| 1. |
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| 2. |
- Blomqvist, Sven, et al.
(author)
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Long overdue improvement of box corer sampling
- 2015
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In: Marine Ecology Progress Series. - : Inter-Research Science Center. - 0171-8630 .- 1616-1599. ; 538, s. 13-21
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Journal article (peer-reviewed)abstract
- An improved, large double-jawed box corer, intended primarily for sampling of soft sediments on continental margins and in large lakes, is described. The device performs reliably when entering the sediment and enclosing the sample, during withdrawal and hoisting on board the ship and also when detaching the collected sediment sample. It offers the following advantages: (1) robust design, (2) minimally impeded flow of water through the box chamber during lowering and (3) an efficient closure mechanism. It is furnished with a supporting stand, a transparent liner and an accessory anti-slosh baffle for insertion in the liner as the corer is set down on the ship's deck. In situ video records and turbidity measurements from field trials, as well as visual inspection of the core and supernatant water after retrieval, show that the device collects minimally disturbed sediment when properly and carefully operated. This contrasts with the bulky United States Naval Electronics Laboratory (USNEL) Spade Corer in which water flow through the box chamber during lowering is impeded, causing a bow-wave ahead of the corer that displaces surficial sediment. In addition, the USNEL's single-spade closing mechanism deforms the sediment sample severely and can even cause loss of sediment. Our new box corer performs much better, making it suitable for quantitative benthic sampling.
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| 3. |
- Bonaglia, Stefano, et al.
(author)
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Sulfide oxidation in deep Baltic Sea sediments upon oxygenation and colonization by macrofauna
- 2019
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In: Marine Biology. - : Springer Science and Business Media LLC. - 0025-3162 .- 1432-1793. ; 166
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Journal article (peer-reviewed)abstract
- Coastal and shelf sediments affected by transient or long-term bottom water anoxia and sulfidic conditions undergo drastic changes in macrofauna communities and abundances. This study investigates how early colonization by two macrofaunal functional traits (epifauna vs. infauna) affects oxygen, sulfide, and pH dynamics in anoxic sediment upon recent bottom water oxygenation. Large mesocosms (area 900 cm(2)) with 150-m-deep Baltic Sea soft sediments were exposed to three treatments: (1) no animals; (2) addition of 170 polychaetes (Marenzelleria arctia); (3) addition of 181 amphipods (Monoporeia affinis). Porewater chemistry was investigated repeatedly by microsensor profiling over a period of 65 days. Colonization by macrofauna did not significantly deepen penetration of oxygen compared to the animal-free sediment. Bioturbation by M. affinis increased the volume of the oxidized, sulfide-free sediment by 66% compared to the animal-free control already after 13 days of incubation. By the end of the experiment M. affinis and M. arctia increased the oxidized sediment volume by 87 and 35%, respectively. Higher efficiency of epifaunal amphipods in removing hydrogen sulfide than deep-burrowing polychaetes is likely due to more substantial re-oxidation of manganese and/or nitrogen compounds associated with amphipod mixing activity. Our results thus indicate that early colonization of different functional groups might have important implications for the later colonization by benthic macrofauna, meiofauna and microbial communities that benefit from oxidized and sulfide-free sediments.
