The fate of 137Cs in coniferous forests following the application of wood-ash

The Science of the Total Environment 280 Ž2001. 133᎐141

The fate of

137

Cs in coniferous forests following the application of wood-ash

U ¨ Lars Hogbom , Hans-Orjan Nohrstedt ¨ SkogForsk, The Forestry Research Institute of Sweden, Uppsala Science Park, Uppsala SE 751-83, Sweden Received 24 January 2001; accepted 23 February 2001

Abstract In the future, it may become common practice in Swedish forestry to recycle wood-ash, a waste product of the combustion of bio-fuel. As a consequence of the Chernobyl radioactive fallout in 1986, large areas of central Sweden were contaminated. Application of recycled wood-ash, originating from contaminated areas, to a previously uncontaminated forest, risks an increase in the concentration of radioactive 137Cs. We measured 137Cs radioactivity in different parts of coniferous forests in seven field experiments. Measurements of radioactivity were made 5᎐8 years after an application of wood-ash equivalent to 3000 kg hay1 . The sites, in a north᎐south transect across Sweden, have a background radioactivity ranging from 0 to 40 kBq my2 , the higher levels are mainly a result of the Chernobyl fall-out. Depending on its origin, the radioactivity of the applied wood-ash ranged from 0.0 to 4.8 kBq kgy1, corresponding to 0.0᎐1.44 kBq my2 . In autumn 1999, samples were taken from the soil, field vegetation, needles and twigs and the levels of 137Cs determined. In addition, soil samples were analysed for extractable K. The highest 137Cs concentration was found in the soil. At six of the seven sites there were no statistically significant effects of wood-ash application on 137Cs activity. This was despite the fact that the wood-ash had, in one case, added the same amount of radioactivity as the background. However, at one site with intermediate 137Cs deposition Ž10᎐20 kBq my2 ., there was a statistically significant decrease in 137Cs radioactivity in the soil, needles and twigs from the plots treated with wood-ash. The decrease in radioactivity was partly due to the fact that one of the main constituents of wood-ash is K, which is antagonistic to 137Cs. Based on our results, it appears that application of wood-ash containing 137Cs does not necessarily increase the 137Cs radioactivity in plants and soil. However, some of the observed effects could be a result of the low number of replicates used in this study. 䊚 2001 Elsevier Science B.V. All rights reserved. Keywords: Bio-fuel; Chernobyl; Radio-caesium

U

Corresponding author. Tel.: q46-18188549; fax: q46-18188600. .. E-mail address: [email protected] ŽL. Hogbom ¨ 0048-9697r01r$ - see front matter 䊚 2001 Elsevier Science B.V. All rights reserved. PII: S 0 0 4 8 - 9 6 9 7 Ž 0 1 . 0 0 8 1 9 - 1

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L. Hogbom, H. Nohrstedt r The Science of the Total En¨ ironment 280 (2001) 133᎐141 ¨

1. Introduction

In Sweden, during the past decade, interest in and use of bio-fuels has increased. Further increases in bio-fuel use, as an alternative to fossil fuel and nuclear energy, are desirable for a number of reasons. Brash from forest felling is considered to be one of the most important sources of bio-fuel. However, the removal of forest brashings causes soil acidification and a considerable loss of nutrients from the forest, since they contain needles and twigs, which are especially rich in nutrients. In order to counteract soil acidification, replenish soil nutrients and sustain forest production, the recycling of the bio-fuel waste wood-ash has been proposed ŽEgnell et al., 1998.. Large areas in the eastern part of central Sweden were affected by radioactive fallout from the Chernobyl accident in the spring of 1986. 137 Cs was one of the most abundant radioactive isotopes amongst those with a medium half-life. The half-life for 137 Cs is 30 years. The greatest deposition, approximately 100 kBq my2 , was found around the town of Gavle ¨ situated on the East Coast of Sweden ŽNylen, 1996.. In the days following the accident, half of the deposited 137 Cs in forests could be found in the three canopy layers ŽNylen, 1996.. However, the 137 Cs within the canopies decreased rapidly in the years following the accident. This was the result of both litter fall and washing off via precipitation. Gradually, increasing amounts of the deposited 137 Cs was incorporated into the soil organic matter. Studies made 1᎐5 years after the accident found only 3᎐8% of the total deposited 137 Cs in the aboveground parts of a forest ŽBunzl et al., 1989; Nylen and Grip, 1997; Tikhomirov and Shchleglov, 1994. and roughly half of the above-ground radioactivity was found in the needles ŽNylen and Grip, 1997.. Thus, tree biomass contains only a small fraction of the total 137 Cs in a forested ecosystem, the majority is in the soil. The extraction of bio-fuels comprising aboveground parts of trees should, therefore, only marginally decrease the amount of 137 Cs. Combustion of bio-fuels concentrates the

