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  • 1.
    Alling, Vanja
    et al.
    Stockholm University, Faculty of Science, Department of Applied Environmental Science (ITM).
    Humborg, Christoph
    Stockholm University, Faculty of Science, Department of Applied Environmental Science (ITM).
    Mörth, Carl-Magnus
    Stockholm University, Faculty of Science, Department of Geological Sciences.
    Rahm, Lars
    Polehne, Falk
    Tracing terrestrial organic matter by delta34S and delta13C signatures in a subarctic estuary2008In: Limnology and Oceanography, ISSN 0024-3590, E-ISSN 1939-5590, Vol. 53, no 6, p. 2594-2602Article in journal (Refereed)
    Abstract [en]

    A key issue to understanding the transformations of terrestrial organic carbon in the ocean is to disentangle the latter from marine-produced organic matter. We applied a multiple stable isotope approach using 34S and 13C isotope signatures from estuarine dissolved organic matter (DOM), enabling us to constrain the contribution of terrestrial-derived DOM in an estuarine gradient of the northern Baltic Sea. The stable isotope signatures for dissolved organic sulfur (34SDOS) have twice the range between terrestrial and marine end members compared to the stable isotope signatures for dissolved organic carbon (13CDOC); hence, the share of terrestrial DOM in the total estuarine DOM can be calculated more precisely. DOM samples from the water column were collected using ultrafiltration on board the German RV Maria S Merian during a winter cruise, in the Bothnian Bay, Bothnian Sea, and Baltic proper. We calculated the terrestrial fraction of the estuarine DOC (DOCter) from both 13CDOC and 34SDOS signatures and applying fixed C: S ratios for riverine and marine end members to convert S isotope signatures into DOC concentrations. The 34SDOS signature of the riverine end member was +7.02‰, and the mean signatures from Bothnian Bay, Bothnian Sea, and Baltic proper were +10.27, +12.51, and +13.67‰, respectively, showing an increasing marine signal southwards (34SDOS marine end member 5 18.1‰). These signatures indicate that 87‰, 75‰, and 67‰, respectively, of the water column DOC is of terrestrial origin (DOCter) in these basins. Comparing the fractions of DOCter in each basin—that are still based on few winter values only—with the annual river input of DOC, it appears that the turnover time for DOCter in the Gulf of Bothnia is much shorter than the hydraulic turnover time, suggesting that high-latitude estuaries might be efficient sinks for DOCter.

  • 2.
    Bonaglia, Stefano
    et al.
    Stockholm University, Faculty of Science, Department of Geological Sciences. Lund University, Sweden.
    Klawonn, Isabell
    Stockholm University, Faculty of Science, Department of Ecology, Environment and Plant Sciences. IGB-Leibniz-Institute of Freshwater Ecology and Inland Fisheries, Germany.
    De Brabandere, Loreto
    Deutsch, Barbara
    Stockholm University, Faculty of Science, Department of Applied Environmental Science (ITM). Stockholm University, Faculty of Science, Stockholm University Baltic Sea Centre.
    Thamdrup, Bo
    Brüchert, Volker
    Stockholm University, Faculty of Science, Department of Geological Sciences.
    Denitrification and DNRA at the Baltic Sea oxic-anoxic interface: Substrate spectrum and kinetics2016In: Limnology and Oceanography, ISSN 0024-3590, E-ISSN 1939-5590, Vol. 61, no 5, p. 1900-1915Article in journal (Refereed)
    Abstract [en]

    The dependence of denitrification and dissimilatory nitrate reduction to ammonium (DNRA) on different electron donors was tested in the nitrate-containing layer immediately below the oxic-anoxic interface (OAI) at three stations in the central anoxic basins of the Baltic Sea. Additionally, pathways and rates of fixed nitrogen transformation were investigated with N-15 incubation techniques without addition of donors. Denitrification and anammox were always detected, but denitrification rates were higher than anammox rates. DNRA occurred at two sites and rates were two orders of magnitude lower than denitrification rates. Separate additions of dissolved organic carbon and sulfide stimulated rates without time lag indicating that both organotrophic and lithotrophic bacterial populations were simultaneously active and that they could carry out denitrification or DNRA. Manganese addition stimulated denitrification and DNRA at one station, but it is not clear whether this was due to a direct or indirect effect. Ammonium oxidation to nitrite was detected on one occasion. During denitrification, the production of nitrous oxide (N2O) was as important as dinitrogen (N-2) production. A high ratio of N2O to N-2 production at one site may be due to copper limitation, which inhibits the last denitrification step. These data demonstrate the coexistence of a range of oxidative and reductive nitrogen cycling processes at the Baltic OAI and suggest that the dominant electron donor supporting denitrification and DNRA is organic matter. Organotrophic denitrification is more important for nitrogen budgets than previously thought, but the large temporal variability in rates calls for long-term seasonal studies.

