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Radionuclides in the Baltic Sea: Ecosystem models and experiments on transport and fate
Stockholm University, Faculty of Science, Department of Systems Ecology.
2004 (English)Doctoral thesis, comprehensive summary (Other academic)
Abstract [en]

Manmade radionuclides have been introduced to the environment for almost a century. The main source has been the nuclear weapons testing programmes, but accidental releases from the nuclear power production industries have also contributed. The risk to humans from potential releases from nuclear facilities is evaluated in safety assessments. Essential components of these assessments are exposure models, which estimate the transport of radionuclides in the environment, the uptake in biota, and transfer to humans. Recently, there has been a growing concern for radiological protection of the whole environment, not only humans, and a first attempt has been to employ model approaches based on stylised environments and transfer functions to biota based exclusively on bioconcentration factors. They are generally of a non-mechanistic nature and involve no knowledge of the actual processes involved, which is a severe limitation when assessing real ecosystems.

The research presented in this thesis attempts to introduce a methodology for modelling exposure of biota that is based on systems ecological theories and concepts. All presented papers concern bioaccumulation and circulation of radionuclides in coastal areas of the Baltic Sea, which is a sea surrounded by several nuclear power plants, waste repositories and reprocessing facilities. Paper I illustrates how an ecosystem model can be used to predict the fate of C-14 in a bay, and to explore the influence of uptake route and water exchange on the concentrations in biota. Due to the longevity of many radionuclides, time spans of thousands of years need to be considered in assessments of nuclear waste facilities. In Paper II, the methodological problems associated with these long timescales are discussed and a new modelling approach is proposed. An extension and generalisation of the C-14 flow model into a generic model for other radionuclides is described and tested in Paper III. This paper also explores the importance of three radionuclide specific mechanisms (plant uptake, excretion and adsorption to organic surfaces) for the concentrations in biota. In Paper IV, the bioaccumulation kinetics of three radionuclides in three key benthic species of the Baltic Sea is studied experimentally. Paper V considers remobilisation and redistribution of sediment-associated radionuclides due to biological mixing, in a microcosm study.

The findings in this thesis show both that it was possible to use an ecosystem approach to assess the exposure to biota, and that this approach can handle many of the problems identified in the use of traditional exposure models for radionuclides. To conclude, frameworks for the protection of the environment from ionising radiation would benefit from implementing methodologies based on ecologically sound principles and modelling techniques.

Place, publisher, year, edition, pages
Stockholm: Institutionen för systemekologi , 2004. , 150 p.
Keyword [en]
radionuclide, baltic sea, ecosystem model, ecosystem dynamics, risk assessment, safety assessment, benthic invertebrates, bioturbation, bioaccumulation, remobilisation
National Category
Ecology
Identifiers
URN: urn:nbn:se:su:diva-175ISBN: 91-7265-891-6 (print)OAI: oai:DiVA.org:su-175DiVA: diva2:190519
Public defence
2004-06-04, Nordenskiöldsalen, Geovetenskapens hus, Svante Arrhenius väg 8 C, Stockholm, 13:00 (English)
Opponent
Supervisors
Available from: 2004-05-13 Created: 2004-05-13 Last updated: 2009-04-22Bibliographically approved
List of papers
1. An ecosystem model of the environmental transport and fate of carbon-14 in a bay of the Baltic Sea
Open this publication in new window or tab >>An ecosystem model of the environmental transport and fate of carbon-14 in a bay of the Baltic Sea
2003 (English)In: Ecological Modelling, ISSN 0304-3800, Vol. 166, no 3, 193-210 p.Article in journal (Refereed) Published
Abstract [en]

The environmental transport and fate of a hypothetical discharge of radioactive 14C from the Swedish final repository for radioactive operational waste (SFR) was investigated using an ecosystem modelling approach. It involved identification, quantification and dynamic modelling of the main flows and storages of carbon both in the physical environment and in the food web of a bay in the Baltic Sea. In the model, 14C was introduced into the food web via photosynthesising organisms. Contamination of the modelled ecosystem was assessed assuming a release of 51.3 MBq per year for 1000 years. The implications of changes of two parameters on the 14C fate were examined: route of 14C entry in the food web and water exchange. Modelling results were also used to estimate steady-state 14C-concentrations in biota, to investigate the time needed to reach steady-state and to calculate the ecological half-life of the radionuclide for the modelled compartments and the ecosystem. Since the modelled area is characterised by a fast water exchange, most of the discharged 14C was flushed out of the system (99.8%), and diluted in a much larger recipient. However, a small fraction of the discharge was assimilated by primary producers, which enabled subsequent transfer of 14C to organisms at higher trophic levels (e.g. fish, seals and humans). In general, the highest 14C-concentrations were observed in benthic plants and benthic macrograzers followed by fish and other organisms. An assumption of 14C entry into the food web via benthic primary producers was found to lead to increased concentrations in biota (especially benthic organisms) and reduced rates of water exchange were also observed to significantly increase the 14C exposure of the organisms.

