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Distribution of radionuclides in forest soils of varying pedochemistry
Radiation Physics and Chemistry 61 (2001) 705–706
Distribution of radionuclides in forest soils of varying pedochemistry S. Schlenkera,*, D. Degeringa, S. Unterrickera, G. Rabenb a
TU Bergakademie Freiberg, Institute of Applied Physics, Bernhard-von-Cotta-Str. 4, D-09596 Freiberg, Germany b Saxon State Agency for Forestry, Bonnewitzer Str. 34, D-01827 Graupa, Germany
Abstract The distribution of radionuclides in soils has been investigated by low-level gamma spectrometry. Four forest sites of different soil types and local vegetation located in Saxony/Germany at Lausnitz, Colditz and two sections at Olbernhau were chosen. For each section thin-layer sampling was applied. The analysed radioisotopes included artificial, cosmogenic and natural nuclides. The radionuclide migration in the investigated soils was found to be governed by the chemical conditions of the layer. r 2001 Elsevier Science Ltd. All rights reserved. Keywords: Radioecology; Gamma spectrometry; Radioisotopes; Forestry
1. Introduction The migration behaviour of trace elements and pollutants can be studied very specifically by means of radioisotopes. For most radioisotopes the time dependence, the quantity and the pathway of the input are known. Therefore radionuclide movement can be used for dating of soil processes. Forest soils are suitable for radionuclide investigations because they are usually not disturbed by cultivation over long periods of time. On the other hand, forests are a natural filter for radioisotope bearing . aerosols (Voland and Gotze, 1988). The main question of the present work concerns how the distribution of radionuclides in soil depends on environmental conditions like vegetation, meteorological conditions, geological background, etc. 2. Experimental details The analysed radionuclides include artificial nuclides from fallout following the nuclear weapon tests in the *Corresponding author. Tel.: +49-3731-39-2163; fax: +493731-39-4004. E-mail address: [email protected] (S. Schlenker).
fifties and sixties (137Cs, (241Pu ) )241Am, 207Bi) and after the Chernobyl accident (137Cs, 134Cs, 125Sb), the cosmogenic 7Be, members of the natural decay series of 238 U (e.g. 238U, 226Ra, 210Pb) and 232Th (228Ra and 228 Th) as well as 40 K. Soil profiles were taken at four intensively monitored forest sites (Level II - European monitoring program). These sites are a part of the European Forestry Environmental Program exploring the conditions and development of forestry ecosystems. They are located in Saxony/Germany at Lausnitz, Cloditz and two sections at Olbernhau. For these places an extensive database is available, which has been collected for more than twenty years (Raben et al., in press). For the measurements, sampling sites representing different soil types (podzol, braunerde-podzol, similigley) and different local vegetation were located in Saxony (Germany). The soil type was determined according to the German nomenclature (Arbeitsgemeinschaft Bodenkunde, 1994). At each section, thin-layer sampling was applied. Layers of 30 30 cm2 area and 1–2 cm thickness each were taken from the surface litter down to the geological subsoil. The samples were dried at 401C, homogenized and stored in Marinelli beakers at least 10 days to restore the
0969-806X/01/$ - see front matter r 2001 Elsevier Science Ltd. All rights reserved. PII: S 0 9 6 9 - 8 0 6 X ( 0 1 ) 0 0 3 8 0 - 2
706
S. Schlenker et al. / Radiation Physics and Chemistry 61 (2001) 705–706
radioactive equilibrium between 226Ra and the Rndaughters. Investigations were carried out using a low-level gamma spectrometry system which comprised two gspectrometers containing a 36% p-type and a 38% ntype HPGe-detector, respectively and analysed by the use of appropriate calibration standards. The effect of self-attenuation was taken into account.
