| 1. |
- Almroth, Elin, 1977, et al.
(författare)
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Effects of resuspension on benthic fluxes of oxygen, nutrients, dissolved inorganic carbon, iron and manganese in the Gulf of Finland, Baltic Sea
- 2009
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Ingår i: Continental Shelf Research. - : Elsevier BV. - 0278-4343. ; 29, s. 807-818
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Tidskriftsartikel (refereegranskat)abstract
- The effect of resuspension on benthic fluxes of oxygen (O2), ammonium (NH4+), nitrate (NO3−), phosphate (PO43−), silicate (Si(OH)4), dissolved inorganic carbon (DIC), total dissolved iron (Fe) and total dissolved manganese (Mn) was studied at three different stations in the Gulf of Finland (GoF), Baltic Sea during three cruises in June–July 2003, September 2004 and May 2005. The stations were situated on different bottom types in the western, central and eastern part, respectively, of the open GoF. The fluxes were measured in-situ using the autonomous Göteborg benthic lander. To simulate resuspension events, the stirring speed was increased in two of the four chambers of the lander after approximately half of the incubation time. The other two chambers were used as control chambers. Clear effects of resuspension were observed on the oxygen fluxes where an increase of the consumption was observed in 88% of the cases and on average with 59% (stdev=53). The NH4+ fluxes were affected in 50% of the cases (4 out of 8 incubations) at stations with low bottom water oxygen concentrations, but in no cases where the bottom water was oxygenated (0 out of 9 incubations). The NH4+ fluxes decreased by 26±27% in 2005 and by 114±19% in 2003. There was no clear effect of resuspension on the fluxes of any of the other solutes in this study. Thus, resuspension events did not play a significant role in release/uptake of NO3−, PO43−, Si(OH)4, DIC, Fe and Mn in GoF sediments. However, increased oxygen consumption as a result of resuspension may lead to spreading of anoxic/suboxic bottom water conditions, and thus indirectly to increased benthic release of phosphate, ammonium and iron.
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| 2. |
- Hall, Per, 1954, et al.
(författare)
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Dissolved organic matter in abyssal sediments: Core recovery artifacts
- 2007
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Ingår i: Limnology and Oceanography. - 0024-3590. ; 52:1, s. 19-31
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Tidskriftsartikel (refereegranskat)abstract
- We report measurements of pore-water dissolved organic carbon (DOC), dissolved organic nitrogen, total dissolved carbohydrates, dissolved free monosaccharides, and ammonium in recovered deep-sea sediments from the Porcupine Abyssal Plain (PAP), Northeast Atlantic. There were distinct maxima close to the sediment–water interface of these constituents at all times of the year. The very high diffusive effluxes calculated from these porewater distributions were not compatible with simultaneous sediment trap measurements of particulate organic carbon, nitrogen, and carbohydrate fluxes toward the seafloor. Effluxes calculated from pore-water DOC distributions in recovered cores from another Atlantic deep-sea site, showing almost identical maxima as those at PAP, were more than an order of magnitude greater than simultaneous in situ chamber DOC flux measurements. We suggest that the dissolved organic matter maxima are predominantly artifacts induced by lysis of, or leakage from, mainly bacterial biomass resulting from decompression and/or warming during recovery of the sediment cores from the abyssal seafloor. Temperature elevation during core recovery from the abyss gives a N2 saturation of about 150%, and the combined effect of warming and decompression results in a CO2 saturation of about 135%, which together plausibly are associated with bubble formation creating cell bursting. Previous estimates of microbial biomass in abyssal sediments may be underestimates because of the difficulty of counting lysed bacterial cells. Since exoenzymes are inducible, previous measurements of their activities in recovered abyssal sediments may be overestimates.
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| 3. |
- Hassellöv, Ida-Maja, 1974, et al.
