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- Larsson, U., et al.
(författare)
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Fractionated Phytoplankton Primary Production, Exudate Release and Bacterial Production in a Baltic Eutrophication Gradient
- 1982
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Ingår i: Marine Biology. - 1230-7688. ; 67:1, s. 57-70
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Tidskriftsartikel (refereegranskat)abstract
- The distribution of phytoplankton primary production into four size fractions (>10 μm, 10-3 μm, 3-0.2 μm and <0.2>μm), the utilization of algal exudates by bacteria and the bacterial production were studied in a eutrophication gradient in the northern Baltic proper. The polluted area exhibits substantially increased nutrient, especially nitrogen, levels while only minor differences occur in salinity and temperature regimes. Total primary production was 160 g C · m-2 · yr-1 at the control station and about 275 g C · m-2 · yr-1 at the eutrophicated stations. The estimated total exudate release was 16% of the totally fixed 14CO2 in the control area and 12% in the eutrophicated area (including the estimated bacterial uptake of exudates). The difference in14CO2 uptake rates between incubation of previously filtered water (<3,><2,><1>μm) and unfiltered water was used to estimate bacterial uptake of phytoplankton exudates which were found to contribute about half of the estimated bacterial carbon requirement in both areas. Bacterial production was estimated by the frequency of dividing cells (FDC) method as being 38 g C · m-2 · yr-1 at the control station and 50 g C · m-2 · yr-1 at the eutrophicated stations. To estimate the mean in situ bacterial cell volume a correlation between FDC and cell volume was used. The increased annual primary production in the eutrophicated area was due mainly to higher production during spring and autumn, largely by phytoplankton cells (mainly diatoms) retained by a 10 μm filter. Primary production duringsummer was similarin the two areas, as was the distribution on different size fractions. This could possibly explain the similar bacterial production in the trophic layers at all stations since the bulk of bacterial production occurs during summer. It was demonstrated that selective filtration does not quantitatively separate photoautotrophs and bacteria. A substantial fraction of the primary production occurs in the size fraction <3>μm. The primary production encountered in the 3-0.2 μm fraction was due to abundant picoplankton (0.5 to 8 · 107 ind · l-1), easily passing a 3 μm filter. The picoplankton was estimated to constitute up to 25% of the total phytoplankton biomass in the control area and up to 10% in the eutrophicated area.
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- Öquist, G., et al.
(författare)
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Chlorophyll a fluorescence an alternative method for estimating primary production
- 1982
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Ingår i: Marine Biology. - 1230-7688. ; 68:1, s. 71-75
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Tidskriftsartikel (refereegranskat)abstract
- The in vivo chlorophyll a fluorescence index (F+DcM u-F-DcMu/F+DcMU) of natural waters was compared to the 14C-determined primary production, and the fluorescence intensity in the presence of 3-(3,4-dichlorophenyl)-l,l-dimethylurea (F + DCM~) was studied as a function of extracted and spectrophotometrically determined chlorophyll concentrations. Samples were taken every second week from May through October, 1979, at the station "Systrarna" situated in a coastal area of the Bottnian Sea. In addition, samples from the Archipelago Sea of the Baltic were collected on board the Finnish research vessel R/S "Aranda" during the September cruise 1979. The correlations between the fluorescence index and the 14C-determined primary production and between F+DcMu and total chlorophyll concentration were good when samples taken over short time intervals were compared. The shortcomings of both the fluorescence and the 14C methods are discussed. It is concluded that the fluorescence method is useful if it is desirable to follow with high time resolution any changes in the potential for photosynthesis (or pirmary production) in a water mass over relatively short time periods; e.g. during an algal bloom. The fluorescence method can furthermore be technically developed for automatic monitoring with a high time resolution. Efforts are being made in our laboratory to develop the method further to give information about the in situ rates of photosynthesis rather than the potential for photosynthesis in a phytoplankton population.
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