  • 3.
    Burian, Alfred
    et al.
    Stockholm University, Faculty of Science, Department of Ecology, Environment and Plant Sciences.
    Schagerl, Michael
    Yasindi, Andrew
    Singer, Gabriel
    Kaggwa, Mary Nakabungo
    Winder, Monika
    Stockholm University, Faculty of Science, Department of Ecology, Environment and Plant Sciences.
    Benthic-pelagic coupling drives non-seasonal zooplankton blooms and restructures energy flows in shallow tropical lakes2016In: Limnology and Oceanography, ISSN 0024-3590, E-ISSN 1939-5590, Vol. 61, no 3, p. 795-805Article in journal (Refereed)
    Abstract [en]

    Zooplankton blooms are a frequent phenomenon in tropical systems. However, drivers of bloom formation and the contribution of emerging resting eggs are largely unexplored. We investigated the dynamics and the triggers of rotifer blooms in African soda-lakes and assessed their impact on other trophic levels. A meta-analysis of rotifer peak densities including abundances of up to 6 × 105 individuals L−1 demonstrated that rotifer bloom formation was uncoupled from the food environment and the seasonality of climatic conditions. A time series with weekly sampling intervals from Lake Nakuru (Kenya) revealed that intrinsic growth factors (food quality and the physicochemical environment) significantly affected rotifer population fluctuations, but were of minor importance for bloom formation. Instead, rotifer bloom formation was linked to sediment resuspension, a prerequisite for hatching of resting-eggs. Population growth rates exceed pelagic birth rates and simulations of rotifer dynamics confirmed the quantitative importance of rotifer emergence from the sediment egg-bank and signifying a decoupling of bloom formation from pelagic reproduction. Rotifer blooms led to a top-down control of small-sized algae and facilitated a switch to more grazing-resistant, filamentous cyanobacteria. This shift in phytoplankton composition cascaded up the food chain and triggered the return of filter-feeding flamingos. Calculations of consequent changes in the lake's energy budget and export of aquatic primary production to terrestrial ecosystems demonstrated the large potential impact of nonseasonal disturbances on the functioning of shallow tropical lakes.

  • 4.
    Gorokhova, Elena
    et al.
    Stockholm University, Faculty of Science, Department of Systems Ecology.
    Lehtiniemi, Maiju
    Finnish Inst Marine Res.
    Viitasalo-Frosen, Satu
    Finnish Inst Marine Res.
    Haddock, Steven H. D.
    Monterey Bay Aquarium Res Inst.
    Molecular evidence for the occurrence of Mertensia ovum in the northern Baltic Sea and implications for the status of Mnemiopsis leidyi invasion.2009In: Limnology and Oceanography, ISSN 0024-3590, E-ISSN 1939-5590, Vol. 54, no 6, p. 2025-2033Article in journal (Refereed)
    Abstract [en]

    Nucleotide sequence analysis of 18S ribosomal RNA gene ( rRNA), internal transcribed spacer, and 5.8S rRNA was used for taxonomic identification of ctenophores collected in the northern Baltic Sea, where invasive Mnemiopsis leidyi and native Pleurobrachia pileus have been reported to occur. Contrary to previous reports, sequence analysis of 53 randomly selected specimens from seven stations revealed that none of them were M. leidyi or P. pileus. The 18S rRNA and 5.8S rRNA sequences were 100% identical to those of Mertensia ovum, a ctenophore with a broad Arctic and circumboreal distribution, which has never been reported to occur in the Baltic Sea. Polymerase chain reaction screening with primers designed to amplify all three species, and using ctenophores collected by vertically stratified sampling, confirmed that all ctenophores collected in this survey were M. ovum. The ctenophore abundance was high, up to 4500 individuals m(-2), positively correlating with salinity. Our findings emphasize the utility of applying molecular tools to biological surveys and the importance of rigorous species identification. They also indicate that M. leidyi, which is a threat to the southern Baltic ecosystem, does not occur in the northern part of the sea, and call for a pan-Baltic survey to establish current distributions of ctenophores, both native and invasive.

  • 5. Hylander, Samuel
    et al.
    Kiørboe, Thomas
    Snoeijs, Pauline
    Stockholm University, Faculty of Science, Department of Ecology, Environment and Plant Sciences.
    Sommaruga, Ruben
    Nielsen, Torkel Gissel
    Concentrations of sunscreens and antioxidant pigments in Arctic Calanus spp. in relation to ice cover, ultraviolet radiation, and the phytoplankton spring bloom2015In: Limnology and Oceanography, ISSN 0024-3590, E-ISSN 1939-5590, Vol. 60, no 6, p. 2197-2206Article in journal (Refereed)
    Abstract [en]

    Arctic zooplankton ascend to shallow depths during spring to graze on the yearly occurring phytoplankton bloom. However, in surface waters they are exposed to detrimental ultraviolet radiation (UVR) levels. Here, we quantified concentrations of substances known to have UVR-protective functions, namely mycosporine-like amino acids (MAAs) and the carotenoid astaxanthin, from March to May in Calanus finmarchicus, Calanus glacialis and Calanus hyperboreus. Ice cover was 100% in the beginning of March, started to break up during April and was gone by the end of May. UVR-exposure in the water column was tightly linked to the ice conditions and water UVR-transparency was up to 6 m (depth where 1% radiation remains). Concentrations of MAAs in C. finmarchicus and C. glacialis increased sharply during ice break-up and peaked concurrently with maximum chlorophyll a (Chl a) levels. MAA-concentrations in C. hyperboreus increased later in accordance with its later arrival to the surface. The concentration of astaxanthin increased in all three species over time but there was no synchrony with ice conditions or the phytoplankton bloom. Even though only the upper 6 m of the water column was affected by UV-radiation, MAAs in the copepods were tightly correlated to the UV-threat. Hence, changes in ice cover are projected to have a large impact on the UVR-exposure of zooplankton emphasizing the importance of the timing of zooplankton ascent from deep waters in relation to the phytoplankton bloom and the ice break-up.

