockholm University, Faculty of Science, Department of Applied Environmental Science (ITM).
    Rahm, Lars
    Modelling nutrient fluxes from sub-arctic basin: Comparison of pristine vs. dammed rivers2008In: Journal of Marine Systems, ISSN 0924-7963, E-ISSN 1879-1573, Vol. 73, no 3-4, p. 236-249Article in journal (Refereed)
    Abstract [en]

    The deterministic Riverstrahler model of river functioning is applied for the first time to sub-arctic catchments. Seasonal nutrient (N, P, Si) deliveries to the coastal zone are simulated, and nutrient annual fluxes are established for the nearly pristine river Kalix (hereafter called Kalixälven) and the heavily dammed river Lule, (hereafter called Luleälven) both located in Northern Sweden and draining into the Bothnian Bay, Baltic Sea.

    For Kalixälven simulations are performed with a runoff calculated from precipitation, evapo-transpiration and temperature data for the period 1990–1999, using a hydrological model calibrated on observed monthly discharges at the river outlet. The same hydrological parameters are used to calculate specific runoff for the Luleälven basin in absence of dam regulation. Reservoir filling and emptying are simulated using a simplified representation of their management rules. Diffuse sources of nutrient are evaluated according to land cover of the catchment. The simulated seasonal trends are within the range of the observed data, in particular for discharge, dissolved silica, total phosphorus, inorganic nitrogen and total organic carbon. Specific runoff is 50% higher in the Luleälven than in the Kalixälven watershed due to higher altitudes and precipitations. Average silica, nitrate and phosphorus concentrations are much lower in Luleälven than in Kalixälven. Comparison of model results for the Luleälven with and without dams shows a reduction of respectively 25% and 30% in silica and phosphorus fluxes delivered at the outlet, while nitrogen delivery is increased by 10% in the dammed vs. undammed river system. The model allows assessing the respective role of reservoir trapping of nutrient in the reservoir through algal uptake and sedimentation, and of changes in the vegetation induced by flooding the valley formerly covered by forests and wetlands.

  • 23. Skogen, Morten D.
    et al.
    Eilola, Kari
    Hansen, Jørgen L. S.
    Meier, H. E. Markus
    Stockholm University, Faculty of Science, Department of Meteorology . Swedish Meteorological and Hydrological Institute, Sweden.
    Molchanov, Mikhail S.
    Ryabchenko, Vladimir A.
    Eutrophication status of the North Sea, Skagerrak, Kattegat and the Baltic Sea in present and future climates: A model study2014In: Journal of Marine Systems, ISSN 0924-7963, E-ISSN 1879-1573, Vol. 132, p. 174-184Article in journal (Refereed)
    Abstract [en]

    A method to combine observations and an ensemble of ecological models has been used to assess eutrophication. Using downscaled forcing from two GCMs under the A1B emission scenario, an assessment of the eutrophication status was made for a control (19702000) and a future climate (20702100) period. By using validation results from a hindcast to compute individual weights between the models, an assessment of eutrophication is done using a set of threshold values. The final classification distinguishes between three categories: problem area, potential problem area, and non-problem area, in accordance with current management practice as suggested by the Oslo and Paris Commissions (OSPAR) and the Helsinki Commission (HELCOM). For the control run the assessment indicates that the Kattegat, the Danish Straits, the Gulf of Finland, the Gotland Basin as well as main parts of the Arkona Basin, the Bornholm Basin, and the Baltic proper may be classified as problem areas. The main part of the North Sea and also the Skagerrak are non-problem areas while the main parts of the Gulf of Bothnia, Gulf of Riga and the entire southeastern continental coast of the North Sea may be classified as potential problem areas. In the future climate scenarios most of the previous potential problem areas in the Baltic Sea have become problem areas, except for the Bothnian Bay where the situation remain fairly unchanged. In the North Sea there seems to be no obvious changes in eutrophication status in the projected future climate.

  • 24.
    Svedén, Jennie B.
    et al.
    Stockholm University, Faculty of Science, Department of Ecology, Environment and Plant Sciences.
    Walve, Jakob
    Stockholm University, Faculty of Science, Department of Ecology, Environment and Plant Sciences.
    Elmgren, Ragnar
    Stockholm University, Faculty of Science, Department of Ecology, Environment and Plant Sciences.
    Larsson, Ulf
    Stockholm University, Faculty of Science, Department of Ecology, Environment and Plant Sciences.
    The bloom of nitrogen-fixing cyanobacteria in the northern Baltic Proper stimulates summer production2016In: Journal of Marine Systems, ISSN 0924-7963, E-ISSN 1879-1573, Vol. 163, p. 102-112Article in journal (Refereed)
    Abstract [en]

    In the northern Baltic Sea Proper, total nitrogen (TN) increases during the summer bloom of filamentous heterocystous cyanobacteria. To follow the fate of the nitrogen they fix, we studied several N fractions during the bloom. We measured cyanobacterial biomass, TN, particulate organic N (PON, two size fractions), dissolved organic N (DON), and PON sedimentation in two areas in 2011. TN increased mainly due to increasing PON, but also to DON. Cyanobacteria contributed about 20% of the PON increase and ~ 10% of the TN increase. About half the PON changes (increase, then decrease) could be explained by the sum of cyanobacteria, other autotrophs (> 2 μm) and zooplankton, indicating that the bloom stimulates primary and secondary production. TN decreased after the bloom mainly due to declining PON > 10 μm, but sedimentation rates did not increase and could explain little of the post-bloom N-loss. There was little settling of undecomposed cyanobacteria.

    The seasonal development of Aphanizomenon sp. and N pools was similar among stations and areas. For Nodularia spumigena between-station variability increased once patchy surface accumulations developed. A brief Dolichospermum spp. bloom indicated that sampling frequency may be more important than spatial resolution for capturing dynamics of this bloom.

  • 25. Timmermann, Karen
    et al.
    Norkko, Joanna
    Janas, Urszula
    Norkko, Alf
    Gustafsson, Bo G.
    Stockholm University, Stockholm Resilience Centre, Baltic Nest Institute.
    Bonsdorff, Erik
    Modelling macrofaunal biomass in relation to hypoxia and nutrient loading2012In: Journal of Marine Systems, ISSN 0924-7963, E-ISSN 1879-1573, Vol. 105-108, p. 60-69Article in journal (Refereed)
    Abstract [en]

    Nutrient loading of aquatic ecosystems results in more food for benthic macrofaunal communities but also increases the risk of hypoxia, resulting in a reduction or complete loss of benthic biomass. This study investigates the interaction between eutrophication, hypoxia and benthic biomass with emphasis on the balance between gains and loss of benthic biomass due to changes in nutrient loadings. A physiological fauna model with 5 functional groups was linked to a 3D coupled hydrodynamic-ecological Baltic Sea model. Model results revealed that benthic biomass increased between 0 and 700% after re-oxygenating bottom waters. Nutrient reduction scenarios indicated improved oxygen concentrations in bottom waters and decreased sedimentation of organic matter up to 40% after a nutrient load reduction following the Baltic Sea Action Plan. The lower food supply to benthos reduced the macrofaunal biomass up to 35% especially in areas not currently affected by hypoxia, whereas benthic biomass increased up to 200% in areas affected by eutrophication-induced hypoxia. The expected changes in benthic biomass resulting from nutrient load reductions and subsequent reduced hypoxia may not only increase the food supply for benthivorous fish, but also significantly affect the biogeochemical functioning of the ecosystem.

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