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This paper presents the results of fractal analysis of fracture systems in upper Triassic dolomites in Žumberak Mountain, Croatia. Mechanical rock characteristics together with structural and diagenetic processes result in fracture systems that can be considered as fractals. They are scale-invariant in a specifi c range of scales. The distribution of fractures can be described with power law distribution and fractal dimension. Fractal dimension is a measure of how fractures fi ll the space. Fractal dimension can be estimated from photographs of outcrops by converting photographs to binary photographs. Binary photo display only black (rock or fractures) and white (fractures or rock). Fractal dimension is then estimated based on the box-counting method. In this paper, we present results of fractal analysis from three outcrops. The results are very similar to previously published results from outcrops of dolomites in Slovenia. The obtained fractal dimensions are in the range 2,69-2,78 and depend on how fracture systems are distributed in the outcrop. Lower values indicate a smaller number of fractures and a higher signifi cance of larger fractures. Higher values indicate the distribution of more similarly sized fractures throughout the whole outcrop. Fractal dimension is a very signifi cant parameter and in the rock fracture system characterisation sense, it describes how fractures are distributed in the outcrop. It can be used in discrete fracture network modelling if spatial distribution of fractures is represented with power law distribution.

Influence of hydrological characteristics and nutrient concentrations on phytoplankton was investigated in four large rivers (Mura, Drava, Danube and Sava) in the Pannonian ecoregion in Croatia to understand how phytoplankton of rivers can be explained by the ''different functional group approach''. To gain a clearer understanding of the factors that affect river phytoplankton, the present study examined phytoplankton biomass and composition in relationship with physical and chemical parameters assessed in detail by preparing self-organising maps using functional groups and morpho-functional groups. Total nitrogen along with water residence time showed to be the best predictor to determine phytoplankton biomass and chlorophyll a.Phytoplankton diversity increased with higher water discharge, but it had the consequence of diluting algae and decreasing biomass. Bacillariophyceae and Chlorophyceae species dominated the phytoplankton assemblages in all rivers. Diatoms predominated in rivers with shorter residence time. Dominant diatom codons of functional groups were C, D and TB while morpho-functional groups were represented by only diatom group VI. As residence time increased, the proportion of chlorococcalean green algae, represented by functional group codon T and morpho-functional group IV grew in summer. Since potamoplankton is dominated by diatoms, functional groups with its fine partition of diatom codons proved to be excellent descriptor of the potamoplankton. Application of morpho-functional groups originally developed from the lake data, showed to be limiting because of the predominating presence of only one diatom group.

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