Markéta Fránková

Identification versus counting protocols as sources of uncertainty in diatom-based ecological status assessments

In 2009, seventeen analysts participated in a pan-European diatom ring-test (intercalibration), analyzing nine samples from seven countries following the European standard EN 14407. The objective of this exercise was to agree on practical conventions on diatom identification to facilitate future intercalibration work and to assess the extent to which national differences in sample analysis (counting protocol and identification conventions) contribute to variability in EU-level comparisons of diatom-based methods. Differences in the reported taxa lists were large, but not a major source of variation in values of a common metric (the phytobenthos Intercalibration Common Metric, ICM). Therefore, every country can apply its own identification conventions for national assessments, and still be fairly confident that the ICM reflects the national classification of its streams. Part of the index variation was due to differences in counting protocols and care should be taken when handling broken valves, girdle views and small taxa. More work at both national and European level is needed to provide a harmonized way of using diatoms for ecological status assessments in the future.

Ecology and Applications of Freshwater Epiphytic Diatoms — Review

Abstract Epiphytic diatoms perform a variety of ecological functions. Diatoms are important primary producers and sources of oxygen which can modify the chemistry of the surrounding aquatic environment. They may live attached to plant surfaces with the help of extracellular polymeric substances and compete with plants for resources (e.g., light, nutrients). Thus, they represent an excellent model system for studies on interactions between epiphytes and their host plants under different environmental conditions. Further, the practical usage of epiphytic diatoms in biomonitoring begs questions concerning substrate specificity, diatom biodiversity, and species delimitations. This review focuses on specific aspects of freshwater epiphytic diatom ecology as adaptations for epiphytic way of life, epiphyte-host relationships, and implications for biomonitoring.

Diatoms in water quality assessment: to count or not to count them?

Abstract Two methods of quantifying diatoms were compared: (i) by counting valves, and (ii) by simple assignment of individual species to a seven-point scale according to their coverage on a glass slide. The saprobity-trophic index introduced in the Czech Republic for assessing the ecological status of running waters in accordance with the requirements of the Water Framework Directive (WFD) was used for comparison. There were no statistically significant differences between the indices as calculated by the studied methods, and therefore the comparable indicative values of the two approaches were demonstrated. In all cases, however, indices based on coverage classes achieved higher correlation with the fundamental water chemistry parameters than did indices based on diatom valve counts. To explain the cause of higher correlations, different variants of editing input data were used. The results support the assumption that the main cause of the poorer predictive value for the index based on diatom valve counts is that the abundant taxa are attributed too much importance in the final assessment of the environment quality. Using degrees of coverage for the quantification of diatoms in evaluating the ecological status thus appears to be preferable (or at least sufficient) for the given purpose.