| 1. |
- Alsterberg, Christian, 1982, et al.
(författare)
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Functioning of a Shallow-Water Sediment System during Experimental Warming and Nutrient Enrichment
- 2012
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Ingår i: Plos One. - : Public Library of Science (PLoS). - 1932-6203. ; 7:12
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Tidskriftsartikel (refereegranskat)abstract
- Effects of warming and nutrient enrichment on intact unvegetated shallow-water sediment were investigated for 5 weeks in the autumn under simulated natural field conditions, with a main focus on trophic state and benthic nitrogen cycling. In a flow-through system, sediment was exposed to either seawater at ambient temperature or seawater heated 4 degrees C above ambient, with either natural or nutrient enriched water. Sediment-water fluxes of oxygen and inorganic nutrients, nitrogen mineralization, and denitrification were measured. Warming resulted in an earlier shift to net heterotrophy due to increased community respiration; primary production was not affected by temperature but (slightly) by nutrient enrichment. The heterotrophic state was, however, not further strengthened by warming, but was rather weakened, probably because increased mineralization induced a shortage of labile organic matter. Climate-related warming of seawater during autumn could therefore, in contrast to previous predictions, induce shorter but more intensive heterotrophic periods in shallow-water sediments, followed by longer autotrophic periods. Increased nitrogen mineralization and subsequent effluxes of ammonium during warming suggested a preferential response of organisms driving nitrogen mineralization when compared to sinks of ammonium such as nitrification and algal assimilation. Warming and nutrient enrichment resulted in non-additive effects on nitrogen mineralization and denitrification (synergism), as well as on benthic fluxes of phosphate (antagonism). The mode of interaction appears to be related to the trophic level of the organisms that are the main drivers of the affected processes. Despite the weak response of benthic microalgae to both warming and nutrient enrichment, the assimilation of nitrogen by microalgae was similar in magnitude to rates of nitrogen mineralization. This implies a sustained filter function and retention capacity of nutrients by the sediment.
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| 2. |
- Alsterberg, Christian, 1982, et al.
(författare)
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Response of a shallow-water sediment system to warming
- 2011
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Ingår i: Limnology and Oceanography. - : Wiley. - 0024-3590. ; 56:6, s. 2147-2160
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Tidskriftsartikel (refereegranskat)abstract
- ABSTRACT: Effects of predicted global warming (+4°C) on the structure and function of a temperate shallow-water sediment system were studied for 1.5 months during spring (March–April), using intact sediment in a flow-through system under close to natural light conditions. Although significant effects from temperature were observed during the entire experimental period, many were rather moderate and probably a combination of both direct and indirect effects. With the exception of an earlier development of floating microalgal mats at raised temperature, dividing the autotrophic compartment into a benthic and pelagic part, autotrophic variables, such as oxygen production, biomass, and species composition of benthic microalgae did not respond to warming. However, uptake of nutrients did increase, strengthening the role of shallow-water sediments as sinks for inorganic nutrients in spring. As hypothesized, heterotrophic variables (bacterial production, meiofaunal biomass, and dark fluxes of oxygen and total alkalinity) responded more clearly to warming than did autotrophic variables. Warming is generally hypothesized to push ecosystems towards heterotrophy, but there was no support for this in the present study. Although community respiration and anaerobic mineralization increased, the system remained highly autotrophic during the entire experiment due to the photosynthetic activity of benthic microalgae. The presence of a well-developed benthic microalgal community, already in early spring, appeared to moderate the temperature response. It therefore seems that, in spring, benthic microalgae dampen ecological consequences of global warming in illuminated sediment systems by maintaining the system net autotrophic.
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| 3. |
- Brandsma, J, et al.
