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Application of benthic diatoms in water quality assessment according to the EU-WFD in Croatian and Hungarian karstic watercourses

According to Water Framework Directive (WFD) European Union member states have to achieve good ecological status and report on the ecological status of all streams whose catchment area exceeds 10 km2. Since assessment is performed looking for deviations from reference conditions, one of the key goals of Water Framework Directive is to classify rivers and streams using biological quality parameters and to describe hydromorphological, physiochemical and biological type specific reference conditions (EC, 2000). That should be determined using five biology quality elements: phytoplankton, phytobenthos, macrophytes, benthic invertebrates and fish. As commonly dominant phytobenthos representatives, benthic diatoms are widely used in Europe and worldwide to access ecological status of running waters (Ács et al., 2005 ; Kireta et al., 2012 ; Martin and Reyes Fernandez, 2012 ; Reid et al., 1995). They have relatively short life cycles and thus rapidly respond to environmental changes. Also, they are relatively easy to sample. All of those properties makes them convenient and practical tool for determining water quality. The goal of this paper is to access the applicability of Croatian and Hungarian system for water quality assessment to karstic waters. The samples in Croatia were collected (during vegetation season, May to September) in freshwater courses of rivers Zrmanja (five sampling points) and Krka (three sampling points) and tributaries Krupa and Otuča as well as Butišnica, Radljevac, Bribišnica, Kosovčica and Orašnica of Zrmanja and Krka, respectively. In Hungary samples were collected in karstic Tárkány- Eger creek complex, in the Bükk Mountain, near Eger city, from source to the inflow during a year (in spring, summer and autumn). Diatoms were sampled from natural substrate (predominantly rocks), fixed in formaldehyde and acid cleaned prior to preparation of permanent slides. Abundance was determined by identification and counting of 400 frustules on each permanent slide. Along with samples of natural benthic diatom communities, samples of water for chemical analyses ware also taken. Water quality of investigated sites was determined using multimetric indices of Croatian (Croatian trophic diatom index - TIDHR, Croatian saprobic index - SIDHRIS and index of diatom sensitivity to pollution – IPS) and Hungarian system (TID, SID and IPS). Primer 6 (Clarke and Warwick, 2001) was used for cluster analysis and MDS ordination of diatom abundance data and calculated indices. RESULTS: During the investigated period in altogether 65 sampling sites, out of which 23 were in Croatia and 42 in Hungary, a total of 281 species was recorded. There were 44 species that were found only in Croatia and 172 only in Hungary whereas 65 species were found in both countries. MDS ordination on abundance dataset clearly shows two different groups: one representing Croatian and other Hungarian sites. Within the groups of each country, there is also clear grouping of sites belonging to the same water body. Concerning the indices, ANOVA with post hoc Bonferoni test reveals that there are no statistically significant differences between indices values between types of waterbodies and waterbodies itself. Only noted statistical differences (p<0.05) are between countries considering TID, IPS and total score for Hungarian index (average of SID, TID and IPS.

benthic diatoms; water quality; WFD; Croatia; Hungary; karstic watercourses

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