Nutrient limitation of primary production in the Baltic Sea area

• 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. 

Subject headings

NATURVETENSKAP  -- Biologi -- Ekologi (hsv//swe)

NATURAL SCIENCES  -- Biological Sciences -- Ecology (hsv//eng)

Keyword

Terrestrial, freshwater and marine ecology

Terrestrisk, limnisk och marin ekologi

Aquatic Ecology

Akvatisk ekologi

Publication and Content Type

ref (subject category)

art (subject category)