  • 6. Joensuu, M.
    et al.
    Pilditch, C. A.
    Harris, R.
    Hietanen, S.
    Pettersson, H.
    Norkko, Alf
    Stockholm University, Faculty of Science, Stockholm University Baltic Sea Centre. University of Helsinki, Finland.
    Sediment properties, biota, and local habitat structure explain variation in the erodibility of coastal sediments2018In: Limnology and Oceanography, ISSN 0024-3590, E-ISSN 1939-5590, Vol. 63, no 1, p. 173-186Article in journal (Refereed)
    Abstract [en]

    Sediment resuspension is a frequent phenomenon in coastal areas and a key driver for many ecosystem functions. Sediment resuspension is often linked to biological and anthropogenic activities, which in combination with hydrodynamic forcing initiate sediment erosion and resuspension, if the erosion threshold (tau(c)) is exceeded. Despite its importance to ecosystem functions very few studies have provided measurements on natural assemblages for subtidal sediments. The aim of this study was to determinate key environmental variables regulating sediment resuspension potential across a sedimentary gradient in a subtidal coastal environment. In order to explore this, we sampled 16 sites encompassing a wide variety in environmental variables (e.g., grain size distribution, macrofaunal communities, vegetation) in the Gulf of Finland, Baltic Sea. A core-based erosion device (EROMES) was used to determine sediment resuspension potential measures of erosion threshold, erosion rate (ER), and erosion constant (m(e)). Based on abiotic and biotic properties sampled, sediments diverged into two distinct groups; cohesive (muddy) and noncohesive (sandy) sediments. Results showed that abiotic sediment properties explained 38-53% and 15-36% of the total variation in resuspension potential measures in muddy and sandy sediments, respectively. In cumulative models, biota accounted for 12-26% and 6-24% to the total variation in muddy and sandy sediments, respectively. Sediment erodibility and resuspension potential of natural sediments is highly variable from local habitats to a larger seascape scale. Our results underline the importance of biota to resuspension potential measures in spatially variable environments.

  • 7.
    Karlson, Agnes
    et al.
    Stockholm University, Faculty of Science, Department of Systems Ecology.
    Nascimento, Francisco
    Stockholm University, Faculty of Science, Department of Systems Ecology.
    Elmgren, Ragnar
    Stockholm University, Faculty of Science, Department of Systems Ecology.
    Incorporation and burial of carbon from settling cyanobacterial blooms by deposit-feeding macrofauna2008In: Limnology and Oceanography, ISSN 0024-3590, E-ISSN 1939-5590, Vol. 53, no 6, p. 2754-2758Article in journal (Refereed)
    Abstract [en]

    Summer blooms of filamentous, nitrogen-fixing cyanobacteria are typical of the Baltic Sea, and recent findings indicate that cyanobacteria may be an important food source for the benthos below the euphotic zone. In a 2-week laboratory experiment, we measured incorporation of cyanobacterial carbon by the deposit-feeding amphipod Monoporeia affinis when exposed to 14C-radiolabeled, natural blooms of cyanobacteria dominated by either the toxic Nodularia spumigena or non-toxic Aphanizomenon sp. Carbon from both cyanobacterial blooms was used, with greater incorporation from Aphanizomenon-dominated bloom material than from N. spumigena, indicating that the latter is less suitable as food. However, neither cyanobacterium supported significant amphipod growth. Also, less cyanobacterial carbon was mixed down in the sediment in the N. spumigena treatment, indicating lower bioturbation activity in this treatment. Long-term effects on feeding and survival remain to be studied, especially for the toxic N. spumigena.

  • 8. Klais, Riina
    et al.
    Tamminen, Timo
    Kremp, Anke
    Spilling, Kristian
    An, Byoung Woong
    Hajdu, Susanna
    Stockholm University, Faculty of Science, Department of Systems Ecology.
    Olli, Kalle
    Spring phytoplankton communities shaped by interannual weather variability and dispersal limitation: Mechanisms of climate change effects on key coastal primary producers2013In: Limnology and Oceanography, ISSN 0024-3590, E-ISSN 1939-5590, Vol. 58, no 2, p. 753-762Article in journal (Refereed)
    Abstract [en]

    Spring bloom composition in the Baltic Sea, a partially ice-covered brackish coastal waterbody, is shaped by winter-spring weather conditions affecting the relative dominance of diatoms and a heterogeneous assemblage of cold-water dinoflagellates, dominated by the chain-forming Peridiniella catenata and a complex of at least three medium-sized, single-celled species: Biecheleria baltica, Gymnodinium corollarium, and Scrippsiella hangoei. During the last decades, the bloom community has dramatically changed in several basins. We analyze here a 30 yr time series of quantitative phytoplankton data, as predicted by hindcast modeled ice thickness and storminess for three distinct Baltic Sea localities, to verify climate-driven mechanisms affecting the spring bloom composition. Thick (> 30 cm) and long-lasting ice cover favored diatom-dominated spring blooms, and mild winters, with storms and thin ice cover (10 to 20 cm), supported blooms of the B. baltica complex. Dispersal limitation plays an important role in the spatial extent of blooms of the B. baltica complex, caused by intricate interplay of local hydrodynamics and the dinoflagellate life cycle. Proportion peaks of key phytoplankton groups have shifted about 10 d earlier in the northwestern Baltic Sea (P. catenata and diatoms) and in the Gulf of Riga (P. catenata). The significant weather effects imply future shifts in spring bloom composition and consequent biogeochemical cycles, driven by the predicted changes in winter storminess and decrease in ice cover extent and duration in climate change models.

