| 1. |
- Bonaglia, Stefano, et al.
(författare)
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Seasonal benthic nutrient cycling in a Baltic sea estuary
- 2012
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Konferensbidrag (övrigt vetenskapligt/konstnärligt)abstract
- Decades of urban, industrial, and agricultural discharge of nitrogen and phosphorus to the Baltic Sea have contributed to the spreading of water column hypoxia and annual widespread cyanobacteria blooms. Central to mitigating Baltic Sea eutrophication is to resolve how much reduction strategies of external N and P loading are offset by internal loading of the Baltic through nutrient recycling from the sediment. We investigated the seasonal variation of benthic nitrogen and phosphorus cycling in an estuary of the Baltic impacted by decades of sewage discharge. Sediment nutrient fluxes, denitrification, Anammox, DNRA, potential nitrification, and total and diffusive oxygen uptake (TOU/DOU) were quantified with 15N-tracer methods and microsensor profiling. Data indicate benthic net efflux of ammonium and phosphorus during the summer months, decreasing N2 loss with increasing organic matter content, and benthic N/P regeneration with a ratio of 3 to 7 compared to the sewage discharge N/P of ≈ 25, and a significant contribution (6 to 25%) of Anammox to N2 loss. On average benthic denitrification and Anammox may reduce the N load to the estuary by up to 54%.
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| 2. |
- Bonaglia, Stefano, 1983-, et al.
(författare)
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Seasonal oxygen, nitrogen and phosphorus benthic cycling along an impacted Baltic Sea estuary: regulation and spatial patterns
- 2014
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Ingår i: Biogeochemistry. - : Springer Science and Business Media LLC. - 0168-2563 .- 1573-515X. ; 119:1-3, s. 139-160
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Tidskriftsartikel (refereegranskat)abstract
- The regulatory roles of temperature, eutrophication and oxygen availability on benthic nitrogen (N) cycling and the stoichiometry of regenerated nitrogen and phosphorus (P) were explored along a Baltic Sea estuary affected by treated sewage discharge. Rates of sediment denitrification, anammox, dissimilatory nitrate reduction to ammonium (DNRA), nutrient exchange, oxygen (O2) uptake and penetration were measured seasonally. Sediments not affected by the nutrient plume released by the sewage treatment plant (STP) showed a strong seasonality in rates of O2 uptake and coupled nitrification-denitrification, with anammox never accounting for more than 20% of the total dinitrogen (N2) production. N cycling in sediments close to the STP was highly dependent on oxygen availability, which masked temperature-related effects. These sediments switched from low N loss and high ammonium (NH4+) efflux under hypoxic conditions in the fall, to a major N loss system in the winter when the sediment surface was oxidized. In the fall DNRA outcompeted denitrification as the main nitrate (NO3-) reduction pathway, resulting in N recycling and potential spreading of eutrophication. A comparison with historical records of nutrient discharge and denitrification indicated that the total N loss in the estuary has been tightly coupled to the total amount of nutrient discharge from the STP. Changes in dissolved inorganic nitrogen (DIN) released from the STP agreed well with variations in sedimentary N2 removal. This indicates that denitrification and anammox efficiently counterbalance N loading in the estuary across the range of historical and present-day anthropogenic nutrient discharge. Overall low N/P ratios of the regenerated nutrient fluxes impose strong N limitation for the pelagic system and generate a high potential for nuisance cyanobacterial blooms.
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| 3. |
- Brüchert, Volker, 1965-, et al.
(författare)
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BENTHIC BOUNDARY LAYER NUTRIENT AND OXYGEN BIOGEOCHEMISTRY IN A EUTROPHIED BALTIC SEA ESTUARY
- 2013
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Konferensbidrag (refereegranskat)abstract
- We present dissolved nutrient and oxygen concentrations determined with a benthic boundary layer profiling system for a set of stations along a eutrophication gradient in a Baltic Sea estuary. The sampling system yields vertically highly resolved CTD, oxygen, and nutrient profiles of the lowermost 80 cm of water overlying the sediment. Continuous oxygen and CTD measurements over 8 – 24 hours at fixed depths above the sediment surface provided information on the temporal variability of nutrients and the physical structure within the benthic boundary layer. These data indicate multiple short-term episodes of vertical mixing and stable stratification within the boundary layer that can lead to short-term fluctuations in bottom water oxygen of more than 100 µM. This high degree of temporal variability needs to be taken into account for benthic flux calculations that assume vertically mixed benthic boundary layers.
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| 4. |
- Deutsch, Barbara, et al.
