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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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