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| 4. |
- Ekeroth, Nils, 1982-
(author)
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Benthic fluxes of biogenic elements in the Baltic Sea : Influence of oxygen and macrofauna
- 2015
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Doctoral thesis (other academic/artistic)abstract
- This thesis investigates how benthic fluxes of phosphorus (P), nitrogen (N), and silicon (Si) change upon oxygenation of anoxic soft bottoms in the brackish, eutrophicated Baltic Sea. Direct measurements in situ by benthic landers demonstrated that fluxes of dissolved inorganic P (DIP) from anoxic bottom sediments in the Eastern Gotland Basin are higher than previously thought (Paper I). It is argued that the benthic DIP flux has a much larger influence on the DIP inventory in the Baltic proper than the external sources. Similarly, benthic fluxes of DIP and dissolved inorganic N (DIN) from anoxic sediment in the coastal Kanholmsfjärden Basin, Stockholm archipelago, were sufficiently high to renew the pools of these nutrients below the upper mixed layer in roughly one year (Paper II).A natural inflow of oxygen rich water into the deep, and previously long-term anoxic part of Kanholmsfjärden Basin, increased the P content in the sediment by 65% and lowered DIP and dissolved silica (DSi) concentrations in the pore water. These changes, as well as the large increases in benthic effluxes of these solutes following de-oxygenation of the bottom water, suggest that they are influenced similarly by changing oxygen conditions.Experimental results in papers III and IV show that common benthic macrofauna species in the Baltic Sea can stimulate benthic release of DIN and DSi, as well as dissolved organic and particulate bound nutrients. Thus, if benthic oxygen conditions would improve in the Baltic, initial effects on benthic–pelagic nutrient coupling will change due to animal colonisation of currently azoic soft bottoms.A new box corer was designed (Paper V) which can be used to obtain highly needed virtually undisturbed samples from soft bottom sediments – if lowered slowly and straight into the bottom strata – as demonstrated by in situ videography and turbidimetry. The commonly used USNEL box corer caused severe biasing during sediment collection.
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| 5. |
- Ekeroth, Nils, et al.
(author)
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Effects of oxygen on recycling of biogenic elements from sediments of a stratified coastal Baltic Sea basin
- 2016
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In: Journal of Marine Systems. - : Elsevier BV. - 0924-7963 .- 1879-1573. ; 154, s. 206-219
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Journal article (peer-reviewed)abstract
- 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.
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| 6. |
- Ekeroth, Nils, et al.
(author)
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Nutrient fluxes from reduced Baltic Sea sediment : effects of oxygenation and macrobenthos
- 2016
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In: Marine Ecology Progress Series. - : Inter-Research Science Center. - 0171-8630 .- 1616-1599. ; 544, s. 77-92
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Journal article (peer-reviewed)abstract
- Effects of bottom water oxygenation and macrofaunal colonisation on benthic fluxes of nitrogen (N), phosphorus (P) and silicon (Si) from long-term anoxic Baltic Sea bottom sediment were investigated. Sediment boxcosms from an anoxic site at 150 m depth in the open Baltic proper were incubated in the laboratory to follow the development of benthic nutrient fluxes during 74 d exposure to flow-through of oxygen-rich water. In contrast to traditional end-point experimental designs, our repeated measurement approach allowed for separation of transient and long-term effects of oxygenation and bioturbation on benthic nutrient recycling. The composition, but not the rate, of the benthic total dissolved N efflux changed by oxygenation from being dominated by NH4 in situ to being mostly composed of NO2 + NO3 and dissolved organic N (DON) under oxic conditions. Oxygenation in the boxcosms decreased the benthic efflux of dissolved silicate (DSi) and essentially shut off the in situ flux of dissolved inorganic phosphorus (DIP). After 20 d of oxygenation, 2 bottom macrofauna taxa, the polychaete Marenzelleria spp. and the amphipod Monoporiea affinis, were introduced to a subset of the boxcosms. Bioturbation by either taxa increased the efflux of dissolved inorganic N (DIN), DON and DSi to the overlying water. The P-rich benthic flux under in situ anoxic conditions roughly approached Redfield N: P stoichiometry after oxygenation in the sediment boxcosms. Upon addition of macrofauna, bioturbation gene rated even higher N:P flux ratios.
