Stocks and dynamics of SOC in relation to soil redistribution by water and tillage erosion

Soil organic carbon (SOC) displaced by soil erosion is the subject of much current research and the fundamental question, whether accelerated soil erosion is a source or sink of atmospheric CO₂, remains unresolved. A toposequence of terraced fields as well as a long slope was selected from hilly areas of the Sichuan Basin, China to determine effects of soil redistribution rates and processes on SOC stocks and dynamics. Soil samples for the determination of caesium‐137 (¹³⁷Cs), SOC, total N and soil particle size fractions were collected at 5 m intervals along a transect down the two toposequences. ¹³⁷Cs data showed that along the long slope transect soil erosion occurred in upper and middle slope positions and soil deposition appeared in the lower part of the slope. Along the terraced transect, soil was lost over the upper parts of the slopes and deposition occurred towards the downslope boundary on each terrace, resulting in very abrupt changes in soil redistribution over short distances either side of terrace boundaries that run parallel with the contour on the steep slopes. These data reflect a difference in erosion process; along the long slope transect, water erosion is the dominant process, while in the terraced landscape soil distribution is mainly the result of tillage erosion. SOC inventories (mass per unit area) show a similar pattern to the ¹³⁷Cs inventory, with relatively low SOC content in the erosional sites and high SOC content in depositional areas. However, in the terraced field landscape C/N ratios were highest in the depositional areas, while along the long slope transect, C/N ratios were highest in the erosional areas. When the samples are subdivided based on ¹³⁷Cs‐derived erosion and deposition data, it is found that the erosional areas have similar C/N ratios for both toposequences, while the C/N ratios in depositional areas are significantly different from each other. These differences are attributed to the difference in soil erosion processes; tillage erosion is mainly responsible for high‐SOC inventories at depositional positions on terraced fields, whereas water erosion plays a primary role in SOC storage at depositional positions on the long slope. These data support the theory that water erosion may cause a loss of SOC due to selective removal of the most labile fraction of SOC, while on the other hand tillage erosion only transports the soil over short distances with less effect on the total SOC stock.     

Movement of [14C]sucrose along the stolon of Saxifraga sarmentosa

Summary The characteristics of ¹³⁷Cs transport along the stolon of Saxifraga previously reported have been confirmed for applied sucrose and natural assimilate. Long-distance transport is strictly unidirectional, with a symmetrical short-distance spread from the point of application. Only the latter takes place in a long piece of excised stolon. Transport is readily reversed when the parent plant is darkened and the daugther, plantlet allowed to photosynthesise. These findings strongly support a mass-flow mechanism for the stolon. They also confirm the value of ¹³⁷Cs as a tracer for assimilate movement, though in contrast to assimilate it suffers appreciable lateral leakage. Pulse labelling of the subtending leaf failed to produce a sharp peak of activity in the stolon. A flattening with time of the ¹⁴C profile is considered to be due to differing linear velocities in parallel sieve tubes.This work formed part of that submitted for the degree, of Ph. D. of the University of London.     

向日葵(Helianthus annuus L.)对133Cs、88Sr的吸收和分布

通过盆栽试验研究了向日葵(Helianthus annuus L.)对土壤中不同处理浓度¹³³Cs和⁸⁸Sr的吸收,以及¹³³Cs和⁸⁸Sr在向日葵不同部位的分布。结果表明：随着处理浓度的增加,植物中¹³³Cs或⁸⁸Sr的含量增加。同一处理浓度下,⁸⁸Sr含量约比¹³³Cs含量高一个数量级。¹³³Cs和⁸⁸Sr在植物不同部位分布不同。根部中¹³³Cs含量高于植物的其他部位（茎、叶、花）。不同于¹³³Cs在植物中的分布,⁸⁸Sr除在根中的分布外,主要转运到了叶片。¹³³Cs和⁸⁸Sr在向日葵体内的分布与目前对放射性¹³⁷Cs和⁹⁰Sr的研究结果相似,所以¹³³Cs和⁸⁸Sr可分别预测¹³⁷Cs和⁹⁰Sr的运转。向日葵是治理大面积低放核素污染土壤的较佳植物种类。     

The Role of Transmembrane Electrical Potential in Determining the Absorption Isotherm for Chloride in Potato

