engleski

Benthic diatoms - indicators of ecological status of karstic lakes

Phytobenthos, one of biological quality elements according to the Water Framework Directive (WFD), is a key component in the evaluation of the ecological status of lake ecosystems. Nevertheless, studies on phytobenthic and periphytic communities in lakes are vastly outnumbered when compared with the corresponding phytoplanktic communities (Cantonati & Lowe 2014). Diatoms, as the most important representatives of phytobenthos, are characterized by having a short life cycle, widespread distribution and a distinct sensitivity to the slightest environmental changes. These features enable a relatively easy monitoring of an ecosystem and detection of changes in the ecological status. Distribution and composition of diatom communities are mainly conditioned by the lake depth and substrate type, the amount of available light and shading effect. The shallow littoral strip of the lake is inhabited by species adapted to high irradiance, large temperature oscillations and constant fluctuations in the water level. In the lake's deep zone, where conditions are often dominated by low light availability, strong effect of shading by phytoplankton and attenuated oxygen concentration with bacterial degradation processes, a distinct diatom community is present. Plitvice Lakes, a specific hydrogeological phenomenon composed of 16 cascading lakes, constitutes a referent lake ecosystem for the water quality evaluation and monitoring of the phytobenthic community. The purpose of this study was to compare differences in the composition and abundance of diatom communities and to determine the ecological status of lakes Kozjak and Prošće. Benthic samples, along with the samples for chemical analysis of water, were collected during 2015 and 2016, from the deepest point and from the shallow littoral point on both lakes. After cleaning of samples and preparation of permanent slides diatoms were identified, measured and counted to 400 frustules on each slide. Water quality of the investigated lakes was determined using several multimetric diatom indices: Croatian saprobic index - SIHRIS, Croatian trophic diatom index - TIDRH, Pollution Sensitivity Index - IPS. The relationship between samples and nutrient concentrations was tested using multivariate analysis of canonical correspondence (CCA) to investigate the influence of chemical and physical factors on the composition of the community.

benthic diatoms; trophic indices; karst lakes

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