Metla Project 3314

Control of radiation risks in forestry

Duration: 2001-2006 Keywords: Norway spruce, Scots pine, countermeasure, fertilisation, radiocaesium, radioecology, silver birch
Research project group: Distinct projects 1 - Structure and function of forest ecosystems

Objectives

It is important to prepare for extensive radioactive fallout situations by planning countermeasures suitable for Finnish forests in advance. This can be done after the sufficient knowledge on the forest radioecology considering Finnish conditions has been obtained. A remarkable part of the results from field experiments measured during the last ten years will be published in this project in co-operation with the Radiation and Nuclear Safety Authority (STUK). New material will be collected from the fertilisation experiments of Norway spruce and silver birch stands growing on fertile sites.

The research project will co-ordinate the participation of the experts of the Finnish Forest Research Institute in co-operation with the relevant interest groups in the evaluation process of the forestry related countermeasures in the radioactive fall-out situation. The aim of the evaluation process is to develop practical guidelines based on results from radioecological research to protect wood production and forestry employees in the radiation circumstances. Though the possibility of a new severe nuclear power plant accident like the Chernobyl disaster is considered small, the preparedness of forest sector for similar disasters is an important part of controlling environmental risks in forestry.

Results

The effects of single and repeated fertilisation on the contents of potassium, 134Cs and 137Cs in different Scots pine (Pinus sylvestris) compartments at different levels above ground and in the peat profile were studied nine years after the Chernobyl disaster. The material was collected from a ditch spacing and fertilisation experiment in Finland. Above a needle potassium concentration of 3.0 mg g-1 in composed crown samples 137Cs and 134Cs concentrations remained at about the same level but below that the values were higher on average. This potassium value corresponded to the potassium concentrations of 3.5-3.6 mg g-1 in the current-year needles of two topmost whorls. The result indicates an enhanced radiocaesium uptake by pine trees under severe potassium deficiency. Fertilisation with potassium-containing fertilisers decreased the caesium uptake considerably. The inhibiting effect of fertilisation on caesium uptake by trees seemed to be fairly long lasting. Fertilisation had sped up the penetration of caesium downwards in the peat profile and its moving out of the active circulation of elements between soil and plants.

The effects of fertilisation and drainage intensity on the needle 134Cs and 137Cs activity in Pinus sylvestris were studied on a pine mire in Finland. The potassium concentrations of the current year needles in 1990 showed severe potassium deficiency on the controls (K 3.6 mg g-1) and slight deficiency on the plots fertilised only once (K 4.2 mg g-1) but no deficiency on the plots fertilised twice (K 4.8 mg g-1). Fertilisation decreased the radiocaesium concentrations and amounts in the needles. The concentrations of 134Cs were 821 in the control, 442 in the single fertilisation and 485 Bq kg-1 in the repeated fertilisation treatment, and the 137Cs concentrations 5378, 2734 and 2104 Bq kg-1, respectively. Drainage intensity (10-100 m) had no significant effect on the needle K concentration or radiocaesium activity.

Undergrowth spruces (Picea abies) in a pine stand in Finland were studied in 1997, 13 years after refertilisation with NPK. The aim of the study was to quantify the effect of NPK fertilisation on the distribution of radiocaesium (137Cs) and dry mass in the trees. Fertilisation decreased the 137Cs concentration in each of the compartments by 73-92%. In the control spruces, the 137Cs concentrations were highest in the stem bark, needles and branches of the upper half of the crown (2455-3443 Bq kg-1 DW) and in the dead branches (2882-4408 Bq kg-1 DW). These concentrations were double those in the lower half of the crown irrespective of the fertiliser treatment. The needles and branches in the lower half of the crown contained 58-62% of the tree biomass and 56-60% of the 137Cs. Changes in the relative vertical distribution of 137Cs in the trees due to fertilisation were small. The total 137Cs content of the trees correlated with the biomass and diameter of the trees.

Effects of liming and soil preparation on radiocesium (137Cs) and radiostrontium (90Sr) uptake of pine saplings (Pinus sylvestris) were studied in a dry heath forest in western Finland. Soil preparation increased highly significantly dry mass of the whole tree and branches and needles of C and C+1 year classes, and significantly masses of roots, stem, and older branches and needles. In all these fractions the content of Sr increased significantly. The 137Cs concentrations in all tree fractions were highest in samples from the control plots, but Sr differed from this pattern. Soil preparation decreased significantly the 137Cs concentrations in roots and living needles. The changes in 137Cs and 90Sr contents in trees may partially be traced back to increased nutrient mobility and root mass and changed root distribution in soil, and also to different relations of Cs-K and Sr-Ca in uptake and translocation processes of trees.

Project leader: Aro, Lasse
The Finnish Forest Research Institute, Parkano Office, Kaironiementie 15, FI-39700 PARKANO, FINLAND
Phone: +358 29 532 4025
E-mail: lasse.aro@metla.fi

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Updated 12.06.2012
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