(författare)
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Verification of a benthic boxcosm system with potential for extrapolating experimental results to the field
- 2007
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Ingår i: Journal of Experimental Marine Biology and Ecology. - : Elsevier BV. - 0022-0981. ; 353:2, s. 265-278
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Tidskriftsartikel (refereegranskat)abstract
- A marine mesocosm system (boxcosm system) was developed for ecological and/or ecotoxicological studies of sediment community function and structure. The system consists of continuous flow-through incubations of intact sediment samples, each with a surface area of 0.25 m2. The experimental setup enables repeated non-destructive measurements of benthic fluxes, such as of nutrients, oxygen and dissolved inorganic carbon, over the sediment–water interface. The benthic fluxes reflect the function of the sediment community, integrating over the chemical, biological and physical activities in the sediment. The suitability of the boxcosm system for controlled, highly ecologically relevant studies of intact sediment communities was evaluated in two experiments of six weeks and five months duration respectively, where the functional and structural development over time was compared to the development of the sampling site. The function of the sediment was measured as nutrient and oxygen fluxes, and the structural component consisted of microbial functional diversity and meio- and macrofauna composition. Differences between the boxcosm and the sampling site were detected especially in nitrate fluxes and meiofauna diversity and abundance, but all differences fell within seasonal and inter-annual variability at the sampling site. The cause of the differences could be referred to differences in oxygen availability, supply of organic matter particles, and recruitment of larvae. These factors can however be compensated for within the present setup. The study shows that the boxcosms are suitable tools for ecologically relevant studies generating comparable conditions to the natural environment.
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| 4. |
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| 5. |
- Kiirikki, Mikko, et al.
(författare)
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A simple sediment process description suitable for 3D-ecosystem modelling — Development and testing in the Gulf of Finland
- 2006
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Ingår i: Journal of Marine Systems. - : Elsevier BV. - 0924-7963. ; 61:1-2, s. 55-66
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Tidskriftsartikel (refereegranskat)abstract
- The ecosystem of the Gulf of Finland is currently dominated by internal phosphorus loading from sediments. The internal load is highly redox sensitive, and its successful modelling on basin-wide scale requires a simplified description of the sediment process. We present here an approach in which redox-sensitive sediment processes are directly linked to the decomposition of carbon instead of the oxygen concentration in near-bottom water. Mineralisation of organic carbon is known to be the major factor controlling sediment nutrient cycling, including denitrification and Fe(III) oxide reduction, giving rise to high phosphorus fluxes from anoxic sediments. Our sediment process description requires only four main parameters, which are here identified by using in situ CO2, dissolved inorganic nitrogen (DIN) and dissolved inorganic phosphorus (DIP) flux measurements carried out by Göteborg University landers. The model was tested with the aid of time series of denitrification and DIP flux rates measured in the western Gulf of Finland. Modelled near-bottom and surface nutrient concentrations were compared with monitoring data from both the eastern and western Gulf of Finland. The model simulations showed that the average net ecosystem production entering the sediment surface from the euphotic layer was 49 g C m− 2 a− 1. This organic load induced an average denitrification rate of 2.5 g N m− 2 a− 1 and DIP flux of 0.67 g P m− 2 a− 1, corresponding to 20,200 t P a− 1 for the whole Gulf of Finland. The model was able to describe the seasonality of denitrification and sediment DIP flux with high precision. Further, the modelled near-bottom and surface nutrient concentrations were compatible with the available data. The results indicate that, on the scales important for coastal and open sea conditions, our simple sediment process description works well. The new tool will help us to use 3D models to study the effects of external load on the production and decomposition of organic matter, and on subsequent benthic nutrient fluxes.
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| 6. |
- Nilsson, Per Anders, 1954, et al.
(författare)
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Elegi
- 2007
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Konstnärligt arbete (övrigt vetenskapligt/konstnärligt)
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| 7. |
- Pakhomova, Svetlana V, et al.
