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The abundance and photosynthetic activity of picocyanobacteria in the oligotrophic alpine lake Traunsee were measured at a station located close to the outlet of industrial soda waste and at a mid-lake reference station during spring, 1999 through to autumn, 2000. Picocyanobacterial numbers measured by flow cytometry in Traunsee (0.7–13.2 × 104 ml-1) were comparable to those of other oligotrophic lakes, and there was no significant difference between the contaminated and the reference sampling location. Picoplankton (<2 μm) photosynthetic rates measured in vitro by the 14C-technique were significantly reduced at the contaminated site relative to the reference station at low photosynthetically available radiation (10 μE m-2 s-1), while no difference between these two stations was found at moderately high light intensity (100 μE m-2 s-1). The investigation was complemented by laboratory experiments with cultured picocyanobacteria. Three Synechococcus spp. strains were exposed to water taken from either of the two Traunsee stations and from a control station located in neighbouring Attersee. Cell-specific photosynthetic activity measured by 4-h in vitro incubations revealed no significant difference among the three stations investigated. Growth rates of the same three Synechococcus spp. strains were measured by flow cytometry over several days in the laboratory. One strain, in particular, was sensitive to water taken from the contaminated site; growth rate of this strain was significantly reduced, relative to when exposed to water taken from the reference station. Taken together, our results demonstrate that picocyanobacteria are highly sensitive bioindicators of contaminant stress. The overall impact of the emissions from the industrial outlet on the picocyanobacteria was, however, relatively minor. [ABSTRACT FROM AUTHOR]

The holomictic Traunsee is the deepest and second largest lake in Austria. The special characteristic of this ecosystem is the fact that local salt and soda industries presumably alter the lake by the discharge of waste materials. Since the beginning of the 20th century salt and soda works are annually releasing up to 50,000 tons of solid wastes and up to 150,000 tons of chloride into Traunsee. To assess potential effects of these anthropogenic impacts on the bacterioplankton three sampling sites, influenced as well as not influenced by the industrial discharge, were chosen for comparison and sampled monthly from November 1997 to October 1998. Bacterial abundance ranged between 0.4 to 3.0 × 106 cells ml-1 with decreasing numbers along the depth profile. The proportion of actively respiring bacteria, i.e. INT [2-(4-iodophenyl)-3-(4-nitrophenyl)-5-phenyltetrazolium chloride] reducing cells, never exceeded 10% of DAPI (4',6'-diamidino-2-phenylindole) stained cells. Fluorescence in situ hybridization (FISH) was used to examine the seasonal and spatial distribution of dominant phylogenetic groups of the bacterioplankton. Up to 84% of bacteria detected with DAPI could be detected via FISH applying the universal bacterial probe EUB338. Percentages of alpha- and beta-Proteobacteria and members of the Cytophaga-Flavobacterium cluster did not exceed 60% of DAPI-stained cells. Beta-Proteobacteria appeared to be the most abundant group, not only in Traunsee but also in two reference lakes, Attersee and Hallstättersee. No significant differences in any of the bacterial parameters could be detected between the three sampling sites and all measurements were found in the range reported for oligotrophic lakes. The high discharge of the Traun River, resulting in a lake water renewal time of only one year, may diminish possible effects of industrial waste discharge in the pelagic zone. [ABSTRACT FROM AUTHOR]

Since nearly one hundred years Traunsee experiences the import of tons of liquid and solid waste originating from salt and soda production. Today, the lake exhibits chloride concentrations of up to 170 mg L-1 and 19% of the lake floor are directly or indirectly influenced by industrial deposits (ID). Based on the comparison of several microbial parameters in unaffected, directly affected and intermediate lake bottom sediments, the ecological integrity of the lake was evaluated. The highly alkaline ID, which were exclusively colonized by microorganisms, harbored a bacterial community reduced by a factor of 10 in abundance and biomass compared to undisturbed sediment areas within the lake. The bacterial community of ID was furthermore characterized by a reduced content of actively respiring cells (INT-formazan reduction), a lower frequency of dividing cells (FDC) and a significantly reduced cell and biomass production. A 80 to 90% reduction in carbon recycling is estimated for the area exclusively covered by ID. Protists, although occasionally absent from the industrial sediments, were in general found to be less sensitive to the contaminant stress. Differences in alkalinity and dissolved organic carbon (DOC) concentrations of sediment porewaters as well as the total organic content and C/N ratios of sediments partly explain the microbial pattern observed at the various sampling sites. Possible consequences of the continuous industrial tailings for the whole lake ecosystem and the validation of the ecological integrity are discussed. [ABSTRACT FROM AUTHOR]