Measurements have been made of the electrical potential differencebetween the vacuoles of single potato tuber cells and externalCl^- solutions over the range 1–40 mM. With K⁺ as the counter-ion,the relationship between this transmembrane electrical potentialand external Cl^- concentration, for fresh cells at 20° C,was found to be one of decreasing negative polarity with increasingCl^- concentration (E at 1 mM Cl^- external = – 81 m V;change in E for a 10-fold change in external concentration,E₁₀ = 46 m V). The linearity of this relationship, apparenton a semi-logarithmic plot, was virtually unaltered by low temperature(0.5–2.5° C) or by previous ageing of the cells forperiods up to four days (indicating that metabolic ion absorptionis not an electrogenic process). When the counter-ion was maintainedat a constant high concentration (40 mM K⁺), the change in potentialover the Cl^- concentration range was only 4 m V, polarity becomingmore negative with increasing Cl^- concentration. With Ca⁺⁺ asthe counter-ion, the potential to external Cl^- concentrationrelationship was similar to that found in KCl solutions, exceptthat E₁₀ was only about 20 m V. Curves for the influx of C1^- to be expected on the basis ofthese electrochemical data alone have been shown to run closelyparallel to Cl^– absorption isotherms previously determinedexperimentally. This confirms the opinion, already formed onthe basis of theoretically derived values for passive Cl^- influx,that Cl^- uptake by both fresh and one-day-aged potato tissue,from KCl solutions and Cl^- solutions with a fixed high K⁺ concentration,is rate-determined at o° C by passive movement across theplasmalemma. Uptake of Cl^- by fresh tissue at 20° C appearsto be similarly regulated. No such parallelism was found between observed and expectedpatterns of Cl^- uptake from CaCl₂ solutions, or from KCl bytwo-day-aged tissue, and here factors in addition to the electrochemicalones must determine low temperature Cl^-uptake.     

Response of changes in soil nutrients to soil erosion on a purple soil of cultivated sloping land

Severe soil erosion of cultivated sloping land in hilly areas of Sichuan, China, has resulted in deterioration of soil quality, and therefore has an adverse impact on crop production. A hillslope of 110 m in length was selected with a slope steepness of 10.12% where the soils were classified as Regosols. Soil samples for determining ¹³⁷Cs, soil organic matter (SOM), total N, P, K, available N, P, K and particle size fraction were collected at 10 m intervals along a transect of the hillslope. Loss of soil nutrients owing to soil erosion was studied by using ¹³⁷Cs technique, and the relationships between ¹³⁷Cs-derived soil redistribution rates and soil nutrients were established over the cultivated sloping land in hilly areas of Sichuan, China (30o26′N, 104o28′E). The values of SOM, total N, available N, P, K and the soil particle fractions of size < 0.002 mm were smaller at upper and middle slope positions where ¹³⁷Cs inventories were lower (i.e., soil erosion rates were higher) than at downslope positions where ¹³⁷Cs inventories were higher (i.e., soil erosion rates were lower). The lowest ¹³⁷Cs inventories were found at the hilltop, showing that besides erosion owing to water flow, tillage also contributed to soil losses, and intensive tillage was mostly responsible for severe erosion at upper slope positions. There were significant differences in SOM, total N, available N, P, K and the soil particle fractions of size < 0.002 mm between different slope segments, and these properties were significantly correlated with slope length. These soil properties were also significantly correlated with ¹³⁷Cs inventories, indicating that both ¹³⁷Cs and nutrient concentrations varied with topographical changes. The variation in soil properties was strongly influenced by erosion-induced soil redistribution, and therefore ¹³⁷Cs inventories mirroring soil redistribution rates would be considered as an integrated indicator of soil quality.     

Identification of processes governing long-term accumulation of 137Cs by forest trees following the Chernobyl accident

The regularities of ¹³⁷Cs distribution in trees (Pinus sylvestris and Betula pendula) growing in different types of forest ecosystems were investigated. High levels of heterogeneity of ¹³⁷Cs activity concentrations in different parts of the trees, resulting from their varied metabolism have been shown. The data obtained demonstrate a non-uniform character of ¹³⁷Cs distribution along the trunks, which can be explained by radio- nuclide fixation by the xylem vessel walls and by geometry changes along the tree trunk. It has been found that the radial distribution of ¹³⁷Cs in the tree trunk is dependent on the availability of ¹³⁷Cs in soil, which governs the transfer of this radionuclide via xylem sap and on the properties of the xylem. The accumulation of ¹³⁷Cs by trees was influenced by the vertical distribution and availability of ¹³⁷Cs in the soil as well as by the root biomass distribution in different soil horizons. A bioavailability factor, which takes into account the vertical distribution of radiocesium in soil, bioavailability of this radionuclide and distribution of root biomass in different soil horizons is proposed for comparative analyses of ¹³⁷Cs transfer from soil to trees in different types of forest ecosystems. Received: 8 February 2000 / Accepted: 1 December 2000     

