Remedial measures against radioactive Caesium in Swedish lake fish after Chernobyl

The aim of this work is to give a summary of the work on Cs-137 in Swedish lakes carried out mainly by our group (the Liming-mercury-caesium project) between 1986 and 1990. The focus is on results from extensive field experiments carried out in 41 lakes testing various remedial measures to speed up the natural recovery of Cs-137 in lakes: Lake liming and wet land liming with primary rock lime, sedimentary rock lime and so-called mixed lime, which also contains nutrients; potash treatment and intensive fishing. Selected results: The remedies have given the intended water-chemical response. None of the methods used works effectively as cure, i.e., no rapid and clear reduction in the concentrations of radioactive caesium in fish is obtained in comparison with lakes where the waterchemical or biological conditions are not changed. In lakes with long water turnover time and with low values of, foremost, conductivity, hardness and potassium, the fish had relatively higher concentrations at the same fallout levels. The differences present between the lakes as regards the continued magnitude of the change in concentration in fish can foremost be linked to factors controlling the secondary load (i.e., the internal loading and the input from the catchment). A successful potash treatment (in oligotrophic lakes) may imply that the natural recovery will be at the most 5% faster compared to no treatment. This would give quite positive implications in the long run since the ecological half-life for Cs-137 in pike (the top predator in these lake types) is very long. The time interval between the remedies and the latest fish analyses (about 2 years on average) is not sufficient to obtain (statistically) clear-cut results on these the small effects of the remedies. A longer time series of data is required for this.     

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.     

Evolution of In Situ Rock Mass Damage Induced by Mechanical–Thermal Loading

To understand and predict the in situ brittle rock mass damage process induced by a coupled thermo-mechanical loading, the knowledge of rock mass yielding strength, scaling relationship between laboratory and in situ and microstructure characterization is required. Difficulties have been recognized due to the seldom availability of in situ experiment and appropriate numerical methodologies. The Äspö Pillar Stability Experiment was used to monitor the evolution of rock mass damage in a pillar of rock separating two 1.75-m diameter vertical boreholes. The loading of the pillar was controlled using the in situ stresses, excavation geometry, and locally increasing the rock temperature. The induced loading resulted in a complex discontinuum process that involved fracture initiation, propagation, interaction and buckling, all dominated by a tensile mechanism. Tracking this damage process was carried out in two steps. Initially, a three-dimensional numerical model was used to generate the stresses from the excavation geometry and thermal loading. The plane strain stresses, at selected locations where detailed displacement monitoring was available, were then used to track the evolution of damage caused by these induced stresses. The grain-based discrete element modeling approach described in Lan et al. (2010), which captures the grain scale heterogeneity of the rock, was used to establish the extent of damage. Good agreement was found between the predicted and measured temperatures and displacements. The grain-based model provided new insights into the progressive failure process.     

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.     

Developmental disorders in larvae of eelpout (Zoarces viviparus) from German and Swedish Baltic coastal waters

Pregnant eelpout were collected for several years at German and Swedish Baltic coastal stations with different impact of pollutants and the prevalence of fry abnormalities compared between sites. Mortality of apparently normal developed larvae was observed with high variability in both German and Swedish sites. Malformation of larvae was a prominent disorder at all German stations with a prevalence ranging from about 50% up to a maximum of 90% in almost all analysed samples. At the Swedish stations malformation rates were significantly lower (range: 0-6%). Growth retardation of fry was clearly more prominent in eelpout from German coastal waters as well. Taken together the field data suggests that impaired larval development was associated with the state of environmental pollution at the sampling locations.     

Temporal Changes in Seawater Carbonate Chemistry and Carbon Export from a Southern California Estuary

Estuaries are important subcomponents of the coastal ocean, but knowledge about the temporal and spatial variability of their carbonate chemistry, as well as their contribution to coastal and global carbon fluxes, are limited. In the present study, we measured the temporal and spatial variability of biogeochemical parameters in a saltmarsh estuary in Southern California, the San Dieguito Lagoon (SDL). We also estimated the flux of dissolved inorganic carbon (DIC) and total organic carbon (TOC) to the adjacent coastal ocean over diel and seasonal timescales. The combined net flux of DIC and TOC (F_DIC?+?TOC) to the ocean during outgoing tides ranged from ??1.8±0.5?×?10³ to 9.5±0.7?×?10³?mol C h^?1 during baseline conditions. Based on these fluxes, a rough estimate of the net annual export of DIC and TOC totaled 10±4?×?10⁶?mol C year^?1. Following a major rain event (36 mm rain in 3 days), F_DIC?+?TOC increased and reached values as high as 29.0 ±?0.7?×?10³?mol C h^?1. Assuming a hypothetical scenario of three similar storm events in a year, our annual net flux estimate more than doubled to 25 ±?4?×?10⁶?mol C year^?1. These findings highlight the importance of assessing coastal carbon fluxes on different timescales and incorporating event scale variations in these assessments. Furthermore, for most of the observations elevated levels of total alkalinity (TA) and pH were observed at the estuary mouth relative to the coastal ocean. This suggests that SDL partly buffers against acidification of adjacent coastal surface waters, although the spatial extent of this buffering is likely small.     

Thallium isotope composition of the upper continental crust and rivers—An investigation of the continental sources of dissolved marine thallium

The thallium (Tl) concentrations and isotope compositions of various river and estuarine waters, suspended riverine particulates and loess have been determined. These data are used to evaluate whether weathering reactions are associated with significant Tl isotope fractionation and to estimate the average Tl isotope composition of the upper continental crust as well as the mean Tl concentration and isotope composition of river water. Such parameters provide key constraints on the dissolved Tl fluxes to the oceans from rivers and mineral aerosols.The Tl isotope data for loess and suspended riverine detritus are relatively uniform with a mean of ε²⁰⁵Tl = −2.0 ± 0.3 (ε²⁰⁵Tl represents the deviation of the ²⁰⁵Tl/²⁰³Tl isotope ratio of a sample from NIST SRM 997 Tl in parts per 10⁴). For waters from four major and eight smaller rivers, the majority were found to have Tl concentrations between 1 and 7 ng/kg. Most have Tl isotope compositions very similar (within ±1.5 ε²⁰⁵Tl) to that deduced for the upper continental crust, which indicates that no significant Tl isotope fractionation occurs during weathering. Based on these results, it is estimated that rivers have a mean natural Tl concentration and isotope composition of 6 ± 4 ng/kg and ε²⁰⁵Tl = −2.5 ± 1.0, respectively.In the Amazon estuary, both additions and losses of Tl were observed, and these correlate with variations in Fe and Mn contents. The changes in Tl concentrations have much lower amplitudes, however, and are not associated with significant Tl isotope effects. In the Kalix estuary, the Tl concentrations and isotope compositions can be explained by two-component mixing between river water and a high-salinity end member that is enriched in Tl relative to seawater. These results indicate that Tl can display variable behavior in estuarine systems but large additions and losses of Tl were not observed in the present study.