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

Ž .The Science of the Total Environment 280 2001 133�141

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

� ¨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 thecombustion of bio-fuel. As a consequence of the Chernobyl radioactive fallout in 1986, large areas of central Swedenwere contaminated. Application of recycled wood-ash, originating from contaminated areas, to a previously uncon-taminated forest, risks an increase in the concentration of radioactive 137Cs. We measured 137Cs radioactivity indifferent parts of coniferous forests in seven field experiments. Measurements of radioactivity were made 5�8 yearsafter an application of wood-ash equivalent to 3000 kg ha�1. The sites, in a north�south transect across Sweden,have a background radioactivity ranging from 0 to 40 kBq m�2, the higher levels are mainly a result of the Chernobylfall-out. Depending on its origin, the radioactivity of the applied wood-ash ranged from 0.0 to 4.8 kBq kg�1,corresponding to 0.0�1.44 kBq m�2. In autumn 1999, samples were taken from the soil, field vegetation, needles andtwigs and the levels of 137Cs determined. In addition, soil samples were analysed for extractable K. The highest 137Csconcentration was found in the soil. At six of the seven sites there were no statistically significant effects of wood-ashapplication on 137Cs activity. This was despite the fact that the wood-ash had, in one case, added the same amount of

137 Ž �2 .radioactivity as the background. However, at one site with intermediate Cs deposition 10�20 kBq m , there wasa statistically significant decrease in 137Cs radioactivity in the soil, needles and twigs from the plots treated withwood-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 notnecessarily increase the 137Cs radioactivity in plants and soil. However, some of the observed effects could be a resultof the low number of replicates used in this study. � 2001 Elsevier Science B.V. All rights reserved.

Keywords: Bio-fuel; Chernobyl; Radio-caesium

� Corresponding author. Tel.: �46-18188549; fax: �46-18188600.Ž .E-mail address: [email protected] L. Hogbom .¨

0048-9697�01�$ - see front matter � 2001 Elsevier Science B.V. All rights reserved.Ž .PII: S 0 0 4 8 - 9 6 9 7 0 1 0 0 8 1 9 - 1

( )L. Hogbom, H. Nohrstedt � The Science of the Total En�ironment 280 2001 133�141¨134

1. Introduction

In Sweden, during the past decade, interest inand use of bio-fuels has increased. Further in-creases in bio-fuel use, as an alternative to fossilfuel and nuclear energy, are desirable for a num-ber of reasons. Brash from forest felling is con-sidered to be one of the most important sourcesof bio-fuel. However, the removal of forest brash-ings causes soil acidification and a considerableloss of nutrients from the forest, since they con-tain needles and twigs, which are especially richin nutrients. In order to counteract soil acidifica-tion, replenish soil nutrients and sustain forestproduction, the recycling of the bio-fuel waste

Ž .wood-ash has been proposed Egnell et al., 1998 .Large areas in the eastern part of central Swe-

den were affected by radioactive fallout from theChernobyl accident in the spring of 1986. 137Cswas one of the most abundant radioactive iso-topes amongst those with a medium half-life. Thehalf-life for 137Cs is 30 years. The greatest deposi-tion, approximately 100 kBq m�2 , was foundaround the town of Gavle situated on the East¨

Ž .Coast of Sweden Nylen, 1996 . In the days fol-lowing the accident, half of the deposited 137Cs inforests could be found in the three canopy layersŽ . 137Nylen, 1996 . However, the Cs within thecanopies decreased rapidly in the years followingthe accident. This was the result of both litter falland washing off via precipitation. Gradually, in-creasing amounts of the deposited 137Cs was in-corporated into the soil organic matter. Studiesmade 1�5 years after the accident found only3�8% of the total deposited 137Cs in the above-

Žground parts of a forest Bunzl et al., 1989; Nylen.and Grip, 1997; Tikhomirov and Shchleglov, 1994

and roughly half of the above-ground radioactiv-Žity was found in the needles Nylen and Grip,

.1997 . Thus, tree biomass contains only a smallfraction of the total 137Cs in a forested ecosystem,the majority is in the soil. The extraction ofbio-fuels comprising aboveground parts of treesshould, therefore, only marginally decrease theamount of 137Cs.