  • 9. Leavitt, Peter R.
    et al.
    Fritz, S.C.
    Anderson, N.J.
    Baker, P.A.
    Blenckner, T.
    Stockholm University, Stockholm Resilience Centre, Baltic Nest Institute.
    Bunting, L.
    Catalan, J
    Conley, D.J.
    Hobbs, W.
    Jeppesen, E.
    Korhola, A.
    McGowan, S.
    Rühland, K
    Rusak, J.A.
    Simpson, G.L.
    Solovieva, N.
    Werne, J.
    Paleolimnological evidence of the effects on lakes of energy and mass transfer from climate and humans.2009In: Limnology and Oceanography, ISSN 0024-3590, E-ISSN 1939-5590, Vol. 54, p. 2330-2348Article in journal (Refereed)
  • 10.
    Lichtschlag, Anna
    et al.
    Max-Planck Institute for marine Microbiology.
    Felden, Janine
    Max-Planck Institute for marine Microbiology.
    Brüchert, Volker
    Stockholm University, Faculty of Science, Department of Geological Sciences.
    Boetius, Antje
    Max-Planck Institute for Marine Microbiology.
    de Beer, Dirk
    Max-Planck Institute for Marine Microbiology.
    Geochemical processes and chemosynthetic primary production in different thiotrophicmats of the Ha°kon Mosby Mud Volcano (Barents Sea)2010In: Limnology and Oceanography, ISSN 0024-3590, E-ISSN 1939-5590, Vol. 55, no 2, p. 931-949Article in journal (Refereed)
    Abstract [en]

    Abstract: We have investigated if in a cold seep methane or sulfide is used for chemosynthetic primary production and if significant amounts of the sulfide produced by anaerobic oxidation of methane are oxidized geochemically and hence are not available for chemosynthetic production. Geochemically controlled redox reactions and biological turnover were compared in different habitats of the Håkon Mosby Mud Volcano. The center of the mud volcano is characterized by the highest fluid flow, and most primary production by the microbial community depends on oxidation of methane. The small amount of sulfide produced is oxidized geochemically with oxygen or is precipitated with dissolved iron. In the medium flow peripheral Beggiatoa habitat sulfide is largely oxidized biologically. The oxygen and nitrate supply is high enough that Beggiatoa can oxidize the sulfide completely, and chemical sulfide oxidation or precipitation is not important. An internally stored nitrate reservoir with average concentrations of 110 mmol L-1 enables the Beggiatoa to oxidize sulfide anaerobically. The pH profile indicates sequential sulfide oxidation with elemental sulfur as an intermediate. Gray thiotrophic mats associated with perturbed sediments showed a high heterogeneity in sulfate turnover and high sulfide fluxes, balanced by the opposing oxygen and nitrate fluxes so that biological oxidation dominates over geochemical sulfide removal processes. The three habitats indicate substantial small-scale variability in carbon fixation pathways, either through direct biological use of methane or through indirect carbon fixation of methane-derived carbon dioxide by chemolithotrophic sulfide oxidation.

  • 11.
    McCrackin, Michelle L.
    et al.
    Stockholm University, Faculty of Science, Stockholm University Baltic Sea Centre.
    Jones, Holly P.
    Jones, Peter C.
    Moreno-Mateos, David
    Recovery of lakes and coastal marine ecosystems from eutrophication: A global meta-analysis2017In: Limnology and Oceanography, ISSN 0024-3590, E-ISSN 1939-5590, Vol. 62, no 2, p. 507-518Article in journal (Refereed)
    Abstract [en]

    In order to inform policies aimed at reducing nutrient emissions to surface waters, it is essential to understand how aquatic ecosystems respond to eutrophication management. Using data from 89 studies worldwide, we examined responses to the reduction or cessation of anthropogenic nutrient inputs relative to baseline conditions. Baseline conditions were pre-disturbance conditions, undisturbed reference sites, restoration targets, or experimental controls. We estimated recovery completeness (% baseline conditions reached) and recovery rate (annual % change relative to baseline conditions) for plant and animal abundance and diversity and for ecosystem functions. Categories were considered fully recovered if the 95% confidence interval (CI) of recovery completeness overlapped 100% and partially recovered if the CI did not overlap either 100% or zero. Cessation of nutrient inputs did not result in more complete or faster recovery than partial nutrient reductions, due likely to insufficient passage of time, nutrients from other sources, or shifting baselines. Together, lakes and coastal marine areas achieved 34% (+/- 16% CI) and 24% (+/- 15% CI) of baseline conditions decades after the cessation or partial reduction of nutrients, respectively. One third of individual response variables showed no change or worsened conditions, suggesting that achieving baseline conditions may not be possible in all cases. Implied recovery times after cessation of nutrient inputs varied widely, from < 1 yr to nearly a century, depending on response. Our results suggest that long-term monitoring is needed to better understand recovery timescales and trajectories and that policy measures must consider the potential for slow and partial recovery.

  • 12.
    Motwani, Nisha H.
    et al.
    Stockholm University, Faculty of Science, Department of Ecology, Environment and Plant Sciences. Stockholm University, Faculty of Science, Department of Environmental Science and Analytical Chemistry.
    Duberg, Jon
    Stockholm University, Faculty of Science, Department of Environmental Science and Analytical Chemistry.
    Svedén, Jennie B.
    Stockholm University, Faculty of Science, Department of Ecology, Environment and Plant Sciences.
    Gorokhova, Elena
    Stockholm University, Faculty of Science, Department of Environmental Science and Analytical Chemistry.
    Grazing on cyanobacteria and transfer of diazotrophic nitrogen to zooplankton in the Baltic Sea2018In: Limnology and Oceanography, ISSN 0024-3590, E-ISSN 1939-5590, Vol. 63, no 2, p. 672-686Article in journal (Refereed)
    Abstract [en]