Place, publisher, year, edition, pages
Elsevier, 2003
Keyword
Ecosystem dynamics; Ecosystem modelling; Carbon flow model; 14C; Radionuclides; Safety assessment; Baltic Sea; MATLAB/SIMULINK Article Outline
National Category
Biological Sciences
Identifiers
urn:nbn:se:su:diva-23174 (URN)10.1016/S0304-3800(03)00135-2 (DOI)
Note
Part of urn:nbn:se:su:diva-175Available from: 2004-05-13 Created: 2004-05-13 Last updated: 2009-12-28Bibliographically approved
2. Effects of land-rise on the development of a coastal ecosystem of the Baltic Sea and its implications for the long-term fate of C-14 discharges
Open this publication in new window or tab >>Effects of land-rise on the development of a coastal ecosystem of the Baltic Sea and its implications for the long-term fate of C-14 discharges
2004 (English)In: Hydrobiologia, ISSN 0018-8158, Vol. 514, no 1-3, 185-196 p.Article in journal (Refereed) Published
Place, publisher, year, edition, pages
Springer, 2004
Identifiers
urn:nbn:se:su:diva-23175 (URN)DOI: 10.1023/B:hydr.0000018218.88946.a4 (DOI)
Note
Part of urn:nbn:se:su:diva-175Available from: 2004-05-13 Created: 2004-05-13 Last updated: 2010-01-29Bibliographically approved
3. Transport and Fate of radionuclides in aquatic environments - the use of ecosystem modelling for exposure assessments of nuclear facilites
Open this publication in new window or tab >>Transport and Fate of radionuclides in aquatic environments - the use of ecosystem modelling for exposure assessments of nuclear facilites
Manuscript (Other academic)
Identifiers
urn:nbn:se:su:diva-23176 (URN)
Note
Part of urn:nbn:se:su:diva-175Available from: 2004-05-13 Created: 2004-05-13 Last updated: 2010-01-13Bibliographically approved
4. Bioaccumulation of Cr-51, Ni-63 and C-14 in Baltic Sea benthos
Open this publication in new window or tab >>Bioaccumulation of Cr-51, Ni-63 and C-14 in Baltic Sea benthos
2005 (English)In: Environmental Pollution, ISSN 1873-6424, Vol. 134, no 1, 45-56 p.Article in journal (Refereed) Published
Abstract [en]

The Baltic Sea is a species-poor, semi-enclosed, brackish sea, whose sediments contain a wide range of contaminants, including sediment-associated metals and radionuclides. In this study, we have examined and compared bioaccumulation kinetics and assimilation efficiencies of sediment-associated 51Cr, 63Ni and 14C in three key benthic invertebrates (the deposit-feeding Monoporeia affinis, the facultative deposit-feeding Macoma baltica, and the omnivorous Halicryptus spinulosus). Our results demonstrate that (i) all radionuclides were accumulated, (ii) the different radionuclides were accumulated to various extents, (iii) small changes in organic carbon concentration can influence the accumulation, and (iv) the degree of accumulation differed only slightly between species. These processes, together with sediment resuspension and bioturbation, may remobilise trace metals from the sediment to the water and to higher trophic levels, and therefore should be taken into account in exposure models and ERAs.

Bioaccumulation of radioisotopes in Baltic Sea benthos has important implications for contaminant transfer and exposure.

Place, publisher, year, edition, pages
Elsevier, 2005
Keyword
Bioaccumulation; Sediment; Benthos; Radionuclides; Trace metals
National Category
Biological Sciences
Identifiers
urn:nbn:se:su:diva-23177 (URN)10.1016/j.envpol.2004.07.017 (DOI)
Note
Part of urn:nbn:se:su:diva-175Available from: 2004-05-13 Created: 2004-05-13 Last updated: 2009-12-28Bibliographically approved
5. Remobilisation of buried radionuclides from anoxic sediments by bioturbation
Open this publication in new window or tab >>Remobilisation of buried radionuclides from anoxic sediments by bioturbation
Manuscript (Other academic)
Identifiers
urn:nbn:se:su:diva-23178 (URN)
Note
Part of urn:nbn:se:su:diva-175Available from: 2004-05-13 Created: 2004-05-13 Last updated: 2010-01-13Bibliographically approved

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