Combustion of bio-fuels concentrates the

amounts of 137Cs. The wood-ash can have a 10�60times higher concentration than the bio-fuelŽ .Hedvall, 1997 . Thus, wood-ash from contami-nated areas can have high levels of 137Cs and, ifadded to a relatively clean environment, can af-fect the radiation levels of that site. However,because of the intrinsic antagonism between Csand K on binding sites at the root surface, theaddition of K-rich material, such as wood-ash,could, hypothetically, decrease the uptake of Csby plants. The uptake mechanisms for Cs are

Ž .described in detail by White and Broadley 2000 .Cs is much more effectively held by the soil

Ž .organic matter than is K Auerbach, 1986 . Hence,in a forested ecosystem, there should be a pro-gressive transfer of Cs from the trees, the initial

Ž .interceptor Ronneau et al., 1987 to the soil,Žwhich is the long-term sink Yamagata et al.,

.1969 .Within the organic soil layers roughly 10�50%

of the 137Cs is associated with fungal hyphaeŽ .Bakken and Olsen, 1990 . Studies of radioactivityin sporocarps have revealed wide variations

Žbetween species Battiston et al., 1989; Bakken.and Olsen, 1990 . Some studies report no correla-

tion between the Cs content of the soil and thatŽ .of fungal fruiting bodies Borio et al., 1991 , while

other work has demonstrated a positive correla-Ž .tion Bakken and Olsen, 1990 . Analyses fol-

lowing the addition of KCl have demonstrated atwo-third reduction in 137Cs in Cantharellus cibar-

Ž . 137ius Fr. at a site with a relatively high CsŽ .content Nohrstedt, 1994 . In addition, by adding

wood-ash containing 1.6 kBq kg�1, the radioactiv-ity in C. cibarius has been reduced by one-third

¨Ž .Hans-Orjan Nohrstedt, unpublished .The effects of wood-ash recycling on 137Cs

dynamics are affected by complex interactionsbetween soil pH, soil K content, soil organicmatter turnover, the background radioactivity of137Cs at the site and the 137Cs and K content ofany wood-ash applied. Factors such as the Cs andK binding within the ash, the solubility of the ashand differences in solubility between K and Cscould be of great importance. The content of137Cs in the vegetation could either increase ordecrease, depending on the initial conditions. The

( )L. Hogbom, H. Nohrstedt � The Science of the Total En�ironment 280 2001 133�141¨ 135

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

Location Site

˚ ¨Aled Torup Riddarhyttan Hassel Vindeln Alvsbyn56�46�N: 56�55�N: 59�48�N: 62�02�N: 64�12�N: 65�37�N:12�56�E 13�05�E 15�32�E 16�48�E 19�28�E 20�54�E

Dominant tree species Picea abies Picea abies Pinus syl�estris Picea abies Pinus Pinussyl�estris syl�estris

Soil type Regosol Regosol Podzol Podzol Podzol PodsolaSite index G33 G32 T24 G22 T25 T20

2 �1Ž .Basal area m ha 40 28.6 22.8 44 25.2 20.5Stand age 59 40 50 72 43 50

Ž .Mean stand height m 21.5 15 16 20 14.3 13.5Standing volume 400 230 170 440 160 160

3 �1Ž .m haExperiment started 1992 1990 1995 1995 1990 1995Background radioactivity �2 �2 �2 30�40 10�20 �2

�2Ž .kBq m

Ash formulation Pelleted Granulated Self- Pelleted Self-harden Granulated Self-hardenafter after harden crushed after crushedaddition of addition of crushed addition ofcompost cement cement

Activity concentration in 0.003 2.1 1.6 4.8 1.6 2.1 1.6the ash

�1Ž .kBq kgRadioactivity added by 0.01 0.63 0.48 1.44 0.48 0.63 0.48

the ash�1Ž .kBq ha

a Ž .According to Hagglund and Lundmark 1977 .¨

addition of 137Cs containing wood-ash will regard-less of the effect on plants increase the gamma-radiation above the forest floor.

