The changes to physical and chemical ecosystem characteristics as a response to pervasive and intensifying land use have the potential to alter the consumer–resource interactions and to rewire the flow of energy through entire food webs. We investigated these structural and functional properties of food webs in stream ecosystems distributed across woodland, agricultural and urban areas in the Zagreb region of Croatia. We compared resource availability and consumer diet composition using stable isotope mixing models and tested how the isotopic variance of basal resources, primary consumers, macroinvertebrate predators and other food web characteristics change with different land‐use types. Combination of increased loading and altered composition of nutrients, lower water discharge and higher light availability at urban sites likely promoted the contribution of aquatic macrophytes to diets of primary consumers. Macroinvertebrate predators shifted their diet, relying more on active filterers at urban sites relative to woodland and agricultural sites. Urban food webs also had lower trophic redundancy (i.e. fewer species at each trophic level) and a more homogenized energy flow from lower to higher trophic levels. There was no effect of land use on isotopic variation of basal resources, primary consumers or macroinvertebrate predators, but all these trophic groups at urban and agricultural sites were 15N‐enriched relative to their counterparts in woodland stream food webs. The physical and chemical ecosystem characteristics associated with intensive land use altered the resource availability, trophic redundancy and the flow of energy to other trophic levels, with potentially negative consequences for community dynamics and ecosystem functioning. These empirical findings indicate that reducing nutrient pollution, agricultural runoffs and maintaining riparian vegetation can mitigate the impacts of land use on structure and function of stream ecosystems.

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Many studies investigate the effects of block vs. traditional class scheduling on the students’ success in high-school science classes. However, it is rare for studies to investigate the interactive effect of class scheduling and students’ average performance on the students’ success. We investigated how block (B) vs. single (S) class scheduling, students’ average performance and their interaction affect students’ success in high school biology course. The study included 281 high school students (1st to 4th grade; 124 students from S-, 157 from B-scheduled classes) participating in: (1) first written exam conducted to evaluate students’ initial knowledge; (2) teaching in block- vs. single-scheduled classes; (3) second written exam conducted to assess students’ achievement after block- vs. single-scheduled classes. Block-scheduled classes improved students’ performance in 3rd grade only. In 1st and 2nd grade, students from single-scheduled classes achieved better results. In 4th grade, there was no significant difference in success among block- vs. single-scheduled classes. Block-scheduled classes did not affect students’ success equally across all student performance categories. When estimating the effects of class scheduling on students’ success, students’ age, prior knowledge, overall performance and complexity of educational topics should be considered.

Tufa-depositing streams provide great microhabitat complexity and are therefore inhabited by various periphytic phagotrophic organisms such as ciliates and amoeboid protists. Recent removal of invasive plant species Ailanthus altissima (Mill.) Swinge from the Skradinski buk tufa barrier (Krka National Park, Croatia) resulted in changes in the barrier hydromorphology including the reactivation (revitalization) of dry streams. The objective of this study was to investigate: (1) the taxonomic and functional response of periphytic ciliates and amoeboid protists to stream revitalization by comparing taxonomic (i.e., abundance, species richness and diversity) and functional (i.e., functional diversity) metrics between revitalized (N) and control sites (C) during 1 and 2-months immersion period; (2) which environmental and (3) periphyton-associated factors shape the taxonomic and functional metrics and to what extent; (4) how duration of immersion affects taxonomic and functional metrics at revitalized sites. Our results showed that taxonomic and functional metrics of ciliates and amoeboid protists responded to the prevailing conditions characteristic of revitalized tufa-depositing streams: changing hydrology (occasional high flow or drought), soil drainage, and extensive inorganic matter, i.e., tufa deposition, although their responses were somewhat different. The two assemblages also showed different responses of taxonomic and functional metrics with respect to immersion duration: while the taxonomic and functional diversity of ciliates at N sites increased with longer immersion, indicating niche diversification, those of amoeboid protists hardly changed with time. Our results suggest that a comprehensive analysis of taxonomic and functional metrics of ciliates and amoeboid protists could be a good proxy for assessing revitalization of tufa-depositing streams. However, the temporal component should always be considered when conducting such studies, as the colonization processes of ciliates and amoeboid protists are quite complex, especially in tufa-depositing streams.

The present study deals with genotoxicity assessment of freshwaters using caged carp (Cyprinus carpio). Carps were transplanted from a fish-farm to three differently polluted sites in eastern Croatia. Two polluted sites were situated in the river Drava, downstream from the cities of Belisće and Osijek, while the reference site was in the Nature Park Kopacki rit, a preserved wetland area with limited anthropogenic influence. Exposure lasted for 3 weeks and was repeated for 3 years (2002-2004). DNA damage was assessed in erythrocytes of the exposed animals by the Comet assay and micronucleus test (MNT). In order to evaluate possible differences in stress responses to polluted water in situ and in aquaria a laboratory exposure was performed with water from the studied location in the second year of the study. Carp from the sites with high anthropogenic influence (Belisće and Osijek) had higher average DNA damage as expressed in both the MNT and Comet assay. Of the two, the Comet assay appeared to be more sensitive following both caging and aquaria exposures. The results from this study suggest that 3 weeks caging exposure of C. carpio may be a useful strategy to monitor for genotoxic agents in freshwater ecosystems.