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- Granéli, Edna, et al.
(författare)
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Nutrient limitation of primary production in the Baltic Sea area
- 1990
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Ingår i: Ambio. - 0044-7447 .- 1654-7209. ; 19:3, s. 142-151
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Tidskriftsartikel (refereegranskat)abstract
- In the Baltic Sea area, including the Kattegat, the external N/P loadingratios are generally well above the 16:1 Redfield ratio for all subareas (theBothnian Bay, the Bothnian Sea, the Baltic proper and the Kattegat).During winter, the inorganic N/P ratio in surface waters varies. Appreciablyhigher values than the loading ratio are found for the northernmostbasin, the low-saline Bothnian Bay, while lower values than the loadingratio are found for the Baltic proper and the Kattegat. Nutrient enrichmenttests indicate general N limitation in the Baltic proper and the Kattegat,although stimulation of algal growth after P enrichment has been found inthe Baltic proper during summer blooms of blue-green algae. Blooms ofblue-green algae are common in the Baltic proper but hardly ever occur inthe Bothnian Bay and the Kattegat. This has been the case for the lastcentury, indicating natural summer N limitation. Full-scale experimentalmanipulation of the external N/P loading ratio has been carried out in theHimmerfjard basin, south of Stockholm. Results suggest nitrogen as themost limiting nutrient in coastal areas of the Baltic proper, uninfluencedby direct nutrient discharges. The knowledge of the effects of alteredexternal nutrient supplies for nutrient limitation in the Baltic Sea systemas a whole is too limited to allow for reliable predictions. However, theBaltic Sea may have developed towards a more pronounced N limitationdue to a twofold historic increase in P supply relative to N supply. Atpresent, the situation may be reversed as N supply is probably increasingmore rapidly than P supply. Management of the Baltic Sea area cannot bebased on removal of either N or P in sewage, but must take both elementsinto consideration, as well as differences between sub-basins andbetween polluted coastal and offshore areas.
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- Granéli, W., et al.
(författare)
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Automatic potentiometric determination of dissolved oxygen
- 1991
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Ingår i: Marine Biology. - 0025-3162 .- 1432-1793. ; 108:2, s. 341-348
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Tidskriftsartikel (refereegranskat)abstract
- Commercially available automatic titration systems were tested in 1988 for potentiometric titration of liberated iodine by the Winkler method of oxygen determination. The potentiometric equivalence point was also compared to the manual starch end point. Finally the automatic method was used in order to estimate below-halocline respiration in the Kattegat, Sweden. Standard deviations of 0.007 ml O2 l-1 or 0.1 to 0.3% coefficients of variation (% standard deviation of the mean) were achieved when titrating 25 ml from replicate 60-ml oxygen bottles using the automatic method, or 50 ml manually. The precision for replicate titrations of 50-ml aliquots of 0.001 N KIO3 was < 0.05% (0.002 ml 0.01 N Na2S2O3) for the automatic method. Titration time for 25-ml aliquots was 2 to 4 min, somewhat longer than for manual titrations (1 to 1.5 min). However, during titration the operator is free to perform other tasks. It is not possible to use automatic sample changers, due to rapid iodine volatilization. The equipment can be handled by relatively unskilled analysts and is suitable for use on board research vessels or in field stations [weight for a Mettler(TM) titrator (Mettler Instrumente AG, Greifensee, Switzerland) < 10 kg, volume < 0.1 m3]. Below-halocline oxygen consumption in the SE Kattegat ranged from 0 to 6 ml O2 m-3 h-1 (mean values for September and October 1988 = 1.69 and 0.66 ml O2 m-3 h-1, respectively, with 95% confidence limits of ca. +/- 0.6 ml O2 m-3 h-1).
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| 12. |
- Granéli, Edna, et al.