137Cs示踪技术研究坡耕地黑土侵蚀和沉积特征

准确地测定研究区137Cs背景值,建立137Cs流失量与土壤再分布速率之间的定量模型是137Cs示踪技术的关键。通过野外选择参照样地和利用热核爆炸源137Cs背景值模型来确定研究区137Cs的背景值,在此基础上用体现耕作迁移的质量平衡模型估算黑土坡耕地不同地貌部位的土壤再分布速率,并对主要参数进行敏感性分析。结果表明(1)研究区实测的137Cs背景值为2376.81±108.46Bq/m2,模型预测值为2318.4Bq/m2,模型预测远离西北核试验基地的地区较为准确。(2)研究区中坡位(坡肩和坡背)137Cs含量最低,侵蚀最为强烈,平均侵蚀速率为33.56t/(hm2·a)和21.67t/(hm2·a);坡麓和坡足则明显表现沉积,平均沉积速率为-4.93t/(hm2·a)和-24.61t/(hm2·a)。(3)模型预测的侵蚀速率与耕层质量深度(d)、张驰深度(H)正相关,而与137Cs年沉降易被迁移的比例(γ)和颗粒校正因子(P)反相关。并且,模型对参数d、p的敏感性分别高于参数H和γ。     

Major and trace elements in the twig axes of Norway spruce and the relationship between twig axis and needles

Summary The concentrations of 23 elements have been determined by instrumental neutron activation analysis in the needles and axes of 1-year-old spruce twigs from 12 different sites. Although the twigs had been washed with toluene and tetrahydrofuran prior to analysis, it was found that the amounts of eight elements (Al, Cr, Eu, Fe, La, Sc, Th and V) present were predominantly due to aerosol particles still being retained on the surface of the axes. The results of the remaining 15 elements (Ba, Br, Ca, Cl, Co, Cs, Hg, K, Mg, Mn, Na, P, Rb, Sr and Zn) were not or only slightly influenced by this effect and are considered to represent their inherent concentrations within the axes. With most of these latter 15 elements there are highly significant and linear correlations between the concentrations in the needles and in the axis, which testify to the great similarity of needles and axis of a twig. The axis/needles ratios are constant for every element (except K), but the individual elements show considerable differentiation, as evidenced by their ratios, which have values between 0.5 and 2.8. Inter-element correlations in the axes are mainly found within two groups of elements. With Na, Cl and Br these correlations are probably due to different pollution levels of the different sites, whereas with Mn, Co, Rb and Cs they are due to the pH of the soil. The activity of ¹³⁷Cs from the Chernobyl fallout represents independent confirmation of the results obtained with the stable elements. With twigs sprouted before the deposition of the fallout, ¹³⁷Cs acts as a tracer for aerosol particles, whereas it forms a tracer for the stable Cs inherent to the plant with twigs sprouted after the deposition.     

The Uptake of Inorganic Ions by Plant Leaves

A technique for estimating the gross uptake of ions by plantleaves is described. Uptake of strontium-89 and caesium-137from droplets applied to plant leaves was greatly affected bythe humidity of the air, the effect being markedly dependenton the initial concentration of the solution. Uptake was greaterin light than in darkness; the effect of temperature was relativelysmall. The percentage uptake of the nuclides was reduced only to arelatively small extent as the concentration of carrier ionwas increased. This was in marked contrast to the situationwhen leaves were fully immersed in solution. ¹³⁷Cs was takenup to a greater extent than iodine, phosphate, or sulphate.The role of exchange and of fixed negative charges in uptakeis discussed.     

Age-dependent accumulation of <Superscript>137</Superscript>Cs by pike <Emphasis Type="Italic">Esox lucius</Emphasis> in the Yenisei River

Age-dependent accumulation of ¹³⁷Cs in the muscles and bodies of the pike Esox lucius (aged two to seven years) inhabiting a section of the Yenisei River polluted with artificial radionuclides has been studied. The content of ¹³⁷Cs in muscles varied from 0.5 to 7.0 Bq/kg of fresh weight. The maximum content of the radionuclide has been found in juveniles. The content of ¹³⁷Cs in pike muscles and body decreased considerably with age. The high content of ¹³⁷Cs in the muscles of juveniles is probably a consequence of their higher intensity of feeding as compared to older individuals, which is due to the intense growth of juveniles.     