amounts of 137 Cs. The wood-ash can have a 10᎐60 times higher concentration than the bio-fuel ŽHedvall, 1997.. Thus, wood-ash from contaminated areas can have high levels of 137 Cs and, if added to a relatively clean environment, can affect the radiation levels of that site. However, because of the intrinsic antagonism between Cs and K on binding sites at the root surface, the addition of K-rich material, such as wood-ash, could, hypothetically, decrease the uptake of Cs by plants. The uptake mechanisms for Cs are described in detail by White and Broadley Ž2000.. Cs is much more effectively held by the soil organic matter than is K ŽAuerbach, 1986.. Hence, in a forested ecosystem, there should be a progressive transfer of Cs from the trees, the initial interceptor ŽRonneau et al., 1987. to the soil, which is the long-term sink ŽYamagata et al., 1969.. Within the organic soil layers roughly 10᎐50% of the 137 Cs is associated with fungal hyphae ŽBakken and Olsen, 1990.. Studies of radioactivity in sporocarps have revealed wide variations between species ŽBattiston et al., 1989; Bakken and Olsen, 1990.. Some studies report no correlation between the Cs content of the soil and that of fungal fruiting bodies ŽBorio et al., 1991., while other work has demonstrated a positive correlation ŽBakken and Olsen, 1990.. Analyses following the addition of KCl have demonstrated a two-third reduction in 137 Cs in Cantharellus cibarius ŽFr.. at a site with a relatively high 137 Cs content ŽNohrstedt, 1994.. In addition, by adding wood-ash containing 1.6 kBq kgy1 , the radioactivity in C. cibarius has been reduced by one-third ¨ ŽHans-Orjan Nohrstedt, unpublished.. The effects of wood-ash recycling on 137 Cs dynamics are affected by complex interactions between soil pH, soil K content, soil organic matter turnover, the background radioactivity of 137 Cs at the site and the 137 Cs and K content of any wood-ash applied. Factors such as the Cs and K binding within the ash, the solubility of the ash and differences in solubility between K and Cs could be of great importance. The content of 137 Cs in the vegetation could either increase or decrease, depending on the initial conditions. The

L. Hogbom, H. Nohrstedt r The Science of the Total En¨ ironment 280 (2001) 133᎐141 ¨

135

Table 1 Site descriptions. Note that at Riddarhyttan two different ashes were used. All stand data refer to the condition prior to wood-ash amendment Location

Site

˚ Aled 56⬚46⬘N: 12⬚56⬘E

Torup 56⬚55⬘N: 13⬚05⬘E

Riddarhyttan 59⬚48⬘N: 15⬚32⬘E

Hassel 62⬚02⬘N: 16⬚48⬘E

Vindeln 64⬚12⬘N: 19⬚28⬘E

¨ Alvsbyn 65⬚37⬘N: 20⬚54⬘E

Dominant tree species

Picea abies

Picea abies

Pinus syl¨ estris

Picea abies

Soil type Site indexa Basal area Žm2 hay1 . Stand age Mean stand height Žm. Standing volume Žm3 hay1 . Experiment started Background radioactivity ŽkBq my2 .

Regosol G33 40 59 21.5 400

Regosol G32 28.6 40 15 230

Podzol T24 22.8 50 16 170

Podzol G22 44 72 20 440

Pinus syl¨ estris Podzol T25 25.2 43 14.3 160

Pinus syl¨ estris Podsol T20 20.5 50 13.5 160

1992 -2

1990 -2

1995 -2

1995 30᎐40

1990 10᎐20

1995 -2

Ash formulation

Pelleted after addition of compost 0.003

Granulated after addition of cement 2.1

SelfPelleted harden crushed

Self-harden crushed

Self-harden crushed

1.6

4.8

1.6

Granulated after addition of cement 2.1

0.01

0.63

0.48

1.44

0.48

0.63

0.48

Activity concentration in the ash ŽkBq kgy1 . Radioactivity added by the ash ŽkBq hay1 .