(författare)
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Fluxes of iron and manganese across the sediment-water interface under various redox conditions
- 2007
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Ingår i: Marine Chemistry. - : Elsevier BV. - 0304-4203. ; 107, s. 319-331
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Tidskriftsartikel (refereegranskat)abstract
- Fluxes of dissolved forms of iron and manganese across the sediment–water interface were studied in situ in the Gulf of Finland and the Vistula Lagoon (Baltic Sea), and in the Golubaya Bay (Black Sea) from 2001 to 2005. Fluxes were measured using chamber incubations, and sediment cores were collected and sliced to assess the porewater and solid phase metal distribution at different depths. Measured and calculated benthic fluxes of manganese and iron were directed out of sediment for all sites and were found to vary between 70–4450 and 5–1000 µmole m− 2 day− 1 for manganese and iron, respectively. The behavior of the studied metals at various redox conditions in the near-bottom water and in the sediment was the main focus in this study. Our results show the importance of bottom water redox conditions for iron fluxes. We measured no fluxes at oxic conditions, intermediate fluxes at anoxic conditions (up to 200 μmole m− 2 day− 1) and high fluxes at suboxic conditions (up to 1000 μmole m− 2 day− 1). Total dissolved iron fluxes were generally dominated by iron(II). Contribution of iron(III) to the total iron flux did not exceed 20%. Obtained fluxes of manganese at all studied regions showed a linear correlation (r2 = 0.97) to its concentration in the porewater of the top sediment layer (0–5 mm) and did not depend on dissolved oxygen concentrations of bottom water. Organically complexed iron and manganese were in most cases not involved in the benthic exchange processes.
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| 8. |
- Tengberg, Anders, 1962, et al.
(författare)
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Intercalibration of benthic flux chambers II. Hydrodynamic characterization and flux comparisons of 14 different designs
- 2005
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Ingår i: Marine Chemistry. - : Elsevier BV. - 0304-4203. ; 94:1-4, s. 147-173
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Tidskriftsartikel (refereegranskat)abstract
- We have compared 14 different sediment incubation chambers, most of them were used on bottom landers. Measurements of mixing time, pressure gradients at the bottom and Diffusive Boundary Layer thickness (DBL) were used to describe the hydrodynamic properties of the chambers and sediment-water solute fluxes of silicate (34 replicates) and oxygen (23 replicates) during three subsequently repeated incubation experiments on a homogenized, macrofauna-free sediment. The silicate fluxes ranged from 0.24 to 1.01 mmol m(-2) day(-1) and the oxygen fluxes from 9.3 to 22.6 mmol m(-2) day(-1). There was no statistically significant correlation between measured fluxes and the chamber design or between measured fluxes and hydrodynamic settings suggesting that type of chamber was not important in these flux measurements. For verification of sediment homogeneity, 61 samples of meiofauna were taken and identified to major taxa. In addition. 13 sediment cores were collected. sectioned into 5-10-mm slices and separated into pore water and solid phase. The pore water profiles of disolved silicale were used to calculate diffusive fluxes of silicate. These fluxes ranged from 0.63 to 0.87 mmol m(-2) day(-1). All of the collected sediment parameters indicated that the sediment homogenization process had been satisfactorily accomplished, hydrodynamic variations inside and between chambers are a reflection of the chamber design and the stirring device, In general. pump stirrers with diffusers give a more even distribution of bottom currents and DBL thicknesses than paddle wheel-type stirrers, Most chambers display no or low static differential pressures when the water is mixed at rates of normal Use, Consequently. there is a low risk of creating stirrer induced pressure effects on the measured fluxes. Centrally placed stirrers are preferable to off-center placed stirrers which are more difficult to map and do not seem to give any hydrodynamic advantages, A vertically rotating stirrer gives about five times lower static differential pressures at the same stirring, speed as the same stirrer mounted horizontally If the aim is to simulate or mimic resuspension at high flow velocities, it cannot be satisfactorily done in a chamber using it horizontal (standing) rotating impeller (as is the case for most chambers in use) due to the creation of unnatural conditions. i,e. large static differential pressures and pre-mature resuspension at certain locations in the chamber. (c) 2004 Elsevier B.V. All rights reserved.
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