Further studies on the metabolism of glucose in the process of "glucose-bleaching" of Chlorella protothecoides

Previous studies have demonstrated that when cells of Chlorellaprotothecoides are incubated in a medium containing glucosebut no nitrogen source, they are profoundly bleached with degenerationof chloroplast structure and photosynthetic activity. When anitrogen source (urea) is added to the glucose medium, bleachingof algal cells is greatly suppressed. In this work the metabolismof glucose in the process of glucose-induced bleaching was studiedusing ¹⁴C-glucose as tracer. Changes in algal cell activityfor ¹⁴CO₂-evolution and ¹⁴C-incorporation into various cellularsubstances from ¹⁴C-glucose were followed. Most conspicuouswere increases in cellular activities for assimilating ¹⁴C-glucoseinto lipids (fatty acids) and glucose polymer. When urea wasadded to the glucose medium, the incorporation of ¹⁴C by algalcells into fatty acids was greatly reduced, while the assimilationof ¹⁴C into glucose polymer was increased. These and previous observations suggest that the formation oflarge amounts of lipids (fatty acids) probably is causally relatedto the induction of algal cell bleaching. (Received March 5, 1969; )     

Caesium,potassium and ammonium distributions in different organs of tropical plants

In the present work the distribution of ions in aboveground plant parts was studied in order to establish the suitability of using radiocaesium as a tracer for the plant absorption of nutrients, such as potassium (K⁺) and ammonium (NH₄⁺). We present the results for the distributions of ¹³⁷Cs, ⁴⁰K and NH₄⁺ from four tropical plant species: lemon (Citrus aurantifolia), orange (Citrus sinensis), guava (Psidium guajava) and chili pepper (Capsicum frutescens). Activity concentrations of ¹³⁷Cs and ⁴⁰K were measured by gamma spectrometry and concentrations of free NH₄⁺ ions by a colorimetric method. Similarly to potassium and ammonium, caesium showed a high mobility within the plants, exhibiting the highest values of concentration in the growing parts of the tree (fruits, new leaves, twigs, and barks). A significant correlation between activity concentrations of ¹³⁷Cs and ⁴⁰K was observed in these tropical plants. The K/Cs discrimination ratios were approximately equal to unity in different compartments of each individual plant, suggesting that caesium could be a good tracer for ⁴⁰K in tropical woody fruit species. Despite the similarity observed for the behaviour of caesium and ammonium in the newly grown plant compartments, ¹³⁷Cs was not well correlated with NH₄⁺. Significant temporal changes in the NH₄⁺ concentrations were observed during the development of fruits, while the ¹³⁷Cs activity concentration alterations were not of great importance, indicating, therefore, that Cs⁺ and free NH₄⁺ ions could have distinct concentration ratios for each particular plant organ.     

Specific antagonists at the pyridine receptor: evidence from electrophysiological studies with acetylpyridines

The effect of structural isomers of acetylpyridine on the responseof single pyridine-sensitive cells was investigated electrophysiologically.4-Acetylpyridine was identified as a strong specific inhibitorof the response to pyrazine-carboxamide, the most effectivestimulant. When 4-acetylpyridine was present in the concentrationrange from 5 x 10^-5 to 5 x 10^-2 mol/l, the dose-response curveswere shifted to the right, the slope and the common saturationlevel remaining unchanged. This effect can be interpreted asa competitive inhibition. It was also consistent with competitiveantagonism that the Schild plot of these data was linear witha slope close to 1 (0.90). Linear regression indicated an inhibitionconstant K₁ = 40 µmol. 2-Acetylpyridine had a less potentantagonistic effect and an agonistic effect only at high concentrations(>10^–3 mol/1).     

Investigation of Bidirectional Movement of Tracers in Sieve Tubes of Salix Viminalis L.

