Per Roos

Colloid dynamics and transport of major elements through a boreal river — brackish bay mixing zone

Abstract A range of biogeochemical methodologies were applied to investigate how aggregation processes affected the phase distribution and mixing of Fe, Si, and organic carbon between the Kalix River and the Bothnic Bay, northernmost Baltic Sea (salinity≤3; the low-salinity zone (LSZ) was stretching over 60 km in the spring). During the dynamic springflood conditions studied, small 238 U– 234 Th disequilibria, low sediment trap fluxes, laboratory mixing experiments, as well as results from an independent two-box, two-dimensional mixing model combine to suggest that no significant removal of Fe, Si, or organic C was occurring in the highly-resolved LSZ. While no conclusions may be drawn based solely on property–salinity plots over narrow salinity ranges, apparently linear graphs for Fe and Si over 3 separate years also suggest minimal removal in this regime. At the same time, size distributions both of elements —from cross-flow ultrafiltration — and of bulk suspended solids — from light scattering (photon correlation spectroscopy [PCS]) — indicated that significant aggregation was taking place. The aggregation-without-significant-settling scenario in this low-salinity mixing regime, with a geochemistry similar to that of neighboring Russian Arctic rivers, is hypothesized to result from a comparatively high organic-to-detrital matter characteristic of the aggregates. While first principles would indeed suggest that decreasing electrostatic repulsion during mixing lead to aggregation, a low specific density of mineral-poor amorphous organic aggregates may lead to transport of these authigenic particles further away from the river mouth. The role of detrital “sinkers” on vertical removal of suspended organic matter is discussed in the wider context of scavenging mechanisms in the ocean.

Climate, hydrographic variations and marine benthic hypoxia in Koljö Fjord, Sweden

Abstract Since the late 1970s, Scandinavian waters have been extensively investigated for human-induced marine pollution, especially marine eutrophication, oxygen deficiency in bottom waters and subsequent benthic mortality. The most serious oxygen deficiencies are noted in the sill fjords along the Swedish west coast, in southern Norway and in large areas of the southern Kattegat and Baltic Sea. One of these sill fjords, Koljo Fjord, is located on the Swedish west coast. This fjord is characterised by frequently occurring episodes of hypoxia/anoxia which last for months or even years. Sediments are laminated and the fjord is generally regarded as seriously affected by human-induced eutrophication. We detail the environmental development of a well-documented fjord by combining high resolution sediment records with long hydrographical and meteorological instrumental data, and we present ultra high-resolution sediment information together with long-term instrumental records of air-temperatures, NAO indices and hydrography from Koljo Fjord. These data show, in contrast to the current opinion focusing on anthropogenic eutrophication, that natural causes are the most important factors controlling the marine environment in this sparsely populated area. Natural variables concerned are fjord physiography, weather and hydrography (including the macro-nutrients DIN and PO 4 -P), sediment laminations and organic carbon. Interactions between fjord physiography, weather and hydrography regulate the possibility for water exchange and deep-water renewals. The present study points to the importance of natural causes for the environmental status of sill basins and semi-enclosed areas along the west coast of Sweden.

Deposition of 210Pb, 137Cs, 239+240Pu, 238Pu, and 241Am in the Antarctic Peninsula area

210Pb, 137Cs, 239+240Pu, 238Pu, and 241Am were analysed in lichen, moss, grass and soil samples, as well as in lake sediments, from the South Shetland Islands, the Antarctic, in order to evaluate the flux and deposition of these elements. Average inventories of the analysed radionuclides in 1988 were 210Pb (excess): 280±110 Bqm−2 (n = 15),137Cs: 155±95 Bqm−2 (n = 19), 239+240Pu: 4·6±2·6 Bqm−2 (n = 19), 238Pu: 0·95±0·5 Bqm−2 (n = 19) and241Am: 1·6±1·0 Bqmsu−2 (n = 19). From the maximum value of unsupported 210Pb the annual deposition is determined to be 18±5 Bqm−2. The ratios 238Pu/239+240Pu and241Am/239+240Pu of 0·21±0·04 and 0·35±0·08 respectively agree well with expected values in this area. A significant difference in 137Cs/239+240Pu ratios between lichens and moss/grass/soil is observed which may be an effect of submerging and melt water altering radio-nuclide ratios. From one of three lakes studied it is possible to perfom 210Pb dating with reasonably accuracy showing an average annual sediment accumulation in this lake of about 45 gm−2.