3. Results In all investigated sections, the nuclides 241Am, 207Bi and 125Sb (Fig. 1) and excess-210Pb (Fig. 2) remain in soil layers of high organic content (O-, Ah-horizon). Their distributions can be used for an age determination of the horizons. The mobility of 134Cs and 137Cs (Fig. 1) is apparently higher. The Cs-nuclides originating from the Chernobyl accident show their maximum in the Of–Oh horizons. 137 Cs containing also a part from nuclear weapons fallout is found down to the C-horizon. Uptake of Cs by plants controls its behaviour in the surface layers. The activity of the natural radioisotope 40 K (not shown) reproduces the concentration of the plant nutrient potassium in the soil. Its activity concentration decreases significantly in the organic horizons (L-, O-, Ah-horizons). Disequilibria between uranium and radium are obvious in the Of-, Oh- as well as in the Bshorizons (Fig. 2). They reflect uranium accumulation by degraded plant material and radium transport, respectively.
Fig. 2. Distribution of members of the 238U decay series exemplary shown at sampling site Olbernhau 1. The excess of 210 Pb over 226Ra is due to its atmospheric input as a Radon daughter nuclide.
4. Conclusion Although in all cases similar sequences of horizons were observed, their thicknesses were different due to differences in vegetation, rainfall, subsoil, etc. The distributions of the radionuclides are influenced by the kind of horizon rather than by the depth. Each horizon is characterized by certain chemical and biological conditions (e.g. redox chemistry, pH-value, degree of plant decomposition, bacterial activity, etc) and these are decisive for the retention time in the horizon, this means that nuclide migration in the investigated soils is mainly governed by the chemical conditions of the layer.
Acknowledgements This work has been financially supported by Deutsche Forschungsgemeinschaft, DFG-Graduate School for Environmental Research in Geoscience and Geotechnics.
References
Fig. 1. Distribution of artifical radionuclides at sampling site Olbernhau 1 (soil type: braunerde-podzol).
Arbeitsgemeinschaft Bodenkunde., 1994. Bodenkundliche Kartieranleitung, 4. Aufl., Schweizerbart, Stuttgart. Raben, G., Andrae, H., Meyer, M., 2000. Long-term acid load and its consequences in forest ecosystems of Saxony (Germany). Water, Earth, Soil Pollution 122(1/2), 93–103. . Voland, B., Gotze, J., 1988. Gesetzm.aigkeiten der geochemischen Zusammensetzung von Aerosolen unterschiedlicher Herkunft. Z. Angew. Geol. 34, 313–318.
Distribution of radionuclides in forest soils of varying pedochemistry S. Schlenkera,*, D. Degeringa, S. Unterrickera, G. Rabenb a
TU Bergakademie Freiberg, Institute of Applied Physics, Bernhard-von-Cotta-Str. 4, D-09596 Freiberg, Germany b Saxon State Agency for Forestry, Bonnewitzer Str. 34, D-01827 Graupa, Germany
Abstract The distribution of radionuclides in soils has been investigated by low-level gamma spectrometry. Four forest sites of different soil types and local vegetation located in Saxony/Germany at Lausnitz, Colditz and two sections at Olbernhau were chosen. For each section thin-layer sampling was applied. The analysed radioisotopes included artificial, cosmogenic and natural nuclides. The radionuclide migration in the investigated soils was found to be governed by the chemical conditions of the layer. r 2001 Elsevier Science Ltd. All rights reserved. Keywords: Radioecology; Gamma spectrometry; Radioisotopes; Forestry
1. Introduction The migration behaviour of trace elements and pollutants can be studied very specifically by means of radioisotopes. For most radioisotopes the time dependence, the quantity and the pathway of the input are known. Therefore radionuclide movement can be used for dating of soil processes. Forest soils are suitable for radionuclide investigations because they are usually not disturbed by cultivation over long periods of time. On the other hand, forests are a natural filter for radioisotope bearing . aerosols (Voland and Gotze, 1988). The main question of the present work concerns how the distribution of radionuclides in soil depends on environmental conditions like vegetation, meteorological conditions, geological background, etc. 2. Experimental details The analysed radionuclides include artificial nuclides from fallout following the nuclear weapon tests in the *Corresponding author. Tel.: +49-3731-39-2163; fax: +493731-39-4004. E-mail address: [email protected] (S. Schlenker).
