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Recent publications

Workreport 2016-55



Results of Forest Monitoring on Olkiluoto Island in 2015


Aro, L., Lindroos, A-J., Rautio, P., Ryynänen, A., Korpela, L., Mäkinen, V., Viherä-Aarnio, A., Salemaa, M.



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The forest investigations form a part of the monitoring programme being carried out on the Olkiluoto Island nuclear waste repository site under the management of Posiva Oy. This report presents results from studies performed on bulk deposition and forest intensive monitoring plots (MRK and FIP plots) in 2015. In addition, soil, ground vegetation and tree foliage surveys were repeated on the FET sampling plot network since the first round in 2005. There were no essential changes to the current monitoring networks during 2015.

In general, the level of precipitation was higher in 2015 than in 2013 or 2014. The NH4-N deposition that decreased in 2012 compared to the situation in 2011 remained relatively low also in 2013 and 2014. However, in 2015 the NH4-N deposition clearly increased again on the bulk deposition plot MRK13. The increase in NH4-N deposition was considered to probably be due to the construction activities in that area. The highest annual NH4-N deposition in stand throughfall during the whole monitoring period 2004-2015 was also measured on the black alder plot in 2015. The NO3-N deposition values increased in 2012 and were the highest for the whole monitoring period during 2004-2012. However, in 2013 the NO3-N deposition decreased, remained at a similar level also in 2014 and decreased even further in 2015. The soil solution quality in 2015 was quite comparable to that in earlier years. The Sr concentration in soil solution in 2015 was much higher than the values in bulk deposition and stand throughfall, and there was also clear variation between the plots. The variation is probably caused by natural factors, such as the release of Sr from soil minerals due to weathering.

Annual total litterfall production (257–526 gdw/m2 without larger branches) was higher in 2014 than in 2013. Annual variations recorded on Olkiluoto Island are due to natural reasons. High Al and Fe concentrations were found in the remaining litter, and were most likely due to soil dust.

The effects of major construction work on Olkiluoto Island were monitored using spruce and pine needles collected from the wet deposition sample plot network (last carried out in 2013). The foliar concentrations of most of the studied elements were not affected by the different washing procedures, which clearly indicates that most of the elements had not accumulated on the needle surfaces. The highest Al and Fe concentrations occurred on the plots that were closest to the landfill site for crushed waste rock. In conclusion, the composition and amount of dust deposited on tree foliage on the studied plots will most probably not cause any long-term effects on the forest ecosystems on Olkiluoto Island.

The vegetation survey was conducted on a smaller set of the FET sampling plots in 2015 than in 2005. Altogether 122 vascular plant species were found within the studied vegetation quadrats. There were no drastic changes in vegetation composition and coverage between 2005 and 2015 in the four main biotopes when surveying exactly the same plots and quadrats in the both years. However, species number of the vascular plants (field layer) had increased in the heath forests. In addition, on the forested peatlands the mean cover of Sphagnum bryophytes and high grasses decreased, and a few Sphagnum species even disappeared. This is most likely a consequence of drainage of peatlands, which promotes stand succession, enhance tree growth, increases canopy shading and the cover of leaf litter on the ground. On the rocky plots the cover of lichens slightely decreased whereas the cover of bryophytes increased. Furthermore, the cover of herbs increased compared to the year 2010. The number of plots studied in both years (2005 and 2015) was too small to catch the comprehensive variation and change in the vegetation on the biotope level representing the whole island.

No harmful effects of human activities on the forest condition were observed in the nature conservation area.


Bulk deposition, forest ecosystems, litterfall production, nutrition, permanent vegetation quadrats, plant cover analysis, soil solution chemistry, stand throughfall, understorey vegetation


WR 2016-55.web (pdf) (6.4 MB)


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