2. Materials and methods

Measurements of 137Cs concentrations wereŽ .made at six experimental sites Table 1, Fig. 1 .

At one of the sites, Riddarhyttan, two differentashes were tested. All experiments had a ran-domised block design, comprising three blocks,each plot was 30�30 m. The amount of wood

�1 ˚ash applied was 3000 kg ha except at the Aledsite, which received 4200 kg ha�1. The wood-ashused had a radioactivity, depending on its origin,ranging from 30 to 4800 Bq kg�1, at our applica-tion rates this was equivalent to 0.03�1.44 kBq

m�2 . The measurements reported here were made5�8 years after the addition of the wood-ash.Throughout this paper the nomenclature for vas-

Ž .cular plants follows Lid 1979 and Soderstrom¨ ¨Ž .and Hedenas 1998 for mosses. Selected site and¨

stand parameters for the different sites are pre-sented in Table 1.

¨� Alvsbyn: the field-layer vegetation was domi-nated by mainly Ericaceous species such asVaccinium myrtillus, V. �itis-idea, V. uliginosumand Ledum palustre. The bottom layer wasdominated by Hylocomium splendens, Pleuroz-ium schreberi and Ptilium crista-castrensis.

� Vindeln: the field-layer vegetation had a ratherhigh species diversity, V. myrtillus, V. �itis-idea,Deschampsia flexuosa, Luzula pilosa and Lineaborealis were among the dominant species.


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

Species such as H. splendens, P. schreberi andP. crista-castrensis were dominant in the bot-tom layer.

� Hassel: the Hassel site lacked field-layer vege-tation except for some sparse tillers of D.flexuosa, therefore, no field-layer vegetationsamples could be taken.

� Riddarhyttan: the Riddarhyttan site field-layervegetation was dominated by V. �itis-idea andV. myrtillus and the bottom layer by lichens,including Cladonia rangiferina, C. stellaria andCetraria islandica. At Riddarhyttan ash fromtwo different sources was tested.

˚� Torup and Aled: no field- or bottom-layerswere present at these two sites.

From each site the following were sampled:current and previous years’ needles and twigs;

Ž .field-layer vegetation if present ; and the litter-Ž . Ž .fermentation LF and humus H layers of the

soil. Needle and twig samples were taken, wherepossible, using pole-scissors, otherwise with ashot-gun and steel pellets. Ten trees per plot weresampled and the material was bulked into a singlesample per plot. Samples of the field-layer vegeta-tion were taken on an area basis. Five sub-plotsŽ 2 .0.25 m were selected at random. Species werenot separated. Twenty soil cores per plot were

Ž .taken core � 6.0 cm and divided into LF- andH-horizons, care was taken to remove mineralsoil and mosses from the samples. The organic

Ž .soil material was sieved 5.6 mm mesh size . Visi-ble wood-ash granules were removed and wereanalysed separately. Material that could not passthrough the sieve, i.e. roots and possibly also rootassociations, was discarded. After sieving, thesamples were bulked into a single sample per plotand horizon. Two sub-samples were taken fromeach bulked sample, one was stored in the freezerawaiting analysis of K content and the other was

Ž . 137dried 70�C for 24 h and used for Cs analysis.Data on 137Cs are presented as radioactivity con-

Ž �1 .centrations Bq kg , but in addition soil dataand field-layer data are presented on an area

Ž �2 . 137basis Bq m . The Cs analyses of soil andfield-layer vegetation were made by GammaDataAB in Uppsala with a NaI gamma ray detectorŽ .SS-EN 45 001 . The analyses of the needles andtwigs were made at the Department of Soil Sci-ence, Swedish University of Agricultural Sciences,Uppsala, with a GeLi detector. The content of Kin the soil was measured after extraction with 1 Mammonium lactate, pH 3.75. This analysis wasconducted by the Department of Soil Science,Swedish University of Agricultural Sciences, Upp-sala. No adjustment of the data due to radioactivedecay was made, because the only comparisonsmade were within sites, and the sampling andmeasurements for each site were made within afew days so time effects would be negligible.

