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Recent publications

Workreport 2017-16



Reference Lake Sediments, Geochemistry and in situ Distribution Coefficients, Kd Values, Southwestern Finland


Lahdenperä, A.



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This work report presents geochemical and physical properties and the in situ distribution coefficients, (Kd values) of the indigenous elements from the eight deep lake sediments profiles in the Reference area. The data extends the understanding of the biosphere site description, radionuclide transport analyses and utilisation in modelling. The post-glacial crustal rebound shapes the landscape from Finnish coastal areas to an inland type within a few millennia in the future. The shoreline displacement will change the local and regional biosphere conditions and influence soil and sediment properties and groundwater flow pattern. The properties of the future lake ecosystems surrounding the Olkiluoto Island can be forecast and radionuclide transport models applied based on the properties of present lakes. Currently, however, there are no lakes on the island. Due to the lack of Olkiluoto specific data, eight lakes being in different successional stages were selected from the within the larger geographical Reference area as analogues of those expected to be formed at the Olkiluoto site.

Sediment samples have been taken from the different lithological units. The lakes were isolated during the Littorina or Limnea Sea stages about 2200-6500 cal yr BP. From the sediment samples, pore water, bioavailable concentrations of elements using NH4Ac extraction, (pH 4.5) and pseudo-total concentrations of elements using HNO3-HF(trace) extraction or LiBO2 fusion method are analysed. pH, dry and organic matter (LOI), total carbon and nitrogen contents, main pore water anions, DIC, DOC, and grain size distribution are measured. Cation exchange capacity (CEC) and base saturation (BS) are calculated using the results of NH4Ac (pH 4.5) extraction. In situ Kd values indicate the relevant mobility and retention of the main indigenous elements and radionuclides. Ag, Cl, Cs, I, Mo, Nb, Ni, Pb, Pd, Se, Sn and Sr are the main interest elements in the biosphere assessment because they are analogues to the highest doses contributing radionuclides from the repositories. In addition, geochemistry and Kd values of main cations (Al, Ca, Fe, K, Mg, Na), P, S, main heavy metals (As, Cd, Cr, Co, Cu, Mn and Zn), Th and U are evaluated. The in situ Kd values are calculated using the formula used by Sheppard et al. (2007). The Kd data of the lake sediments inherently extremely variable, but it also varies systematically withing the key environmental factors, thus their co-influence is important for each individual element as well as their acting in different sediment types by site to site and by sediment depths. Organic matter content, pH and sediment mineral composition, especially clay and silt fraction, have a distinct influence on the Kd values. However, only the bioavailable Kd values of Cl, I, Nb, Pb, Se and Sr show correlation with LOI content, and Kd values of I, Mo and Se with the clay content. Only the pseudo-total Kd values of Cl, I and Se correlated with the LOI content, and slightly or not at all with the clay content.


Deep lake sediments, Reference Area, geochemistry, distribution coefficients


WR 2017-16_web (pdf) (6.5 MB)


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