Abstract Denitrification is a critical process that can alleviate the effects of excessive nitrogen availability in aquatic ecosystems subject to eutrophication. An important part denitrification occurs benthic systems where bioturbation by meiofauna (invertebrates <1 mm) and its effect on element cycling are still not well understood. Here we study quantitative impact populations different abundance diversity, presence absence macrofauna, nitrate reduction, carbon mineralization methane...

Filamentous, nitrogen-fixing cyanobacteria form extensive summer blooms in the Baltic Sea. Their ability to fix dissolved N2 allows circumvent general nitrogen limitation, while also generating a supply of novel bioavailable for food web. However, fate fixed by remains unresolved, as does its importance secondary production Here, we synthesize recent experimental and field studies providing strong empirical evidence that cyanobacterial is efficiently assimilated transferred webs via two...

Microbial interactions in aquatic environments profoundly affect global biogeochemical cycles, but the role of microparasites has been largely overlooked. Using a model pathosystem, we studied hitherto cryptic between microparasitic fungi (chytrid

Since the start of synthetic fertilizer production more than a hundred years ago, coastal ocean has been exposed to increasing nutrient loading, which led eutrophication and extensive algal blooms. Such hypereutrophic waters might harbor anaerobic nitrogen (N) cycling processes due low-oxygen microniches associated with abundant organic particles, but studies on nitrate reduction in pelagic environments are scarce. Here, we report 15N isotope-labeling experiments, metagenome, RT-qPCR data...

Abstract Recent discovery of methane (CH 4 ) production in oxic waters challenges the conventional understanding strict anoxic requirement for biological CH production. High‐resolution field measurements Lake Stechlin, as well incubation experiments, suggested that oxic‐water occurred throughout much water column and was associated with phytoplankton especially diatoms, cyanobacteria, green algae, cryptophytes. In situ concentrations δ 13 C values were negatively correlated soluble reactive...

We analysed N2 - and carbon (C) fixation in individual cells of Baltic Sea cyanobacteria by combining stable isotope incubations with secondary ion mass spectrometry (SIMS). Specific growth rates based on C-fixation were higher for Dolichospermum spp. than Aphanizomenon sp. Nodularia spumigena. The cyanobacterial biomass, however, was dominated sp., which contributed most to total -fixation surface waters the Northern Proper. Pseudanabaena colonial picocyanobacteria not detectable. N....

Recent findings revealed that the commonly used (15)N2 tracer assay for determination of dinitrogen (N2) fixation can underestimate activity aquatic N2-fixing organisms. Therefore, a modification to method using pre-prepared (15-15)N2-enriched water was proposed. Here, we present rigorous assessment and outline simple procedure preparation water. We recommend fill sterile-filtered into serum bottles add (15-15)N2 gas in amounts exceeding standard N2 solubility, followed by vigorous agitation...

The dependence of denitrification and dissimilatory nitrate reduction to ammonium (DNRA) on different electron donors was tested in the nitrate-containing layer immediately below oxic–anoxic interface (OAI) at three stations central anoxic basins Baltic Sea. Additionally, pathways rates fixed nitrogen transformation were investigated with 15N incubation techniques without addition donors. Denitrification anammox always detected, but higher than rates. DNRA occurred two sites orders magnitude...

Abstract Ammonium is a central nutrient in aquatic systems. Yet, cell-specific ammonium assimilation among diverse functional plankton poorly documented field communities. Combining stable-isotope incubations (15N-ammonium, 15N2 and 13C-bicarbonate) with secondary-ion mass spectrometry, we quantified bulk dynamics, N2-fixation carbon (C) fixation, as well single-cell C-fixation within communities nitrogen (N)-depleted surface waters during summer the Baltic Sea. production resulted from...

Dense blooms of diazotrophic filamentous cyanobacteria are formed every summer in the Baltic Sea. We estimated their contribution to nitrogen fixation by combining two decades cyanobacterial biovolume monitoring data with recently measured genera-specific rates. In Bothnian Sea, rates were 80 kt N year-1, which has doubled during recent and now exceeds external loading from rivers atmospheric deposition 69 year-1. The Proper was 399 agrees well previous estimates using other approaches is...

Abstract Gradients of oxygen (O2) and pH, as well small-scale fluxes carbon (C), nitrogen (N) O2 were investigated under different partial pressures dioxide (pCO2) in field-collected colonies the marine dinitrogen (N2)-fixing cyanobacterium Trichodesmium. Microsensor measurements indicated that cells within experienced large fluctuations O2, pH CO2 concentrations over a day–night cycle. varied with light intensity time day, yet exposed to supersaturated (up ~200%) throughout period anoxia...

Abstract Trichodesmium is an important dinitrogen (N2)-fixing cyanobacterium in marine ecosystems. Recent nucleic acid analyses indicate that colonies with their diverse epibionts support various nitrogen (N) transformations beyond N2 fixation. However, rates of these and concentration gradients N compounds remain largely unresolved. We combined isotope-tracer incubations, micro-profiling numeric modelling to explore carbon fixation, cycling processes as well oxygen, ammonium nitrate...

Abstract Phytoplankton forms the base of aquatic food webs and element cycling in diverse systems. The fate phytoplankton-derived organic matter, however, often remains unresolved as it is controlled by complex, interlinked remineralization sedimentation processes. We here investigate a rarely considered control mechanism on sinking matter fluxes: fungal parasites infecting phytoplankton. demonstrate that bacterial colonization promoted 3.5-fold fungal-infected phytoplankton cells comparison...

Fungal microparasites (here chytrids) are widely distributed and yet, they often overlooked in aquatic environments. To facilitate the detection of microparasites, we revisited applicability two fungal cell wall markers, Calcofluor White (CFW) wheat germ agglutinin (WGA), for direct visualization chytrid infections on phytoplankton laboratory-maintained isolates field-sampled communities. Using a comprehensive set chytrid-phytoplankton model pathosystems, verified staining pattern diverse...

Abstract Bacterial degradation of sinking diatom aggregates is key for the availability organic matter in deep-ocean. Yet, little known about impact aggregate colonization by different bacterial taxa on carbon and nutrient cycling within aggregates. Here, we tracked (C) nitrogen (N) transfer from Leptocylindrus danicus to environmental groups using a combination 13 C 15 N isotope incubation (incubated 72 h), CARD-FISH nanoSIMS single-cell analysis. Pseudoalteromonas group was first...

Abstract. Estuarine systems, being situated at the interface between land and marine environments, are important sites for nitrate (NO3–) retention processing due to large inputs, long time, high biogeochemical activity. However, it remains uncertain how pelagic benthic processes control NO3– cycling these differ contrasting seasons. In this study, we measured assimilatory dissimilatory in a lagoon (Curonian Lagoon, SE Baltic Sea) understand changes relation variation riverine inputs shifts...

Estuarine systems, being situated at the interface between land and marine environments, are important sites for nitrate (NO 3 – ) retention processing due to large inputs, long time, high biogeochemical activity. However, it remains uncertain how pelagic benthic processes control NO cycling relative importance of these is affected by seasonal changes in estuarine conditions. We measured suite governing Curonian Lagoon (Southeast Baltic Sea) during two time periods representing spring summer...

Abstract The marine biological carbon pump is mainly driven by the interplay between aggregate sinking velocity and remineralization. Sinking of natural aggregates not routinely measured but often calculated using Stokes’ law, which does consider size-dependent changes in porosity. We analyzed flow fields around 81 situ -formed Particle Image Velocimetry (PIV) to determine factors controlling settling. Using an independently derived scaling porosity with size, we predicted laboratory-formed...