The effects of wood-ash addition were assessedusing a Student’s t-test, except for the data fromRiddarhyttan, which were analysed using a one-way ANOVA to compare the two treatments withthe single control plot. For this site a two-wayANOVA had indicated that there were no blockeffects. Levels of significance are indicated as


dictated by convention: P�0.05�� ; P�0.01�� ; and P�0.001��.

3. Results

Samples that were analysed by both detectorsŽ 2 .showed a high correlation R �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 sam-pling. This was the case for the pelleted ash at˚ �1 �2Ž .Aled 196 Bq kg , equivalent to 0.10 kBq m

Ž �1and Riddarhyttan II 2479 Bq kg , equivalent to�2 .0.20 kBq m and the granulated ash at Vindeln

Ž �1 �2 .2267 Bq kg , equivalent to 0.40 kBq m andŽ �1Torup 1418 Bq kg , equivalent to 0.33 kBq

�2 .m . The values within parentheses are the ac-tual activities measured for the ashes sampled.These pellets or granules were all present in theupper-most layer of the horizons sampled. Theywere removed and analysed separately, and theresults were added to those for the main sample.For these four cases radioactivity data are pre-sented both with and without ash. The wood-ashpellets or granules at other sites did not add tothe total 137Cs activity of the sites.

In the soil, there was no evidence that radioac-tivity was consistently higher on wood-ashamended plots than on control plots, for either

Ž .the LF- or H-horizons Table 2 . There weredifferences in the amounts of soil organic matter

Ž .turnover between plots Table 3 . When calculat-Ž �2 .ing the radioactivity on an area basis Bq m

rather than on a weight basis, some of the differ-ences between treated and control plots were

Žincreased, while others were reduced Tables 2.and 4 .

As expected, those sites with the lowest back-ground radioactivity on the basis of reference

˚Žmaps namely Aled, Torup, Riddarhyttan and¨ .Alvsbyn also had the lowest activity measured in

Ž .the soil Table 4 . Despite differences in theradioactivity of the wood-ash applied, rangingfrom 0.03 to 4.8 kBq kg�1, no increase in 137Csactivity was detected following application at these

Ž .low-activity sites Table 4 when the wood-ashgranules were removed. On the contrary, a statis-

tically significant decrease in the amount of ra-dioactivity in the H-layer at the Torup site was

Ž .found Table 4 . Of particular interest is the site,which received the highest relative addition, Rid-darhyttan, where a doubling of the radioactivity,because of the wood-ash application, was ex-pected. However, there was no significant differ-ence between the control and the treated plotsŽ .Table 4 .

At the two sites with the highest backgroundŽ .radioactivity Hassel and Vindeln , the radioactiv-

ity in the organic soil layers was significantlylower in the ash-amended plots than in the con-

Ž .trol plots at Vindeln Table 4 , while the radioac-Ž .tivity was unaffected at Hassel Table 4 .

The K content in the soil 5�8 years after treat-ment, was generally unaffected by the wood-ash

Ž .application Table 4 . In the H-layer at Vindeln,a significantly lower concentration of K wasmeasured in the plots with wood-ash applicationŽ .Table 4 . The same wood-ash caused no sucheffect at the Torup site.

