Landscape and Urban Planning, 21 ( 1993) 91-96 Elsevier Science Publishers B.V., Amsterdam

91

Geochemical landscape strategy in monitoring the areas contaminated by the Chernobyl radionuclides

E.M. Korobova*, V.G. Linnik Department of Geoinformation Investigations, Russian Scientific-Practical and Expert-Analytical Centre (RNEC). Moscow,

Varshavskoje shosse 46, Russia

Abstract

The Chernobyl accident led to radionuclide contamination of vast areas that now need to be monitored; the develop- ment of a regional land use strategy is now needed. Landscape geochemistry enables us to structure, classify and map the environmental factors responsible for the redistribution of radionuclides (i.e. soil-forming rocks and soil properties, veg- etation cover, types of ground water migration, and vertical and lateral geochemical barriers). Combined with land use information, regional geochemical landscape maps serve as the basis to map in toposequence conditions of mass migration and accumulation in natural and cultivated landscapes. Such mapping makes it easier to choose representative monitoring sites. This type of mapping is also helpful to interrelate and extrapolate the data already obtained on radionuclides’ envi- ronmental migration for different groups of geochemical landscapes with similar types of contamination, migration and accumulation patterns. A geochemical landscape approach is demonstrated using the example of part of the Bryansk region (Russia), which is considerably contaminated with ‘34Cs and ‘37p- L-5.

Introduction

More than 4 million people live in an area of 130 000 km2 of the former USSR with a con- tamination density of 13’Cs of over 1 Ci kmm2. In Russia the problem is more evident in the western part of the Bryansk region, where the level of contamination exceeds 15 Ci kmm2, and in certain locations reaches 40 Ci kmm2. The most contaminated areas cover about 3 10 km2.

The Chernobyl accident stimulated the rapid development of different monitoring systems for various environmental factors (air, water, land and living organisms) traditionally in- cluded in the fields of hydrometeorology, for- estry, agriculture and water management. A review of the results obtained in radioecologi- cal studies that started in the late 1950s as a result of bomb testing, as well as the latest in-

*Corresponding author.

vestigations of the consequences of the Cher- nobyl accident, show that landscape features play an important role in both the primary de- position and secondary redistribution of radionuclides in the environment.

Geochemical landscape factors of radionuclide migration

The influence of landscape on primary aer- ial deposition is probably due to the surface roughness caused by relief and vegetation cover. It has been reported that in at least 40- 50% of cases the patchy nature of the Chemo- by1 contamination could be explained by this factor. On a macroscale the most dissected and upland areas in distant regions were likely to be more contaminated compared with low- lands (Kvasnikova, 1993). The effect of the Urals as a barrier to the eastern trace is evi- dent, and is indicated by lichens and mosses of the Middle Urals (Nifontova, 199 1). The same

0 1993 Elsevier Science Publishers B.V. All rights reserved 0169-2046/93/$06.00

92 E..l4 Korohooa, L:G L~nnrk /Landscape and L’rhan Plannrng 27 (1993) 91-96

is true for the lower scales. Our examination at a distance of 30-60 km from the Chernobyl nuclear power plant a year after the accident showed higher contamination of the forested river terraces and especially forest belts com- pared with flood plains and terrace-edge depressions (Korobova and Korovjakov, 1991).

Further radionuclide behaviour in the envi- ronment and food chains is defined by the mi- gration of elements in the wind, waters, bio- mass and by human activities. The following factors have proved to be important: solubility in natural waters; physical and chemical soil parameters (pH, Eh, cation exchange capacity (CEC ), organic matter and tine fractions con- tent, and water regime); systematic and eco- logical peculiarities of vegetation and culti- vated crops. Most of these factors are closely interrelated and form in combination a partic- ular natural, semi-natural or cultivated geo- chemical landscape type. For monitoring pur- poses, it is important to point out differences in landscapes that are significant for radio- nuclide accumulation in plants, animals and man (Khitrov et al., 1991).

In landscape geochemistry, the classifica- tion is based on degree of landscape dissection, which defines the intensity of erosion and water exchange in toposequence; the origin and li- thology of the parent rocks are related to the possibility of vertical migration and sorption, for example, and soil-water pH-Eh conditions are closely connected with the type of water migration (acid, acid gley, alkaline, etc. ) . Ac- cumulation in soils and rocks is classified as a geochemical barrier. Toposequence is treated as the catenary elementary landscape (auton- omous, eluvial-transitional-supra-aqueous) (Perelman, 1975 ). The type of vegetation now closely connected with land use (woodlands, grasslands, marshes or agrocoenoses) is re- flected in geochemical landscape groups. The geochemical landscape map created on such a basis may be transformed in landscape groups

with similar migration conditions that are very important in spatial extrapolation of monitor- ing results that are significant for environmen- tal protection and land use strategy (Linnik et al., 199 1). The other aspect of a geochemical landscape strategy is to reveal the accumula- tion zones and to monitor objects of primary importance as a result of enhanced accumula- tion of radionuclides in particular landscape conditions.