Long-term study of 99Tc in the marine environment on the Swedish west coast

The activity concentration of (99)Tc in brown seaweed (Fucus vesiculosus and Fucus serratus) and seawater were analysed in samples collected in 1991, 1995 and 2001 at several stations along the Swedish west coast. In addition to these locations, a well-defined site (Särdal, 56.76 degrees N, 12.63 degrees E) was included with (99)Tc activity concentration data in seaweed from 1967 to 2000. Over the years, the major source of (99)Tc in the coastal waters of western Sweden has been the radioactive liquid discharge from the nuclear fuel reprocessing plant in Sellafield (UK) transported via ocean currents in the North Sea. The (99)Tc activity concentration in seaweed at the Särdal site increased from approximately 30 Bq kg(-1) up to 230 Bq kg(-1) (dry weight) between 1997 and 2000 due to the Sellafield EARP (Enhanced Actinide Removal Plant) discharges in 1995-1996, yielding an approximate transport time of 4-5 years between the Irish Sea and the Kattegat. Due to the very sharp gradient in (99)Tc concentration between the Baltic Sea and the North Sea, (99)Tc is presently one of the best transit tracers for the recent ventilation events in the Baltic Sea.

In situ sorption of technetium using activated carbon

The sorption of technetium in pertechnetate form on carbon has been investigated. The sorption is pH dependent with maximal distribution coefficients, Kd, in the order of 10(6) at pH 2-4 for activated carbon with a grain size < or = 100 microm. The equilibrium time to reach such distribution coefficient was about 5 h at room temperature. The exact mechanisms for the sorption are not fully understood but reduction of Tc by the carbon might be an important process. Technetium can effectively and rapidly (5 l min(-1)) be sorbed from very large volumes (several hundred liters) of environmental waters on commercial cartridge filters impregnated with activated carbon. After incineration, the filters can be analyzed for 99Tc by conventional methods.

Radiocaesium and Plutonium in Atlantic Surface Waters from 73 °N to 72 °S

During the recent Swedish Antarctic research Expedition (SWEDARP 89/89) samples of surface sea water were collected on board the Stena Arctica during steaming between Gothenburg, Sweden and the Antarctic Peninsula. Radio chemical separation was performed for radio caesium on 200 l samples and for plutonium on samples between 200 and 1500 1. The results are compared with those of the GEOSECS expedition in the North and South Atlantic in 1972–73 and the Polish expedition in 1977–78. They show that radio caesium has behaved rather conservatively and that the decrease in surface water concentrations during 16 years mainly is due to physical decay. On the other hand levels of 239+240Pu have decreased by a factor of 4–5 giving a half life of 7–8 years in open Atlantic surface waters.

Radionuclide fluxes at a plant manufacturing dicalcium phosphate for domestic animals.

We have studied a phosphate rock plant which produces dicalcium phosphate (DCP), used as a source of calcium and phosphorus for domestic animals. A by-product in the manufacturing process is calcium chloride which is used in the oil industry, the food industry and as road-salt. The objectives of our study were to describe the fluxes of radionuclides from the 238U decay series and to estimate the radiation doses to workers at the plant. The radionuclides in the phosphate rock were found to be in secular radioactive equilibrium with 238U, with an average activity concentration of 837 Bq kg-1. Separation and concentration processes were observed at different stages in the plant. Most of the 226Ra was found in the calcium chloride, while the major part of the 238U, about 950 Bq kg-1, was found in the dicalcium phosphate. The annual occupational effective dose to the workers was found to be below the 1 mSv limit recommended by ICRP (1991a) for the public. This study has shown a good example of an important non-nuclear industry with a high input of natural radionuclides with several conceivable pathways to man.