(författare)
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Effects of river water of different origin on the growth of marine dinoflagellates and diatoms in laboratory cultures
- 1990
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Ingår i: Journal of Experimental Marine Biology and Ecology. - 0022-0981 .- 1879-1697. ; 136:2, s. 89-106
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Tidskriftsartikel (refereegranskat)abstract
- The hypothesis that acid humic-rich river water selectively favours dinoflagellates in comparison to diatoms in coastal waters was tested in two sets of laboratory experiments using unialgal cultures of marine phytoplankton. In the first experiment, three dinoflagellates, i.e., Prorocentrum minimum (Pav.) J. Schiller, P. micans Ehrenberg and Amphidinium carterae Hulburt, and three diatoms, i.e., Attheya decora T. West, Skeletonema costatum (Grev.) Cleve and Phaeodactylum tricornutum Bohlin, were grown in a mixture of 80% coastal (S 20%.) and 20% river water. Water from seven different rivers was used. Four rivers had a high humic content (yellow substance 22.1 ± 0.9 · m−1) but lower inorganic N and P concentrations ("forest rivers") while three rivers ("agricultural rivers") had a lower humic content (10.7 ± 1.3 · m−1) but inorganic nutrient concentrations approximately three times as high as the forest rivers. The growth rates for the dinoflagellates were significantly higher in the medium with forest river water compared to the mixtures with agricultural river water while the opposite was true for the diatoms. In the second type of experiment, the diatom Ditylum brightwellii (T. West) Grun and the dinoflagellate P. minimum were grown, as semicontinuous dilution cultures, in mixtures of 90% coastal water (S 20%.) and 10% river water. Water from four different rivers was used, one draining mainly agricultural soils and the other acidified humic-rich forested soils. River water of agricultural origin supported a higher D. brightwellii biomass and growth rate than river water draining forested soils while for P. minimum the opposite was true. Decreasing cell P quotas and increasing alkaline phosphatase activity indicated that D. brightwellii was P-deficient, especially when agricultural river water was added, while these physiological indices suggested that P. minimum cultures were not P-starved. Our results support the hypothesis that the discharge of acidified river water, rich in humic substances, to coastal waters, can play a role in shifting the species composition from diatoms to dinoflagellates.
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- Maestrini, S Y, et al.
(författare)
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Environmental conditions and ecophysiological mechanisms which led to the 1988 Chrysochromulina polylepis bloom: an hypothesis
- 1991
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Ingår i: Oceanologica Acta. - 0399-1784 .- 1878-4143. ; 14:4, s. 397-413
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Tidskriftsartikel (refereegranskat)abstract
- Information available on the 1988 Chrysochromulina polylepis bloom in Scandinavian coastal waters is evaluated. Special attention is paid to the early bloom stage and the sequence of both environmental and physiological mechanisms leading to the bloom, and a tentative, integrated timing schema is given of causes which led to the observed events. Environmental conditions favourable for Chrysochromulina polylepis are considered to have resulted from : a) an exceptionally high runoff of nitrogen-rich water in winter and early spring; b) strong mixing of the water column, immediately followed by a long period of vertical stability and stratification; c) a diatom bloom 30 % larger than usual, peaking around 20 March; and d) a second diatom bloom in mid April, largely dominated by Skeletonema costatum. These events combined to cause the euphotic layer to become silicate-exhausted, phosphorus-poor and fairly nitrogen-rich. The lack of silicate prevented diatom growth. Weak turbulence and strong stratification favoured growth of non-siliceous, motile nanoplankton. C. polylepis is believed to have outcompeted co-existing algal species by producing a toxin acting first as a grazer repellent, while its cell density was still below 10(4) individuals.1(-1). At the conjectured location of first appearance of the bloom (or at one of several locations), in the Skagerrak near Gullmar Fjord, the grazing repellent forced a shift of grazing to other algae around the latter part of April. With increased population density of C. polylepis (10(6) cells.l(-1)), the toxin then became sufficiently concentrated to affect directly not only grazers, but all other organisms. From late April, the C. polylepis population increased free from grazing and other losses. In conditions of light and nutrient sufficiency, a high growth rate (corresponding to 0.8 div.d-1) was achieved. Actively growing cells were buoyant and remained in the upper part of the water column. With increasing population density (10(7) cells.l(-1)), nutrients became exhausted and self-shading decreased available light. By mid May, the growth rate had decreased to zero, and the population started to become senescent. C. polylepis deteriorated in physiological state, perhaps partly because of self-poisoning, and this led to sinking. No further growth occurred, but cell densities showed higher values (several 10(7) cells.l(-1), with maximum density between 5 a 10 m) because distribution became patchy both horizontally and vertically. At the end of May a significant part of the population had died, and cell leakage produced an increase in dissolved organic matter. The resultant lower turbidity and regenerated nutrients then allowed other flagellates and some diatoms to resume growth. The remaining C. polylepis cells sunk to the pycnocline (15-20 m), which acted as a barrier and greatly retarded this sinking, by which means the cells became concentrated, and produced the highest reported cell densities at the pycnocline. It is assumed that the bloom later sedimented. Since relevant environmental conditions for the initiation of the bloom occurred over a very large area (75.10(3) km2) and the dominant currents were not altogether consistent with the spreading of the bloom, polygenesis of the bloom should be considered a possibility. To what extent long-term global change and eutrophication might have contributed to this exceptional bloom remains unclear. Since the production of the toxin seems to be favoured by phosphorus deficiency, however, a large input of nitrogen in combination with a reduction in the phosphorus loading is believed to have contributed indirectly to the bloom, by changing the nutrient status of the coastal waters from being nitrogen- to phosphorus-limited.