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| 7. |
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| 8. |
- Ekeroth, Nils
(author)
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On benthic fluxes of phosphorus in the Baltic Sea proper – drivers and estimates
- 2012
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Licentiate thesis (other academic/artistic)abstract
- This Thesis focuses on the exchange of phosphorus (P) across the sediment–water interface in the Baltic Sea proper, with particular attention to the influence of bioturbating macrofauna and benthic redox conditions. Benthic P fluxes have major influence on P availability in the water column, which in turn regulates growth conditions for dinitrogen fixating cyanobacteria in the Baltic proper. Presently, a very large area of bottom sediment is overlain by oxygen depleted bottom water and is therefore devoid of aerobic organisms.In paper I, anoxic sediment from the Western Gotland Basin was oxygenated and exposed to bioturbation by three macrofauna species in a laboratory experiment. The experimental design allowed for detailed studies of how bioturbating animals influence the P fluxes on a species-specific level. All species (Monoporeia affinis, Mysis mixta, and Macoma balthica) mobilised dissolved organic P from the bottom sediment to the supernatant water. Also, particulate P was released by the two former species. None of these P fractions showed any mobility in control sections of the aquarium system. These animal-dependent P fluxes are a previously largely overlooked but potentially significant source of bioavailable P in coastal marine areas, such as the Baltic Sea.In paper II, we estimate a contemporary reflux of 146 kton dissolved inorganic P (DIP) from bottom sediments in the Baltic proper. This estimate is based on data from a large number of in situ benthic flux measurements using benthic chamber landers along a depth gradient in the Eastern Gotland Basin. DIP effluxes increased with increasing water depth, and decreasing bottom water oxygen concentrations. Bottom water anoxia was identified as a major driver for the mobilisation of DIP from bottom sediments. During such conditions, the DIP efflux was well correlated to carbon oxidation rate, while on oxic bottoms DIP fluxes were low irrespectively of the carbon oxidation rate. Our data support the hypothesis of a positive feedback loop of self-amplifying eutrophication in the Baltic Sea. Thus, both nutrient emission cuts and active mitigation actions to strengthen sedimentary P sinks are warranted for effective remediation of eutrophication in the Baltic Sea.
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| 9. |
- Ekeroth, Nils, 1982-, et al.
(author)
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Recolonisation by macrobenthos mobilises organic phosphorus from reoxidised Baltic Sea sediments
- 2012
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In: Aquatic geochemistry. - : Springer Science and Business Media LLC. - 1380-6165 .- 1573-1421. ; 18:6, s. 499-513
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Journal article (peer-reviewed)abstract
- In recent decades, eutrophication has increased the extent of hypoxic and anoxic conditions in many coastal marine environments. In such conditions, the nutrient flux across the sediment–water interface is a key process controlling the biogeochemical dynamics, and thereby the level and character of biological production. In some areas, management attempts to drive the ecosystem towards phosphorus (P) limitation, which calls for reliable knowledge on the mechanisms controlling P-cycling. We report a well-controlled laboratory experiment on benthic fluxes of P, when shifting from a state of hypoxic and azoic sediments to oxic and zoic bottom conditions. Adding any of three types of macrobenthic fauna (mysid shrimp, pontoporeid amphipod and tellinid clam) to oxygenated aquarium sections resulted in benthic P fluxes that differed consistently from the azoic control sections. All species caused liberation of dissolved organically bound P (DOP) from the sediment, in contrast to the azoic systems. The shrimp and the amphipod also resuspended the sediment, which resulted in a release of P bound to particles (>0.45 μm). Dissolved inorganic phosphate (DIP) was released during hypoxic conditions, but was taken up after oxygenation, irrespective of the presence or absence of bottom fauna. In the presence of fauna, the uptake of DIP roughly equalled the release of DOP, suggesting that the benthic efflux of DOP following oxygenation and bottom fauna (re)colonisation might be considerable. This is an hitherto overlooked animal-controlled nutrient flux, which is missing from coastal marine P budgets.
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| 10. |
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| 11. |
- Ekeroth, Sebastian, 1988-, et al.
