| 1. |
- Andersson, Agneta, et al.
(författare)
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Succession and growth limitation of phytoplankton in the Gulf of Bothnia (Baltic Sea)
- 1996
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Ingår i: Marine Biology. - 0025-3162 .- 1432-1793. ; 126:4, s. 791-801
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Tidskriftsartikel (refereegranskat)abstract
- A one year field study of four stations in the Gulf of Bothnia during 1991 showed that the biomass was ca. two times, and primary productivity ca, four times, lower in the north (Bothnian Bay) than in the south (Bothnian Sea) during the summer. Nutrient addition experiments indicated phosphorus limitation of phytoplankton in the Bothnian Bay and the coastal areas in the northern Bothnian Sea, but nitrogen limitation in the open Bothnian Sea. A positive correlation between the phosphate concentration and the production/biomass ratio of phytoplankton was demonstrated, which partly explained the differences in the specific growth rate of the phytoplankton during the summer. Differences in photosynthetic active radiation between the stations also showed a covariation with the primary productivity. The relative importance of nutrient or light limitation for photosynthetic carbon fixation could not, however, be conclusively determined from this study. Marked differences in phytoplankton species composition from north to south were also observed. The number of dominating species was higher in the Bothnian Sea than in the Bothnian Bay. The distribution of some species could be explained as due to nutrient availability (e.g. Nodularia spumigena, Aphanizomenon sp.), while salinity probably limits the distribution of some limnic as well as marine species. The potentially toxic phytoplankton N. spumigena, Dinophysis acuminata and Chrysochromulina spp. were common in the Bothnian Sea but not in the Bothnian Bay. The pico- and nanoplankton biomass during late summer was higher than previously reported due to a revised carbon/volume ratio.
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| 2. |
- Andersson, Agneta, et al.
(författare)
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Vattenmassans biologi
- 1999
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Rapport (övrigt vetenskapligt/konstnärligt)abstract
- Inga statistiskt säkerställda förändringar kan påvisas bland de biologiska variabler som speglar näringstillgången i vattenmassan i Bottniska viken. Både växtplanktonarter och syrekonsumtion som redovisas nedan är exempel på detta. Tillsammans med stabila tidsserier av syre och närsalter tyder resultaten på en jämn näringstillgång i Bottniska vikens utsjöbassänger under övervakningsperioden.
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| 3. |
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| 4. |
- Bertilsson, Stefan, et al.
(författare)
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Photochemically induced changes in bioavailable carbon and nitrogen pools in a boreal watershed
- 1999
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Ingår i: Aquatic Microbial Ecology. - Oldendorf : Inter-Research. - 0948-3055 .- 1616-1564. ; 19:1, s. 47-56
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Tidskriftsartikel (refereegranskat)abstract
- In several recent studies, a net stimulation of bacterial growth has been demonstrated after exposing humic surface waters to solar radiation or artificial ultraviolet radiation. This stimulation has been attributed to a photochemical release of bioavailable carbon or nitrogen compounds (ammonium). In a synoptic experiment, we exposed 0.2 mu m filtered water from 12 different habitats in a river system, dominated by allochthonous carbon input, to mild artificial UV radiation. A significant photochemical release of carboxylic acids of low molecular weight occurred. Furthermore, the exposure increased carbon-limited bacterial yield on average by a factor of 1.7. No photochemical production of free ammonium could be detected, which was in accordance with the lack of effects of radiation on bacterial growth yield under nitrogen-limited conditions. We conclude that, in boreal systems dominated by allochthonous carbon input, photochemical production of bioavailable carbon rather than nitrogen compounds is likely to positively influence the total substrate pool available for bacterial utilization.
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| 5. |
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| 6. |
- Blackburn, Nicholas, et al.
(författare)
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Rapid determination of bacterial abundance, biovolume, morphology, and growth by neural network-based image analysis
- 1998
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Ingår i: Applied and Environmental Microbiology. - : American Society for Microbiology. - 0099-2240 .- 1098-5336. ; 64:9, s. 3246-3255
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Tidskriftsartikel (refereegranskat)abstract
- Annual bacterial plankton dynamics at several depths and locations in the Baltic Sea were studied by image analysis. Individual bacteria were classified by using an artificial neural network which also effectively identified nonbacterial objects, Cell counts and frequencies of dividing cells were determined, and the data obtained agreed well with visual observations and previously published values. Cell volumes were measured accurately by comparison with bead standards. The survey included 690 images from a total of 138 samples. Each image contained approximately 200 bacteria. The images were analyzed automatically at a rate of 100 images per h, Bacterial abundance exhibited coherent patterns with time and depth, and there were distinct subsurface peaks in the summer months. Four distinct morphological classes were resolved by the image analyzer, and the dynamics of each could be visualized. The bacterial growth rates estimated from frequencies of dividing cells were different from the bacterial growth rates estimated by the thymidine incorporation method. With minor modifications, the image analysis technique described here can be used to analyze other planktonic classes.
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| 7. |
- Kuparinen, Jorma, et al.