Several sites which had field-layer vegetation¨Ž .Alvsbyn, Vindeln and Riddarhyttan . The ra-

dioactivity within the field-vegetation was one-fifththat of the soil at Vindeln but was comparable atthe other two sites. As expected, the highestradioactivity was measured at Vindeln, but nostatistically significant differences between con-

Žtrol plots and ash-treated plots were found Table.4 .Effects of the previous wood-ash application on

137Cs in the canopy could only be detected at theŽ .Vindeln site Table 2 . The wood-ash application

significantly reduced 137Cs activity in the needlesand current-year twigs. Apparently at Vindeln,the wood-ash application had reduced the plant-available 137Cs. Despite the lack of statisticallysignificant results at the other sites, there was, inmost cases, a tendency towards a reduction in

Žradioactivity in the wood-ash treated plots Table.2 .

4. Discussion

K salts have been shown to be an effectiveagent for redistribution of 137Cs within the soil


Table 2137 �1Ž .Radioactivity concentrations of Cs Bq kg . 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.�not analysed. For the siteRiddarhyttan, values not followed by the same letter columnwise are significantly different at the P�0.05 level

Site Background Soil LF- Soil H- Current year Needles of Current year Twigs ofactivity incl. horizon horizon needles previous twigs previousash activity year year

�2Ž .kBq m

AledControl 0�2 74.0�4.43 65.0�3.18 50.1�34.8 35.6�6.4 46.9�18.8 69.2�26.4Ash �0.01 60.3�4.43 72.0�2.08 37.8�11.8 17.1�10.5 47.3�25.2 62.3�56.4P-value 0.11 0.18 0.38 0.11 0.49 0.46

TorupControl 0�2 75.7�4.40 53.0�1.35 83.2�8.21 55.9�4.2 75.4�26.3 71.0�13.3Ash �0.63 87.3�6.05 43.7�1.35 63.2�15.4 50.1�7.1 80.9�3.72 56.7�7.31

�P-value 0.21 0.05 0.17 0.27 0.42 0.21

RiddarhyttanaControl 0�2 166�1.92 126�3.34 103�23.1 112�87.0 76.4�7.94 27.1�4.02abAsh I �0.48 215�16.3 123�6.88 55.3�10.2 18.6�5.59 40.0�17.8 22.9�12.4bAsh II �1.44 303�9.46 131�2.12 76.2�16.0 29.8�4.11 43.6�25.0 41.8�27.4

�P-value 0.05 0.84 0.22 0.51 0.36 0.74

HasselControl 30�40 2380�67.3 2000�60.9 872�37.7 694�49.3 1150�158 580�100Ash �0.48 2190�4.25 2230�80.4 944�233 521�70.7 1130�232 744�186P-value 0.12 0.14 0.39 0.06 0.48 0.24

VindelnControl 10�20 1900�79.5 1240�91.5 304�44.2 161�35.8 219�15.5 140�12.7Ash �0.63 1780�194 1420�60.7 171�40.7 62.3�19.5 135�29.1 135�33.4

� � �P-value 0.38 0.20 0.05 0.05 0.04 0.45

AlvsbynControl 0�2 39.7�9.05 55.3�1.90 42.0�10.5 19.4�9.82 58.0�20.4 63.5�42.4Ash �0.48 84.3�10.5 87.0�3.18 22.1�13.7 11.0�3.20 44.2�22.5 0.00�0.00

��P-value 0.07 0.006 0.16 0.25 0.34 0.14

system. For a large number of soil profiles, SchulzŽ .et al. 1959 demonstrated a rapid decrease in

137Cs activity after the addition of KCl. However,depending on the soil type and the dominant claymineral, the effect varied substantially, from adecrease of few percent to one of almost 80%.

Ž .Bunzl et al. 1989 reported on a migration ratefor 137Cs of between 2 and 4 cm year�1 for theirsite at Hoglwald in Bavaria, Germany. However,¨since a large part of the 137Cs radioactivity isassociated with fungal material in the soil, it islikely that relocation occurs within the soil systemvia fungal mycelia.

