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Here we present the results of a mayfly study conducted on a hydromorphologically altered lowland river in Croatia, the Bednja River. Twenty-two mayfly species were recorded, Baetis fuscatus (Linnaeus, 1761) and Serratella ignita (Poda, 1761) being the most widespread and Paraleptophlebia submarginata (Stephens, 1836) and Cloeon dipterum (Linnaeus, 1761) the rarest species. A significant increase in mayfly species richness was observed along the river course. Nevertheless, cluster analysis showed that their assemblages were not grouped according to the study position along the Bednja River. The lowest species richness and diversity were recorded for the spring area. Surprisingly, the highest species richness was found at a site with moderate hydromorphological alterations, and the highest diversity at a site with severe hydromorphological alterations. This could be because the river is connected to numerous lateral streams and a variety of microhabitats are available. New distribution records in Croatia are presented for some rare species in Croatian freshwater habitats, such as Heptagenia longicauda (Stephens, 1836). Ephemera lineata Eaton, 1870 was recorded for the first time in the Pannonian lowland ecoregion (ER 11) in Croatia. Caenis cf. pseudorivulorum Keffermüller, 1960 has not yet been recorded in Croatian freshwater habitats, but since our identifications are based on juvenile specimens, its occurrence is still to be confirmed.

The Mirna River is the longest river in Istria with a length of 53 km. Benthic macroinvertebrates are a community of macroscopically visible aquatic invertebrates that spend most of their lives on and in the bottom of the water body. The objective of this study was to compare the benthic macroinvertebrate composition along the course of the Mirna River. Sampling was conducted once in May 2022 at 3 sites along the Mirna River. Samples were collected using a 25 x 25 cm hand net and stored in 80 % ethanol. Basic physical and chemical parameters were measured at each station. The highest diversity was recorded at the most upstream station, Kamenita Vrata, where 14 taxa of benthic macroinvertebrates were recorded, of which the order Ephemeroptera and the family Chironomidae had the highest abundance. In the sample from the next downstream station, Portonski Most, 10 taxa were detected, with Amphipoda being the most abundant. At the station near the mouth, Dionzijev Most, the lowest diversity was recorded, with 8 taxa, and the Polychaeta group was the most numerous. The highest species richness of chironomids was recorded at the station Kamenita Vrata. Chironomid species Halocladius variabilis (Staeger, 1839), characteristic of salt or brackish water, was recorded only at the station Dionizijev Most. These differences in the composition of benthic macroinvertebrate communities are the result of differences in physical and chemical water properties at the individual stations, and the strongest influence of sea water is manifested in the high conductivity at the Dionizijev Most station.

Trzalci su najraznolikija i često najbrojnija skupina makrozoobentosa u slatkim vodama. Cilj ovog istraživanja je odrediti utjecaj klimatskih promjena na sastav zajednice trzalaca sedrene barijere Kozjak–Milanovac. Istraživanje je provedeno u Nacionalnom parku Plitvička jezera koji se sastoji od 16 oligotrofnih protočnih jezera povezanih sedrenim barijerama. Odrasli trzalci su sakupljani na sedrenoj barijeri Kozjak- Milanovac od 2007. do kraja 2020. godine emergencijskim piramidama. Temperatura vode je mjerena 2 puta dnevno „data logerima“. Podaci o protoku su dobiveni od Državnog hidrometeorološkog zavoda, a podaci o količini organske tvari od uprave parka. Brzina strujanja vode je mjerena mjesečno tijekom sakupljanja materijala. Tijekom 14 godina sakupljeno je više od 13 000 jedinki koje pripadaju unutar više od 80 taksona. Uočen je porast vrijednosti temperature vode, protoka i brzine strujanja vode te kemijske potrošnje kisika (KPK). Tijekom godina nije došlo do promjene u brojnosti i bogatstvu vrsta trzalaca, ali je došlo do promjena u sastavu zajednice i trofičke strukture. Brojnost aktivnih filtratora i detritivora kao što su Polypedilum scalaenum i Tanytarsus signatus se smanjila dok je brojnost reofilnih pasivnih filtratora poput Rheotanytarsus reissi i R. curtistylus porasla. Iako brojnost i bogatstvo vrsta nisu ukazali na promjenu, sastav zajednice jest, što upućuje na važnost taksonomije u otkrivanju najsuptilnijih odgovora zajednica na promjene u okolišu.

Flow intermittency, manifested in drying and rewetting events, is the main driver of ecological processes in intermittent rivers. It leads to an alternation of aquatic and terrestrial phases, forming a habitat mosaic of lotic, lentic and terrestrial patches, and resulting in spatio- temporal variability of environmental parameters. The objective of this study is to determine spatio-temporal differences in multiple environmental parameters in the intermittent Dinaric karst rivers. The study was conducted at four intermittent rivers belonging to the Adriatic watershed: the Krčić, Čikola, Guduča and Miljašić Jaruga rivers, with three study sites per river. Water and soil environmental parameters were measured in situ by point sampling at each study site and by continuous sampling using data loggers. Physico-chemical water parameters measured by point sampling with multiple replicates (e.g. temperature, velocity, pH, nitrate concentration), differed significantly among the studied sites. Physico-chemical soil parameters were measured in three main habitat types: dry riverbed, riparian and adjacent upland habitats. Statistically significant differences in soil temperature, moisture and pH were recorded using statistical models for both point and continuous sampling. These results indicate that differences in mean values of environmental parameters among the studied habitat types can be determined with equal efficiency by point sampling with multiple replicates and continuous sampling using data loggers.