(author)
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Catalytic nanotruss structures realized by magnetic self-assembly in pulsed plasma
- 2018
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In: Nano Letters. - : American Chemical Society (ACS). - 1530-6984 .- 1530-6992. ; 18:5, s. 3132-3137
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Journal article (peer-reviewed)abstract
- Tunable nanostructures that feature a high surface area are firmly attached to a conducting substrate and can be fabricated efficiently over significant areas, which are of interest for a wide variety of applications in, for instance, energy storage and catalysis. We present a novel approach to fabricate Fe nanoparticles using a pulsed-plasma process and their subsequent guidance and self-organization into well-defined nanostructures on a substrate of choice by the use of an external magnetic field. A systematic analysis and study of the growth procedure demonstrate that nondesired nanoparticle agglomeration in the plasma phase is hindered by electrostatic repulsion, that a polydisperse nanoparticle distribution is a consequence of the magnetic collection, and that the formation of highly networked nanotruss structures is a direct result of the polydisperse nanoparticle distribution. The nanoparticles in the nanotruss are strongly connected, and their outer surfaces are covered with a 2 nm layer of iron oxide. A 10 μm thick nanotruss structure was grown on a lightweight, flexible and conducting carbon-paper substrate, which enabled the efficient production of H2 gas from water splitting at a low overpotential of 210 mV and at a current density of 10 mA/cm2.
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| 12. |
- Ekeroth, Sebastian, et al.
(author)
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Magnetically Collected Platinum/Nickel Alloy Nanoparticles as Catalysts for Hydrogen Evolution
- 2021
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In: ACS Applied Nano Materials. - : American Chemical Society (ACS). - 2574-0970. ; 4:12, s. 12957-12965
-
Journal article (peer-reviewed)abstract
- The hydrogen evolution reaction (HER) is a key process in electrochemical water splitting. To lower the cost and environmental impact of this process, it is highly motivated to develop electrocatalysts with low or no content of noble metals. Here, we report on an ingenious synthesis of hybrid PtxNi1-x electrocatalysts in the form of a nanoparticle-nanonetwork structure with very low noble metal content. The structure possesses important features such as good electrical conductivity, high surface area, strong interlinking, and substrate adhesion, which render an excellent HER activity. Specifically, the best performing Pt0.05Ni0.95 sample demonstrates a Tafel slope of 30 mV dec-1 in 0.5 M H2SO4 and an overpotential of 20 mV at a current density of 10 mA cm-2 with high stability. The impressive catalytic performance is further rationalized in a theoretical study, which provides insight into the mechanism on how such small platinum content can allow for close-to-optimal adsorption energies for hydrogen.
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| 13. |
- Ekeroth, Sebastian, 1988-
(author)
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Plasma Synthesis and Self-Assembly of Magnetic Nanoparticles
- 2019
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Doctoral thesis (other academic/artistic)abstract
- Nanomaterials are important tools for enabling technological progress as they can provide dramatically different properties as compared to the bulk counterparts. The field of nanoparticles is one of the most investigated within nanomaterials, thanks to the existing, relatively simple, means of manufacturing. In this thesis, high-power pulsed hollow cathode sputtering is used to nucleate and grow magnetic nanoparticles in a plasma. This sputtering technique provides a high degree of ionization of the sputtered material, which has previously been shown to aid in the growth of the nanoparticles. The magnetic properties of the particles are utilized and makes it possible for the grown particles to act as building blocks for self-assembly into more sophisticated nano structures, particularly when an external magnetic field is applied. These structures created are termed “nanowires” or “nanotrusses”, depending on the level of branching and inter-linking that occurs.Several different elements have been investigated in this thesis. In a novel approach, it is shown how nanoparticles with more advanced structures, and containing material from two hollow cathodes, can be fabricated using high-power pulses. The dual-element particles are achieved by using two distinct and individual elemental cathodes, and a pulse process that allows tuning of individual pulses separately to them. Nanoparticles grown and investigated are Fe, Ni, Pt, Fe-Ni and Ni-Pt. Alternatively, the addition of oxygen to the process allows the formation of oxide or hybrid metal oxide – metal particles. For all nanoparticles containing several elements, it is demonstrated that the stoichiometry can be easily varied, either by the amount of reactive gas let into the process or by tuning the amount of sputtered material through adjusting the electric power supplied to the different cathodes.One aim of the presented work is to find a suitable material for the use as a catalyst in the production of H2 gas through the process of water splitting. H2 is a good candidate to replace fossil fuels as an energy carrier. However, rare elements (such as Ir or Pt) needs to be used as the catalyst, otherwise a high overpotential is required for the splitting to occur, leading to a low efficiency. This work demonstrates a possible route to avoid this, by using nanomaterials to increase the surface-to-volume ratio, as well as optimizing the elemental ratio between different materials to lower the amount of noble elements required.
