Iron–manganese concretions contribute to benthic release of phosphorus and arsenic in anoxic conditions in the Baltic Sea

Purpose

Deposits of iron–manganese (Fe, Mn) concretions forming a large storage of phosphorus (P) and arsenic (As) are frequently under pressure of oscillating oxygen conditions in the eutrophic Gulf of Finland, the Baltic Sea. Yet, there is a poor understanding how anaerobic microbial processes regulate the cycling of elements in the concretions. The objective of this study was to highlight how the microbial processes control the release of elements from the concretions to brackish water during anoxia.

Materials and methods

Spherical concretions were collected from the oxic bottoms of the Gulf of Finland in the summer. Concretions and autoclaved controls were incubated in anoxic artificial brackish seawater with and without labile carbon, plus supplied with ammonium at 5, 10, and 20 °C for 15 weeks. Concentrations of Fe, Mn, P, and As were measured from the intact concretions and the ambient solutions during the experiment. Also, the consumption of the added ammonium and organic carbon and the formation of dissolved inorganic carbon were measured.

Results and discussion

At near-bottom temperature 5 °C, the concretions released at highest 0.12, 0.42, 0.02, and 0.0002 μmol g^?1 day^?1 of Fe, Mn, P, and As, respectively. The rates were significant only in the microcosms with added labile carbon, and only minor proportions (0.1–0.4 %) of their total contents were released during the incubations. The concretions removed completely the supplied ammonium only without carbon addition. We find that concretion deposit may form a local hot spot for the microbial reduction of Fe and Mn and release significant amounts of P and As, and participate in N cycling besides the bottom sediments of the Gulf of Finland during prolonged anoxia. However, the concretions may maintain their binding capacity for P and As longer than the fine-grained organic-rich sediment during anoxia.

Conclusions

During anoxia concretion deposits may form a temporal source of bioavailable P having ecological significance in the Gulf of Finland when concretions have access to labile organic carbon. Concretions from the Baltic Sea, the oceans, lakes, and soils contain high concentrations of Mn and Fe, but their proportions vary considerably. Anaerobic microbial processes may thus affect the stability of concretions from the different environments, but the outcome may depend on the ambient geochemical conditions.

     

Water activity-temperature state diagram of amorphous lactose

Development in the glass transition temperature, Tg, to reach a stabilized value for amorphous lactose stored at 5, 25, and 38 degrees C at different water activities varying from aw = 0.21 to 0.59 was followed by differential scanning calorimetry. Combinations of stabilized Tg and water activity were used for interpolation of the value of water activity, where Tg was equal to the storage temperature. These values of water activity were used to construct a state diagram in the (aw,T)-plane for lactose in the amorphous state from which critical combinations of water activity and storage temperature may be obtained for optimization of storage conditions of lactose-based dry products.     

Comment on "Saturation of the southern ocean CO2 sink due to recent climate change"

Unlike Le Quéré et al. (Reports, 22 June 2007, p. 1735), we do not find a saturating Southern Ocean carbon sink due to recent climate change. In our ocean model, observed wind forcing causes reduced carbon uptake, but heat and freshwater flux forcing cause increased uptake. Our inversions of atmospheric carbon dioxide show that the Southern Ocean sink trend is dependent on network choice.     

Two-dimensional single strand conformation polymorphism (SSCP) of 16S rRNA gene fragments reveals highly dissimilar bacterial communities in an acidic fen

Genetic fingerprinting methods such as denaturing gradient gel electrophoresis (DGGE) and single strand conformation polymorphism (SSCP) are only able to separate about 20–40 well-distinguishable bands (signals) within each sample. As a result, the diversity of 16S rRNA genes within biological samples may be underestimated, because multiple sequences can migrate at the same rate to form a single band. This study reports a two-dimensional SSCP fingerprinting method that has the capability to resolve hundreds of signals in a single fingerprint by using different gel temperatures in the two dimensions of the separation (20 °C and 30 °C, respectively). Unlike previous two-dimensional approaches, the method presented in this study does not rely on DNA products of variable lengths but is able to separate 16S rRNA gene fragments of the same length. To demonstrate the effectiveness of this new method, DNA samples from oxic and anoxic zones of an acidic fen were examined. Whereas one-dimensional SSCP fingerprints indicated high similarity (>93%) between 16S rRNA gene fragments from oxic and anoxic zones of the fen, the two-dimensional SSCP approach virtually found no similarities.     

Health in fishing communities: A global perspective

In resource‐dependent communities such as fishing communities, human health underpins the ability of individuals and families to maintain viable livelihoods. Fishing is a dangerous occupation, in which fishers are exposed to health risks both on and offshore. Many of these risks and associated health concerns also extend to fishing families and wider communities. Despite the importance of health, there is a lack of understanding of the breadth of health issues affecting people associated with fishing. This study presents the findings of a scoping review of peer‐reviewed literature that identifies the range of health issues and health determinants studied in fishing communities around the world. The findings reveal a wide variety of documented health issues, but with greater emphasis on physical health and occupational and behavioral factors, with limited attention paid to mental health. The majority of studies focused on fishers themselves, as opposed to other subgroups within fishing communities. Geographic differences in the health topics investigated highlight prevalent concerns and offer potential to share insights and solutions across contexts. The breadth of findings illustrates the complexity of health for people dependent on fishing, and the relevance of the many health determinants in maintaining viable fishing communities. We propose that a social well‐being approach offers an integrative lens through which a better understanding of human health in fisheries can be achieved and used to inform fisheries management that is ecologically and socially sustainable.     

Substantial advancement in aquaria rearing methods to assist recovery of an Endangered soft coral

1. The temperate soft coral Dendronephthya australis has been listed as Endangered in NSW, Australia, owing to its restricted geographic range, rapidly declining populations, and a number of escalating threats. Research to assess practical methods for aquarium cultivation of D. australis for rehabilitation of wild populations is considered a high priority.
2. Previous attempts at restoration by transplanting D. australis fragments have had limited success, but identified key challenges, which included achieving attachment to substrates and identifying appropriate foods to maximize survival.
3. This study presents the results of experiments promoting the attachment of cuttings (nubbins) removed from donor colonies to moveable substrates (small concrete discs). Using a balanced orthogonal experimental design, three feeding regimes were tested: live artemia, live rotifers and dry powdered zooplankton.
4. Donor colony survival and growth were also monitored over a 6 month period in the field.
5. An overall nubbin survival rate of 100% was achieved under all three feeding regimes. Attachment rates were similar across feeding treatments, although nubbin behavioural responses (percentage of open polyps before feeding) suggested some preference for live rotifers.
6. The cutting removal process had no significant effect on donor colonies in the wild, indicating that this is a sustainable approach for restoration.
7. Overall, this study substantially advances the methodology for maintaining an Endangered azooxanthellate soft coral in aquaria and provides valuable input for management programmes aimed at implementing transplantation into the wild to aid species recovery.