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| 15. |
- Olsson, P, et al.
(författare)
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Observations on diurnal vertical migration and phased cell division for three coexisting marine dinoflagellates
- 1991
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Ingår i: Journal of Plankton Research. - : Oxford University Press (OUP). - 0142-7873 .- 1464-3774. ; 13, s. 1313-1324
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Tidskriftsartikel (refereegranskat)abstract
- An experiment was performed in the beginning of September 1988 in the Gullmar Fjord, eastern Skagerrak, in order to study diurnal vertical migration and phased cell division for a natural phytoplankton community dominated by the dinoflagellates Prorocentrum minimum, Prorocentrum micans and Cerattum furca. A 1 80 m high and 0.30 wide non-transparent PVC cylinder was filled with surface water containing the dominant dinoflagellates. An artificial halocline was created by adding high salinity, nutrient-rich bottom water to the bottom of the cylinder Cell densities were measured at seven depths at 11 times during 48 h Physical parameters (temperature, salinity, phosphate, nitrate, ammonia and silicate) were measured at the start and at the end of the experiment in the water column above and below the halocline. Strong diurnal vertical migration patterns were found for all three species with an aggregation of cells at the surface in the morning and during the day and at the bottom at night. The descent and ascent seemed to start before sunset and sunrise respectively and all species were able to migrate through the strong artificial halocline. Some differences were found in the speed and timing of migration between the species with P.minimum having the most pronounced and fastest migration of the three Cell division frequency was highest at 05.00 at the bottom and also at the surface At other times and depths the division was always close to zero. The decrease in especially nitrate concentrations in the bottom water of the cylinder suggests that these dinoflagellates are capable of dark nitrogen assimilation.
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| 19. |
- Turner, J. T., et al.
(författare)
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ZOOPLANKTON FEEDING ECOLOGY - GRAZING DURING ENCLOSURE STUDIES OF PHYTOPLANKTON BLOOMS FROM THE WEST-COAST OF SWEDEN
- 1992
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Ingår i: Journal of Experimental Marine Biology and Ecology. - : Elsevier BV. - 0022-0981. ; 157:1, s. 19-31
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Tidskriftsartikel (refereegranskat)abstract
- The effects of grazing on natural phytoplankton populations was examined during enclosure studies on the effects of nutrients, zooplankton, and ctenophores on phytoplankton bloom dynamics on the west coast of Sweden in May, 1990. Grazers included the copepods Acartia clausi Giesbrecht, Centropages hamatus Lilljeborg, and Oithona similis Claus, and the marine cladoceran Podon polyphemoides Leuckart. These species ingested various diatoms, dinoflagellates and athecate microflagellates, but grazing was minimal. Clearance rates of the copepods were < 1 ml.animal-1.h-1, while those of cladocerans reached 2.5 ml.animal-1.h-1, at microflagellate concentrations of 1442-3519 cells.ml-1. Despite the low levels of copepod and cladoceran grazing, there was considerable removal of Chl a by grazers < 90-mu-m in longest dimension. These micrograzers were present in experimental and control containers. Athecate ciliates < 20-mu-m in longest dimension were abundant (up to 1730 cells.ml-1) in some samples, and these ciliates were the most probable micrograzers. Rates of clearance of these ciliates by A. clausi (0.13-0.81 ml.animal-1.h-1) and C. hamatus (0.46-0.81 ml.animal-1.h-1) were high, even though ciliates were less abundant than most co-occurring phytoplankton taxa. Copepod and cladoceran grazing appeared to have little impact on phytoplankton dynamics. Rather, copepods were selective consumers of the ciliates that were probably the dominant grazers.
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