(författare)
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A multi-proxy study of anaerobic ammonium oxidation in marine sediments of the Gullmar Fjord, Sweden
- 2011
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Ingår i: ENVIRONMENTAL MICROBIOLOGY REPORTS. - : Wiley. - 1758-2229. ; 3:3, s. 360-366
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Tidskriftsartikel (refereegranskat)abstract
- Anaerobic ammonium oxidation (anammox) is an important process for nitrogen removal in marine pelagic and benthic environments and represents a major sink in the global nitrogen cycle. We applied a suite of complementary methods for the detection and enumeration of anammox activity and anammox bacteria in marine sediments of the Gullmar Fjord, and compared the results obtained with each technique. 15N labelling experiments showed that nitrogen removal through N2 production was essentially limited to the upper 2 cm of the sediment, where anammox contributed 23–47% of the total production. The presence of marine anammox bacteria belonging to the genus ‘Candidatus Scalindua’ was shown by 16S rRNA gene sequence comparison. FISH counts of anammox bacteria correlated well with anammox activity, while quantitative PCR may have underestimated the number of anammox bacterial 16S rRNA gene copies at this site. Potential nitrogen conversion by anammox ranged from 0.6 to 4.8 fmol N cell−1 day−1, in agreement with previous measurements in the marine environment and in bioreactors. Finally, intact ladderane glycerophospholipid concentrations better reflected anammox activity and abundance than ladderane core lipid concentrations, most likely because the core lipid fraction contained a substantial fossil component, especially deeper in the sediment.
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| 4. |
- Engelsen, Anna, 1964, et al.
(författare)
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Links Between Bottom-Water Anoxia, the Polychaete Nereis diversicolor, and the Growth of Green-Algal Mats
- 2010
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Ingår i: Estuaries and Coasts. - : Springer Science and Business Media LLC. - 1559-2723 .- 1559-2731. ; 33:6, s. 1365-1376
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Tidskriftsartikel (refereegranskat)abstract
- Sediment-water incubations were used to study effects of episodic anoxia on filamentous Ulva sp. Treatments included undisturbed sediment with (AnoxSed) and without (NatSed) exposure to 5 days of anoxia, and cores with only the top 0.5 cm of sediment (SurfSed; no macrofauna, restricted pore-water nutrient pool). All three treatments contained Ulva propagules. An Ulva mat developed in the SurfSed, and after the anoxic period in the AnoxSed cores. No growth was observed in the NatSed treatment. In the AnoxSed, Ulva was progressively removed upon reoxygenation through grazing by Nereis. The results suggest that episodic anoxia stimulates the growth of macroalgal mats not only by increasing the availability of nutrients from the sediment, but also by reducing macrofaunal grazing pressure. Infauna (grazing and bioturbation), benthic microalgae (nutrient competition and retention), and pore-water nutrients appear key components in a biogeochemical network with complex feedbacks controlling the growth of green-algal mats in shallow-water systems.
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| 5. |
- Hakonen, Aron, 1970, et al.
(författare)
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A DHPDS-based fluorosensor for high-precision measurements of pH in the pH interval 6-9
- 2010
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Ingår i: Talanta. - 0039-9140. ; 80:5, s. 1964-1969
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Tidskriftsartikel (refereegranskat)abstract
- This study presents a high-performance ratiometric pH optode based on the fluorophore 6,8-dihydroxypyrene-1,3-disulfonic acid (DHPDS). The two pH-sensitive terminal hydroxy groups of DHPDS facilitated dual excitation/dual emission (F1: λ1,ex = 420 nm, λ1,em = 462 nm; F2: λ2,ex = 470 nm, λ2,em = 498 nm) properties for ratiometric (RF1,F2 = F1/F2) normalization of sensor signal. The sensor demonstrated an exponentially decreasing ratiometric response with increasing pH, with a linear correlation (R2 = 0.9936) between 10log(RF1,F2) and pH within the pH interval 6–9. Precision determined as the IUPAC pooled standard deviation for the pH values 6.00, 7.01 and 9.01, was 0.0057 pH units for the fluorosensor and 0.0054 for a commercially available pH electrode used for comparison. Between the end-points of calibration at pH 7.01, the precision of the sensor was 0.0037 pH units. Effects from changes in ionic strength (Itot, 10–700 mM) were more pronounced for the electrode, with a linear (R2 = 0.9976) increase in response (δE/δpH) with increasing Itot. The DHPDS-based fluorosensor, however, retained sensitivity (δ10log(RF1,F2)/δpH = 0.8024 ± 0.0145), though with an overall increase in ratiometric signal with increasing Itot. The preserved sensitivity despite changes in ionic strength was possibly a consequence from the dual photo-acidic properties of DHPDS. Analytical characteristics of immobilized DHPDS therefore not only facilitated high-performance measurements over a wide pH range, but also opened for straightforward simultaneous measurements of pH and ionic strength.