In general, the 137Cs activity in the wood-ashes

applied did not increase the radioactivity withinthe vegetation or the soil. On the contrary,radioactivity tended to decrease following thewood-ash application. The effect was mostpronounced at the Vindeln site, where a statisti-cally significant effect was found, both in the soilorganic matter and in needles and twigs of P.syl�estris. The wood-ash used at Vindeln was alsoused at Torup. At the latter site, however, asignificant decrease of the activity of 137Cs wasfound only in the soil H-layer. Some of theseeffects are caused by the reduction in soil organicmatter following wood-ash application.

The intrinsic antagonistic behaviour between K


Table 3�2Ž .Weight kg d.m. m of the soil organic horizons at the study sites

Site Background Soil LF- Soil H- Totalactivity horizon horizon organicincl. ash soilactivity horizon

�2Ž .kBq m

AledControl 0�2 24.6�0.88 46.9�2.95 71.5�3.64Ash �0.01 30.6�1.06 44.2�2.02 74.8�2.80

�P-value 0.04 0.35 0.35

TorupControl 0�2 27.4�2.14 31.2�1.49 58.7�3.61Ash �0.63 25.1�1.22 26.3�2.49 51.5�3.32P-value 0.31 0.20 0.22

RiddarhyttanControl 0�2 4.00�0.34 6.08�0.99 10.1�1.13Ash I �0.48 3.68�0.22 7.78�0.74 11.5�0.97Ash II �1.44 2.88�0.20 4.31�1.03 7.20�1.15P-value 0.27 0.38 0.33

HasselControl 30�40 10.4�1.20 20.7�1.83 31.1�3.02Ash �0.48 12.0�1.02 17.3�0.81 29.3�1.63P-value 0.29 0.20 0.39

VindelnControl 10�20 6.82�0.53 12.0�1.07 18.8�1.60Ash �0.63 5.23�0.60 6.36�0.48 11.6�1.05

� �P-value 0.16 0.04 0.05

AlvsbynControl 0�2 7.69�0.92 12.1�1.38 19.8�1.28Ash �0.48 5.78�0.18 8.08�0.50 13.9�0.68

�P-value 0.17 0.11 0.05

and Cs, and differences in solubility between theashes in use are the most likely reasons for thesedifferences in effects. The internal relocation of137Cs follows the same general pattern as for K.This means that higher concentrations of 137Csare found in new shoots than in older ones. Inmost cases for needles in our study, this pattern

Ž .could be discerned Table 2 . In the case of thetwigs, the difference between current year twigsand 1-year-old twigs was minute. In contrast,

Ž . 137Ronneau et al. 1987 reported higher Cs activ-ity in current year shoots compared with 1-year-old shoots.

We did not find any statistically significantchanges in the radioactivity of the field-layer veg-etation due to the application of ash. At Rid-darhyttan, however, there were indications that

Ž .one of the ash treatments Ash I reduced ra-dioactivity. This could be an effect of differentK-release speeds in the two ashes. However, laterstudies of K distribution at that site did not revealany differences in K distribution within the soil

Žprofile Hogbom and Nohrstedt personal commu-¨.nication . Other studies have examined field-layer

Ž .vegetation, e.g. Levoula et al. 2000 found adecrease in 137Cs activity following wood-ash ad-


Table 4137 aŽ .Radioactivity of Cs mean values�1.S.E. in soil and field-layer vegetation following wood-ash amendment

�2 �2Ž . Ž .Site Background Field-Soil activity kBq m K content g mactivity incl. vegetationF-layer H-layer Total soil F-layer H-layer Total soilash activity activity

�2 �2Ž . Ž .kBq m Bq m

Aled No field-Control 0�2 1.82�0.05 3.18�0.13 5.06�0.69 layer 1.55�0.04 1.50�0.17 3.05�0.21

Ž .Ash �0.01 2.73�0.33 3.20�0.37 5.00 5.10 �0.07 2.00�0.32 1.37�0.14 3.36�0.45P-value 0.45 0.49 0.47 0.12 0.29 0.28

