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Abstract: The determination of the metabolic activity of organisms at various trophic levels is crucial for the proper assessment of the energy flow through the ecosystem, which is the basic process determining ecosystem functioning. We estimated the respiration rate in nine shallow, eutrophic lakes (macrophyte-dominated and phytoplankton-dominated) from north-eastern Poland. Respiratory carbon loss (RCL) through bottom microbial communities, macrophytes, plankton and macrozoobenthos was estimated by measuring the Electron Transport System activity. The shares of the particular ecosystem components in respiration processes differed among the lake types and seasons. The bottom microbial communities contributed most to the RCL (from 50% in the macrophyte-dominated lakes to 90% in the shallower phytoplankton-dominated lakes) except in macrophytes-dominated lakes in summer, where the macrophyte contribution prevailed (80%). The contribution of plankton was considerable only in the deeper phytoplankton-dominated lakes (20%). Macrozoobenthos was important (20%) only in the macrophyte-dominated lakes in spring and autumn. The RCL through bottom microbial communities was substantially higher in the shallow lakes (especially phytoplankton-dominated) than in deep, stratified eutrophic lakes. Shallow eutrophic lakes can be highly productive due to intensive organic matter mineralization at the bottom and rapid flow and cycling of carbon and nutrients resulting from their polymictic character.
Keywords: shallow lakes, ETS activity, respiratory carbon loss, abiotic parameters
Published in DiRROS: 23.07.2024; Views: 273; Downloads: 229
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Abstract: Carbonate sediments in non-vegetated habitats on the north-east Adriatic shelf are dominated by shells of molluscs. However, the rate of carbonate molluscan production prior to the 20th century eutrophication and overfishing on this and other shelves remains unknown because: (i) monitoring of ecosystems prior to the 20th century was scarce; and (ii) ecosystem history inferred from cores is masked by condensation and mixing. Here, based on geochronological dating of four bivalve species, carbonate production during the Holocene is assessed in the Gulf of Trieste, where algal and seagrass habitats underwent a major decline during the 20th century. Assemblages of sand-dwelling Gouldia minima and opportunistic Corbula gibba are time-averaged to >1000 years and Corbula gibba shells are older by >2000 years than shells of co-occurring Gouldia minima. This age difference is driven by temporally disjunct production of two species coupled with decimetre-scale mixing. Stratigraphic unmixing shows that Corbula gibba declined in abundance during the highstand phase and increased again during the 20th century. In contrast, one of the major contributors to carbonate sands – Gouldia minima – increased in abundance during the highstand phase, but declined to almost zero abundance over the past two centuries. Gouldia minima and herbivorous gastropods associated with macroalgae or seagrasses are abundant in the top-core increments but are rarely alive. Although Gouldia minima is not limited to vegetated habitats, it is abundant in such habitats elsewhere in the Mediterranean Sea. This live–dead mismatch reflects the difference between highstand baseline communities (with soft-bottom vegetated zones and hard-bottom Arca beds) and present-day oligophotic communities with organic-loving species. Therefore, the decline in light penetration and the loss of vegetated habitats with high molluscan production traces back to the 19th century. More than 50% of the shells on the sea floor in the Gulf of Trieste reflect inactive production that was sourced by heterozoan carbonate factory in algal or seagrass habitats.
Keywords: bioturbation, carbonate production, mollusca, northern Adriatic Sea, taphonomy, time averaging
Published in DiRROS: 23.07.2024; Views: 239; Downloads: 175
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Abstract: The crystallization of glass microspheres in the Y2O3–Al2O3-system produced from precursor powders of four different nominal compositions via flame synthesis is analyzed in detail by electron microscopy with a focus on electron backscatter diffraction (EBSD). Growth models are formulated for individual microspheres crystallized during flame synthesis as well as after an additional heat treatment step. 16 different types of crystallized bodies are cataloged for future reference. They are presented without regard for their relative occurrence; some are extremely rare but illustrate the possibilities of flame synthesis in the analyzed system. All three phases in the binary Y2O3–Al2O3-phase diagram (Y3Al5O12, YAlO3 and Y4Al2O9) and α-alumina are located by EBSD. Energy dispersive X-ray spectrometry results obtained from these microspheres show that their chemical composition can deviate from the nominal composition of the precursor powder. The multitude of differing microsphere types showing polygon and dendritic crystal growth as well as phase separation indicate that flame synthesis can lead to a wide variety of parameters during microsphere production, e.g. via irregular flight paths through the flame, contaminants or irregular cooling rates.
Keywords: Y2O3-Al2O3, microsphere crystallization, flame synthesis, EBSD
Published in DiRROS: 23.07.2024; Views: 256; Downloads: 193
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Abstract: Simultaneous occurrence of cylindrospermopsin (CYN) and microcystin-LR (MCLR) has been reported in the aquatic environment and thus human exposure to such mixtures is possible. As data on the combined effects of CYN/MCLR are scarce, we aimed to investigate the adverse effects related to genotoxic activities induced by CYN (0.125, 0.25 and 0.5 µg/mL) and MCLR (1 µg/mL) as single compounds and their combinations in HepG2 cells after 24 and 72 h exposure. CYN and CYN/MCLR induced DNA double-strand breaks after 72 h exposure, while cell cycle analysis revealed that CYN and CYN/MCLR arrested HepG2 cells in G0/G1 phase. Moreover, CYN and the combination with MCLR upregulated CYP1A1 and target genes involved in DNA-damage response (CDKN1A, GADD45A). Altogether, the results showed that after 72 h exposure genotoxic activity of CYN/MCLR mixture was comparable to the one of pure CYN. On the contrary, MCLR (1 µg/mL) had no effect on the viability of cells and had no influence on cell division. It did not induce DNA damage and did not deregulate studied genes after prolonged exposure. The outcomes of the study confirm the importance of investigating the combined effects of several toxins as the effects can differ from those induced by single compounds.
Published in DiRROS: 23.07.2024; Views: 261; Downloads: 207
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Abstract: Long-term variations of ecological status in a Mediterranean coastal lagoon (Sacca di Goro, Northern Adriatic) were investigated, combining data on the concentration of surface sediment contaminants and on the structure of the macrobenthic community. The aim was to assess any amount of chemical contamination and check the response of the macrobenthic community to sediment contamination. Over the studied period, the sediments of the lagoon showed contamination by trace metals and organochlorine pesticides, with most of them exceeding the thresholds indicated by the Italian legislation in many samples. Contamination by polychlorinated dibenzodioxins and dibenzofurans (PCDD/Fs) and polycyclic aromatic hydrocarbons (PAHs) instead never exceeded the threshold. The ecological status based on the macrobenthic community, evaluated through biotic indices (AMBI and M-AMBI), fell below the Good/Moderate threshold in most samples. The results indicate a possible influence of toxic compounds in sediment on benthic organisms, but most of the variability shown by the macrobenthic community is probably due to other factors. The difficulty in establishing a cause/effect relationship was due to the co-occurrence and variability of various stressors (both natural and anthropogenic) and their interactions. The methods currently used for monitoring transitional waters thus seem insufficient to disentangle the effect of pollutants and other environmental variables on the benthos. Integrated approaches (e.g., bioaccumulation and toxicity tests) are thus needed for a more precise identification of the risk posed by a high concentration of pollutants in such environments.
Keywords: coastal lagoon, macrobenthos, trace elements, organochlorine pesticides, PAHs, PCDD/Fs
Published in DiRROS: 23.07.2024; Views: 275; Downloads: 236
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