Sieve-tube sap was collected as honeydew from the aphid Tuberolachnussalignus (Gmelin) feeding on a young shoot or a mature stemof willow (Salix viminalis L.). Two radioactive tracers (either³H-glucose and ¹⁴C-sucrose, or ¹⁴CO₂, Na₂ ¹⁴CO₃, and ³²P-orthophosphate)were applied to leaves or to bark abrasions at each end of thestem. In some experiments the tracers were applied after thestart of honeydew production, whilst in others the tracers wereapplied before the aphids were sited. In most cases aphids feeding between the tracer applicationpoints produced doubly-labelled honeydew during a 24–48-hperiod from tracer application. In some instances the firstdrops of honeydew contained one tracer, followed several hourslater by the other tracer, whilst some aphids produced doubly-labelledhoneydew from the first drop. Singly-labelled or inactive honeydewwas found in only a few cases. It was demonstrated that when ³H-glucose and ¹⁴C-sucrose wereapplied at opposite ends of a stem that the tracers moved inopposite directions in the form of sucrose. The data suggest that a simultaneous bidirectional movementof two tracers may occur in the same sieve tube. However, thepossibility that the doubly-labelled honeydew could be producedby lateral movement from one sieve tube carrying one tracerto an adjacent punctured sieve tube carrying the other tracercannot be discounted.     

Nitrogen and carbon isotope fractionation between mothers, neonates, and nursing offspring

Stable isotope signatures of lactating females and their nursing offspring were measured on 11 species, including herbivores, carnivores, hibernators, and non-hibernators. We hypothesized that: (1) nursing offspring would have stable isotope signatures that were a trophic level higher than their mothers, and (2) this pattern would be species-independent. The plasma of adult females had a '¹⁵N enrichment over their diets of 4.1ǂ.7‰, but offspring plasma had a mean '¹⁵N enrichment over maternal plasma of 0.9ǂ.8‰ and no C enrichment (0.0ǂ.6‰). The trophic level enrichment did not occur between mother and offspring because milk was depleted in both '¹⁵N (1.0ǂ.5‰) and '¹³C (2.1ǂ.9‰) relative to maternal plasma. Milk to offspring plasma enrichment was relatively small ('¹⁵N enrichment of 1.9ǂ.7‰ and '¹³C enrichment of 1.9ǂ.8‰) compared to the trophic level enrichment between the adults and their diets. While some species did have significant differences between the isotope signatures of mother and offspring, the differences were not related to whether they were hibernators or non-hibernators, carnivores or herbivores. Investigators wanting to use stable isotopes to quantify weaning or other lactation processes or diets of predators when both adults and nursing offspring are consumed must first establish the parameters that apply to a particular species/environment/diet combination.     

Dynamics and distribution of radiocaesium in broiler chicken

The distribution and biological half-life of radiocaesium (¹³⁷Cs) in broiler chickens after three oral applications (in course of 1 day at the age of 14 days) of artificially contaminated feed mixture were studied. There was a rapid uptake of the orally administered ¹³⁷Cs (within a few hours) and also a rapid loss of ¹³⁷Cs which varied in the different organs (the initial biological half-life was: liver 0.6 day, intestine 0.6 day, breast meat 2 days, leg meat 1.2 days). More than one-half of the total administered ¹³⁷Cs activity (55%) was excreted from the body within the 1st day after dosage, and after 14 days more than 90% had been excreted. The highest accumulation of ¹³⁷Cs occurred in meat (50%–90%), and the proportion of total activity in breast and leg meat varied during decontamination. The transfer of radiocaesium from feed into the chicken body (measured as ratios of the ¹³⁷Cs activity concentrations in the organ to the ¹³⁷Cs activity concentration in the applied dose) 1 day after application was: 0.0220, 0.0294, 0.0216 and 0.0195 for breast meat, leg meat, intestine and liver, respectively. Significant differences between the values were demonstrated (P<0.05) except between those of breast meat and intestine. For the first 3 days there was a higher proportion of ¹³⁷Cs activity in leg meat, whereas from the 4th day a greater part of total activity was found in breast meat. The latter results were confirmed in a subsequent study. Data from this study suggest that if broiler chickens are contaminated by radiocaesium to a level of 5 kBq/chicken in the course of 1 day at the age of 14 days, then immediate feeding with uncontaminated feed mixture for 18 days should be effective in decontaminating the chicken's meat below the intervention levels for radiocaesium in animal products, i.e. below 1000 Bq ⋅ kg^–1. Received: 30 December 1996 / Accepted in revised form: 13 May 1997     

