| 1. |
- Dedieu, K, et al.
(författare)
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Coupling of carbon, nitrogen and oxygen cycles in sediments from a Mediterranean lagoon: a seasonal perspective
- 2007
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Ingår i: Marine ecology progress series. - 0171-8630. ; 346, s. 45-59
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Tidskriftsartikel (refereegranskat)abstract
- Experimental data and simulations were used to investigate the seasonal coupling between carbon, nitrogen and oxygen cycles in marine sediments from a eutrophic shallow lagoon in the Mediterranean Sea area. A negative seasonal correlation was observed between oxygen consumption and coupled nitrification–denitrification rates in surface sediments. Elevated values of oxygen consumption rates were reached during warm periods (up to 87.7 mmol m–2 d–1) whereas nitrification and denitrification rates remained close to the lowest rates reported for coastal sediments (values around 0.021 to 0.35 mmol N m–2 d–1 for nitrification and 0.014 to 0.045 mmol N m–2 d–1 for denitrification). A steady-state diagenetic model closely represented the seasonal negative correlation of oxygen uptake, coupled nitrification–denitrification rates, the vertical distribution patterns of pore water oxygen and the solid phase distribution of organic carbon when nitrification inhibition by sulfide was included. Simulation adjusted to field data also highlighted the importance of oxygen penetration depth in the seasonal variation of nitrification. The modelling indicated that anaerobic metabolism was the most significant pathway (65 to 80%) during organic matter mineralization with a clear seasonal increase during warm periods. These warm periods were also characterized by the higher benthic demand of oxygen mostly used to re-oxidize the by-products from anaerobic reactions (from 57 to 82%), the other part being used for carbon mineralization.
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| 2. |
- Engelsen, Anna, 1964, et al.
(författare)
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Benthic trophic status and nutrient fluxes in shallow-water sediments
- 2008
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Ingår i: Estuarine, Coastal and Shelf Science. - : Elsevier BV. - 0272-7714. ; 78:4, s. 783-795
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Tidskriftsartikel (refereegranskat)abstract
- Proliferation of fast-growing ephemeral macroalgae in shallow-water embayments constitutes a large-scale environmental change of coastal marine ecosystems. Since inorganic nutrients essential for the initiation and maintenance of macroalgal growth may be supplied from the underlying sediment, we investigated the coupling between benthic inorganic nutrient (mainly N and P) fluxes and sediment properties in 6 bays representing a wide gradient of sediment characteristics (grain size, organic matter content, solid phase C and N). The initial characterization of bays was made in June and also included measurements of oxygen flux and microphytobenthic and macrofaunal biomass. In September, still within the growth season of the macroalgae, complementary experiments with sediment-water incubations for benthic flux measurements of oxygen and nutrients focused on trophic status (balance between auto- and heterotrophy) as a controlling factor for rates of measured benthic nutrient fluxes. Generally, sediments rendered autotrophic by microphytobenthic photosynthesis removed nutrients from the overlying water, while heterotrophic sediments supplied nutrients to the overlying bottom water. Estimations of the green-algal nutrient demand suggested that late in the growth season, net heterotrophic sediments could cover 20% of the N-demand and 70% of the P demand. As the benthic trophic status is a functional variable more closely coupled to nutrient fluxes than the comparably conservative structural parameter organic matter content, we suggest that the trophic status is a more viable parameter to classify sediments and predict benthic nutrient fluxes in shallow-water environments.
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| 3. |
- Engström, Pia, 1970, et al.
(författare)
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Anaerobic ammonium oxidation by nitrite (anammox): Implications for N-2 production in coastal marine sediments
- 2005
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Ingår i: Geochimica Et Cosmochimica Acta. - : Elsevier BV. - 0016-7037. ; 69:8, s. 2057-2065
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Tidskriftsartikel (refereegranskat)abstract
- The respiratory reduction of nitrate (denitrification) is acknowledged as the most important process that converts biologically available nitrogen to gaseous dinitrogen (N-2) in marine ecosystems. Recent findings, however, indicate that anaerobic ammonium oxidation by nitrite (anammox) may be an important pathway for N-2 formation and N removal in coastal marine sediments and in anoxic water columns of the oceans. In the present study, we explored this novel mechanism during N mineralization by 15 N amendments (single and coupled additions of (NH4+)-N-15, (NO3-)-N-14 and (NO3-)-N-15) to surface sediments with a wide range of characteristics and overall reactivity. Patterns of N-29/30(2) production in the pore water during closed sediment incubations demonstrated anammox at all 7 of the investigated sites. Stoichiometric calculations revealed that 4% to 79% of total N-2 production was due to this novel route. The relative importance of anammox for N2 release was inversely correlated with remineralized solute production, benthic O-2 consumption, and surface sediment Ch1 a. The observed correlations indicate competition between reductants for pore water nitrite during early diagenesis and that additional factors (e.g. availability of Mn-oxides), superimposed on overall patterns of diagenetic activity, are important for determining absolute and relative rates of anammox in coastal marine sediments. Copyright (c) 2005 Elsevier Ltd
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| 4. |
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| 5. |
- Gilbert, F., et al.
