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Cyanobacterial blooms in marine and freshwater ecosystems have increased in magnitude, frequency, and distribution worldwide during recent decades. Filamentous cyanobacteria are of unsuitable size for mesozooplankton feeding and of poorer nutritional quality than other phytoplankton taxa. The production and quality of higher trophic levels are therefore expected to decrease when cyanobacterial blooms increase. We conducted a mesocosm experiment using natural seawater from the northern Baltic Sea to contrast the effects of cyanobacteria- (Aphanizomenon flosaquae) and diatom-dominated phytoplankton communities on mesozooplankton production and nutritional quality. A low and a high hydrological mixing regime was applied. The δ15N isotopic signal of seston and mesozooplankton was lower in the cyanobacteria-based food web, demonstrating that Aphanizomenon fixed atmospheric nitrogen, which was transferred in the food web. The biomass of edible-sized phytoplankton (2–50 μm) was lower in the cyanobacteria-based food web. The fatty acid quality, indicated by the ω3:ω6 ratio, was lower in the cyanobacteria-based food web for both phytoplankton and mesozooplankton. Together, this resulted in 75–80% lower copepod production and food web efficiency (FWE) in the cyanobacteria-based food web than in the diatom-based food web. The hydrological mixing regime did not affect the biological production and quality. The results demonstrate that copepod production and FWE were driven by the quality and production of edible-sized phytoplankton. The study implies that climate-induced increases of filamentous cyanobacterial blooms will cause decreased production and nutritional quality of higher trophic levels.

Climate change is projected to cause elevated precipitation in northern Europe, leading to increased runoff of terrestrial matter to coastal areas. The consequences for food web production and ecosystem function remain unclear. A mesocosm experiment was performed to investigate the impacts of elevated terrestrial matter input, using a natural plankton community from the northern Baltic Sea with added young-of-the-year perch as planktivorous top consumer. Addition of terrestrial matter caused water browning and increased dissolved organic carbon and inorganic nutrient concentrations. Phytoplankton primary production showed a negative response to terrestrial matter due to decreased light availability, while heterotrophic bacterial production increased. The trophic balance, calculated as the difference between primary production and heterotrophic bacterial production, indicated that net-heterotrophy was triggered by terrestrial matter enrichment. Primary production was identified as the main basal energy source for fish. Addition of terrestrial matter reduced the food web efficiency, calculated as the ratio between fish production and basal production (primary production?+?heterotrophic bacterial production). Furthermore, stable isotope analysis of seston and fish indicated that the added terrestrial matter was not efficiently incorporated in the food web and only marginally altered the food web trophic positions. The results suggest that the main food chain consisted of phytoplankton, mesozooplankton, and fish, and that the ecosystem production was overall light driven. Under a changing climate, several negative effects can be expected, including a poorer light climate, reduced ecosystem production and net-heterotrophy. These alterations have potentially significant consequences for ecosystem functioning, fish production, and thus ecosystem services.

Här presenteras resultaten från forskningsprojektet ”Eutrofiering och närsalter iBottniska viken - Ett ekosystem i förändring”. Projektet är ett av fyra syntesprojektsom genomförts inom forskningssatsningen Avloppsvatten och övergödning.

Med de fyra syntesarbeten ville Naturvårdsverket och Havs- och vattenmyndighetenfå sammanfattad och analyserad kunskapsläge och kunskapsbehovinom områdena avloppsvatten och övergödning. Det övergripande syftet medsynteserna var att bidra till policyutveckling inom hållbar vattenhantering så attvi uppnår miljömålen på lång sikt och att miljöns tillstånd förbättras. Utlysningenvar inriktad på tre områden varav ett var om övergödning i kust och hav i Bottniskaviken.

Projektet har finansierats med medel från Naturvårdsverkets miljöforskningsanslag.

Rapporten har skrivits av Agneta Andersson, Siv Huseby, Joakim Ahlgren,Karolina Eriksson och Sonia Brugel från Umeå universitet.

Rapporten har granskats för vetenskaplig kvalitet av Jens Fölster (SLU) samtför praktisk relevans av Lars Åkesson (Havs- och vattenmyndigheten), Anneli Sedin(Länsstyrelsen i Västerbotten) samt Kerstin Rosén Nilsson (Naturvårdsverket).

Författarna svarar för rapportens innehåll.

This report presents results from a project investigating the use of microbes as indicators of mercury (Hg) pollution in sediments. Microbes respond rapidly to environmental change, making them excellent bioindicators. However, to ensure reliable results, it is essential to analyze microbial communities soon after sampling to prevent degradation or loss of activity.