    Nitrogen-fixing cyanobacteria (NFC) are important primary producers in many freshwater and marine systems, including the Baltic Sea. In this system, NFC circumvent summer nitrogen limitation, while also generating a supply of novel combined nitrogen and thus supporting food webs. Using field observations on zooplankton and phytoplankton development during a growth season in the northern Baltic Proper, we show that cyanobacterial nitrogen is assimilated and transferred to zooplankton via both direct grazing on NFC and indirectly through grazing on picoplankton, such as picocyanobacteria. The key findings supporting these conclusions are: (1) all zooplankton grazers were found to ingest NFC (Nodularia spumigena) and picocyanobacteria (Synechococcus spp.); (2) ingestion of both NFC and picocyanobacteria measured by quantitative polymerase chain reaction analysis was highly correlated with ambient stocks of the respective cyanobacteria; (3) consumption of NFC and picocyanobacteria translated into decreased delta N-15 signature of zooplankton indicative of diazotrophic nitrogen input; (4) growth and reproduction indices in zooplankters were significantly positively related to NFC and picocyanobacteria; and (5) zooplankton biomass was positively related to the increasing nitrogen content of particulate organic matter (POM<10 mu m) and was highest at low POM delta N-15 values; the latter reflected overlap in zooplankton production and diazotroph seasonal dynamics. These findings provide empirical evidence that both NFC and picoplankton are readily ingested and assimilated by zooplankton, albeit with differential effects on growth and recruitment.

  • 13.
    Nascimento, F.J.A.
    et al.
    Stockholm University, Faculty of Science, Department of Systems Ecology.
    Karlson, A.M.L.
    Stockholm University, Faculty of Science, Department of Systems Ecology.
    Elmgren, R.
    Stockholm University, Faculty of Science, Department of Systems Ecology.
    Settling blooms of filamentous cyanobacteria as food for meiofauna assemblages.2008In: Limnology and Oceanography, ISSN 0024-3590, E-ISSN 1939-5590, Vol. 53, no 6, p. 2636-2643Article in journal (Refereed)
    Abstract [en]

    Summer blooms of filamentous nitrogen-fixing cyanobacteria in the Baltic Sea are normally dominated by Aphanizomenon sp. and the toxin-producing Nodularia spumigena. In a 2-week laboratory experiment, we followed the uptake by representative benthic meiofauna species of C-14-labeled organic carbon from blooms, each dominated by one of these cyanobacteria. Natural bloom material was collected and labeled by incubation with (NaHCO3)-C-14. Uptake of cyanobacterial carbon was recorded for the major meiofauna taxa living in the first-centimeter layer, namely ostracods, harpacticoids, and nematodes. The uptake rates were within the range found for diatoms in other studies, indicating that cyanobacteria may be an important food resource for the meiobenthos. The uptake of cyanobacterial carbon varied significantly among species, even within the same class. The ostracod Candona neglecta showed the highest uptake values, whereas two other ostracod species took up very little of the label. There was no significant difference in utilization of carbon from Aphanizomenon sp. and N. spumigena and no reduction in the abundance of the meiofaunal taxa analyzed compared to unexposed controls, indicating that Baltic meiofaunal assemblages in general experience no mortality when exposed to settled cyanobacteria, even the hepatotoxic N. spumigena.

  • 14. Natchimuthu, Sivakiruthika
    et al.
    Sundgren, Ingrid
    Gålfalk, Magnus
    Klemedtsson, Leif
    Crill, Patrick
    Stockholm University, Faculty of Science, Department of Geological Sciences.
    Danielsson, Åsa
    Bastviken, David
    Spatio-temporal variability of lake CH4 fluxes and its influence on annual whole lake emission estimates2016In: Limnology and Oceanography, ISSN 0024-3590, E-ISSN 1939-5590, Vol. 61, p. S13-S26Article in journal (Refereed)
    Abstract [en]

    Lakes are major sources of methane (CH4) to the atmosphere that contribute significantly to the global budget. Recent studies have shown that diffusive fluxes, ebullition and surface water CH4 concentrations can differ significantly within lakesspatially and temporally. CH4 fluxes may be affected at longer scales in response to seasons, temperature, lake mixing events, short term weather events like pressure variations, shifting winds and diel cycles. Frequent measurements of fluxes in the same system and integrated assessments of the impacts of the spatio-temporal variability are rare. Thereby, large scale assessments frequently lack information on this variability which can potentially lead to biased estimates. In this study, we analysed the variability of CH4 fluxes and surface water CH4 concentrations across open water areas of lakes in a small catchment in southwest Sweden over two annual cycles. Significant patterns in CH4 concentrations, diffusive fluxes, ebullition and total fluxes were observed in space (between and within lakes) and in time (over diel cycles to years). Differences observed among the lakes can be associated with lake characteristics. The spatial variability within lakes was linked to depth or distance to stream inlets. Temporal variability was observed at diel to seasonal scales and was influenced by weather events. The fluxes increased exponentially with temperature in all three lakes, with stronger temperature dependence with decreasing depth. By comparing subsets of our data with estimates using all data we show that considering the spatio-temporal variability in CH4 fluxes is critical when making whole lake or annual budgets.

  • 15.
    Nie, Xiang-Ping
    et al.
    Stockholm University, Faculty of Science, Department of Systems Ecology.
    Zie, Jenny
    Stockholm University, Faculty of Science, Department of Systems Ecology.
    Haeubner, Norbert
    Tallmark, Bo
    Snoeijs, Pauline
    Stockholm University, Faculty of Science, Department of Systems Ecology.
    Why Baltic herring and sprat are weak conduits for astaxanthin from zooplankton to piscivorous fish2011In: Limnology and Oceanography, ISSN 0024-3590, E-ISSN 1939-5590, Vol. 56, no 3, p. 1155-1167Article in journal (Refereed)
    Abstract [en]

