Vertical distribution of microbiological and hydrographic-chemical parameters in different areas of the Baltic Sea

• Published in: Marine ecology. Progress series (Halstenbek) 1989-01, Vol.52 (1), p.55-70
• Main Authors: Rheinheimer, Gerhard, Gocke, Klaus, Hoppe, Hans-Georg
• Format: Article
• Language: English
• Subjects: Bacteria; Bacterial biomass; Marine; Nitrates; Oxygen; Salinity; Saprophytes; Sea water; Seas; Surface water; Vertical distribution
• ISSN: 0171-8630; 1616-1599
• DOI: 10.3354/meps052055

During 2 cruises with RV 'Poseidon' in August 1982 and August 1986 in the Baltic Sea, a series of vertical profiles between the Fehmarn Belt and the northern Gulf of Bothnia was investigated. Among the bacteriological variables determined were total bacteria number, bacterial biomass, saprophyte count on different media, turnover rate and maximum uptake velocity of glucose, and, for some stations, extracellular enzyme activity. Highest bacteria numbers and biomass values were always found in the photic zone. In the colder waters below the mixed layer all microbiological values decrease. In the boundary layer of the central Gotland Sea, especially between the oxic and anoxic hydrogen sulfide-containing zone bacteriological values increase markedly. In the water layer above the sediment another increase of bacterial stock and activity measurements was occasionally determined. In the Gulf of Bothnia, where the whole wate column is sufficiently aerated, only in bottom waters may an increase in bacterial values occur. Depending on the oxygen regime, bacterial nitrogen conversion is very different in the individual areas of the Baltic Sea. Comparison of nitrite and nitrate concentrations shows that nitrification in the Gotland Deep occurs down to the chemocline. Below this a narrow denitrification zone (about 10 m) was found in which nitrate almost completely disappears. In the Gulf of Bothnia, as a result of the favorable oxygen conditions, the nitrification zone extends down to the sea bottom.