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| 14. |
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| 15. |
- Hjorth, Tomas, et al.
(author)
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Undersökning av limniska sediment : Konsultrapport inom regeringsuppdraget RUFS
- 2023
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Reports (other academic/artistic)abstract
- Regeringen gav 2019 i uppdrag till ett antal myndigheter, under ledning av Naturvårdsverket, att förbättra kunskapen om förorenade sediment. Denna rapport redovisar fältundersökningar av sediment i sjöar och vattendrag i Sverige utförda av NIRAS Sweden AB på uppdrag av Sveriges geologiska undersökning (SGU). Fältundersökningarna har genomförts inom ett delprojekt inom regeringsuppdraget där SGU, Naturvårdsverket, länsstyrelserna och Havs- och vattenmyndigheten har medverkat. Parallellt har även sediment i kustområden och i Vänern undersökts. Syftet med fältundersökningarna har varit att bidra till en förbättrad nationell överblick och kunskapsgrund för prioriteringar av kommande inventeringar och åtgärder av förorenade sediment. De har också syftat till att ta fram underlag för fortsatt utveckling av inventeringsmetodik.Inledningsvis valdes undersökningsområden ut utifrån bedömd påverkansbild av miljögifter inom vattenförvaltningen från pågående miljöfarlig verksamhet och förorenade områden från historiska verksamheter, tillgängliga kartor (flygfoton, djupkartor och geologiska kartor), och tillgänglig information om tidigare undersökningar. Urvalet förfinades utifrån prioriterade branscher att undersöka och i dialog med berörda länsstyrelser och resulterade i 55 undersöknings områden, av vilka 34 förekom i sjöar och 21 i vattendrag. Underlaget ingick i SGU:s uppdragsbeskrivning och NIRAS Sweden AB fortsatte skrivbordsinventeringen för att utforma mer detaljerade underlag inför provtagning i fält.Fältarbetet utfördes under år 2021 och 2022. Det inleddes i varje område med hydroakustiska undersökningar, i de flesta fall genom mätning med enkelstrålande ekolod. Vid elva områden användes mer avancerade hydroakustiska mätmetoder. Resultaten av de hydroakustiska mätningarna indikerar var på bottnarna det kan finnas sediment som avsatts under industrialismen och som kan vara påverkade av mänskliga aktiviteter. Utifrån denna information justerades placeringen av de preliminärt föreslagna provpunkterna. Prov hämtades från en till fyra lokaler inom 53 undersökningsområden. Två av de planerade undersökningsområden utgick på grund av att strömförhållanden medförde att det inte gick att genomföra provtagningen. Rörprovtagare användes för att kunna ta ytprover (0–5 cm) och djupare prover (15–20 cm), men för tio av undersökningsområdena medförde botten- eller strömförhållandena för ett eller flera av proverna att lådprovtagare behövde användas istället för rörprovtagare. För dessa prover togs endast samlingsprover och inte definierade yt- eller djupprover.Sedimentproverna analyserades avseende kemiska och fysikaliska parametrar och i vissa områden avseende toxisk respons med så kallade CALUX-metoder. De kemiska analyserna delades in i olika paket; ett grundpaket av fysikaliska parametrar och ämnesgrupper som antogs vara vanligt förekommande i sediment och som analyserades i samtliga yt- och djupprover, samt flera olika tilläggspaket som analyserades i ytprover utifrån de branschtypiska ämnen som skulle kunna förekomma utifrån påverkansbilden i respektive undersökningsområde. Resultaten stöder antagandet att ämnesgrupperna som inkluderades i grundpaketet