    Atlantic salmon living in the brackish Baltic Sea have lower muscle pigmentation than populations elsewhere. The pigment in question is the antioxidant and vitamin A precursor astaxanthin, which is synthesized by crustaceans from algal carotenoids. Baltic salmon feed nearly exclusively on the clupeids sprat and herring. To evaluate astaxanthin availability to salmon we assessed astaxanthin levels and isomeric composition in their prey fish. We also analyzed astaxanthin dynamics in the dominant piscivorous fish in the Baltic Sea, the Atlantic cod. The geometrical E-(trans-) and Z-(cis-) isomers were distributed selectively in fish tissues, with highest E : Z ratios in salmon gonads (82 : 18) and lowest in herring gonads (24 : 76). Sprat and herring are not ideal prey with respect to their high whole-body concentrations of Z-isomers, which have low bioavailability for salmon and cod. These Z-isomers predominantly accumulate in the clupeid gonads. A crucial mechanism for the transport of astaxanthin from clupeids to piscivores is the direct transfer of crustacean astaxanthin (mainly all-E) from the clupeid stomachs. Low stomach astaxanthin content in clupeids decreases total astaxanthin transfer to higher trophic levels. In autumn, herring stomachs (including contents) had 12.5 times lower astaxanthin concentrations than sprat stomachs, and herring had 2.8 times less whole-body all-E-astaxanthin (by weight) than sprat. These results confirm recent reports of starvation in the Baltic herring, which may further decrease astaxanthin levels in the Baltic salmon. Cod did not have lower astaxanthin levels than their Atlantic counterpart, which may be attributed to their lower need for astaxanthin and higher food diversity.

  • 16. Reed, Daniel C.
    et al.
    Slomp, Caroline P.
    Gustafsson, Bo G.
    Stockholm University, Stockholm Resilience Centre, Baltic Nest Institute.
    Sedimentary phosphorus dynamics and the evolution of bottom-water hypoxia: A coupled benthic-pelagic model of a coastal system2011In: Limnology and Oceanography, ISSN 0024-3590, E-ISSN 1939-5590, Vol. 56, no 3, p. 1075-1092Article in journal (Refereed)
    Abstract [en]

    The present study examines oxygen and phosphorus dynamics at a seasonally hypoxic site in the Arkona basin of the Baltic Sea. A coupled benthic-pelagic reactive-transport model is used to describe the evolution of bottom-water solute concentrations, as well as pore-water and sediment profiles. Aerobic respiration dominates remineralization, with iron reduction, denitrification, and sulphate reduction playing secondary roles, while other pathways are negligible. Sediments represent a significant oxygen sink chiefly due to the aerobic degradation of organic matter, as well as nitrification and iron oxyhydroxide precipitation. Most phosphorus deposited in sediments is in organic matter, yet cycling is dominated by iron-bound phosphorus due to rapid dissimilatory iron reduction coupled with aerobic iron oxyhydroxide formation. Sustained hypoxia results in an initial decrease in sediment phosphorus content due to dissolution of phosphorus-bearing iron oxyhydroxides, resulting in a pulse of phosphate to overlying waters. Although an organic-rich layer is formed under low-oxygen conditions, enhanced remineralization of organic phosphorus relative to organic carbon tempers sedimentary phosphorus accumulation. Upon reoxygenation of bottom waters after a decade of sustained hypoxia, oxygen concentrations do not immediately achieve values observed prior to hypoxia because the organic-rich layer creates a higher benthic oxygen demand. Artificial reoxygenation of bottom waters leads to a substantial increase in the iron-bound phosphorus pool; the total phosphorus content of the sediment, however, is unaffected. A relapse into hypoxia would consequently produce a large pulse of phosphate to the overlying waters potentially exacerbating the situation.

  • 17. Rosen, P.
    et al.
    Cunningham, L.
    Vonk, Jorien
    Stockholm University, Faculty of Science, Department of Applied Environmental Science (ITM).
    Karlsson, J.
    Effects of climate on organic carbon and the ratio of planktonic to benthic primary producers in a subarctic lake during the past 45 years2009In: Limnology and Oceanography, ISSN 0024-3590, E-ISSN 1939-5590, Vol. 54, no 5, p. 1723-1732Article in journal (Refereed)
    Abstract [en]

    The effects of climatic variables on lake-water total organic carbon (TOC) concentrations and benthic and pelagic primary producers during the past 45 yr were assessed using the sediment records of two subarctic lakes, one with mires and one without mires connected to the lake. The lake with a mire showed large and synchronous changes in the planktonic to benthic (P : B) ratio of diatoms and concentrations of TOC inferred from near-infrared spectroscopy. During periods of warm temperatures, high precipitation, and long ice-free conditions, we inferred high TOC in the lake, and the diatom community was dominated by planktonic species. The stable carbon isotopic (delta C-13) values of sediment organic matter were negatively correlated with inferred TOC concentration and P : B ratio. We suggest that the changes in TOC and P : B ratio were a result of changing climate, permafrost degradation, and related changes in the catchment. Terrestrial organic matter, by its strong effect on the penetration of light through the lake water, possibly affected the habitats available for benthic photosynthesis and thus the delta C-13 of the sediment organic matter. The large changes in recent times may also be because of unusually long ice-free periods, warmer temperatures, and other associated limnological changes. The lake with no mire next to the lake showed only minor changes in lake-water TOC during the same period and P : B ratio remained almost constant until the past 5 yr, when the P : B ratio increased rapidly. The observed changes in P : B ratio within this lake may be because of complex interactions of several climate-related variables

  • 18.
    Savage, Candida
    et al.
    Stockholm University, Faculty of Science, Department of Systems Ecology.
    Leavitt, Peter R.
    Elmgren, Ragnar
    Stockholm University, Faculty of Science, Department of Systems Ecology.
    Effects of land use, urbanization, and climate variability on coastal eutrophication in the Baltic Sea2010In: Limnology and Oceanography, ISSN 0024-3590, E-ISSN 1939-5590, Vol. 55, no 3, p. 1033-1046Article in journal (Refereed)
    Abstract [en]