To address this, a portable molecular sequencing laboratory, OmiBox, was developed, enabling near in situ analysis of microbial taxonomic composition and gene expression. Additionally, microbial community composition was studied in Hg-contaminated fiber banks in the Gulf of Bothnia. The results revealed that certain taxonomic groups, such as bacteria from the phyla Campylobacterota and Desulfobacterota, were enriched in fiber-rich, Hg-polluted sediments.

The study also included tolerance experiments comparing bacteria from clean and contaminated sediments in response to Hg addition. Bacteria from polluted sites exhibited significantly greater tolerance, suggesting evolved resistance and retained microbial functionality. Nonetheless, Hg-contaminated sediments pose ecological risks, as methylmercury (MeHg) can bioaccumulate and magnify through the food web.

This project contributes a framework for understanding how bacterial community structure and function respond to Hg pollution in sediments, offering valuable tools for environmental monitoring and assessment.

Kemiska föroreningar orsakar problem världen över. Miljögifter som hamnat i akvatiska miljöer ackumuleras ofta till nivåer som har skadliga effekter på organismerna och hela ekosystemen. Inom EU-lagstiftningen används biomarkörer för att analysera statusen på naturliga miljöer. Mikroorganismer skulle kunna vara väl lämpade som bioindikator, eftersom de i stort sett finns överallt på jorden och snabbt svarar på miljöförändringar.

Målsättningen med detta projekt var att klarlägga om bakterier kan användas som indikator för kontaminerade sediment. Vi fokuserade på kvicksilver, som är ett vanligt förekommande miljögift i fiberrika sediment i Bottniska viken. Inom projektet utvecklades ett portabelt molekylärt sekvenseringslaboratorium (Omibox), experiment utfördes för att testa effekter av terrestra organiska ämnen samt mikroorganismers toleransnivåer för kvicksilverbelastning. Därutöver utfördes fältstudier i gradienter av kvicksilverbelastade områden i Bottniska viken för att hitta möjliga indikatorer i bakteriesamhället.

The Baltic Sea is one of the largest brackish water environments on earth and is characterised by pronounced physicochemical gradients and seasonal dynamics. Although the Baltic Sea has a long history of microscopy-based plankton monitoring, DNA-based metabarcoding has so far mainly been limited to individual transect cruises or time-series of single stations. Here we report a dataset covering spatiotemporal variation in prokaryotic and eukaryotic microbial communities and physicochemical parameters. Within 13-months between January 2019 and February 2020, 341 water samples were collected at 22 stations during monthly cruises along the salinity gradient. Both salinity and seasonality are strongly reflected in the data. Since the dataset was generated with both metabarcoding and microscopy-based methods, it provides unique opportunities for both technical and ecological analyses, and is a valuable biodiversity reference for future studies, in the prospect of climate change.

Växtplankton, som utgör grunden i den marina näringsväven, har länge använts för att mäta miljöförändringar. Just nu sker det en snabb utveckling av DNA-metoder för miljöövervakning. 

Forskningsprojektets syfte har varit att utveckla DNA-streckkodning av marina växtplankton som ett verktyg för miljöövervakning. DNA-metoden har visat sig ha en stor potential för att visa planktonsamhällenas sammansättning och diversitet, samt som en mätare på förändringar i miljön. Men projektet har även fångat upp förekomster av organismer som inte tillhör växtplankton. 

Forskningsprojektet även visat på att metoden behöver vidareutvecklas, då den bara fångar upp 50 % av den genetiska variationen inom en växtplanktonart (ASV, amplicon sequence variants), vilket gör gränsdragningen mot andra arter svår. 

Projektet har finansierats med medel från Naturvårdsverkets miljöforskningsanslag som finansierar forskning till stöd för Naturvårdsverkets och Havs- och vattenmyndighetens kunskapsbehov.

Climate change is having many negative impacts worldwide. Increased rainfall caused by climate change has become a serious issue in the northern parts of the world. With more rainfall, a larger amount of brown-colored decaying plant material is transported from the land to oceans, making the seawater browner. The brown color reduces the amount of sunlight that penetrates into the seawater, which can decrease the growth of microscopic plant-like organisms called phytoplankton that rely on sunlight to grow. Phytoplankton are an important food source for ocean animals, such as tiny creatures called zooplankton. This study explored the effects of seawater browning on phytoplankton and zooplankton in the northern Baltic Sea.

