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Seasonal Dataset of DO, δ¹⁸ODO and Biogeochemical Parameters in the Danube River (2023–2024)

This dataset contains dissolved oxygen (DO) concentrations, stable oxygen isotope ratios of DO (δ¹⁸ODO), particulate organic carbon (POC) concentrations, and respiration/photosynthesis (R/P) ratios, along with corresponding parameters (temperature, δ¹⁸OH2O, nitrate) collected from the Danube River and its key tributaries during five seasonal sampling campaigns in 2023 and 2024. Water samples were collected using a weighted 2 L sampling bottle submerged 1–2 meters below the surface, with sampling conducted from the river center via bridges or passenger boats, and occasionally from the riverbank. In situ temperature measurements were taken with a multiparameter instrument (HQ40d, HACH™, Loveland, CO, USA). δ¹⁸ODO was analyzed using a modified automated equilibration system (Gasbench II, ThermoFisher Scientific™) coupled to a DELTA V Advantage isotope ratio mass spectrometer (IRMS, ThermoFisher Scientific™). This dataset captures seasonal variations in DO dynamics and provides valuable insights into oxygen sources and sinks within the Danube River. The data support the study of biogeochemical cycling in large river systems and can inform ecosystem management and conservation strategies in the face of environmental and climate change.

Water chemistry of the Rappbode water reservoir

We present concentrations and carbon stable isotope data of dissolved inorganic carbon (DIC) and of various phases of OM including DOC, autochthonous particulate organic carbon (auto-POC) and sedimentary matter (SED) in a temperate drinking water reservoir (Rappbode Reservoir, Germany; 51°44'19"N, 10°53'30"E). This data cover a time period between March 2020 and December 2020 and refer to depths belonging to the metalimnion and the hypolimnion of the reservoir.

Concentrations of allochthonous particulate organic carbon (allo-POC) from the Rappbode water reservoir

We present wintertime concentrations of allochthonous particulate organic carbon (allo-POC) in a temperate drinking water reservoir (Rappbode Reservoir, Germany; 51°44'19"N, 10°53'30"E).

The occurrence of Vibrio spp. in the salinity gradient of shallow coastal waters of the Baltic Sea – data set including environmental and microbiological data (EU Biodiversa project BaltVib).

The main aim of the BaltVib sampling campaign was to analyse the microbial community composition in pelagic and benthic habitats with special focus on Vibrio spp. bacteria inside and outside of eelgrass meadows (Zostera marina), and selected macroalgae populations (Fucus spp.) in the salinity gradient of shallow coastal waters of the Baltic Sea. The temporal extent of the dataset is 25.07.2021 to 02.09.2021. The geographic extent of the dataset is spanning from 9°52,655 E to 25°00,698 W and 60°06,547 N to 54°00,8666 S. The measurement depth ranges from 0.2 meters to 7 meters. Salinity ranges from 4 to 14. Environmental parameters measured are: conductivity, temperature, pH, Secchi depth, chlorophyll a, dissolved oxygen, ammonium, nitrate, nitrite, phosphate, silicate, grain size, dissolved organic carbon, dissolved nitrogen, particulate organic nitrogen, particulate organic carbon. Vibrio spp. colony forming units were counted using TCBS agar plates. Abundance of Vibrio vulnificus was determined by ddPCR in water and sediment samples as well as in Zostera marina surface biofilm. Cell counts by flow cytometry contain: Synechococcus, Picoeukaryota, Nanoeukaryota, high-nucleic acid bacteria, low-nucleic acid bacteria. Macrophyte abundance was measured for Zostera marina and Fucus spp..

Global particulate organic carbon flux derived from Th-234: 13 ocean regions, 3 export depths