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| 6. |
- Hakonen, Aron, 1970, et al.
(författare)
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A potential tool for high-resolution monitoring of ocean acidification.
- 2013
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Ingår i: Analytica Chimica Acta. - : Elsevier BV. - 0003-2670 .- 1873-4324. ; 786, s. 1-7
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Tidskriftsartikel (refereegranskat)abstract
- Current anthropogenic carbon dioxide emissions generate besides global warming unprecedented acid-ification rates of the oceans. Recent evidence indicates the possibility that ocean acidification and lowoceanic pH may be a major reason for several mass extinctions in the past. However, a major bottleneck forresearch on ocean acidification is long-term monitoring and the collection of consistent high-resolutionpH measurements. This study presents a low-power (<1 W) small sample volume (25l) semiconductor based fluorescence method for real-time ship-board pH measurements at high temporal and spatialresolution (approximately 15 s and 100 m between samples). A 405 nm light emitting diode and the blueand green channels from a digital camera was used for swift detection of fluorescence from the pH sen-sitive dye 6,8-Dihydroxypyrene-1,3-disulfonic acid in real-time. Main principles were demonstrated byautomated continuous measurements of pH in the surface water across the Baltic Sea and the Kattegatregion with a large range in salinity (∼3–30) and temperature (∼0–25◦C). Ship-board precision of salinityand temperature adjusted pH measurements were estimated as low as 0.0001 pH units.
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| 7. |
- Hakonen, Aron, 1970, et al.
(författare)
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Analytical performance during ratiometric long-term imaging of pH in bioturbated sediments
- 2010
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Ingår i: Talanta. - : Elsevier BV. - 0039-9140. ; 81:4-5, s. 1393-1401
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Tidskriftsartikel (refereegranskat)abstract
- In this study, the long-term analytical performance of a high-resolution ratiometric imaging sensor for pH was quantitatively determined The sensor was applied in an experimental microcosm to Illustrate biogeochemical consequences from mining activities by the chemosymbiotic bivalve Thyasira sarsi. Utilizing time-correlated pixel-by-pixel calibration protocols during imaging, close 10 90% of the pixels were associated with a precision (S D) of <0.05 pH units at the end of an experimental period of 17 days For comparison, a precision of <0 05 pH units was achieved for less than 50% of the pixels throughout experiments using conventional pre-sample calibration procedures. The average standard deviation of pixels was 001 pH units. Image analysis of single pixel derivatives and pH measurements over time suggested that T. sarsi affect pH distributions and general sediment geochemistry more than would be expected based on the small size of the bivalves. A significant decrease of pH in the overlying water suggested a considerable release of reduced compounds from the exhalent stream of the thyasirids. Strong pH gradients were demonstrated not only across the sediment-water interface but, also associated with bioturbation activities immediately adjacent to T. sarsi burrowing tracts, inhalant tubes and pedal tracts in the sediment maim. Gradients of up to 1 16 pH units per mm were observed. (C) 2010 Elsevier B V All rights reserved
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| 8. |
- Karlsson, R., et al.
(författare)
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Subcellular localization of an ATPase in anammox bacteria using proteomics and immunogold electron microscopy
- 2014
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Ingår i: Fems Microbiology Letters. - : Oxford University Press (OUP). - 0378-1097. ; 354:1, s. 10-18
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Tidskriftsartikel (refereegranskat)abstract
- Anaerobic ammonium oxidation (anammox) has received significant attention during optimization of waste-water treatment and constitutes an important pathway for the removal of bioavailable nitrogen from natural environments. Studies of key catabolic enzymes indicate that the anammox reaction takes place inside the anammoxosome, an organelle-like membranous compartment of anammox bacteria. The anammoxosome has also been suggested as a site for ATP synthesis. A lipid-based protein immobilization technique, previously used to identify proteins essential for the anammox reaction, was in this study used to select linear epitopes for antibodies specifically targeted against an identified ATPase. The approach of using proteomics and bioinformatics as tools for selecting antibody targets for immunolocalization provides an important alternative to traditional methods for selection of specific antibodies. Immunogold electron microscopy and statistical evaluations indicated that the antibodies against the ATPase were exclusively found associated with the anammoxosome membrane. This provides strong evidence for ATP synthesis by an intracellular proton motive force in anammox bacteria. Within prokaryotes, an ATP synthase associated with an intracellular compartment is a feature unique for anammox bacteria.