Torup No field-Control 0�2 2.04�0.19 1.65�0.11 3.68�0.29 layer 1.54�0.20 1.30�0.16 2.85�0.33

Ž .Ash �0.63 2.27�0.40 1.13�0.13 3.36 3.69 �0.45 1.73�0.28 1.15�0.16 2.88�0.42�P-value 0.35 0.02 0.29 0.31 0.28 0.47

RiddarhyttanControl 0�2 0.66�0.11 0.77�0.22 1.43�0.24 7.75�2.13 0.77�0.15 1.06�0.19 1.83�0.32Ash I �0.48 0.71�0.03 1.24�0.17 1.57�0.20 2.37�0.48 1.01�0.32 1.54�0.08 2.55�0.25

Ž .Ash II �1.44 0.87�0.11 1.04�0.42 1.32 1.52 �0.43 7.75�1.85 0.95�0.09 1.08�0.24 2.03�0.30P-value 0.53 0.89 0.93 0.31 0.73 0.18 0.27

Hassel No field-Control 30�40 24.3�3.62 40.8�3.88 65.1�7.42 layer 1.26�0.24 1.55�0.29 2.81�0.53Ash �0.48 25.6�4.65 38.0�0.99 63.6�4.72 1.54�0.28 1.86�0.17 3.40�0.34P-value 0.42 0.27 0.44 0.25 0.21 0.20

VindelnControl 10�20 12.9�1.64 14.3�0.72 27.3�1.86 72.4�24.0 0.87�0.11 0.97�0.05 1.84�0.14

Ž .Ash �0.63 8.84�1.10 8.94�1.10 17.8 18.0 �1.94 59.9�13.8 0.94�0.21 0.77�0.04 1.71�0.23� �� P-value 0.05 0.01 0.01 0.38 0.39 0.02 0.33

AlvsbynControl 0�2 0.29�0.10 0.65�0.09 0.95�0.18 3.86�2.00 0.82�0.19 1.08�0.19 1.91�0.36Ash �0.48 0.48�0.09 0.71�0.11 1.19�0.14 2.89�1.66 0.76�0.07 1.29�0.20 2.05�0.25P-value 0.13 0.36 0.18 0.35 0.39 0.25 0.38

a The P-value given is for each comparison between control and ash amended plots. The values in parentheses include that forthe 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-ideain Finland.

Based on our observations the following hy-pothesis was formulated, this could be the subjectof future are more detailed investigations. Theaddition of wood-ash increased the downwardmigration velocity of 137Cs, probably because ofthe K content of the wood-ash and a postulatedpH increase. However, this may be partially coun-teracted by the content and internal redistribu-tion of 137Cs within fungal mycelia and the my-corrhizal network. The effect of a wood-ash addi-

tion on soil radiation ecology is dependent on alarge number of factors, including: 137Cs migra-tion rate, which is affected by soil type, claycontent and the type of clay minerals present; Krelease from the wood-ash particles and pHeffects; plant K demand and type; and the abun-dance of fungal species. The effects of wood-ashaddition on forests requires further studies involv-ing long-term monitoring of the transport andmovement of radio-caesium within the forestecosystem. Future work should examine differentapplication rates of wood-ash and short-term


studies of K addition, as well as more detailedstudies on the turnover of soil organic matter.

In conclusion, the application of wood-ash con-taminated with 137Cs did not significantly increasethe 137Cs radioactivity within the biological sys-tem. On the contrary, there were tendencies to-wards a decrease in 137Cs activity concentrationsand in one case this decrease was statisticallysignificant, but this could partly be an effect ofthe low number of replicates.

Acknowledgements

We would like to thank Dr Klas Rosen, De-´partment of Soil Science, Swedish University ofAgricultural Sciences, Uppsala and Anund Lind-holm, GammaData AB, Uppsala, for conductingthe analyses. This study was supported financiallyby the Swedish National Energy AdministrationŽ .STEM and the Swedish Radiation Protection

Ž .Institute SSI .

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

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