Early diagenesis and isotopic composition of lead in Lake Laisan, northern Sweden

Water column (dissolved/suspended phase, sediment traps) and sediment data (pore-water, solid-phase sediment) were combined with stable Pb and Pb-210 isotope data to trace the early diagenetic behaviour and geochemical cycling of Pb in Lake Laisan, a lake which has received large quantities of anthropogenic Pb since the early 1940s. Early diagenetic remobilisation of Pb is indicated by a subsurface pore-water Pb maximum (120 mug 1(-1)) in the oxic surface layer of the sediment, where the solid-phase Pb concentration is 3400-4600 mug g(-1). The remobilisation of Pb appears to be caused by a pH-controlled desorption of Pb from solid-phase sediment, which is consistent with a model describing surface complexation of Pb(II) on hydrous goethite surfaces. The diffusive Pb flux from the subsurface pore-water maximum towards the sediment surface (36 mug cm(-2) year(-1)) exceeds the depositional Pb flux (8.6 mug cm(-2) year(-1)) by approximately a factor of four, indicating that Pb is highly mobile in the sediment. Stable Pb isotope data and a mass balance calculation suggest that Pb diffusing upwards is, to a large extent, trapped in the surface sediment. Lead that may diffuse into the slightly alkaline lake water appears to be efficiently sorbed to suspended particulate matter, resulting in low dissolved Pb concentrations in the water column (0.040-0.046 mug 1(-1)). Sorption of Pb to suspended particulate matter is consistent with the elevated suspended particulate Pb concentrations in the hypolimnion (3800-4000 mug g(-1)), and the fact that the stable Pb isotopic compositions of suspended matter and pore-water are similar. (Less)

Analysis of radionuclides using ICP-MS

Publisher Summary This chapter analyzes radionuclides using inductively coupled plasma mass spectrometry (ICP-MS). The inductively coupled plasma (ICP) ion source has successfully been interfaced to most mass analyzers such as the linear quadrupole, time of flight (TOF), Fourier transform ion cyclotron resonance (FTICR) and the electric/magnetic sector. Quadrupole mass analyzers are widely used because of their good sensitivity, wide dynamic range, robustness and relatively low cost. The different ways in which these interferences are minimized has been by using high-resolution (magnetic sector) instruments, matrix separation techniques, cold plasma and more recently by collision and/or reaction cells. The use of matrix separation in connection with radiometric measurement techniques requiring alpha or beta counting is well developed within the radioanalytical sciences. Because of the enormous specificity of the reaction gases with certain ions and the large number of different reaction gases combined with a comprehensive knowledge on these reactions the use of reaction cells to remove most kind of interfering ions seems at a first glimpse very attractive.

Distribution of Plutonium and its oxidation states in Framvaren and Hellvik fjords, Norway

Waters from the Skagerrak Sea entering the system of fjords inside Farsund in the southern tip of Norway (including Lyngsdal, Hellvik and Framvaren fjords) contain plutonium derived from European nuclear fuel reprocessing facilities in the United Kingdom and France, as shown by the 238Pu/239,240Pu activity ratios measured for water samples from Hellvik and Framvaren fjords. The shallow sills interconnecting this series of fjords, however, severely restrict water exchange. Thus, at the northernmost Framvaren fjord (connected to Hellvik fjord by a 500-m channel of 2 m depth), the 238Pu/239,240Pu signature for Pu derived from fuel reprocessing is found only in the surface layer (upper 20 m) while global fallout Pu ratios are observed in the permanently anoxic zone of this fjord. Plutonium oxidation state measurements in waters collected from Hellvikkand Framvaren fjords show that water exchange occurs between these two basins by a process of interleaving, with subsequent reduction of oxidized Pu species as these reach the anoxic zone. Plutonium serves as a useful tracer for water exchange between these fjords and the Skagerrak Sea.