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| 9. |
- Lindqvist, Stina, 1981, et al.
(författare)
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Activities by Hediste diversicolor under different light regimes: Experimental quantification of particle reworking using time-resolved imaging
- 2013
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Ingår i: Journal of Experimental Marine Biology and Ecology. - : Elsevier BV. - 0022-0981. ; 448, s. 240-249
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Tidskriftsartikel (refereegranskat)abstract
- Particle reworking by the ragworm Hediste diversicolor was assessed by quantifying the transport of fluorescent particles (luminophores) added to the surface sediment during a 10 day experiment. Plexiglass cores and thin glass aquaria with fauna and controls were exposed to either 12 hour light/dark cycles or constant darkness. Luminophore distributions were evaluated by side-view imaging of the aquaria together with destructive sectioning and quantification of tracer distributions in both types of microcosms at the end of experiments. Tracer distributions were evaluated by the gallery-diffusor model, from which the biodiffusion (Db) and the non-local transport (r) coefficients were determined. In addition, the maximum penetration depth (MPD) of luminophores, the 2-D redistribution coefficient, and the transport rate were used as a suite of proxies to quantify particle reworking by fauna. All measured reworking proxies demonstrated a general decrease in transport of luminophores in darkness compared to light/dark cycles. The difference was significant for proxies determined from sectioning. Imaging of particle transport demonstrated that rates were ~ 30% higher during light/dark cycles, with ~ constant amount of particles transported on a daily basis. The effect of light was consistent in the two microcosm types. However, there was a significant difference in Db, while r and MPD were not significantly different between the cores and aquaria. Overall, these results suggest a light-triggered surface feeding by H. diversicolor. Our study highlights the importance of experimental settings for quantification of particle transport by fauna, and that light conditions and types of experimental microcosms need to be carefully considered during investigations of bioturbation in illuminated environments.
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| 10. |
- Ulfsbo, Adam, 1985, et al.
(författare)
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pH and biogeochemical processes in the Gotland Basin of the Baltic Sea
- 2011
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Ingår i: Marine Chemistry. ; 127:1-4, s. 20-30
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Tidskriftsartikel (refereegranskat)abstract
- The Baltic Sea is a semi-enclosed sea characterized by a limited water exchange, large input of river runoff and a low salinity. Data collected in 1995 and 2008 in the Gotland Deep have been evaluated with the objective to assess how pH couples to biogeochemical processes. One result of the density stratification between 60 and ~ 100 m, is the difference in dominating biogeochemical reactions in the surface layer compared to those in the bottom water. In the surface layer, distributions of seawater constituents were mainly determined by the seasonal balance between primary production and respiration. Chemical composition in the bottom water was governed by the availability of oxygen and the frequency of bottom-water intrusions. In 1995, oxygen was present throughout the water column and, as a consequence, nitrate concentrations were high (~ 10 μmol/kg) also in the bottom water. In contrast, there was no oxygen or nitrate in the bottom water in 2008, while hydrogen sulfide was detected at significant concentrations (up to ~ 100 μmol/kg). The largest decrease in pH was observed in the layer where oxygen decreased from ~ 300 μmol/kg to about zero. When oxygen was low or hydrogen sulfide was present pH was nearly constant both in 1995 and 2008 at a low level of ~ 7.2. The distributions of chemical constituents with depth in the water column showed that a major fraction of organic matter mineralization was caused by oxygen and sulfate as electron acceptors, while nitrate played a minor role in the low oxygen or anoxic environment. The small variability in pH under conditions of low oxygen concentrations indicated that Fe- and Mn-oxides were of minor importance as electron acceptors during organic matter mineralization at this site. In oxic environments, observed data were consistent with mineralization of the model substance (CH2O)45(CH2)44(NHCH2CO)16(CHPO4Me). Under anoxic conditions, however, the observed changes in pH and DIC could be explained by mineralization of organic matter with significantly lower lipid content, e.g. material of terrestrial origin. In parallel, denitrification of preformed nitrate in the bottom layer may have contributed to changes in pH and DIC.
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