(författare)
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Food web structure and function in the Gulf of Bothnia, the Baltic Sea
- 1996
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Ingår i: Ambio. - Stockholm : Swedish Royal Academy of Sciences. - 0044-7447 .- 1654-7209. ; , s. 13-21
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Tidskriftsartikel (refereegranskat)abstract
- To improve the spatio-temporal information of ecological variables, a multidisciplinary joint study between Finnish and Swedish marine scientists was conducted in the Gulf of Bothnia, 1991. The study corroborated previous reports, suggesting a markedly lower phytoplankton production and biomass of benthic fauna in the Bothnian Bay than in the Bothnian Sea, However, contrary to the general view, the offshore carbon fixation in the Bothnian Sea exceeded that at the corresponding coastal station. The results further indicated a greater importance of bacterioplankton production to the food web in the Bothnian Bay than previously assumed. The total carbon requirement of bacteria and zooplankton was estimated to exceed carbon fixation by a factor of 1.7 in the northern basin, possibly a result of the discharge of riverine organic carbon. Diversity and biomass of both fish and benthic fauna were lower in the Bothnian Bay, with benthic meiofauna being of relatively greater importance than macrofauna in this basin.
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| 8. |
- Tan, Nianxiong, et al.
(författare)
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Differential Line Driver
- 1999
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Patent (populärvet., debatt m.m.)abstract
- A fully differential line driver, especially for twisted copper pairs. It includes two current amplifiers made in standard CMOS technique, each having an input and an output, the latter being connected via terminal resistors to a voltage source, which may be set to a larger voltage than that used for driving the CMOS amplifiers. Accordingly, a low output impedance can be combined with a large swing. Further, feedback is not necessary, avoiding problems like potential instability. A very low-impedance input makes it appropriate for connecting to a DAC, thus reducing distortion of its output signal. The driver is suitable for very-high-speed-digital-subscriber-line modems.
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| 9. |
- Wikner, Johan, 1961-, et al.
(författare)
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Bacterioplankton intra-annual variability: importance of hydrography and competition
- 1999
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Ingår i: Aquatic Microbial Ecology. - Oldendorf : Inter-Research. - 0948-3055 .- 1616-1564. ; 20:3, s. 245-260
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Tidskriftsartikel (refereegranskat)abstract
- Field data from a 1.5 yr intensive study of 1 coastal (0 to 20 m) and 2 offshore stations (0 to 100 m) in the northern Baltic were analysed. Specific interest was paid to the difference in the spatiotemporal variation of bacterioplankton and its controlling factors. Less than 31% of the annual bacterial biomass production (P-b) occurred in the photic zone during the productive season at the offshore stations. This suggested an uncoupling between P-b and phytoplankton carbon fixation, which was further supported by the lack of a significant correlation between these variables in the photic zone. The basin with high allochthonous loading and long residence time showed high P-b relative to autochthonous carbon fixation and low variance of P-b and bacterial abundance (N-b), suggesting an important contribution of terrestrial dissolved organic carbon to the carbon and energy supply. Bacterial per capita growth rate (r(c)) was highest during spring, while P-b was highest during summer at all stations. The seasonal variation in P-b was mainly explained by variation in the r(c), rather than in N-b. A positive correlation of N-b with temperature. and a negative correlation with salinity, suggested that >61% of the seasonal variation in N-b was a consequence of the formation of a stratified photic zone with a higher carrying capacity. Temperature limitation of r(c) only occurred in the stratified photic zone, suggesting that other growth factors were sufficient during this period. A density limitation of the maximum r(c) was observed at all stations during autumn and winter in both depth layers, suggesting competition to be of periodic importance. Bacterioplankton with a low r (intrinsic growth rate) and high K (carrying capacity) strategy dominated when sedimenting particles were a major resource in the aphotic zone, while the opposite strategy dominated during winter at low cell densities, when dissolved substrates were the major resource.
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| 10. |
- Wikner, Johan, 1961-, et al.
(författare)
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Differences in consumption of allochthonous DOC under limnic and estuarine conditions in a watershed
- 1999
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Ingår i: Aquatic Microbial Ecology. - Oldendorf : Inter-Research. - 0948-3055 .- 1616-1564. ; 17:3, s. 289-299
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Tidskriftsartikel (refereegranskat)abstract
- A temporal study of the bacterial utilisation of allochthonous dissolved organic carbon (DOC) was performed in a lake and estuary situated in the same boreal watershed. A greater utilisation of allochthonous DOC was observed under estuarine as compared to Limnic conditions. However, the bacterial biomass yield was not significantly different between the environments, indicating a lower growth efficiency on allochthonous DOC by the estuarine bacterioplankton. The largest fraction of the allochthonous DOC utilised (20 %) was observed under estuarine conditions and coincided with the spring flood. The utilisation of allochthonous DOC and bacterial biomass yield in the experimental bottles was Limited by the availability of nitrogen or phosphorus in both environments. Our results showed that the major bacterial transformation of DOC occurred in the estuarine rather than the Limnic environment, due to the shift in physicochemical milieu and bacterial assemblage. However, the estuarine bacteria also respired a greater fraction of the DOC utilised than their limnic counterparts.
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