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For the first time in Belgium and Luxembourg, the diversity and taxonomy of 95 cyanobacterial strains isolated from freshwater blooms were assessed by the comparison of phenotypes and partial 16S rRNA gene sequences. The results showed the high diversity of nanoplanktonic, picoplanktonic, and benthic–periphytic cyanobacteria accompanying the main bloom-forming taxa. Indeed, besides 15 morphotypes of bloom-forming taxa, seven non-bloom-forming planktonic morphotypes and 11 morphotypes from benthic–periphytic taxa were isolated in culture from the plankton samples of 35 water bodies. The bloom-forming strains belonged to the genera Microcystis, Woronichinia, Planktothrix, Anabaena, and Aphanizomenon, whereas the other strains isolated from the same samples were assigned to the nanoplanktonic Aphanocapsa, Aphanothece, Snowella, and Pseudanabaena; to the picoplanktonic Cyanobium; and to the benthic–periphytic Geitlerinema, Komvophoron, Leptolyngbya, Lyngbya, Phormidium, Calothrix, Nostoc, and Trichormus. The results supported both the polyphyletism of genera such as Aphanocapsa, Aphanothece, Leptolyngbya, Geitlerinema, Anabaena, and Aphanizomenon as well as the validity of genera such as Microcystis, Planktothrix, and Pseudanabaena with gas vesicles and cells constricted at the cross wall. The results obtained showed the close relationship between Snowella and Woronichinia for which very few sequences exist. The first sequence of Komvophoron appeared poorly related to other available cyanobacterial sequences. Although in a few cases a good agreement existed between phenotypic and genotypic features, there was generally a discrepancy. Strains with identical morphotypes show small differences in the 16S rRNA sequences, which might be related to the different chemical properties of their habitats. The results showed the importance of the polyphasic approach in order to improve the taxonomy of cyanobacteria. [ABSTRACT FROM AUTHOR]

Relationships between littoral surface-sediment diatom assemblages and ambient limnological conditions were examined in 186 lentic fresh waters throughout lower Belgium (Flanders). Most of these waters were small, unstratified, alkaline and rich in nutrients. Using weighted-averaging techniques, robust and accurate transfer functions were developed for median pH-values ranging from 3.4 to 9.3 and dissolved inorganic carbon concentrations from <1.6 to 63 mg l−1 (jackknifed r2≈ 0.87, RMSEP <10% of the observed range), while a less precise model was obtained for sodium (2–571 mg l−1; jackknifed r2 0.69, RMSEP 9.9% of the range). Restricting the data set to circumneutral and alkaline sites (pH≥6.5) revealed the importance of additional variables, including calcium, silica, chemical oxygen demand and potential gross oxygen production (a proxy for metabolic activity and phytoplankton abundance). Calibration models for these variables were strong enough to be useful (jackknifed r2 0.57–0.59, RMSEP 13.1–16.4% of the observed range), although estimations should not always be considered entirely independent. Except for the predominant pH gradient, removal of all taxa with a distribution unrelated to the variable of interest improved model performance. In general, such taxa were proportionally represented among taxa classified according to their principal habitat. Application of the present models to diatom assemblages of shallow-water sediments obtained from historical samples and, most importantly, herbarium-macrophyte specimens, will improve hindsight into regional freshwater conditions and add to base-line setting of ecological quality standards in a highly impacted region. [ABSTRACT FROM AUTHOR]

Abundance-weighted averages of diatom indicator values for pH, salinity, organic nitrogen availability, oxygen saturation, saprobity and trophic status according to van Dam et al. [Neth. J. Aquat. Ecol. 28 (1994) 117] were calculated for surface sediment and epiphytic diatom assemblages in 186 standing waters distributed throughout Flanders, Belgium, and tested against environmental variables measured in the water column, covering water chemistry, trophic status and organic load. With exception of the pH indication, most scores related rather poorly to variables which they are assumed to reflect and correlated even more strongly to non-target variables. For instance, the trophic indication provided a measure of pH and base status rather than of nutrient levels or phytoplankton productivity. Relations to measured variables differed according to the pH regime. Correction for uneven distribution of indicator values in the species pool usually yielded little improvement and was detrimental in some cases. Compared to epiphyton, weighted averages of species indicator values derived from sediment assemblages tended to be higher in water bodies yielding the most elevated indication scores. Except for the pH and salinity indication, differences between weighted averages pertaining to these different habitats were often considerable. Limitations to the use of abundance-weighted averages of diatom indicator values for environmental monitoring and assessment of lentic waters are discussed. [Copyright &y& Elsevier]