The 234Th–238U disequilibrium technique has been widely used to estimate the amount of particulate organic carbon (POC) exported from surface ocean layers to the deep sea. This method is based on determining 234Th fluxes from vertical 234Th–238U profiles in the water column and converting them into POC fluxes using POC/234Th ratios measured in sinking particles at a given calculation depth. We present here an extensive repository of POC fluxes, together with Th fluxes and POC/234Th ratios. Covering all the global ocean, classified in 13 regions, season and moment of the bloom and calculated at three different depths: i) a fixed depth (100 m) ii) the reference depth in the paper associated to the base of the euphotic zone iii) the 234Th–238U equilibrium depth. To ensure a compilation representative of the global ocean, the dataset were selected using the division areas proposed by the international network JETZON (Joint Exploration of the Twilight Zone Ocean Network); that agreed a division of the oceans in 13 regions based on their contrasted physics and biogeochemical characteristics. The stations from 234Th publications associated to each JETZON region were carefully selected according to their ability to represent regional environmental conditions. Furthermore, station selection was based on essential criteria such as data quality and accessibility, availability of time series, clear definition of export depth, measurements from established programs, e.g. GEOTRACES, and the presence of other additional relevant ancillary data. The data in the compilation are thus organized by region and include geographic coordinates, season, selected export depth, and other key factors (such as a description of the flux evaluation depth or the export depth zone). After 234Th–238U compilation, 234Th fluxes were calculated, when possible, at the three different depths, i), ii) and iii), under the assumption of steady-state conditions, following Le Moigne et al. 2013. Using POC/234Th ratios, POC fluxes are estimated from Th fluxes and both fluxes were included in the repository. POC/234Th ratios were chosen from pump samples, prioritizing particles larger than 53 μm when available. These ratios must be estimated at the flux calculation depth [i), ii) and iii)]. When they were not available at the calculation depth POC/234Th values were interpolated as described in the readme text file. The values of the ratios are included in the repository, specifying the depth at which they were determined and indicating whether they have been interpolated. Similarly, when 234Th, 238U concentrations were not available at the calculation depth, values were interpolated (see readme text file).

Thorium-234 basierte Residenzzeitberechnung des bodennahen partikulären Materials in der Mecklenburger Bucht.

Der Austausch von Partikeln zwischen Wasser und Sediment ist ein wesentlicher Teil des Stoffkreislaufes zwischen Pelagial und Benthal. Ein ständiger Austausch findet so zwischen der bodennahen Trübezone (BTZ) und dem bioturbat durchmischtem Sediment statt, der z.B. in der Tiefsee im Bereich von wenigen Tagen liegen kann (Resuspensionsschleife). Ziel dieses Antrages ist, mit Hilfe des 234Thorium/238Uran Gleichgewichts Residenzzeiten der Partikel im Wasser, in der BTZ und im Sediment der Mecklenburger Bucht zu ermitteln. Um diesen in der Tiefsee bereits erprobten Ansatz auf Flachwasserverhältnisse übertragen zu können, sollen einige für diese Situation spezifischen Randbedingen, nämlich die Adsorption von Thorium an Partikel mit höherem mineralischen Anteil und relativ frischer organischer Substanz (Alginin, Fucoidan und Chondroitin) untersucht werden (Kooperation mit Prof Carol Arnosti, Chapal Hill). Des Weiteren sollen in Strömungskanaluntersuchungen die Auswirkungen der bodennahen erhöhten Turbulenzen und Scherungen auf das Adsorptionsverhalten von Thorium analysiert werden. In den im zweiten Jahr vorgesehenen Felduntersuchungen soll mit Hilfe der Residenzzeiten eine Bilanz des partikulären Kohlenstoffs auf einem Transekt vom sandigen Flachwasser zum siltigen tieferen Sediment hin erstellt. Zusätzlich soll berechnet werden, wie lange sich POC in den verschiedenen Sedimenttypen und den anderen Kompartimenten der Resuspensionsschleife aufhält.

Project: BaltVib - Pathogenic Vibrio bacteria in the current and future Baltic Sea waters: mitigating the problem

Vibrio – microbes that are part of the natural bacterioplankton in temperate marine waters – have in recent years flourished in the Baltic Sea, probably stimulated by elevated surface water temperatures. Several Vibrio species are human pathogens. It is hence of great concern that Vibrio-related wound infections and fatalities have increased dramatically along the Baltic coasts. Future climate change is predicted to escalate this problem, posing a significant threat to human health and the Baltic tourism industry. However, the projections do not yet take into account the influence of ‘ecosystem engineers’ such as mussels and macrophytes on Vibrio diversity and abundance. Recent data indicate that in some of the ‘ecosystem engineers’ habitats the abundance of pathogenic Vibrio spp. is reduced. This opens up the option for nature-based solution (NbS) strategies to control pathogenic vibrios in the nearshore habitat where humans interact with the sea. However, climate change will also affect the structure and functioning of the ecosystem engineers, with as yet unknown consequences for the Vibrio populations in the Baltic Sea. BaltVib aims to delineate the current and future Vibrio status, determine biotic and abiotic key factors regulating Vibrio prevalence, and identify NbSs to mitigate the problem. This will be accomplished through interdisciplinary integration of marine, microbiological, molecular and socio-ecological expertise carried by partners from seven Baltic nations.

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