Levels and patterns of polychlorinated dibenzo-p-dioxins, dibenzofurans and biphenyls in surface sediments from the western Baltic Sea (Arkona Basin) and the Oder River estuarine system

Surface sediment samples were collected from the western Baltic Sea (Arkona Basin) and the Oder River estuarine system in May and August 1995 and analysed for polychlorinated dibenzo-p-dioxins, dibenzofurans and biphenyls. Contents of PCDF (sum) and PCDD (sum) varied from 2.5 to 820.0 pg g⁻¹ dw and from 12.7 to 2991.0 pg g⁻¹ dw, respectively. PCB contents (sum of 23 congeners) ranged between < 130.0 and 16267.0 pg g⁻¹ dw. Only slight variations in PCDF/D and PCB contents on dry weight basis were found between the Oder River estuarine system and the open Baltic Sea. TOC-normalization of the data showed an approximately homogen PCDF/D distribution in the study area. The distribution pattern for PCDF/D and PCB may be attributed to high sediment dynamics combined with transport processes from the temporary sedimentation basin (Oderhaff) to the deeper parts of the Baltic Sea.     

Directional interpolation of multicomponent data

A method for interpolation of multicomponent streamer data based on using the local directionality structure is presented. The derivative components are used to estimate a vector field that locally describes the direction with the least variability. Given this vector field, the interpolation can be phrased in terms of the solution of a partial differential equation that describes how energy is transported between regions of missing data. The approach can be efficiently implemented using readily available routines for computer graphics. The method is robust to noise in the measurements and particularly towards high levels of low‐frequent noise that is present in the derivative components of the multicomponent streamer data.     

Fish assemblages in Tanzanian mangrove creek systems influenced by solar salt farm constructions

Deforestation of mangrove forests is common occurrence worldwide. We examined fish assemblage composition in three mangrove creek systems in Tanzania (East Africa), including two creeks where the upper parts were partly clear-cut of mangrove forest due to the construction of solar salt farms, and one creek with undisturbed mangrove forest. Fish were caught monthly for one year using a seine net (each haul covering 170 m²) within three locations in each creek, i.e. at the upper, intermediate and lower reaches. Density, biomass and species number of fish were lower in the upper deforested sites compared to the mangrove-fringed sites at the intermediate and lower parts in the two creeks affected by deforestation, whereas there were no differences among the three sites in the undisturbed mangrove creek system. In addition, multivariate analyses showed that the structure of fish assemblages varied between forested and clear-cut sites within the two disturbed creeks, but not within the undisturbed creek. Across the season, we found no significant differences except for a tendency of a minor increase in fish densities during the rainy season. At least 75% of the fishes were juveniles and of commercial interest for coastal fisheries and/or aquaculture. Mugil cephalus, Gerres oyena and Chanos chanos were the most abundant species in the forested sites. The dominant species in the clear-cut areas were M. cephalus and Elops machnata, which were both found in relatively low abundances compared to the undisturbed areas. The conversion of mangrove forests into solar salt farms not only altered fish assemblage composition, but also water and sediment conditions. In comparison with undisturbed areas, the clear-cut sites showed higher salinity, water temperature as well as organic matter and chlorophyll a in the sediments. Our results suggest that mangrove habitat loss and changes in environmental conditions caused by salt farm developments will decrease fish densities, biomass and species numbers as well as alter the overall fish assemblage composition in the salt farm area but not downstream in the creek.     

Modelling the dynamics of superfluid neutron stars

In this brief summary I describe our recent work on superfluid neutron star dynamics. I review results on shear viscosity, hyperon bulk viscosity, vortex mediated mutual friction and the modelling of multifluid systems in general. For each problem I provide a set of questions that need to be addressed by future work.     