(författare)
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Denitrification in sediments as a major nitrogen sink in the Baltic Sea : an extrapolation using sediment characteristics
- 2010
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Ingår i: Biogeosciences. - : Copernicus GmbH. - 1726-4170 .- 1726-4189. ; 7:10, s. 3259-3271
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Tidskriftsartikel (refereegranskat)abstract
- Rates of denitrification in sediments were measured with the isotope pairing technique at different sites in the southern and central Baltic Sea. The rates varied between 0.5 mu mol N m(-2) h(-1) in sands and 28.7 mu mol N m(-2) h-1 in muddy sediments and showed a good correlation to the organic carbon contents of the surface sediments. N-removal rates via sedimentary denitrification were estimated for the entire Baltic Sea calculating sediment specific denitrification rates and interpolating them to the whole Baltic Sea area. Another approach was carried out by using the relationship between the organic carbon content and the rate of denitrification. The N-removal by denitrification in sediments varied between 426-652 kt Na-1, which is around 48-73% of the external N inputs delivered via rivers, coastal point sources, and atmospheric deposition. Moreover, an expansion of the anoxic bottom areas was considered under the assumption of a rising oxycline from 100 to 80 m water depth. This leads to an increase of the area with anoxic conditions and an overall decrease in sedimentary denitrification by 14%. Overall, we show here that this type of data extrapolation is a powerful tool to estimate the nitrogen losses for a whole coastal sea and may be applicable to other coastal regions and enclosed seas.
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| 5. |
- Deutsch, Barbara, et al.
(författare)
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Tracing inputs of terrestrial high molecular weight dissolved organic matter within the Baltic Sea ecosystem
- 2012
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Ingår i: Biogeosciences. - : Copernicus GmbH. - 1726-4170 .- 1726-4189. ; 9:11, s. 4465-4475
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Tidskriftsartikel (refereegranskat)abstract
- To test the hypothesis whether high molecular weight dissolved organic matter (HMW-DOM) in a high latitude marginal sea is dominated by terrestrial derived matter, 10 stations were sampled along the salinity gradient of the central and northern Baltic Sea and were analyzed for concentrations of dissolved organic carbon as well as δ13C values of HMW-DOM. Different end-member-mixing models were applied to quantify the influence of terrestrial DOM and to test for conservative versus non-conservative behavior of the terrestrial DOM in the different Baltic Sea basins. The share of terrestrial DOM to the total HMW-DOM was calculated for each station, ranging from 43 to 83%. This shows the high influence of terrestrial DOM inputs for the Baltic Sea ecosystem. The data also suggest that terrestrial DOM reaching the open Baltic Sea is not subject to substantial removal anymore. However compared to riverine DOM concentrations, our results indicate that substantial amounts of HMW-DOM (> 50%) seem to be removed near the coastline during estuarine mixing. A budget approach yielded residence times for terrestrial DOM of 2.8, 3.0, and 4.5 yr for the Bothnian Bay, the Bothnian Sea and the Baltic Proper.
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| 6. |
- Gustafsson, Erik, et al.
(författare)
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Carbon cycling in the Baltic Sea - The fate of allochthonous organic carbon and its impact on air-sea CO2 exchange
- 2014
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Ingår i: Journal of Marine Systems. - : Elsevier BV. - 0924-7963 .- 1879-1573. ; 129, s. 289-302
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Tidskriftsartikel (refereegranskat)abstract
- A coupled physical-biogeochemical model (BALTSEM) is used to estimate carbon fluxes in the Baltic Sea over the 1980-2006 period. Budget calculations for organic carbon indicate that of the total allochthonous organic carbon (TOCT) supplied to the system, on average 56% is mineralized, 36% is exported out of the system, and the remainder is buried. River discharge is the main source of dissolved inorganic carbon (DIC) to the Baltic Sea. However, model results indicate that in the Gulf of Bothnia (northern Baltic Sea), the contribution to the DIC stock by TOCT mineralization is of the same order as direct river input of DIC In the Kattegat and Danish Straits (southwestern Baltic Sea) on the other hand, net uptake of atmospheric CO2 comprises the major DIC source. Despite large variations within the system, with net outgassing from some sub-basins and net absorption in others, the Baltic Sea as a whole was estimated to be a net sink for atmospheric CO2. Mineralization of allochthonous dissolved organic carbon (DOCT) influences air-sea CO2 exchange. A sensitivity study indicates that depending on the labile fraction of DOCT, the contribution from CO2 absorption to total external DIC sources can amount to 10-25%.
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| 7. |
- Korth, F., et al.