ofta förekommer i vattenmiljön. Metaller uppmättes i samtliga prover, och de organiska ämnesgrupperna som ingick i grundpaketet (PAHer och PCBer) uppmättes även ofta. Flertalet PAHer och PCBer påträffades över rapporteringsgränserna i 75 % av proverna.I jämförelse med ämnesgrupperna i grundpaketet uppmättes ämnesgrupperna i tilläggspaketen mer sällan. Läkemedel var den ämnesgrupp som påträffades i lägst grad. Höga rapporteringsgränser och matriseffekter kan ha bidragit till att vissa ämnen i tilläggspaketen inte kunde uppmätas.Vid en jämförelse med bedömningsgrunder och jämförelsevärden framgick att uppmätta halter av bly, kadmium, koppar, TBT och antracen överskred vattendirektivets gränsvärden i omkring 20–40 % av ytproverna. Siloxaner som analyserades i prover från recipienter till avloppsreningsverk påträffades sällan över rapporteringsgränsen, men i de tre prover där siloxanen D4 kunde uppmätas överskreds den effektbaserade bedömningsgrunden (HVMFS 2019:25). Metallhalter avvek i flera undersökningsområden stort från bakgrundshalter, och även från medianvärden inom undersökningen. Det gäller framför allt för arsenik, men även för bly, koppar, krom, kvicksilver, tenn och zink, exempelvis i recipienter till gruvor (Saivatj/Aisjaure, Ruttjejaure och Bruträsket) och stålindustri med ytbehandling (Lill-Gösken).Påverkansbildens komplexitet varierade mycket mellan undersökningsområdena. Eftersom både antal och typ av bransch varierade, och därmed urval av tilläggspaket, ger resultaten endast indikationer om vilka ämnen och ämnesgrupper som kan kopplas till specifika branscher. Likväl tyder resultaten på att den största belastningen i de områden som ingick i undersökningen av både antal ämnen och uppmätta halter var som störst i recipienter till massa- och pappersbruk, avloppsreningsverk och tätorter, men också recipienter till gruvor, stålindustrier och avfallshantering och deponier.För att uppskatta effekten på levande organismer i vattenmiljön utfördes så kallade toxicitetstester enligt CALUX-metoden avseende dioxinlika ämnen, PAHer och östrogenlika ämnen. Resultaten från dessa analyser uppvisar över lag god samvariation med kemiskt uppmätta halter av respektive ämnesgrupp. Responsen på dioxinlika ämnen indikerar dessutom att det finns fler föreningar än PCDD/F och DL-PCB som ger upphov till dioxinlika effekter. Toxicitetstester kan på detta sätt utgöra ett viktigt komplement till kemiska analyser.En erfarenhet från fältundersökningarna inom regeringsuppdraget är att sammanställningar av tillgänglig information om påverkanskällor och sedimentgeologiska förhållanden i vattenområden är mycket viktiga underlag för att prioritera vilka områden som bör undersökas. Träffsäkerheten i detta förfarande kan förväntas öka varefter fler områden undersöks i framtiden och kunskapen ökar om föroreningars koppling till olika källor. Kommande fältundersökningar bör utföras med så jämförbara metoder som möjligt, och erfarenheterna från fältmetoderna som tillämpats under regeringsuppdraget kan bidra med viktig kunskap. Fler metodstudier skulle ytterligare kunna balansera omfattning och noggrannhet i såväl inledande ekolodsmätningar (hydroakustik) som provtagningsteknik. Detta skulle bidra till att uppnå undersökningsresultat med tillräcklig kvalitet så kostnadseffektivt som möjligt. Fler undersökningar skulle även bidra med underlag till bedömningsgrunder för miljöföroreningar som hittills saknar sådana, exempelvis dioxiner och dioxinlika föreningar.
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| 16. |
- Kononets, Mikhail Y, 1978, et al.
