The semi-enclosed Baltic Sea experiences regular summer blooms of diazotrophic cyanobacteria. Previously it has been conclusively demonstrated that in open nitrogen-limited parts of the Baltic Sea, cyanobacteria successfully fix atmospheric N2. At the same time, diazotrophic activity is still poorly understood in Baltic Sea sub-regions where nitrogen and phosphorus are co-limiting primary production. To address this gap in research, we used 15 N tracer method for in situ incubations and measured N2-fixation rate of heterocyst-forming cyanobacteria and picocyanobacteria in the Gulf of Riga, Baltic Sea, from April to September. Physicochemical variables and phytoplankton community composition were also determined. Our results show that the dominant species of cyanobacteria for this region (Aphanizomenon flosaquae) was present in the phytoplankton community during most of the study period. We also establish that the N2-fixation rate has a strong correlation with the proportion of A. flosaquae biomass containing heterocysts (r = 0.80). Our findings highlight the importance of a heterocyst-focused approach for an accurate diazotrophic activity evaluation that is one of the foundations for future management and protection of the Baltic Sea.
Geosynthetic materials are applied in measures for coastal protection. Weathering or any damage of constructions, as shown by a field study in Kaliningrad Oblast (Russia), could lead to the littering of the beach or the sea (marine littering) and the discharge of possibly harmful additives into the marine environment. The ageing behavior of a widely used geotextile made of polypropylene was studied by artificial accelerated ageing in water-filled autoclaves at temperatures of 30 to 80 °C and pressures of 10 to 50 bar. Tensile strength tests were used to evaluate the progress of ageing, concluding that temperature rather than pressure was the main factor influencing the ageing of geotextiles. Using a modified Arrhenius equation, it was possible to calculate the half-life for the loss of 50% of the strain, which corresponds to approximately 330 years. Dynamic surface leaching and ecotoxicological tests were performed to determine the possible release of contaminants. No harmful effects on the test organisms were observed.
The ratio of stable carbon and nitrogen isotopes in the suspended particulate matter has been widely used to study processes occurring in the marine ecosystem. At the same time, the signals provided by isotope ratios in coastal ecosystems can be difficult to interpret, due to several, often contradictory processes taking place simultaneously. In this study, we hypothesized that the carbon and nitrogen isotopic variation is predominantly affected by seasonally occurring phytoplankton species succession in the Gulf of Riga, Baltic Sea. Cyclical seasonal patterns were observed for carbon and nitrogen isotopic compositions of both SPM and phytoplankton data. Enrichment of heavy isotopes in the Gulf of Riga took place during spring phytoplankton bloom (from on average between + 7.1 and + 8.8 ‰, and between − 23.7 and − 21.9 ‰ for δ15N and δ13C, respectively) and pooled at significantly lower values (from + 3.1 to + 5.1 ‰ and from − 28.7 to − 25.1 ‰ for δ15N and δ13C, respectively) for the rest of the year. At the same time, the spatial gradient of isotope ratios was sporadic and inconclusive. The results showed that terrestrial and anthropogenic input to particulate matter is negligible from spring to autumn. Multivariate analysis revealed that the observed seasonal variability was indeed driven by variation in phytoplankton species composition. The diatoms, dinoflagellates, and the ciliate Mesodinium rubrum facilitated enrichment of 15N and 13C in spring. In contrast, atmospheric nitrogen fixation by cyanobacteria and the assimilation of their released nutrients by other organisms resulted in lower δ15N values during summer. This variability requires careful considerations for conducting food web studies in temperate coastal and estuarine environments during high phytoplankton biomass periods.
scite is a Brooklyn-based organization that helps researchers better discover and understand research articles through Smart Citations–citations that display the context of the citation and describe whether the article provides supporting or contrasting evidence. scite is used by students and researchers from around the world and is funded in part by the National Science Foundation and the National Institute on Drug Abuse of the National Institutes of Health.
hi@scite.ai
10624 S. Eastern Ave., Ste. A-614
Henderson, NV 89052, USA
Copyright © 2024 scite LLC. All rights reserved.
Made with 💙 for researchers
Part of the Research Solutions Family.