    Sedimentary records of organic matter inputs (stable nitrogen isotopes [delta N-15], nitrogen [N], and carbon [C] content), phytoplankton abundance (pigments, stable carbon isotopes [delta C-13]), and community composition (pigments) were used to reconstruct the history and pathway to water-quality degradation in a Swedish Baltic coastal bay. Changes in nutrient sources and cycling began in the 1800s, but eutrophication intensified only after the 1950s, coincident with intensified agricultural practices. Specifically, sedimentary N and C content doubled, delta 13C increased, and concentrations of pigments indicative of total algal biomass (beta-carotene, Chlorophyll a), diatoms (fucoxanthin, diatoxanthin), chlorophytes (lutein-zeaxanthin, Chlorophyll b), and cyanobacteria (canthaxanthin) increased significantly after 1950. Enhanced algal abundance was most strongly related to total N influx and secondly to total P influx. In particular, historical change in algae was related to agricultural N influx and only weakly to agricultural P. In recent decades, wastewater N influx has further stimulated algal biomass, particularly diatoms. In contrast, colonial cyanobacteria were more correlated to total P than total N inputs. Variance-partitioning analysis explained 60% of the changes in algal abundance and community composition since 1880, with diffuse and point nutrients jointly explaining 36% of the long-term change in algal biomass. Climate variability has become more important as a factor influencing coastal eutrophication in recent decades, explaining 14% of the variance in the algal data since 1975. Both urban and agricultural sources of nutrients have degraded water quality, illustrating the need for cooperation between stakeholders at regional levels to achieve ""good ecological status'' in the Baltic coastal environment.

  • 19. Tang, Kam W.
    et al.
    McGinnis, Daniel F.
    Frindte, Katharina
    Brüchert,, Volker
    Stockholm University, Faculty of Science, Department of Geological Sciences.
    Grossart, Hans-Peter
    Paradox reconsidered: Methane oversaturation in well-oxygenated lake waters2014In: Limnology and Oceanography, ISSN 0024-3590, E-ISSN 1939-5590, Vol. 59, no 1, p. 275-284Article in journal (Refereed)
    Abstract [en]

    The widely reported paradox of methane oversaturation in oxygenated water challenges the prevailing paradigm that microbial methanogenesis only occurs under anoxic conditions. Using a combination of field sampling, incubation experiments, and modeling, we show that the recurring mid-water methane peak in Lake Stechlin, northeast Germany, was not dependent on methane input from the littoral zone or bottom sediment or on the presence of known micro-anoxic zones. The methane peak repeatedly overlapped with oxygen oversaturation in the seasonal thermocline. Incubation experiments and isotope analysis indicated active methane production, which was likely linked to photosynthesis and/or nitrogen fixation within the oxygenated water, whereas lessening of methane oxidation by light allowed accumulation of methane in the oxygen-rich upper layer. Estimated methane efflux from the surface water was up to 5 mmol m(-2) d(-1). Mid-water methane oversaturation was also observed in nine other lakes that collectively showed a strongly negative gradient of methane concentration within 0-20% dissolved oxygen (DO) in the bottom water, and a positive gradient within >= 20% DO in the upper water column. Further investigation into the responsible organisms and biochemical pathways will help improve our understanding of the global methane cycle.

  • 20. von Wachenfeldt, Eddie
    et al.
    Bastviken, David
    Stockholm University, Faculty of Science, Department of Geology and Geochemistry.
    Tranvik, Lars J.
    Microbially induced flocculation of allochthonous dissolved organic carbon in lakes2009In: Limnology and Oceanography, ISSN 0024-3590, E-ISSN 1939-5590, Vol. 54, no 5, p. 1811-1818Article in journal (Refereed)
    Abstract [en]

    The flocculation of allochthonous dissolved organic carbon (DOC) in lakes was investigated in a series of laboratory experiments. Flocculation was enhanced by increased temperatures, and addition of glucose increased the flocculation further. A change in pH within the range of 3.3 to 7.3 resulted in decreased flocculation with increasing deviation from the original pH. Flocculation was similar under oxic and anoxic conditions. For all treatments (i.e., temperature and glucose, pH, and O2 regime), occulation was positively correlated to bacterial respiration. However, bacterial biomass made up a negligible fraction of the formed flocs, suggesting that the formation of detrital particles was a result of bacterial activity, but there was no significant contribution of bacteria to the mass of the particles formed. In all experiments, both the concentration of DOC and concentration of colored dissolved organic matter (CDOM) decreased concomitantly with flocculation, suggesting that CDOM is the precursor of the flocs. Bacteria mediate a translocation of DOC in the water column into particles prone to gravitational settling.

  • 21. von Wachenfeldt, Eddie
    et al.
    Sobek, Sebastian
    Bastviken, David
    Stockholm University, Faculty of Science, Department of Geology and Geochemistry.
    Tranvik, Lars J.
    Linking allochthonous dissolved organic matter and boreal lake sediment carbon sequestration: The role of light-mediated flocculation2008In: Limnology and Oceanography, ISSN 0024-3590, E-ISSN 1939-5590, Vol. 53, no 6, p. 2416-2426Article in journal (Refereed)
    Abstract [en]

    We measured flocculation of dissolved organic carbon (DOC) in the water from a humic lake (DOC = 14.9 mg C L-1) and from an adjacent mire (DOC = 25.7 mg C L-1), in in situ enclosure experiments with different light regimes. Light stimulated the formation of organic particles in both waters, and organic particle formation was observed at all incubation depths, even in the dark controls. Production of phytoplankton biomass was negligible, and allochthonous DOC was the most important precursor of the sinking particles. 8-22% and 25-60% of the loss of DOC in lake and mire water, respectively, could be accounted for by flocculation. Depth-integrated flocculation based on the enclosure experiments was 14.7 mg C m(-2) d(-1). Lake-water DOC concentration and water color has been increasing during the last decade, and sediment trap studies show that gross sedimentation of organic carbon also increased. Thus flocculation of allochthonous DOC, stimulated by light, constitutes a pathway for the sequestration of carbon in lake sediments.

