This paper presents the results of the research on the overall distribution of selenium (Se) in various aquatic compartments (water, sediment, plankton and macrophytes) at six selected sites of the ...Croatian part of the Drava and Danube rivers, the connected floodplain lake and the melioration channel system carried out in two sampling periods (flooding in June and the drought period in September). In addition, the physicochemical water properties, plankton composition and biomass were analysed. Our study revealed low mean Se contents in sediments and water, indicating Se deficiency in the studied freshwater systems. The physicochemical environment, including Se distribution, was primarily influenced by hydrology rather than site-specific biogeochemical and morphological characteristics. The flooding period was characterised by higher Se content in water and higher transparency, nitrate and total nitrogen concentrations than drought conditions. At the river sites, sediment Se content was the highest during the flood period, while at all other sites, higher concentrations were found during the drought, reaching the maximum in the lake. Although Se concentrations were below the threshold for aquatic ecotoxicity, they increased in the following order: water (0.021–0.187 μg Se L−1) < sediments (0.005–0.352 mg Se kg−1) < macrophytes (0.010–0.413 mg Se kg−1) < plankton (0.044–0.518 mg Se kg−1) indicating its possible biomagnification at the bottom of the food chain. Species known for high Se accumulation potential dominated the biomass of the main plankton groups and the composition of the macrophyte community, which may provide a more sensitive and accurate steady-state compartment monitor for Se assessment in freshwater biotopes.
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•Low Se content in sediments and water indicates Se deficiency in the studied area.•Se concentration increased in the order: water < sediments < macrophytes < plankton.•Hydrology influences the Se distribution in aquatic compartments.•Se potentially accumulates at the bottom of the food web.
Lake Jošava (Croatia) is a shallow reservoir surrounded by agricultural land. In the present study, the trophic cascade was tested by examining the effects of stocking with common carp on plankton ...and periphytic microphytes. Before stocking, the phytoplankton community was dominated by the chrysophyte
Synura uvella
. In the epilithon and epiphyton, the predominant diatoms were prostrate, stalk-forming, and motile taxa representing an important food source for adult copepods. After stocking, phytoplankton biomass declined and the community shifted towards small centric diatoms, allowing the small-bodied zooplankton to exploit them. The lower biomass of adult copepods allowed rotifers to proliferate and exploit phytoplankton, while small cladocerans and nauplii fed primarily on epilithon. One month after stocking, phytoplankton was dominated by cryptophytes, small centric diatoms and chlorophytes, which were an important food for rotifers, while none of the zooplankton groups showed a significant relationship with the epilithic and epiphytic communities. By the end of the experiment, food was scarce due to reduced biomass of autotrophs, and zooplankton possibly began to feed on other sources. Our results add to the knowledge about the trophic cascade hypothesis in small shallow reservoirs.
To study the early colonization processes, polyethylene terephthalate (PET) microfragments were immersed in Lake Sakadaš and the Drava River and sampled weekly together with the surrounding biotic ...communities - phytoplankton, zooplankton, epixylon in the lake and epilithon in the river. At the end of the study, a rise in water level occurred in the river, which altered the environmental conditions and plankton communities. In studied environments, all of the sampled biotic communities were diverse and abundant. Plastispheres formed in both waters by the seventh day of incubation and developed rapidly, reaching a peak in abundance on the last day of the study. Initial colonization was supported equally by planktonic and periphytic taxa in both environments, but after initial settlement, plastisphere assemblages were affected differently in the river and lake. This study suggests that PET microfragments are a suitable substrate for microphyte settlement and may provide an important pathway for their transport in dynamic freshwater floodplains and river systems.
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•The PET fragments support the rapid development of three-dimensional plastispheres.•Initial colonization is supported by planktonic and periphytic taxa equally.•Following succession, the plastispheres in the lake resemble an epixylic community.•Progression of plastispheres in the river favours the settlement of planktonic taxa.
Changes in the functional groups of zooplankton were studied in autumn in a temperate floodplain lake (Lake Sakadaš, Kopački Rit Nature Park, Croatia) and in the Drava River (in the Croatian part of ...the river). Various abiotic parameters as well as available food sources (phytoplankton and microphytes (algae and cyanobacteria) developing on epixylon, epilithon and artificially introduced microplastics called “plastisphere”) were also studied. The lake was hydrologically isolated from the main river during the study, while the water level of the Drava River fluctuated, resulting in larger variations in limnological parameters. Due to stable conditions in the lake, zooplankton abundance, biomass, and species richness were higher than in the Drava River. In both environments, zooplankton species feeding on bacteria, detrital suspensions, and small algae were most abundant, with predators and microfilter-feeders being more abundant in the lake. Microphytes were diverse and mostly small and medium-sized in phytoplankton and all substrate types. Stable lake conditions promoted higher abundance of the zooplankton group, which effectively uses larger algae as a food source. The lower abundance of zooplankton feeding on larger algae and predatory species in the river suggests that the epilithon and plastisphere community was a less mature community compared to the lake, and the heterotrophic component with ciliates and/or other small heterotrophs was not well developed. The importance of plastispheres was particularly evident under the turbid hydrologic conditions that prevailed in the river at the end of the study, when phytoplankton biomass decreased and zooplankton abundance steadily increased, suggesting that microphytes colonised on microplastics were an additional food source for higher trophic levels.
Plodovi čivitnjače (Amorpha fruticosa L.), invazivne biljne vrste, prikupljani su tijekom 2017. godine na području Pokupskog bazena i u Županji. Na plodovima žljezdastim mahunama uočeni su izletni ...otvori te je utvrđena prisutnost invazivne vrste kukca Acanthoscelides pallidipennis (Motschulsky, 1873). Ova je vrsta autohtona na području Sjeverne Amerike, a njezina rasprostranjenost usko je vezana uz staništa čivitnjače i puteve širenja ove invazivne biljne vrste. Na području Pokupskog bazena u prikupljenim su uzorcima zabilježene ukupno 554 infestirane mahune, dok su u Županji bile infestirane 434 mahune te nije utvrđena statistički značajna razlika između dvaju istraživanih područja. Rezultati ukazuju na to da je kukac A. pallidipennis raširen u sastojinama čivitnjače na obama područjima te da je potrebno pratiti potencijal njegova širenja kako bi se spriječila infestacija i drugih biljnih vrsta, posebice onih iz porodice Fabaceae koje učestalo napada.
Istraživanje prisutnosti pajasena (Ailanthus altissima (Mill.) Swingle) na području grada Osijeka
provedeno je u ljetnom razdoblju 2017. godine. Na 130 lokaliteta zabilježeno je ukupno 589 jedinki
...stabala pajasena. Pajasen je rastao pojedinačno ili u skupinama, uglavnom na napuštenim područjima,
dok je na uređenim i održavanim površinama bio rijetko prisutan. U neposrednoj blizini pajasena
zabilježene su korovne, višegodišnje zeljaste biljke koje uspijevaju na različitim tipovima staništa. U
svrhu sprječavanja nekontroliranog širenja ove invazivne biljke u gradskoj sredini potrebno je
kontinuirano provoditi praćenje i pravovremeno uklanjanje pajasena, kao i kontinuiranu edukaciju šire
javnosti o nepovoljnom utjecaju ove vrste na okoliš i biološku raznolikost.
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