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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.

Bottniska viken har inte ansetts vara påverkad av övergödning. Men nu syns tecken på stora förändringar i ekosystemet.Närsalter har ökat under de senaste 30 åren, vilket påverkar växtplanktonsamhället. Inom en snar framtid kan Bottniska viken brottas med samma problem som Egentliga Östersjön.

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 perfoliate pondweed, Potamogeton perfoliatus, is a common macrophyte in freshwater and subarctic coastal areas. This species builds extensive meadows that play a role as a filter removing nutrients traversing from land to sea and maintain essential ecosystem functions. Here, we investigated the function of perfoliate pondweed as a filter of potentially pathogenic bacteria by combining culture-dependent and 16S rRNA metabarcoding approaches. Our results suggest no significant nutrient reduction in the meadow region but the enrichment of potentially pathogenic bacteria, such as Vibrio, Legionella and Leptospira, particularly attached to macrophyte leaves. The bacterial community composition differed between seawater and macrophyte habitats, with higher relative abundances of Cyanobacteriia attached to macrophytes, without affecting alpha-diversity. The metabolic pathways of bacteria for aromatic and polymer compound degradation were enriched in the macrophytes, attributed to members of the genera Pseudorhodobacter, Novosphingobium and Erythrobacter. Functions related to such degradation suggest that the bacteria may be able to remove complex organic compounds coming from land. We argue that the macrophyte meadows may be relevant to both animal and human health, as these habitats can be hot spots for potentially pathogenic bacteria.

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.

Measurements of dissolved organic carbon (DOC), nitrogen (DON), and phosphorus (DOP) concentrations are used to characterize the dissolved organic matter (DOM) pool and are important components ofbiogeochemical cycling in the coastal ocean. Here, we present the first edition of a global database (CoastDOMv1; available at https://doi.org/10.1594/PANGAEA.964012, Lønborg et al., 2023) compiling previously published and unpublished measurements of DOC, DON, and DOP in coastal waters. These data are complementedby hydrographic data such as temperature and salinity and, to the extent possible, other biogeochemical variables(e.g. chlorophyll a, inorganic nutrients) and the inorganic carbon system (e.g. dissolved inorganic carbon andtotal alkalinity). Overall, CoastDOM v1 includes observations of concentrations from all continents. However,most data were collected in the Northern Hemisphere, with a clear gap in DOM measurements from the SouthernHemisphere. The data included were collected from 1978 to 2022 and consist of 62 338 data points for DOC,20 356 for DON, and 13 533 for DOP. The number of measurements decreases progressively in the sequenceDOC > DON > DOP, reflecting both differences in the maturity of the analytical methods and the greater focuson carbon cycling by the aquatic science community. The global database shows that the average DOC concentration in coastal waters (average ± standard deviation (SD): 182±314 µmolC L⁻¹; median: 103 µmolC L⁻¹) is13-fold higher than the average coastal DON concentration (13.6 ± 30.4 µmol N L⁻¹; median: 8.0 µmol N L⁻¹),which is itself 39-fold higher than the average coastal DOP concentration (0.34 ± 1.11 µmol P L⁻¹; median:0.18 µmol P L⁻¹). This dataset will be useful for identifying global spatial and temporal patterns in DOM and willhelp facilitate the reuse of DOC, DON, and DOP data in studies aimed at better characterizing local biogeochemical processes; closing nutrient budgets; estimating carbon, nitrogen, and phosphorous pools; and establishing abaseline for modelling future changes in coastal waters. 

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.