Bacteria are major consumers of dissolved organic matter (DOM) in aquatic systems. In coastal zones, bacteria are exposed to a variety of DOM types originating from land and open sea. Climate change is expected to cause increased inflows of freshwater to the northern coastal zones, which may lead either to eutrophication or to increased inputs of refractory terrestrial compounds. The compositional and functional response of bacterial communities to such changes is not well understood. We performed a 2-day microcosm experiment in two bays in the coastal northern Baltic Sea, where we added plankton extract to simulate eutrophication and soil extract to simulate increased inputs of refractory terrestrial compounds. Our results showed that the bacterial communities responded differently to the two types of food substrates but responded in a similar compositional and functional way in both bays. Plankton extract addition induced a change of bacterial community composition, while no significant changes occurred in soil extract treatments. Gammaproteobacteria were promoted by plankton extract, while Alphaproteobacteria dominated in soil extract addition and in the non-amended controls. Carbohydrate metabolism genes, such as aminoglycan and chitin degradation, were enriched by plankton extract, but not soil extract. In conclusion, the coastal bacterial communities rapidly responded to highly bioavailable substrates, while terrestrial matter had minor influence and degraded slowly. Thus, in the northern Baltic Sea, if climate change leads to eutrophication, large changes of the bacterial community composition and function can be expected, while if climate change leads to increased inflow of refractory terrestrial organic matter the bacterial communities will not show fast compositional and functional changes. Degradation of terrestrial organic matter may instead occur over longer periods of time, e.g. years. These findings help to better understand the ability of bacterial communities to utilize different carbon sources and their role in the ecosystem.

Halomethoxybenzenes (HMBs) are a group of compounds with natural and anthropogenic origins. Here we extend a 2002–2015 survey of bromoanisoles (BAs) in the air and precipitation at Råö on the Swedish west coast and Pallas in Subarctic Finland. New BAs data are reported for 2018 and 2019 and chlorinated HMBs are included for these and some previous years: drosophilin A methyl ether (DAME: 1,2,4,5-tetrachloro-3,6-dimethoxybenzene), tetrachloroveratrole (TeCV: 1,2,3,4-tetrachloro-5,6-dimethoxybenzene), and pentachloroanisole (PeCA). The order of abundance of HMBs at Råö was ΣBAs > DAME > TeCV > PeCA, whereas at Pallas the order of abundance was DAME > ΣBAs > TeCA > PeCA. The lower abundance of BAs at Pallas reflects its inland location, away from direct marine influence. Clausius-Clapeyron (CC) plots of log partial pressure (P_air)/Pa versus 1/T suggested distant transport at both sites for PeCA and local exchange for DAME and TeCV. BAs were dominated by distant transport at Pallas and by both local and distant sources at Råö. Relationships between air and precipitation concentrations were examined by scavenging ratios, SR = (ng m⁻³)_precip/(ng m⁻³)_air. SRs were higher at Pallas than Råö due to greater Henry's law partitioning of gaseous compounds into precipitation at colder temperatures. DAME is produced by terrestrial fungi. We screened 19 fungal species from Swedish forests and found seven of them contained 0.01–3.8 mg DAME per kg fresh weight. We suggest that the volatilization of DAME from fungi and forest litter containing fungal mycelia may contribute to atmospheric levels at both sites.

Phytoplankton are used worldwide to monitor environmental status in aquatic systems. Long-time series of microscopy-analyzed phytoplankton are available from many monitoring stations. The microscopy-method is however time consuming and has short-comings. DNA metabarcoding has been suggested as an alternative method, but the consistency between different methods need further investigation. We performed a comparative study of microscopy and metabarcoding analyzing micro- and nanophytoplankton. For metabarcoding, 25-1000 ml seawater were filtered, DNA extracted and the 18S and 16S rRNA gene amplicons sequenced. For microscopy, based on the Utermöhl method we evaluated the use of three metrics: abundance, biovolume and carbon biomass. At the genus, species, and unidentified taxa level, metabarcoding generally showed higher taxonomic diversity than microscopy, and diversity was already captured at the lowest filtration volume tested, 25 ml. Metabarcoding and microscopy displayed relatively similar distribution pattern at the group level. The results showed that the relative abundances of the 18S rRNA amplicon at the group level best fitted the microscopy carbon biomass metric. The results are promising for implementing DNA metabarcoding as a complement to microscopy in phytoplankton monitoring, especially if databases would be improved and group level indexes could be applied to classify the environmental state of water bodies.