  • 22. Vuorio, K.
    et al.
    Meili, Markus
    Stockholm University, Faculty of Science, Department of Applied Environmental Science (ITM).
    Sarvala, J.
    Natural isotopic composition of carbon (delta C-13) correlates with colony size in the planktonic cyanobacterium Gloeotrichia echinulata2009In: Limnology and Oceanography, ISSN 0024-3590, E-ISSN 1939-5590, Vol. 54, no 3, p. 925-929Article in journal (Refereed)
    Abstract [en]

    To assess variability in carbon isotope signatures (delta C-13) between and within populations under natural conditions, with a particular emphasis on colony size, we repeatedly collected planktonic colonies of a freshwater cyanobacterium Gloeotrichia echinulata in two lakes, Pyhajarvi (southwest Finland) and Erken (southeast Sweden). Despite substantial differences in the average delta C-13 signature of Gloeotrichia between lakes (-6.9 parts per thousand in Pyhajarvi and -20.7 parts per thousand in Erken), a similar, systematic increase in delta C-13 with colony size was observed in both lakes (of 2-3 parts per thousand in Pyhajarvi and 3-5 parts per thousand in Erken). This suggests declining isotope fractionation with increasing colony size, probably related to diffusion limitation of carbon availability. Temporal variation explained a minor fraction of total subsample variability (range delta C-13 similar to 4 parts per thousand in Pyhajarvi and similar to 6 parts per thousand in Erken). Isotopic C-13 fractionation in Gloeotrichia was likely affected both by carbon source and by colony size.

  • 23.
    Winder, Monika
    et al.
    Stockholm University, Faculty of Science, Department of Ecology, Environment and Plant Sciences.
    Bouquet, Jean-Marie
    Bermudez, J. Rafael
    Berger, Stella A.
    Hansen, Thomas
    Brandes, Jay
    Sazhin, Andrey F.
    Nejstgaard, Jens C.
    Bamstedt, Ulf
    Jakobsen, Hans H.
    Dutz, Joerg
    Frischer, Marc E.
    Troedsson, Christofer
    Thompson, Eric M.
    Increased appendicularian zooplankton alter carbon cycling under warmer more acidified ocean conditions2017In: Limnology and Oceanography, ISSN 0024-3590, E-ISSN 1939-5590, Vol. 62, no 4, p. 1541-1551Article in journal (Refereed)
    Abstract [en]

    Anthropogenic atmospheric loading of CO2 raises concerns about combined effects of increasing ocean temperature and acidification, on biological processes. In particular, the response of appendicularian zooplankton to climate change may have significant ecosystem implications as they can alter biogeochemical cycling compared to classical copepod dominated food webs. However, the response of appendicularians to multiple climate drivers and effect on carbon cycling are still not well understood. Here, we investigated how gelatinous zooplankton (appendicularians) affect carbon cycling of marine food webs under conditions predicted by future climate scenarios. Appendicularians performed well in warmer conditions and benefited from low pH levels, which in turn altered the direction of carbon flow. Increased appendicularians removed particles from the water column that might otherwise nourish copepods by increasing carbon transport to depth from continuous discarding of filtration houses and fecal pellets. This helps to remove CO2 from the atmosphere, and may also have fisheries implications.

  • 24.
    Winder, Monika
    et al.
    Stockholm University, Faculty of Science, Department of Ecology, Environment and Plant Sciences.
    Carstensen, Jacob
    Galloway, Aaron W. E.
    Jakobsen, Hans H.
    Cloern, James E.
    The land-sea interface: A source of high-quality phytoplankton to support secondary production2017In: Limnology and Oceanography, ISSN 0024-3590, E-ISSN 1939-5590, Vol. 62, p. S258-S271Article in journal (Refereed)
    Abstract [en]

    Coastal-estuarine systems are among the most productive marine ecosystems and their special role in producing harvestable fish and shellfish has been attributed to high primary production fueled by nutrient runoff from land and efficient trophic transfer. Here we ask if phytoplankton species composition and their food quality based on the percentage of long-chain essential fatty acids (LCEFA) is another factor contributing to high secondary production in these ecosystems. We used long-term measurements of major phytoplankton taxonomic groups and estimated their content of LCEFA along the salinity gradient in coastal-estuarine ecosystems, with emphasis on Chesapeake Bay and the Baltic Sea, and an oceanic transect. Our data show that cyanobacteria with low nutritional quality often dominate at low-salinity regions, while intermediate to higher salinity regions produce diatoms and dinoflagellates that have a higher content of LCEFA and are thus a higher-quality food resource for consumers. Higher salinity regions have less pronounced seasonal changes in the percentage of phytoplankton LCEFA compared to low salinity regions, providing a stable supply of nutritious phytoplankton to consumers. The phytoplankton LCEFA content is similarly high in coastal upwelling systems and it decreases further offshore in oligotrophic oceanic regions dominated by picophytoplankton. Our results from a broad range of coastal-ecosystem types show that ecosystems at the land-sea interface provide a valuable service by producing phytoplankton enriched in the biochemicals essential for consumers. High primary production, coupled with high quality of that production, explain why the production of fish and shellfish is high where land and sea meet.

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