Stratification of waters in the Arctic fjords occurs due to the different water
masses inflows and influence of the atmospheric conditions. Several layers may be
usually observed (Węsławski et al. 2006; maps at: www.iopan.gda.pl). Fjord surface waters are characterized by the lowest salinity (28–30 salinity units) because of
glacier ice melting processes and freshwater inflow. They occupy the upper few
meters of the water column but the additional topmost water layer may be separated
and defined due to the strongest solar heating impact. In summer brackish top
waters may reach even around 4 °C, which is higher than cold melted-ice waters
below (Piwosz et al. 2009). Deeper strata under the surface waters usually reflect
the activity of the ocean currents. Finally, bottom water masses are the coldest
(temperature as low as −1.4 °C) and of the highest salinity in the entire water
column (Svendsen et al. 2002).
2.2 Sampling
The research in each fjord was conducted on three sampling stations located on the
vertexes of the equilateral triangle (arm of length around 1.5 km), in the inner part
of the fjords. Water samples were taken from 4 depths in Hornsund (shallower
fjord) and 5 depths from Kongsfjorden. Surface and fluorescence maximum were
taken into consideration while establishing the sampling depths. At all stations the
salinity and temperature of water were measured using CTD probe SEABIRD SBE
49. Water was sampled using Niskin bottles and stored in sterile plastic containers
(50 ml) and fixed with particle-free formaldehyde solution (final concentration
2 %). Samples were kept at 4 °C until the microscopic analysis.
2.3 DAPI Staining and Direct Microscopic Counting
Total bacterial number and biomass were determined using DAPI (4′, 6-diamidino2-phenylindole) direct count method (Porter and Feig 1980). 5 ml subsamples of
each seawater sample were stained with DAPI solution to a final concentration of
1 μg/ml for 10–15 min and filtered on 25 mm polycarbonate filters (Milipore,
0.2 μm pore diameter).
Cells were counted using an epifluorescence microscope, the Nikon Eclipse 80i
under 1,000-fold magnification. An HBO-103 W high pressure mercury burner,
330–380 nm excitation filter, 420 nm barrier filter and 400 nm dichroic mirror were
used. The image analysis system of Świątecki (1997) was applied. It included the use
of a PC, a high resolution CCD digital camera Nikon DS-5 Mc-U2 and MultiScan
v.14.02 counting program with the modification of Świątecki (1997). Bacteria
abundance, morphology and biomass was determined on the basis of 2 series of 10
fields from each depth. The mean value of two series was calculated for each sample.
Blue fluorescing bacterial cells were classified into five size classes and three
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119
masses inflows and influence of the atmospheric conditions. Several layers may be
usually observed (Węsławski et al. 2006; maps at: www.iopan.gda.pl). Fjord surface waters are characterized by the lowest salinity (28–30 salinity units) because of
glacier ice melting processes and freshwater inflow. They occupy the upper few
meters of the water column but the additional topmost water layer may be separated
and defined due to the strongest solar heating impact. In summer brackish top
waters may reach even around 4 °C, which is higher than cold melted-ice waters
below (Piwosz et al. 2009). Deeper strata under the surface waters usually reflect
the activity of the ocean currents. Finally, bottom water masses are the coldest
(temperature as low as −1.4 °C) and of the highest salinity in the entire water
column (Svendsen et al. 2002).
2.2 Sampling
The research in each fjord was conducted on three sampling stations located on the
vertexes of the equilateral triangle (arm of length around 1.5 km), in the inner part
of the fjords. Water samples were taken from 4 depths in Hornsund (shallower
fjord) and 5 depths from Kongsfjorden. Surface and fluorescence maximum were
taken into consideration while establishing the sampling depths. At all stations the
salinity and temperature of water were measured using CTD probe SEABIRD SBE
49. Water was sampled using Niskin bottles and stored in sterile plastic containers
(50 ml) and fixed with particle-free formaldehyde solution (final concentration
2 %). Samples were kept at 4 °C until the microscopic analysis.
2.3 DAPI Staining and Direct Microscopic Counting
Total bacterial number and biomass were determined using DAPI (4′, 6-diamidino2-phenylindole) direct count method (Porter and Feig 1980). 5 ml subsamples of
each seawater sample were stained with DAPI solution to a final concentration of
1 μg/ml for 10–15 min and filtered on 25 mm polycarbonate filters (Milipore,
0.2 μm pore diameter).
Cells were counted using an epifluorescence microscope, the Nikon Eclipse 80i
under 1,000-fold magnification. An HBO-103 W high pressure mercury burner,
330–380 nm excitation filter, 420 nm barrier filter and 400 nm dichroic mirror were
used. The image analysis system of Świątecki (1997) was applied. It included the use
of a PC, a high resolution CCD digital camera Nikon DS-5 Mc-U2 and MultiScan
v.14.02 counting program with the modification of Świątecki (1997). Bacteria
abundance, morphology and biomass was determined on the basis of 2 series of 10
fields from each depth. The mean value of two series was calculated for each sample.
Blue fluorescing bacterial cells were classified into five size classes and three
Microbiological Survey in Two Arctic Fjords …
119