1.6

a

According to Hagglund and Lundmark Ž1977.. ¨

addition of 137 Cs containing wood-ash will regardless of the effect on plants increase the gammaradiation above the forest floor.

2. Materials and methods Measurements of 137 Cs concentrations were made at six experimental sites ŽTable 1, Fig. 1.. At one of the sites, Riddarhyttan, two different ashes were tested. All experiments had a randomised block design, comprising three blocks, each plot was 30 = 30 m. The amount of wood ˚ ash applied was 3000 kg hay1 except at the Aled site, which received 4200 kg hay1 . The wood-ash used had a radioactivity, depending on its origin, ranging from 30 to 4800 Bq kgy1 , at our application rates this was equivalent to 0.03᎐1.44 kBq

my2 . The measurements reported here were made 5᎐8 years after the addition of the wood-ash. Throughout this paper the nomenclature for vascular plants follows Lid Ž1979. and Soderstrom ¨ ¨ and Hedenas ¨ Ž1998. for mosses. Selected site and stand parameters for the different sites are presented in Table 1. 䢇

䢇

¨ Alvsbyn: the field-layer vegetation was dominated by mainly Ericaceous species such as Vaccinium myrtillus, V. ¨ itis-idea, V. uliginosum and Ledum palustre. The bottom layer was dominated by Hylocomium splendens, Pleurozium schreberi and Ptilium crista-castrensis. Vindeln: the field-layer vegetation had a rather high species diversity, V. myrtillus, V. ¨ itis-idea, Deschampsia flexuosa, Luzula pilosa and Linea borealis were among the dominant species.

136

L. Hogbom, H. Nohrstedt r The Science of the Total En¨ ironment 280 (2001) 133᎐141 ¨

Fig. 1. Map of Sweden indicating the location of each site.

䢇

䢇

䢇

Species such as H. splendens, P. schreberi and P. crista-castrensis were dominant in the bottom layer. Hassel: the Hassel site lacked field-layer vegetation except for some sparse tillers of D. flexuosa, therefore, no field-layer vegetation samples could be taken. Riddarhyttan: the Riddarhyttan site field-layer vegetation was dominated by V. ¨ itis-idea and V. myrtillus and the bottom layer by lichens, including Cladonia rangiferina, C. stellaria and Cetraria islandica. At Riddarhyttan ash from two different sources was tested. ˚ Torup and Aled: no field- or bottom-layers were present at these two sites.

From each site the following were sampled: current and previous years’ needles and twigs; field-layer vegetation Žif present.; and the litterfermentation ŽLF. and humus ŽH. layers of the

soil. Needle and twig samples were taken, where possible, using pole-scissors, otherwise with a shot-gun and steel pellets. Ten trees per plot were sampled and the material was bulked into a single sample per plot. Samples of the field-layer vegetation were taken on an area basis. Five sub-plots Ž0.25 m2 . were selected at random. Species were not separated. Twenty soil cores per plot were taken Žcore ⭋ 6.0 cm. and divided into LF- and H-horizons, care was taken to remove mineral soil and mosses from the samples. The organic soil material was sieved Ž5.6 mm mesh size.. Visible wood-ash granules were removed and were analysed separately. Material that could not pass through the sieve, i.e. roots and possibly also root associations, was discarded. After sieving, the samples were bulked into a single sample per plot and horizon. Two sub-samples were taken from each bulked sample, one was stored in the freezer awaiting analysis of K content and the other was dried Ž70⬚C for 24 h. and used for 137 Cs analysis. Data on 137 Cs are presented as radioactivity concentrations ŽBq kgy1 ., but in addition soil data and field-layer data are presented on an area basis ŽBq my2 .. The 137 Cs analyses of soil and field-layer vegetation were made by GammaData AB in Uppsala with a NaI gamma ray detector ŽSS-EN 45 001.. The analyses of the needles and twigs were made at the Department of Soil Science, Swedish University of Agricultural Sciences, Uppsala, with a GeLi detector. The content of K in the soil was measured after extraction with 1 M ammonium lactate, pH 3.75. This analysis was conducted by the Department of Soil Science, Swedish University of Agricultural Sciences, Uppsala. No adjustment of the data due to radioactive decay was made, because the only comparisons made were within sites, and the sampling and measurements for each site were made within a few days so time effects would be negligible. The effects of wood-ash addition were assessed using a Student’s t-test, except for the data from Riddarhyttan, which were analysed using a oneway ANOVA to compare the two treatments with the single control plot. For this site a two-way ANOVA had indicated that there were no block effects. Levels of significance are indicated as

L. Hogbom, H. Nohrstedt r The Science of the Total En¨ ironment 280 (2001) 133᎐141 ¨

dictated by convention: P- 0.05sU ; P- 0.01 sUU ; and P- 0.001sUUU .