(author)
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In situ incubations with the Gothenburg benthic chamber landers : Applications and quality control
- 2021
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In: Journal of Marine Systems. - : Elsevier BV. - 0924-7963 .- 1879-1573. ; 214
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Journal article (peer-reviewed)abstract
- In situ incubations of sediment with overlying water provide valuable and consistent information about benthic fluxes and processes at the sediment-water interface. In this paper, we describe our experiences and a variety of applications from the last 14 years and 308 deployments with the Gothenburg benthic chamber lander systems. We give examples of how we use sensor measurements for chamber leakage control, in situ chamber volume determination, control of syringe sampling times, sediment resuspension and stirring quality. We present examples of incubation data for in situ measurements of benthic fluxes of oxygen, dissolved inorganic carbon, nutrients, metals and gases made with our chamber landers, as well as manipulative injection experiments to study nitrogen cycling (injections of N-15 nitrate), phosphate retention (injections of marl suspension) and targeted sediment resuspension. Our main goal is to demonstrate the possibilities that benthic chamber lander systems offer to measure solute fluxes and study processes at the sediment-water interface. Based on our experience, we recommend procedures to be used in order to obtain high quality data with benthic chamber landers.
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| 17. |
- Nilsson, Madeleine, et al.
(author)
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Particle shuttling and oxidation capacity of sedimentary organic carbon on the Baltic Sea system scale
- 2021
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In: Marine Chemistry. - : Elsevier BV. - 0304-4203. ; 232
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Journal article (peer-reviewed)abstract
- Continental margin sediments receive most of the particulate organic carbon (POC) deposited on the global seafloor, making them crucial locations in the carbon cycle. However, the complex environments in coastal oceans make it challenging to predict the fate of sedimentary organic carbon (OC) in these areas. Here we use data from 21 sites in the Baltic Sea, representing different biological and physiochemical regimes, to explore controls on sedimentary OC cycling. To this end, we combine in situ measured benthic fluxes of dissolved inorganic carbon (DIC; proxy for OC oxidation) with data on sediment properties. In the Gulf of Bothnia, low sedimentary OC oxidation capacities (yearly DIC flux divided by sedimentary POC inventory) were likely caused by a large fraction of terrestrial material in the POC pool, indicated by low sedimentary chlorophyll a content and high (> 10) carbon:nitrogen ratios. The highest OC oxidation capacities were measured at shallow, permanently oxic sites in the Baltic Proper, where bioturbation likely stimulates OC oxidation. The other sites in the Baltic Proper and all stations in the Gulf of Finland displayed increasing OC oxidation capacities with increasing normalised water depth (station depth divided by maximal depth in the basin). This pattern suggests that substantial quantities of POC are shuttled, through repeated cycles of resuspension-redeposition, from shallow erosion-transport (ET) areas to deep accumulation (A) areas. This interpretation was supported by decreasing sediment age and increasing sedimentary inventories of POC and chlorophyll a with normalised water depth. Our calculations indicate that particle shuttling redistributes almost half of the deposited export production from ET areas to A areas in the Baltic Proper, and that substantial amounts of terrestrial organic material are transported through particle shuttling to the deeper parts of the Gulf of Finland and Gulf of Bothnia. Depositional setting and POC origin can thus be central factors in predicting the distribution and fate of OC in coastal and shelf sediments.
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| 18. |
- Viktorsson, Lena, 1980, et al.