U elaboratu se iznose i komentiraju rezultati godišnjeg istraživanja fizikalno-kemijskih, bioloških i ihtioloških značajki nadzemnih voda rijeke Drave na području utjecaja hidroelektrana Varaždin, Čakovec i Dubrava tijekom 2021. godine.

Dugo vremena se na povremene tekućice gledalo kao na staništa u kojima je raznolikost vrsta mala, a kako bi se dobila potpuna slika potrebno je uzeti u obzir akvatičke, semiakvatičke i terestričke organizme, koji žive u koritu u svim fazama vodotoka (tekuća, prijelazna, presušivanje).

Chironomids are the most diverse and usually most abundant macroinvertebrates in freshwater ecosystems. Plitvice Lakes National Park is located in the Dinaric Western Balkan Ecoregion of Croatia and it consists of 16 oligotrophic, dimictic and fluvial lakes divided by tufa barriers. The goal of this study is to evaluate effects of climate change on the chironomid composition of tufa barrier Kozjak- Milanovac. The study was conducted in Plitvice Lakes NP due to minimal anthropogenic impact on the system. Adult chironomids were collected monthly from 2007 to 2020 using emergence traps. Traps were pyramid- shaped with a 45x45 cm base and 50 cm height, with 1 mm mesh walls A collection container was placed on top of each trap, filled with a 2 % formaldehyde solution. The larvae were free to enter and exit the base of the trap. Water temperature was recorded 2 times a day with data loggers. Current velocity was measured monthly during collection of the animals. Discharge values were provided by Croatian Meteorological and Hydrological Service and data on organic material by Plitvice Lakes NP. In 14 years more than 13, 000 adults were collected belonging to more than 80 taxa. In this time span, water temperature, velocity, discharge and amount of organic material increased, while chironomid abundance and number of species did not change significantly. On the other hand, community structure changed. Specifically, decreasing abundance of active filter feeders and detritivores like Polypedilum scalaenum and Tanytarsus signatus and increasing abundance of rheophilic passive filter feeders like Rheotanytarsus reissi and R. curtistylus was observed. Overall abundance of predators decreased but abundance of Rheopelopia maculipennis, a predatory species that is usually found among tubes of Rheotanytarsus genus, increased in these new conditions characterized by increase in frequency and strength of spates. Number of species and abundance did not indicate any change over the years however community structure did, directing us towards high-level taxonomy and its impact on fine resolution of community response.

Trzalci (Chironomidae) su najraznolikija i često najbrojnija skupina makrozoobentosa u slatkim vodama. Cilj ovog istraživanja je odrediti utjecaj klimatskih promjena na sastav zajednice trzalaca sedrene barijere Kozjak–Milanovac. Istraživanje je provedeno u Nacionalnom parku Plitvička jezera koji se sastoji od 16 oligotrofnih protočnih jezera povezanih sedrenim barijerama. Odrasli trzalci su sakupljani na sedrenoj barijeri Kozjak- Milanovac od 2007. do kraja 2020. godine emergencijskim piramidama. Temperatura vode je mjerena 2 puta dnevno „data logerima“. Podaci o protoku su dobiveni od Državnog hidrometeorološkog zavoda, a podaci o količini organske tvari od uprave parka. Brzina strujanja vode je mjerena mjesečno tijekom sakupljanja materijala. Tijekom 14 godina sakupljeno je više od 13 000 jedinki koje pripadaju unutar više od 80 taksona. Uočen je porast vrijednosti temperature vode, količine organskih tvari, protoka i brzine strujanja vode. Tijekom godina nije došlo do promjene u brojnosti i bogatstvu vrsta trzalaca, ali je došlo do promjena u sastavu zajednice i trofičke strukture. Brojnost aktivnih filtratora i detritivora kao što su Polypedilum scalaenum i Tanytarsus signatus se smanjila dok je brojnost reofilnih pasivnih filtratora poput Rheotanytarsus reissi i R. curtistylus porasla. Iako brojnost i bogatstvo vrsta nisu ukazali na promjenu, sastav zajednice jest, što upućuje na važnost taksonomije u otkrivanju najsuptilnijih odgovora zajednica na promjene u okolišu.

U elaboratu se iznose i komentiraju rezultati godišnjeg istraživanja fizikalno-kemijskih, bioloških i ihtioloških značajki nadzemnih voda rijeke Drave na području utjecaja hidroelektrana Varaždin, Čakovec i Dubrava tijekom 2020. godine.