Identification of Cyanobacteria in a Eutrophic Coastal Lagoon on the Southern Baltic Coast

Cyanobacteria are found worldwide in various habitats. Members of the picocyanobacteria genera Synechococcus and Prochlorococcus dominate in oligotrophic ocean waters. Other picocyanobacteria dominate in eutrophic fresh or brackish waters. Usually, these are morphologically determined as species of the order Chroococcales/clade B2. The phytoplankton of a shallow, eutrophic brackish lagoon was investigated. Phytoplankton was dominated by Aphanothece-like morphospecies year-round for more than 20 years, along a trophy and salinity gradient. A biphasic approach using a culture-independent and a culture-dependent analysis was applied to identify the dominant species genetically. The 16S rRNA gene phylogeny of clone sequences and isolates indicated the dominance of Cyanobium species (order Synechococcales sensu Komárek/clade C1 sensu Shih). This difference between morphologically and genetically based species identifications has consequences for applying the Reynolds functional-groups system, and for validity long-term monitoring data. The literature shows the same pattern as our results: morphologically, Aphanothece-like species are abundant in eutrophic shallow lagoons, and genetically, Cyanobium is found in similar habitats. This discrepancy is found worldwide in the literature on fresh- and brackish-water habitats. Thus, most Aphanothece-like morphospecies may be, genetically, members of Cyanobium

Oxygen production assays in bentho-pelagic mesocosms and the Zingster Strom (southern Baltic Sea) in 2014

This data set contains the measured oxygen saturation concentration, and the calculated oxygen concentration corrected for temperature and salinity (according to Benson and Krause, 1984) of one ecosystem site (Zingster Strom, Darss-Zingst lagoon system, southern Baltic Sea) and six bentho-pelagic mesocosms close by. Temperature correction was based on simultaneous measured temperature values, salinity stayed constant in the mesocosms, and salinity correction in the ecosystem was based on daily values. The mesocosms were either phytoplankton, or macrophyte dominated (each n = 3). Measurement intervals were every 5 min (mesocosms) to 10 min (ecosystem). Additionally, Chlorophyll a were included where available and reported as daily values (Zingster Strom n= 365, mesocosms each n = 10), or fitted values (mesocosms, based on available daily values)

Phosphorus Contents Re-visited After 40 Years in Muddy and Sandy Sediments of a Temperate Lagoon System

Worldwide, coastal water bodies suffer from anthropogenically elevated nutrient inputs, which led to eutrophication. Sediments in eutrophic systems are assumed to be an important internal nutrient source. The total phosphorus (TP) concentration (mg g-1 dry mass) is widely used as a proxy for the sediment nutrient load. 2-D distribution maps of TP concentrations are used for management plans, where areas of high TP values are marked in red. However, the sediment density is lowered at increasing water content, which can lead to different TP stocks per g m-2. The aim of this study was, to do a re-evaluation of TP concentrations and stocks in the model ecosystem of the Darß-Zingst Bodden chain, a typical lagoon system of the southern Baltic Sea. Sediment cores were taken at eight stations along transects from shallow to deeper parts of the lagoon. Samples were analyzed for TP, water and organic content, as well as density. This data set was compared to results from a sediment survey during the time of highest nutrient inputs (40 years ago) at the same sampling stations. TP concentrations from 40 years ago and today were in the same range. The highest TP concentrations (up to 0.6 mg TP g-1 dry mass) were found in the deeper basins and lowest concentrations in the shallow areas of the lagoon (down to 0.05 mg TP g-1 dry mass). However, normalization over dry bulk density (DBD) reversed some results. The highest TP stocks (up to 5 g TP m-2) were then found in the shallow areas and lowest stocks (down to 0.2 g TP m-2) in the deeper parts of the lagoon. Some stations did not exhibit any differences of TP at all, even after including the DBD. These findings suggest that there seems to be no up-, or downward trend in nutrient concentrations of sediments even after 25 years of reduced external nutrient inputs. Furthermore, TP stocks point to possible diffuse P entry pathways that counteract external nutrient reductions. These findings can have an impact on possible countermeasures for ecosystems rehabilitation, like sediment removal or nutrient reductions in the adjacent land

Spatial and temporal dynamics of water isotopes in the riverine‐marine mixing zone along the German Baltic Sea coast