Carbon isotope discrimination in photosynthetic bark

We developed and tested a theoretical model describing carbon isotope discrimination during photosynthesis in tree bark. Bark photosynthesis reduces losses of respired CO₂ from the underlying stem. As a consequence, the isotopic composition of source CO₂ and the CO₂ concentration around the chloroplasts are quite different from those of photosynthesizing leaves. We found three lines of evidence that bark photosynthesis discriminates against ¹³C. First, in bark of Populus tremuloides, the '¹³C of CO₂ efflux increased from -24.2‰ in darkness to -15.8‰ in the light. In Pinus monticola, the '¹³C of CO₂ efflux increased from -27.7‰ in darkness to -10.2‰ in the light. Observed increases in '¹³C were generally in good agreement with predictions from the theoretical model. Second, we found that '¹³C of dark-respired CO₂ decreased following 2-3 h of illumination (P<0.01 for Populus tremuloides, P<0.001 for Pinus monticola). These decreases suggest that refixed photosynthate rapidly mixes into the respiratory substrate pool. Third, a field experiment demonstrated that bark photosynthesis influenced whole-tissue '¹³C. Long-term light exclusion caused a localized increase in the '¹³C of whole bark and current-year wood in branches of P. monticola (P<0.001 and P<0.0001, respectively). Thus bark photosynthesis was shown to discriminate against ¹³C and create a pool of photosynthate isotopically lighter than the dark respiratory pool in all three experiments. Failure to account for discrimination during bark photosynthesis could interfere with interpretation of the '¹³C in woody tissues or in woody-tissue respiration.     

Natural abundance of 13C in CO2 respired from forest soils reveals speed of link between tree photosynthesis and root respiration

Soil respiration from a boreal mixed coniferous forest showed large seasonal variation in natural abundance of ¹³C, ranging from -21.6‰ to -26.5‰. We tested if weather conditions could explain this variation in '¹³C of respired CO₂, and found that the air relative humidity 1-4 days before the days of CO₂ sampling best explained the variation. This suggested that high '¹³C values were caused by effects of air humidity on isotope fractionation during photosynthesis and that it took 1-4 days for the C from canopy photosynthesis of 20-25 m trees to become available for root/rhizosphere respiration. We calculated that these new photoassimilates could account for at least 65% of total soil respiration.     

Long-term trends and variation in <Superscript>137</Superscript>Cs activity concentrations in brown trout (<Emphasis Type="Italic">Salmo trutta</Emphasis>) from Øvre Heimdalsvatn,a Norwegian subalpine lake

The Norwegian mountain lake, Øvre Heimdalsvatn, received major fallout from the Chernobyl accident in the spring of 1986. Activity concentrations of ¹³⁷Cs have been monitored annually in the brown trout (Salmo trutta) population of the lake over a 22-year period since 1986. The activity concentrations of ¹³⁷Cs in brown trout have declined over the period, although in recent years there has been little or no reduction in activity concentrations. Throughout the period, there has been considerable individual variation in ¹³⁷Cs activity concentrations. Within a single year, fish weight was the most significant factor affecting activity concentrations of ¹³⁷Cs in individual fish, although sex and age·weight were significant explanatory variables. The “size effect” was not significant during the initial period after fallout and in some recent years. During the first years after fallout, the ecological half-life of ¹³⁷Cs in brown trout was 3–4 years, but during the last decade this has increased significantly and has approached the physical half-life of 30 years for ¹³⁷Cs, suggesting a dynamic equilibrium between catchments inputs, possible remobilisation from lake sediments and lake outputs of ¹³⁷Cs.     

The use of fallout 137Cs and 239,240Pu for dating of lake sediments

The distribution of ¹³⁷Cs and ^239,240Pu in sediment core samples of the Finnish lakes Laukunlampi, Lovojärvi and Pääjärvi were determined. The sediment samples were collected using dry ice and liquid nitrogen freezing methods. The sediments of these lakes are annually laminated. A clear maximum concentration of ¹³⁷Cs and ^239,240Pu was found in sediment layers formed during 1962–1964, the years of maximum fallout, and the middle of the 1950's can be estimated from the ¹³⁷Cs and ^239,240Pu profiles. The highest concentrations, 11 500 and 820 pCi kg^–1 dry wt for ¹³⁷Cs and ^239,240Pu, respectively, were found in the sediment of Laukunlampi. The vertical distribution was similar for ¹³⁷Cs and ^239,240Pu in the lakes investigated. A slight migration of ^239,240Pu and ¹³⁷Cs was found and the migration of ¹³⁷Cs seems to be higher than that of ^239,240Pu. The advantages of ¹³⁷Cs dating method are rapidity and simplicity. ^239,240Pu is preferable when the sample size is small. The agreement found between ¹³⁷Cs and ^239,240Pu dates and the annual laminae show that these fallout radio isotopes can be used for dating sediments formed during the past 25 years.