3. Results Samples that were analysed by both detectors showed a high correlation Ž R 2 s 0.95. and the slope of the regression line was close to 1.0. At some of the sites the wood-ash pellets or granules were still present at the time of sampling. This was the case for the pelleted ash at ˚ Ž196 Bq kgy1 , equivalent to 0.10 kBq my2 . Aled and Riddarhyttan II Ž2479 Bq kgy1 , equivalent to 0.20 kBq my2 . and the granulated ash at Vindeln Ž2267 Bq kgy1 , equivalent to 0.40 kBq my2 . and Torup Ž1418 Bq kgy1 , equivalent to 0.33 kBq my2 .. The values within parentheses are the actual activities measured for the ashes sampled. These pellets or granules were all present in the upper-most layer of the horizons sampled. They were removed and analysed separately, and the results were added to those for the main sample. For these four cases radioactivity data are presented both with and without ash. The wood-ash pellets or granules at other sites did not add to the total 137 Cs activity of the sites. In the soil, there was no evidence that radioactivity was consistently higher on wood-ash amended plots than on control plots, for either the LF- or H-horizons ŽTable 2.. There were differences in the amounts of soil organic matter turnover between plots ŽTable 3.. When calculating the radioactivity on an area basis ŽBq my2 . rather than on a weight basis, some of the differences between treated and control plots were increased, while others were reduced ŽTables 2 and 4.. As expected, those sites with the lowest background radioactivity on the basis of reference ˚ maps Žnamely Aled, Torup, Riddarhyttan and ¨ . also had the lowest activity measured in Alvsbyn the soil ŽTable 4.. Despite differences in the radioactivity of the wood-ash applied, ranging from 0.03 to 4.8 kBq kgy1 , no increase in 137 Cs activity was detected following application at these low-activity sites ŽTable 4. when the wood-ash granules were removed. On the contrary, a statis-

137

tically significant decrease in the amount of radioactivity in the H-layer at the Torup site was found ŽTable 4.. Of particular interest is the site, which received the highest relative addition, Riddarhyttan, where a doubling of the radioactivity, because of the wood-ash application, was expected. However, there was no significant difference between the control and the treated plots ŽTable 4.. At the two sites with the highest background radioactivity ŽHassel and Vindeln., the radioactivity in the organic soil layers was significantly lower in the ash-amended plots than in the control plots at Vindeln ŽTable 4., while the radioactivity was unaffected at Hassel ŽTable 4.. The K content in the soil 5᎐8 years after treatment, was generally unaffected by the wood-ash application ŽTable 4.. In the H-layer at Vindeln, a significantly lower concentration of K was measured in the plots with wood-ash application ŽTable 4.. The same wood-ash caused no such effect at the Torup site. Several sites which had field-layer vegetation ¨ ŽAlvsbyn, Vindeln and Riddarhyttan.. The radioactivity within the field-vegetation was one-fifth that of the soil at Vindeln but was comparable at the other two sites. As expected, the highest radioactivity was measured at Vindeln, but no statistically significant differences between control plots and ash-treated plots were found ŽTable 4.. Effects of the previous wood-ash application on 137 Cs in the canopy could only be detected at the Vindeln site ŽTable 2.. The wood-ash application significantly reduced 137 Cs activity in the needles and current-year twigs. Apparently at Vindeln, the wood-ash application had reduced the plantavailable 137 Cs. Despite the lack of statistically significant results at the other sites, there was, in most cases, a tendency towards a reduction in radioactivity in the wood-ash treated plots ŽTable 2..

4. Discussion K salts have been shown to be an effective agent for redistribution of 137 Cs within the soil

L. Hogbom, H. Nohrstedt r The Science of the Total En¨ ironment 280 (2001) 133᎐141 ¨

138

Table 2 Radioactivity concentrations of 137 Cs ŽBq kgy1 .. Mean values " 1 S.E., in different parts of the dominant tree species at the study sites. The P-value is given for each comparison between control and ash treated plots. N.A.s not analysed. For the site Riddarhyttan, values not followed by the same letter columnwise are significantly different at the P- 0.05 level Site

Background activity incl. ash activity ŽkBq my2 .