River estuaries are characterized by mixing processes between freshwater discharge and marine water masses. Since the first are depleted in heavier stable isotopes compared with the marine realm, estuaries often show a linear correlation between salinity and water stable isotopes (δ18O and δ2H values). In this study, we evaluated spatial and seasonal isotope dynamics along three estuarine lagoon transects, located at the northern German Baltic Sea coast. The data show strong seasonality of isotope values, even at locations located furthest from the river mouths. They further reveal a positive and linear salinity‐isotope correlation in spring, but ‐in two of the three studied transects‐ hyperbolic and partially reverse correlations in summers. We conclude that additional hydrological processes partially overprint the two‐phase mixing correlation during summers: aside from the isotope seasonality of the riverine inflows, the shallow inner lagoons in the studied estuaries are influenced by evaporation processes. In contrast the estuarine outflow regions are under impact of significant salinity and isotope fluctuations of the Baltic Sea. Deciphering those processes is crucial for the understanding of water isotope and salinity dynamics. This is also of relevance in context of ecological studies, for example, when interpreting oxygen and hydrogen isotope data in aquatic organisms that depend on ambient estuarine waters.Spatial and seasonal water isotope dynamics were evaluated along three estuarine lagoon transects at the German Baltic Sea coast. Data reveal a positive and linear salinity‐isotope correlation in spring, but partially reverse correlations in summers. The results show that evaporation processes in the shallow inner lagoons and varying Baltic Sea influence in the outer estuary regions are able to overprint the two‐phase mixing correlation between riverine and marine water masses.Deutsche Forschungsgemeinschaft http://dx.doi.org/10.13039/501100001659https://doi.org/10.1594/PANGAEA.93799

New and Fast Method To Quantify Respiration Rates of Bacterial and Plankton Communities in Freshwater Ecosystems by Using Optical Oxygen Sensor Spots▿

A new method of respiration rate measurement based on oxygen luminescence quenching in sensor spots was evaluated for the first time for aquatic bacterial communities. The commonly used Winkler and Clark electrode methods to quantify oxygen concentration both require long incubation times, and the latter additionally causes signal drift due to oxygen consumption at the cathode. The sensor spots proved to be advantageous over those methods in terms of precise and quick oxygen measurements in natural bacterial communities, guaranteeing a respiration rate estimate during a time interval short enough to neglect variations in organism composition, abundance, and activity. Furthermore, no signal drift occurs during measurements, and respiration rate measurements are reliable even at low temperatures and low oxygen consumption rates. Both a natural bacterioplankton sample and a bacterial isolate from a eutrophic river were evaluated in order to optimize the new method for aquatic microorganisms. A minimum abundance of 2.2 × 106 respiring cells ml−1 of a bacterial isolate was sufficient to obtain a distinct oxygen depletion signal within 20 min at 20°C with the new oxygen sensor spot method. Thus, a culture of a bacterial isolate from a eutrophic river (OW 144; 20 × 106 respiring bacteria ml−1) decreased the oxygen saturation about 8% within 20 min. The natural bacterioplankton sample respired 2.8% from initially 94% oxygen-saturated water in 30 min. During the growth season in 2005, the planktonic community of a eutrophic river consumed between 0.7 and 15.6 μmol O2 liter−1 h−1. The contribution of bacterial respiration to the total plankton community oxygen consumption varied seasonally between 11 and 100%

Sediment, water and biomass characteristics along gradients in Kongsfjorden, Svalbard

In contrast to numerous studies on the biomass of marine microphytobenthos from temperate coastal ecosystems, little is known from polar regions. Therefore, microphytobenthos biomass was measured at several coastal sites in Arctic Kongsfjorden (Spitsbergen) during the polar summer (June-August 2006). On sandy sediments, chla varied between 8 and 200 mg/m**2 and was related to water depth, current/wave exposure and geographical location. Biomass was rather independent of abiotic parameters such as sediment properties, salinity, temperature or light availability. At three stations, sediments at water depths of 3-4, 10, 15, 20 and 30 m were investigated to evaluate the effect of light availability on microalgae. Significant differences in distribution patterns of biomass in relation to deeper waters >10 m were found. The productive periods were not as distinct as phytoplankton blooms. Only at 3-4 m water depth at all three stations were two- to threefold increases of biomass measured during the investigation period. Hydrodynamic conditions seemed to be the driving force for differences in sediment colonisation by benthic microalgae. In spite of the extreme Arctic environmental conditions for algal growth, microphytobenthos biomass was comparable to marine temperate waters