(author)
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Phosphorus recycling in sediments of the central Baltic Sea
- 2013
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In: Biogeosciences. - : Copernicus GmbH. - 1726-4170 .- 1726-4189. ; 10, s. 3901-3916
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Journal article (peer-reviewed)abstract
- Benthic fluxes of phosphorus (P) were measured in situ in the Eastern Gotland Basin (EGB), central Baltic Sea, using benthic landers. A total of 40 flux measurements of dissolved inorganic P (DIP) on 13 stations at water depths ranging 30–210 m and under different oxygen regimes were carried out on three cruises during three consecutive years (2008–2010) in August–September. Our study is the first to report in situ DIP fluxes in the Baltic proper, and it provides the most comprehensive dataset of benthic fluxes of DIP and dissolved organic P (DOP) in the Baltic proper existing to date. DIP fluxes increased with increasing water depth and with decreasing bottom water oxygen concentration. Average DIP fluxes were calculated for oxic bottom water conditions (−0.003±0.040 mmol m−2 d−1), hypoxic conditions (0.027±0.067 mmol m−2 d−1) and anoxic conditions (0.376±0.214 mmol m−2 d−1). The mean DIP flux at anoxic bottoms was higher than previous estimates based on ex situ measurements of pore water gradients. The DIP flux was positively correlated with the organic carbon inventory of sediment, and the benthic flux of dissolved inorganic carbon (DIC) at anoxic stations, but these variables were uncorrelated at oxic stations. The positive correlation between DIP and DIC fluxes suggests that the benthic DIP efflux from anoxic bottoms in the Baltic Proper is mainly controlled by rates of deposition and degradation of organic matter. The flux from anoxic sediment was very P rich in relation to both C and nitrogen (N). The average C : P ratio in fluxes at anoxic accumulation bottoms was 69±15, which is well below the Redfield C : P ratio of 106 : 1. At oxic stations, however, the C : P flux ratio was much higher than the Redfield ratio, consistent with well-known P retention mechanisms associated with iron and bacteria in oxidised sediment. Using a benthic mass balance approach, a burial efficiency estimate of 0.2–12% was calculated for the anoxic part of the EGB, which suggests that anoxic Baltic sediments are very efficient in recycling deposited P. Based on the measured fluxes and the average areal extent of anoxic bottoms during years 1999–2006, an internal DIP load of 152 kton yr−1 was calculated. This is almost 9 times higher than the average external total phosphorus (TP) supply to the Baltic proper during the same period. This comparison clearly highlights the dominance of internally regenerated P as a DIP source in the Baltic Sea.
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| 19. |
- Viktorsson, L., et al.
(author)
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Phosphorus recycling in sediments of the Central Baltic Sea
- 2012
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In: Biogeosciences Discussions. - : Copernicus GmbH. - 1810-6277 .- 1810-6285. ; 9, s. 15459-15500
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Journal article (peer-reviewed)abstract
- Benthic fluxes of dissolved inorganic phosphorus (DIP) were measured in situ in the Eastern Gotland Basin (EGB), Central Baltic Sea, using benthic landers. A total of 40 flux measurements on 13 stations at water depths ranging from 30–210 m and under different oxygen regimes were carried out on three cruises during three consecutive years (2008–2010) in August–September. Our study is the first to report in situ DIP fluxes in the Baltic Proper, and it provides the most comprehensive data set of benthic DIP fluxes in the Baltic Proper existing to date. DIP fluxes increased with increasing water depth and with decreasing bottom water oxygen concentration. Average fluxes were calculated for oxic bottom water conditions (−0.003 ± 0.040 mmol m−2 d−1), hypoxic conditions (0.027 ± 0.067 mmol m−2 d−1) and anoxic conditions (0.376 ± 0.214 mmol m−2 d−1). The mean flux on anoxic bottoms was ca. 5–10 times higher than previous estimates based on ex situ measurements, but agreed well with previous flux estimations from changes in the basin water DIP pool. The DIP flux was positively correlated with the organic carbon inventory of sediment and the benthic flux of dissolved inorganic carbon (DIC) on anoxic stations, but these variables were uncorrelated on oxic stations. The positive correlation between DIP and DIC fluxes suggests that the benthic DIP flux on anoxic bottoms in the Baltic Proper is mainly controlled by rates of deposition and degradation of organic matter. The flux from anoxic sediment was very P rich in relation to both C and N, and the average C:P ratio in fluxes on anoxic accumulation bottoms was 69 ± 15, which is well below the Redfield C:P ratio of 106:1. On oxic stations, however, the C:P flux ratio was much higher than the Redfield ratio, consistent with well-known P retention mechanisms associated with iron and bacteria in oxidized sediment. Using a benthic mass balance approach, a burial efficiency of 4% was calculated for the anoxic part of the EGB, which suggests that anoxic Baltic sediments are very efficient in recycling deposited P. Based on the measured fluxes and recent estimates of the areal extent of anoxic and hypoxic bottoms, an internal load of 146 kton yr−1 was calculated. This is 7–12 times higher than recent estimates of the external load and clearly highlights the dominance of anoxic sediments as a P source in the Baltic Sea.
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