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Bacterial production and the accompanying environmental factors were measured in the water columns of two Arctic fjords during the cruise in July and August 2013. Water samples were collected at six stations located in the central part of Hornsund and Kongsfjorden. In Hornsund, where average water temperatures were 1.25-fold lower than in Kongsfjorden, the bacterial production was twice as high (0.116 ± 0.102 vs 0.05 ± 0.03 mg C m−3 h−1). Statistical analysis indicated that chlorophyll a concentration itself was not a significant factor that affected bacterial production, in contrast to its decomposition product, pheophytin, originating from senescent algal cells or herbivorous activity of zooplankton. Single and multiple regression analysis revealed that water temperature, dissolved organic carbon (DOC), and pheophytin concentration were the main factors affecting bacterial production in both fjords.
The paper presents the results of investigations concerning the number, distribution and physiological activity of sulphate-reducing bacteria (SRB) inhabiting the bottom sediments of the Gulf of Gdańsk. The numbers of this group of bacteria range between 0.76 × 103 and 1.27 × 104 cells per g wet sediment. The bacterial sulphate reduction rate in bottom sediments of this area of the Baltic Sea varies from 1.89 to 31.6 nM SO2− 4 g−1 24 h−1. The numbers of SRB and their physiological activity were subject to considerable seasonal fluctuations, maximum values being noted in summer (June) and minima in spring (April). A direct relationship has been found between the number of SRB and hydrogen sulphide concentrations; there is, however, no such relationship with reference to sulphate concentrations. The numbers and distributions of SRB demonstrated considerable variation in a depth profile of bottom sediments. SRB inhabiting the bottom sediments of the Gulf of Gdańsk were able to use three different organic substrates (lactate, acetate, propionate) as electron donors and as carbon and energy sources.
Studies on the spatial and vertical variability of saprophytic bacteria abundance and their physiological properties were carried out in Sopot (the Gulf of Gdańsk) during the summer of 1998 at four different points along a transect perpendicular to the water line. Colony forming units (CFU) bacterial counts reached 104-106 g dry wt. of sediment -1. Bacteria were most abundant in the dune, and least abundant in the beach sand. Halotolerant bacteria were more numerous than limnotolerant ones. Ammonifying and uric acid decomposing bacteria constituted the most abundant physiological groups; sulphate reducing bacteria were least numerous.
Bacterial production, primary production and a number of other environmental factors were measured during six cruises in the Gulf of Gdańsk conducted in various seasons from 1995 to 2001. Bacterial production (BP) in the epipelagic layer ranged from 1.5% (April) to 80% (July) of the gross primary production (PP). Significant differences were observed between the BP/PP ratios in estuarine and open-water areas. The highest values were recorded in the coastal area and near the mouth of the river Vistula. It suggests that allochthonous organic matter has a great influence on BP. The correlations between particular parameters and regression analyses indicated that BP in the Gulf of Gdańsk depended on temperature, organic nitrogen concentration, PP, chlorophyll a concentration, organic phosphorus concentration, salinity and biochemical oxygen demand. Of all the independent variables, the temperature had the greatest impact on BP (R2 = 0.62). There was an inverse parabolic relationship between bacterial production and temperature. It appears that above a temperature of 12◦C bacterial production depended on substrates to a higher degree than on temperature. The negative correlation between BP and concentrations of mineral nitrogen and phosphorus in the annual cycle were probably due to an indirect dependence. A multiple regression equation, which included temperature and organic phosphorus concentrations, explained 78% of the variation in BP. Increasing BP resulted in an increasing biomass of bacterivorous nanoflagellates and of bacterivorous ciliates, which is indicative of bottom-up control in this segment of the trophic chain.
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