(författare)
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Sediment reworking by marine benthic species from the Gullmar Fjord (Western Sweden): Importance of faunal biovolume
- 2007
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Ingår i: Journal of Experimental Marine Biology and Ecology. - : Elsevier BV. - 0022-0981. ; 348:1-2, s. 133-144
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Tidskriftsartikel (refereegranskat)abstract
- In order to compare and quantify sediment reworking activities by different species/functional groups of macrofauna, a laboratory experiment was carried out with species from the Gullmarsfjord (Western Sweden). Monospecific communities of Amphiura filiformis, Echinocardium cordatum, Scalibregma inflatum and Abra nitida were introduced in experimental mesocosms, with identical densities (795 ind. m(-2)), for 10 days. Sediment reworking was studied by quantifying downward and upward movements of fluorescent inert tracers (luminophores). Luminophores with different colour were initially deposited both at the sediment surface and within the sediments. Population biomass and biovolume were also determined. Surface tracers reworking coefficients ranged from 0.6 to 2.2 cm(2) y(-1) and 0.9 to 4.1 y(-1), respectively for the biodiffusive-like and non-local transports. Calculated biodiffusive-like coefficient was between 1.0 and 2.3 cm(2) y(-1) for the deep tracers. For both tracers, the E. cordatum population presented the highest reworking coefficients. Among the morphological and/or ethological parameters that could determine overall patterns of reworking and differences between species, results have shown a direct relationship between the apparent biodiffusive mixing and the biovolume of the individuals (D-b=0.35 * Biovolume). This suggests that the biovolume-of macrofauna may allow a rough estimate of the biodiffusive-like reworking intensity of particles deposited on the sediment surface. (c) 2007 Elsevier B.V. All rights reserved.
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| 6. |
- Hakonen, Aron, 1970, et al.
(författare)
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A high-precision ratiometric fluorosensor for pH: Implementing time-dependent non-linear calibration protocols for drift compensation
- 2007
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Ingår i: Analytica Chimica Acta. - : Elsevier BV. - 0003-2670. ; 606:1, s. 63-71
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Tidskriftsartikel (refereegranskat)abstract
- We present a versatile time-dependent non-linear calibration protocol for optical sensors, implemented on the pH sensitive ratiometric fluorophore 8-hydroxypyrene-1,3,6-trisulfonic acid (HPTS) immobilized in ethyl-cellulose. The calibration protocol individually compensated for the progressive drift of calibration parameters, whereby sensor precision and accuracy, as well as applicable lifetime were improved. A severely reduced photoacidity was observed for the immobilized fluorophore, for which excited state dynamics was characterized and benefited from during measurements. Due to the significantly reduced photoacidity of HPTS immobilized in the ethyl-cellulose sensing membrane, a dual excitation/dual emission (F1, ex/em: 405/440 nm and F2, ex/em: 465/510 nm) ratiometric (RF1,F2 = F1/F2) sensing scheme could be used to amplify sensor response. The signal to noise (S/N) ratio was enhanced by 400% utilizing the dual excitation/dual emission ratiometric sensing scheme, rather than the more commonly used protocol of dual excitation/single emission for HPTS fluorescence. Apparent pKa of the fluorophore ranged from 6.74 to 8.50, mainly determined by the immobilization procedure. The repeatability (IUPAC, pooled standard deviation) over three pH values (6.986, 7.702 and 7.828) was 0.0044 pH units for the optical sensor, compared to 0.0046 for the electrode used for standardization. Sensor analytical characteristics were thereby in principle limited by the performance of the standardization procedure.
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| 7. |
- Hakonen, Aron, 1970, et al.
(författare)
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Applications of imaging optodes
- 2007
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Ingår i: Pittsburg Conference on Analytical Chemistry (PITTCON).
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Konferensbidrag (refereegranskat)
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