Soil LFhorizon

Soil Hhorizon

Current year needles

Needles of previous year

Current year twigs

Twigs of previous year

˚ led A Control Ash P-value

0᎐2 q0.01

74.0" 4.43 60.3" 4.43 0.11

65.0" 3.18 72.0" 2.08 0.18

50.1" 34.8 37.8" 11.8 0.38

35.6" 6.4 17.1" 10.5 0.11

46.9" 18.8 47.3" 25.2 0.49

69.2" 26.4 62.3" 56.4 0.46

Torup Control Ash P-value

0᎐2 q0.63

75.7" 4.40 87.3" 6.05 0.21

53.0" 1.35 43.7" 1.35 0.05U

83.2" 8.21 63.2" 15.4 0.17

55.9" 4.2 50.1" 7.1 0.27

75.4" 26.3 80.9" 3.72 0.42

71.0" 13.3 56.7" 7.31 0.21

Riddarhyttan Control Ash I Ash II P-value

0᎐2 q0.48 q1.44

166 " 1.92a 215 " 16.3ab 303 " 9.46b 0.05U

126 " 3.34 123 " 6.88 131 " 2.12 0.84

103 " 23.1 55.3" 10.2 76.2" 16.0 0.22

112 " 87.0 18.6" 5.59 29.8" 4.11 0.51

76.4" 7.94 40.0" 17.8 43.6" 25.0 0.36

27.1" 4.02 22.9" 12.4 41.8" 27.4 0.74

Hassel Control Ash P-value

30᎐40 q0.48

2380 " 67.3 2190 " 4.25 0.12

2000 " 60.9 2230 " 80.4 0.14

872 " 37.7 944 " 233 0.39

694 " 49.3 521 " 70.7 0.06

1150 " 158 1130 " 232 0.48

580 " 100 744 " 186 0.24

Vindeln Control Ash P-value

10᎐20 q0.63

1900 " 79.5 1780 " 194 0.38

1240 " 91.5 1420 " 60.7 0.20

304 " 44.2 171 " 40.7 0.05U

161 " 35.8 62.3" 19.5 0.05U

219 " 15.5 135 " 29.1 0.04U

140 " 12.7 135 " 33.4 0.45

¨ lvsbyn A Control Ash P-value

0᎐2 q0.48

39.7" 9.05 84.3" 10.5 0.07

55.3" 1.90 87.0" 3.18 0.006UU

42.0" 10.5 22.1" 13.7 0.16

19.4" 9.82 11.0" 3.20 0.25

58.0" 20.4 44.2" 22.5 0.34

63.5" 42.4 0.00" 0.00 0.14

system. For a large number of soil profiles, Schulz et al. Ž1959. demonstrated a rapid decrease in 137 Cs activity after the addition of KCl. However, depending on the soil type and the dominant clay mineral, the effect varied substantially, from a decrease of few percent to one of almost 80%. Bunzl et al. Ž1989. reported on a migration rate for 137 Cs of between 2 and 4 cm yeary1 for their site at Hoglwald in Bavaria, Germany. However, ¨ since a large part of the 137 Cs radioactivity is associated with fungal material in the soil, it is likely that relocation occurs within the soil system via fungal mycelia. In general, the 137 Cs activity in the wood-ashes

applied did not increase the radioactivity within the vegetation or the soil. On the contrary, radioactivity tended to decrease following the wood-ash application. The effect was most pronounced at the Vindeln site, where a statistically significant effect was found, both in the soil organic matter and in needles and twigs of P. syl¨ estris. The wood-ash used at Vindeln was also used at Torup. At the latter site, however, a significant decrease of the activity of 137 Cs was found only in the soil H-layer. Some of these effects are caused by the reduction in soil organic matter following wood-ash application. The intrinsic antagonistic behaviour between K

L. Hogbom, H. Nohrstedt r The Science of the Total En¨ ironment 280 (2001) 133᎐141 ¨

139

Table 3 Weight Žkg d.m. my2 . of the soil organic horizons at the study sites Site

Background activity incl. ash activity ŽkBq my2 .