fifties and sixties (137Cs, (241Pu ) )241Am, 207Bi) and after the Chernobyl accident (137Cs, 134Cs, 125Sb), the cosmogenic 7Be, members of the natural decay series of 238 U (e.g. 238U, 226Ra, 210Pb) and 232Th (228Ra and 228 Th) as well as 40 K. Soil profiles were taken at four intensively monitored forest sites (Level II - European monitoring program). These sites are a part of the European Forestry Environmental Program exploring the conditions and development of forestry ecosystems. They are located in Saxony/Germany at Lausnitz, Cloditz and two sections at Olbernhau. For these places an extensive database is available, which has been collected for more than twenty years (Raben et al., in press). For the measurements, sampling sites representing different soil types (podzol, braunerde-podzol, similigley) and different local vegetation were located in Saxony (Germany). The soil type was determined according to the German nomenclature (Arbeitsgemeinschaft Bodenkunde, 1994). At each section, thin-layer sampling was applied. Layers of 30 30 cm2 area and 1–2 cm thickness each were taken from the surface litter down to the geological subsoil. The samples were dried at 401C, homogenized and stored in Marinelli beakers at least 10 days to restore the
0969-806X/01/$ - see front matter r 2001 Elsevier Science Ltd. All rights reserved. PII: S 0 9 6 9 - 8 0 6 X ( 0 1 ) 0 0 3 8 0 - 2
706
S. Schlenker et al. / Radiation Physics and Chemistry 61 (2001) 705–706
radioactive equilibrium between 226Ra and the Rndaughters. Investigations were carried out using a low-level gamma spectrometry system which comprised two gspectrometers containing a 36% p-type and a 38% ntype HPGe-detector, respectively and analysed by the use of appropriate calibration standards. The effect of self-attenuation was taken into account.
3. Results In all investigated sections, the nuclides 241Am, 207Bi and 125Sb (Fig. 1) and excess-210Pb (Fig. 2) remain in soil layers of high organic content (O-, Ah-horizon). Their distributions can be used for an age determination of the horizons. The mobility of 134Cs and 137Cs (Fig. 1) is apparently higher. The Cs-nuclides originating from the Chernobyl accident show their maximum in the Of–Oh horizons. 137 Cs containing also a part from nuclear weapons fallout is found down to the C-horizon. Uptake of Cs by plants controls its behaviour in the surface layers. The activity of the natural radioisotope 40 K (not shown) reproduces the concentration of the plant nutrient potassium in the soil. Its activity concentration decreases significantly in the organic horizons (L-, O-, Ah-horizons). Disequilibria between uranium and radium are obvious in the Of-, Oh- as well as in the Bshorizons (Fig. 2). They reflect uranium accumulation by degraded plant material and radium transport, respectively.
Fig. 2. Distribution of members of the 238U decay series exemplary shown at sampling site Olbernhau 1. The excess of 210 Pb over 226Ra is due to its atmospheric input as a Radon daughter nuclide.
4. Conclusion Although in all cases similar sequences of horizons were observed, their thicknesses were different due to differences in vegetation, rainfall, subsoil, etc. The distributions of the radionuclides are influenced by the kind of horizon rather than by the depth. Each horizon is characterized by certain chemical and biological conditions (e.g. redox chemistry, pH-value, degree of plant decomposition, bacterial activity, etc) and these are decisive for the retention time in the horizon, this means that nuclide migration in the investigated soils is mainly governed by the chemical conditions of the layer.
Acknowledgements This work has been financially supported by Deutsche Forschungsgemeinschaft, DFG-Graduate School for Environmental Research in Geoscience and Geotechnics.
References
Fig. 1. Distribution of artifical radionuclides at sampling site Olbernhau 1 (soil type: braunerde-podzol).
Arbeitsgemeinschaft Bodenkunde., 1994. Bodenkundliche Kartieranleitung, 4. Aufl., Schweizerbart, Stuttgart. Raben, G., Andrae, H., Meyer, M., 2000. Long-term acid load and its consequences in forest ecosystems of Saxony (Germany). Water, Earth, Soil Pollution 122(1/2), 93–103. . Voland, B., Gotze, J., 1988. Gesetzm.aigkeiten der geochemischen Zusammensetzung von Aerosolen unterschiedlicher Herkunft. Z. Angew. Geol. 34, 313–318.