(författare)
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Nitrate source identification in the Baltic Sea using its isotopic ratios in combination with a Bayesian isotope mixing model
- 2014
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Ingår i: Biogeosciences. - : Copernicus GmbH. - 1726-4170 .- 1726-4189. ; 11:17, s. 4913-4924
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Tidskriftsartikel (refereegranskat)abstract
- Nitrate (NO3-) is the major nutrient responsible for coastal eutrophication worldwide and its production is related to intensive food production and fossil-fuel combustion. In the Baltic Sea NO3- inputs have increased 4-fold over recent decades and now remain constantly high. NO3- source identification is therefore an important consideration in environmental management strategies. In this study focusing on the Baltic Sea, we used a method to estimate the proportional contributions of NO3- from atmospheric deposition, N-2 fixation, and runoff from pristine soils as well as from agricultural land. Our approach combines data on the dual isotopes of NO3- (delta N-15-NO3- and delta O-18-NO3-) in winter surface waters with a Bayesian isotope mixing model (Stable Isotope Analysis in R, SIAR). Based on data gathered from 47 sampling locations over the entire Baltic Sea, the majority of the NO3- in the southern Baltic was shown to derive from runoff from agricultural land (33-100 %), whereas in the northern Baltic, i.e. the Gulf of Bothnia, NO3- originates from nitrification in pristine soils (34-100 %). Atmospheric deposition accounts for only a small percentage of NO3- levels in the Baltic Sea, except for contributions from northern rivers, where the levels of atmospheric NO3- are higher. An additional important source in the central Baltic Sea is N-2 fixation by diazotrophs, which contributes 49-65% of the overall NO3- pool at this site. The results obtained with this method are in good agreement with source estimates based upon delta N-15 values in sediments and a three-dimensional ecosystem model, ERGOM. We suggest that this approach can be easily modified to determine NO3- sources in other marginal seas or larger near-coastal areas where NO3- is abundant in winter surface waters when fractionation processes are minor.
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| 8. |
- Korth, Frederike, et al.
(författare)
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Uptake of dissolved organic nitrogen by size-fractionated plankton along a salinity gradient from the North Sea to the Baltic Sea
- 2012
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Ingår i: Biogeochemistry. - : Springer Science and Business Media LLC. - 0168-2563 .- 1573-515X. ; 111:1-3, s. 347-360
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Tidskriftsartikel (refereegranskat)abstract
- The Baltic Sea is known for its ecological problems due to eutrophication caused by high nutrient input via nitrogen fixation and rivers, which deliver up to 70% of nitrogen in the form of dissolved organic nitrogen (DON) compounds. We therefore measured organic nitrogen uptake rates using self produced N-15 labeled allochthonous (derived from Brassica napus and Phragmites sp.) and autochthonous (derived from Skeletonema costatum) DON at twelve stations along a salinity gradient (34 to 2) from the North Sea to the Baltic Sea in August/September 2009. Both labeled DON sources were exploited by the size fractions 0.2-1.6 mu m (bacteria size fraction) and > 1.6 mu m (phytoplankton size fraction). Higher DON uptake rates were measured in the Baltic Sea compared to the North Sea, with rates of up to 1213 nmol N l(-1) h(-1). The autochthonous DON was the dominant nitrogen form used by the phytoplankton size fraction, whereas the heterotrophic bacteria size fraction preferred the allochthonous DON. We detected a moderate shift from > 1.6 mu m plankton dominated DON uptake in the North Sea and central Baltic Sea towards a 0.2-1.6 mu m dominated DON uptake in the Bothnian Bay and a weak positive relationship between DON concentrations and uptake. These findings indicate that DON is an important component of plankton nutrition and can fuel primary production. It may therefore also contribute substantially to eutrophication in the Baltic Sea especially when inorganic nitrogen sources are depleted.
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| 9. |
- Leitsch, David, et al.
(författare)
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Proteomic aspects of Parachlamydia acanthamoebae infection in Acanthamoeba spp.
- 2010
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Ingår i: The ISME Journal. - : Springer Science and Business Media LLC. - 1751-7362 .- 1751-7370. ; 4:11, s. 1366-1374
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Tidskriftsartikel (refereegranskat)abstract
- The free-living but facultatively pathogenic amoebae of the genus Acanthamoeba are frequently infected with bacterial endosymbionts that can have a profound influence on the physiology and viability of their host. Parachlamydia acanthamoebae, a chlamydial endosymbiont in acanthamoebae, is known to be either symbiotic or lytic to its host, depending on the ambient conditions, for example, temperature. Moreover, parachlamydiae can also inhibit the encystment process in Acanthamoeba, an essential survival strategy of their host for the evasion of chemotherapeutic agents, heat, desiccation and radiation. To obtain a more detailed picture of the intracellular interactions of parachlamydiae and acanthamoebae, we studied parachlamydial infection in several Acanthamoeba isolates at the proteomic level by means of two-dimensional gel electrophoresis (2DE) and mass spectrometry. We observed that P. acanthamoebae can infect all three morphological subtypes of the genus Acanthamoeba and that the proteome pattern of released P. acanthamoebae elementary bodies was always practically identical regardless of the Acanthamoeba strain infected. Moreover, by comparing proteome patterns of encysting cells from infected and uninfected Acanthamoeba cultures, it was shown that encystment is blocked by P. acanthamoebae at a very early stage. Finally, on 2D-gels of purified P. acanthamoebae from culture supernatants, a subunit of the NADH-ubiquinone oxidoreductase complex, that is, an enzyme that has been described as an indicator for bacterial virulence was identified by a mass spectrometric and bioinformatic approach.
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