Soil LFhorizon

Soil Hhorizon

Total organic soil horizon

˚ led A Control Ash P-value

0᎐2 q0.01

24.6" 0.88 30.6" 1.06 0.04U

46.9" 2.95 44.2" 2.02 0.35

71.5" 3.64 74.8" 2.80 0.35

Torup Control Ash P-value

0᎐2 q0.63

27.4" 2.14 25.1" 1.22 0.31

31.2" 1.49 26.3" 2.49 0.20

58.7" 3.61 51.5" 3.32 0.22

Riddarhyttan Control Ash I Ash II P-value

0᎐2 q0.48 q1.44

4.00" 0.34 3.68" 0.22 2.88" 0.20 0.27

6.08" 0.99 7.78" 0.74 4.31" 1.03 0.38

10.1" 1.13 11.5" 0.97 7.20" 1.15 0.33

Hassel Control Ash P-value

30᎐40 q0.48

10.4" 1.20 12.0" 1.02 0.29

20.7 " 1.83 17.3" 0.81 0.20

31.1" 3.02 29.3" 1.63 0.39

Vindeln Control Ash P-value

10᎐20 q0.63

6.82" 0.53 5.23" 0.60 0.16

12.0" 1.07 6.36" 0.48 0.04U

18.8" 1.60 11.6" 1.05 0.05U

¨ lvsbyn A Control Ash P-value

0᎐2 q0.48

7.69" 0.92 5.78" 0.18 0.17

12.1" 1.38 8.08" 0.50 0.11

19.8" 1.28 13.9" 0.68 0.05U

and Cs, and differences in solubility between the ashes in use are the most likely reasons for these differences in effects. The internal relocation of 137 Cs follows the same general pattern as for K. This means that higher concentrations of 137 Cs are found in new shoots than in older ones. In most cases for needles in our study, this pattern could be discerned ŽTable 2.. In the case of the twigs, the difference between current year twigs and 1-year-old twigs was minute. In contrast, Ronneau et al. Ž1987. reported higher 137 Cs activity in current year shoots compared with 1-yearold shoots.

We did not find any statistically significant changes in the radioactivity of the field-layer vegetation due to the application of ash. At Riddarhyttan, however, there were indications that one of the ash treatments ŽAsh I. reduced radioactivity. This could be an effect of different K-release speeds in the two ashes. However, later studies of K distribution at that site did not reveal any differences in K distribution within the soil profile ŽHogbom and Nohrstedt personal commu¨ nication.. Other studies have examined field-layer vegetation, e.g. Levoula et al. Ž2000. found a decrease in 137 Cs activity following wood-ash ad-

L. Hogbom, H. Nohrstedt r The Science of the Total En¨ ironment 280 (2001) 133᎐141 ¨

140 Table 4 Radioactivity of

137

Cs Žmean values " 1.S.E.. in soil and field-layer vegetation following wood-ash amendment a

Background activity incl. ash activity ŽkBq my2 .

Soil activity ŽkBq my2 . F-layer

H-layer

Total soil

˚ led A Control Ash P-value

0᎐2 q0.01

1.82" 0.05 2.73" 0.33 0.45

3.18" 0.13 3.20" 0.37 0.49

5.06" 0.69 5.00 Ž5.10. " 0.07 0.47

Torup Control Ash P-value

0᎐2 q0.63

2.04" 0.19 2.27" 0.40 0.35

1.65" 0.11 1.13" 0.13 0.02U

3.68" 0.29 3.36 Ž3.69. " 0.45 0.29

Riddarhyttan Control Ash I Ash II P-value

0᎐2 q0.48 q1.44

0.66" 0.11 0.71" 0.03 0.87" 0.11 0.53

0.77" 0.22 1.24" 0.17 1.04" 0.42 0.89

1.43" 0.24 1.57" 0.20 1.32 Ž1.52. " 0.43 0.93

Hassel Control Ash P-value

30᎐40 q0.48

24.3" 3.62 25.6" 4.65 0.42

40.8" 3.88 38.0" 0.99 0.27

65.1" 7.42 63.6" 4.72 0.44

Vindeln Control Ash P-value

10᎐20 q0.63

12.9" 1.64 8.84" 1.10 0.05U

14.3" 0.72 8.94" 1.10 0.01UU

27.3" 1.86 17.8 Ž18.0. " 1.94 0.01UU

¨ lvsbyn A Control Ash P-value

0᎐2 q0.48

0.29" 0.10 0.48" 0.09 0.13

0.65" 0.09 0.71" 0.11 0.36

0.95" 0.18 1.19 " 0.14 0.18

Site

Fieldvegetation activity ŽBq my2 .

