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Benthic diatoms and Implementation of Water Framework Directive in Croatia

Due to great importance of running waters as one of the most valuable natural resources, it is of necessary to have adequate tools for assessment and monitoring the water quality. With the EC Water Framework Directive (WFD ; Directive 2000/60/EC), a new legal structure for the assessment of all types of water bodies in Europe is defined. The focus of the WFD in stream assessment is the use of biotic indicators (phytoplankton, phytobentos, macrophytes, bentic invertebrates, and fish) together with hydromorphological and chemical elements. Current approaches for using phytobenthos for monitoring in Europe generally focus on a representative diatoms taxonomic groups sampled from a representative habitat (Kelly et al., 1998 ; Prygiel et al., 2002 ; Rott et al., 2003 ; King et al., 2006). The purpose of this paper is to present diatom assemblages in Croatian rivers and streams, to access the relationship between diatom species composition and environmental variables and to set boundaries for water quality classes using Croatian diatom trophic index. Investigations were performed during spring and summer in 2006, 2007 and 2009. Altogether, samples were collected on 141 sampling points on 92 different rivers and streams in Croatia. For additional analyses dataset with physical and chemical properties (water temperature, pH, conductivity, oxygen, oxygen saturation, nitrate, nitrite, ammonia, orthophosphate and total phosphorus) of investigated sites was also used. Values of water temperature, pH, conductivity, oxygen concentration, and oxygen saturation were measured using WTW Multi 340i handheld meter along with sampling of diatoms. Concentrations of nitrate, nitrite, ammonia, orthophosphate and total phosphorus were determined from water samples collected at the same time and measured in laboratory using standard methods (APHA, 1995). As for abiotic typology, water types system B was used to describe 24 different water types (Mihaljević et al. 2011). Altogether 182 diatom species were noted and used for the analysis. Cluster analysis was employed to group the samples and 10 groups emerged. ANOVA revealed that among SOM groups there was, according to environmental parameters, a statistically significant difference (F=2.15952, p<0.001). To single out parameters that contributed towards statistical significance, post hoc Tukey hsd test was performed. It revealed that group 6 is statistically different (p<0.05) from all other groups concerning concentrations of ammonia, nitrates, orthophosphates and total phosphorus. ANOVA on diatom abundance data set revealed that groups statistically significantly differ one from another (F=138.08, p<0.001). Ind-val analysis was used to find characteristic species for each group. Each group was represented with at least one (groups 4 and 1) species and group 8 with 12 different species. Composition of diatom communities and the characteristic (indicator) species from this set of Croatian samples closely corresponded to those observed in other geographical areas (Tison et al., 2005 ; Tornés et al., 2007). Diatom assemblages are influenced by many factors including those that are site specific at various temporal and species scales (DeNicola et al., 2004) as well as those that reflect human interventions in the environment. Those factors include chemical properties of the water (Potapova, 1996), nutrient load (Rott, 1995) and also flow velocity and type of substrate (Plenković, 1989). Canonical analysis of principal coordinates (CAP) showed that there were some strong and significant correlations between the diatom abundance and the environmental variables (P=0.001). First canonical correlation was 0.74 and second one 0.67. CAP axis 1 was correlated with oxygen saturation (r=-0.924) and CAP axis 2 with total P (r=0.571) and NO3- (r=0.490). It seems that nutrients, especially phosphorus, have more important role concerning diatom assemblages when we look into the data at regional scale. As published in many other studies (Stanley et al., 1990) phosphorus, both as orthophosphate and total phosphorus, has been shown to be an important factor in the development of benthic diatom community. Phosphorus and nitrogen fractions have been generally considered to be most critical factors (Hutchinson, 1967). Because of such strong influence of phosphorus on diatom asemblages, trophic index was chosen as a metric for estimation of water quality in running waters in Croatia. 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Benthic diatoms; Water Framework Directive; Croatia

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