Colloidal rare earth elements in a boreal river: Changing sources and distributions during the spring flood

Variations in the physico-chemical speciation of the rare earth elements (REE) have been investigated in a subarctic boreal river during an intense spring flood event using prefiltered (<100 μm) samples, cross-flow (ultra)filtration (CFF), flow field-flow fractionation (FlFFF), and diffusive gradients in thin films (DGT). This combination of techniques has provided new information regarding the release and transport of the REE in river water. The colloidal material can be described in terms of two fractions dominated by carbon and iron, respectively. These two fractions, termed colloidal carrier phases, showed significant temporal changes in concentration and size distribution. Before the spring flood, colloidal carbon concentrations were low, the colloids being dominated by relatively large iron colloids. Colloidal concentrations increased sharply during the spring flood, with smaller carbon colloids dominating. Following the spring flood, colloidal concentrations decreased again, smaller carbon colloids still dominating. The REE are transported mainly in the particulate and colloidal phases. Before the spring flood, the REE composition of all measured fractions was similar to local till. During the spring flood, the REE concentrations in the colloidal and particulate fractions increased. The increase was most marked for the lighter REE, which therefore showed a strong enrichment when normalized to local till. Following the spring flood, the REE concentrations decreased again and reverted to a distribution similar to local till. These changes in the concentration and distributions of carbon iron and REE are interpreted in terms of changing hydrological flow paths in soil and bedrock which occur during the spring flood.     

A search for millimeter-wave emission from HCN and other molecules in Comet Bradfield (1979l)

Millimeter-wave emission from HCN, CS, CH₃OH, and two unidentified lines (previously observed in Comet Kohoutek (1973 XII)) was sought and not detected from Comet Bradfield (1979l) after perihelion passage. Limits on column densities and production rates are derived. In the case of HCN, the production rate is less than that reported for Comet Kohoutek, even after scaling relative to the observed OH emission from each comet.     

Seasonal changes in the distribution and exchange of inorganic nitrogen between sediment and water in the Northern Baltic (Gulf of Bothnia)

The concentration profiles of nitrate plus nitrite, ammonium, and redox potential in sediment and water column were determined in late winter and summer at a sampling site off Norrbyn, northern Sweden, in the Gulf of Bothnia. The sediment had an oxidized surface layer during winter and spring, and nitrification occurred. Nitrate but not ammonium was present in the water column at this time. During summer a layer of planktonic detritus was deposited onto the sediment and led to its deoxygenation and reduction. Ammonium was then the predominant form of inorganic nitrogen in the water column.Laboratory experiments confirmed that nitrification in the surface layer of sediment prevented ammonium export during winter. Enhanced temperature or organic detritus deoxygenated the surface sediment and inhibited nitrification, and export of ammonium from the sediment increased. Although nitrification was important in determining the flow of nitrogen in the sediment it accounted for at most only 5% of the total oxygen uptake by the sediment.     

The impact of musk ketone on reproduction in zebrafish (Danio rerio).

Nitro musks are a group of nitrated benzenes mainly used by the fragrance industry as a substitute for natural musk. Two of the most common nitro musks, musk xylene and musk ketone, have been detected in water, fish, human adipose tissue, as well as in human breast milk. In this study, female zebrafish were dietary-exposed to musk ketone, prior to spawning with unexposed males. The fish were exposed for 8 weeks at two different dose levels. Accumulation of the compound in the fish as well as reproductive success were studied. Exposed females had reduced body weight and length, as well as reduced liver- and gonad somatic index. The results from the reproduction study showed a dose-dependent reduction in fecundity. Early life-stage mortality was increased and the median survival time was reduced. In addition, an embryo/larvae toxicity test was performed, using newly fertilized zebrafish eggs from unexposed parental fish. Eggs were exposed to a series of different concentrations of musk ketone via the surrounding water. A NOEC value of 10 micrograms/l and a LOEC value of 33 micrograms/l was determined. Conclusively, the present study clearly shows that musk ketone negatively affects reproduction and early life-stage survival in zebrafish.