K content Žg my2 . F-layer

H-layer

Total soil

1.55" 0.04 2.00" 0.32 0.12

1.50" 0.17 1.37" 0.14 0.29

3.05" 0.21 3.36" 0.45 0.28

1.54" 0.20 1.73" 0.28 0.31

1.30" 0.16 1.15" 0.16 0.28

2.85" 0.33 2.88" 0.42 0.47

0.77" 0.15 1.01" 0.32 0.95" 0.09 0.73

1.06" 0.19 1.54" 0.08 1.08" 0.24 0.18

1.83" 0.32 2.55" 0.25 2.03 " 0.30 0.27

1.26" 0.24 1.54" 0.28 0.25

1.55" 0.29 1.86" 0.17 0.21

2.81" 0.53 3.40" 0.34 0.20

72.4 " 24.0 59.9" 13.8 0.38

0.87" 0.11 0.94" 0.21 0.39

0.97" 0.05 0.77" 0.04 0.02U

1.84" 0.14 1.71" 0.23 0.33

3.86" 2.00 2.89" 1.66 0.35

0.82" 0.19 0.76" 0.07 0.39

1.08" 0.19 1.29" 0.20 0.25

1.91" 0.36 2.05" 0.25 0.38

No fieldlayer

No fieldlayer

7.75" 2.13 2.37" 0.48 7.75" 1.85 0.31 No fieldlayer

a

The P-value given is for each comparison between control and ash amended plots. The values in parentheses include that for the wood-ash pellets, which were analysed separately. Please note the change in units between the different layers.

dition in a study of berries of Vaccinium ¨ itis-idea in Finland. Based on our observations the following hypothesis was formulated, this could be the subject of future are more detailed investigations. The addition of wood-ash increased the downward migration velocity of 137 Cs, probably because of the K content of the wood-ash and a postulated pH increase. However, this may be partially counteracted by the content and internal redistribution of 137 Cs within fungal mycelia and the mycorrhizal network. The effect of a wood-ash addi-

tion on soil radiation ecology is dependent on a large number of factors, including: 137 Cs migration rate, which is affected by soil type, clay content and the type of clay minerals present; K release from the wood-ash particles and pH effects; plant K demand and type; and the abundance of fungal species. The effects of wood-ash addition on forests requires further studies involving long-term monitoring of the transport and movement of radio-caesium within the forest ecosystem. Future work should examine different application rates of wood-ash and short-term

L. Hogbom, H. Nohrstedt r The Science of the Total En¨ ironment 280 (2001) 133᎐141 ¨

studies of K addition, as well as more detailed studies on the turnover of soil organic matter. In conclusion, the application of wood-ash contaminated with 137 Cs did not significantly increase the 137 Cs radioactivity within the biological system. On the contrary, there were tendencies towards a decrease in 137 Cs activity concentrations and in one case this decrease was statistically significant, but this could partly be an effect of the low number of replicates.

Acknowledgements We would like to thank Dr Klas Rosen, ´ Department of Soil Science, Swedish University of Agricultural Sciences, Uppsala and Anund Lindholm, GammaData AB, Uppsala, for conducting the analyses. This study was supported financially by the Swedish National Energy Administration ŽSTEM. and the Swedish Radiation Protection Institute ŽSSI.. References Auerbach, S.I. Comparative behaviour of three long-lived radionuclides in forest ecosystems. CEC-CIEMAT Ann. Seminar on ‘The Cycling of Long-Lived Radionuclides in the Biosphere: Observations and Models’, 15-19 Sept 1986, Madrid. Bakken LR, Olsen RA. Accumulation of radiocaesium in fungi. Can J Microbiol 1990;36:704᎐710. Battiston GA, Degetto S, Gerbasi R, Sbrignadello G. Radioactivity in mushrooms in Northeast Italy following the Chernobyl accident. J Environ Radioact 1989;9:53᎐60. Borio R, Chiocchini S, Cicioni R, Degli Esposti P, Rongoni A, Sabatini P, Scampoli P, Antonini A, Salvadoro P. Uptake of radiocaesium by mushrooms. Sci Total Environ 1991; 106:183᎐190. Bunzl K, Schimmack W, Kreutzer K, Schierl R. The migration

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