The two main Chernobyl radionuclides, 13’Cs and 90Sr, have different mobilities in the environment. Up to 90-95% of 13’Cs is quickly fixed by soil particles and typomorphic com- pounds. This element is actively captured by litter, organic matter and minerals. Its transfer coefficient to plants is an order of magnitude lower than that of 90Sr. By now, most of this radionuclide is concentrated in the upper 5 cm soil layer. Land cultivation and liming de- crease its uptake by plants by 2-l 0 times. Thus, its bioaccumulation is most important and needs to be monitored, especially in wood- lands, where it is fixed in lichens, mosses and litter, which leads to contamination of berries and mushrooms in regions with high external irradiation doses, and in natural pastures and hayfields, where soil ingestion by grazing ani- mals could be considerable. Erosion and resus- pension processes are also important for this element. 90Sr is more easily mobilized in soils; in polesje podzolic and bogged soils it is found at a depth of more than 30 cm, with 40-60% in topsoil, which may lead to underestimation of its pool in cases of topsoil sampling. It is ac- cumulated in soils on sorption and carbonate geochemical barriers in forest-steppes and steppe regions; erosion processes in these land- scapes could also be important for 90Sr. This radionuclide has proved to be the most com- mon in accumulation in hydromorphic plants, bottomland vegetation and the milk of agricul- tural animals. Besides bioaccumulation, mon- itoring of this radionuclide should include the evaluation of water migration.

EM Korobova. VG. Linnik /Landscape and Urban Planning 27 (1993) 91-96 93

Geochemical landscape features of the study area

In the study area of the Bryansk region, two main geochemical landscape types are com- mon, and are similar to those of the Chernobyl region. These are medium-dissected, relatively high (up to 170 m absolute height) moraine landscapes on glacial sands and sandy loams, and lowland ( 130- 140 m absolute height ) po- lesje landscapes on sandy, loamy-sand flu- vioglacial and ancient alluvial deposits. Wa- tershed autonomous landscapes with water percolation through poor sandy rocks belong to landscapes which are acid (H, i.e. pHHZO< 6.5, or acid, acid gley, i.e. with tem- porary or local reduction conditions (H, H- Fe). They are represented by pine and mixed forests of low quality and productivity (1.5- 3.0 x 100 kg ha- ’ ) on poor sandy (80-90% of fraction greater than 0.01 mm) podzolic and sod-podzolic soils, or, locally, humic-podzolic soils in the case of perched waters. Podzolic soils have low humus content (0.5-l .5%; up to 4.5% in humic-podzolic soils), a rapidly de- creasing soil profile, low CEC ( 1.2-5.7 me- quiv per 100 g) and saturation with bases ( 15- 50% for topsoils). Mixed forests on two-lay- ered parent rocks are more productive (annual biomass fall is about 5.5-6.0~ 100 kg ha-‘). The yield of meadows formed on felled areas is equal to 2-6x 100 kg ha-’ and 5-14x 100 kg ha-’ respectively, and up to 30 x 100 kg ha- ’ in depressions. Subordinate supera- queous and trans-superaqueous flood plain landscapes where ground waters are close to the surface mainly belong to the acid, or some- times neutral and alkaline gley, class (pH 4.8- 7.6). Humus content varies from 0.1 to 5.6%. Marshes usually have higher pH (about 6.2) and ash content from 15 to 84%. About 60- 70% of the meadows are bottomland. Fine grasses produce about 1 O-20 x 100 kg ha- 1 an- nually, whereas tall grass communities are more productive ( 15-25 x 100 kg ha- ’ ) . Wa- tershed natural forests (pine and pine-broad-

leaved forests with an admixture of small- leaved species) are characterized by a slow perennial cycle. More than 50% of the total contaminated area is now cultivated. Different biocycling makes it reasonable to distinguish semi-natural and cultivated landscapes (ara- ble or pastures).

Radionuclide migration in landscapes and the strategy for its monitoring

The map of migration and accumulation processes in landscapes overlain by a contam- ination map shows the sites of primary impor- tance for the monitoring of local long-term radionuclide migration and accumulation in waters, soils and plants. Mass migration with the wind is possible only for loose sands on river terraces, arable lands during their culti- vation and overdrained peats. These areas with a high contamination level should be treated as potentially dangerous for radionuclide re- suspension, and it would be reasonable to monitor these areas during dry summers.

Solid runoff with waters in woodlands and grasslands is practically absent (0.2 t ha-’ at most). Therefore, considerable lateral radio- nuclide accumulation is possible only on the edges of the ploughed slopes of the moraine hills and ranges in local zones (up to 10 t ha- 1

(Larionov et al., 199 1) and these areas should be monitored for several years after the accident.

Water migration in soluble form is most pro- nounced in acid sandy and bogged soils of the polesje landscapes, which are noted for the faster radionuclide transfer to plants and food chains. By now, recommended transfer coeffi- cients for the forecast of radionuclide contam- ination of forage, milk and meat takes into ac- count the increase of its value for natural vegetation as compared with crops and for sandy soils in comparison with loamy var- iants. They do not reflect already observed higher bioaccumulation of radioisotopes in the same plant species in depressions and flood plains of the subordinate landscapes (in some

94 EM. Korobova, I/G. Lumk /Landscape and Urban Planning 2 7 (1553) 91-96

mushroom species, the bark of the trees and bilberries). Our calculations based on these data show that for mushrooms with the lowest transfer coefficient value and which are safe for consumption at a density of soil contamina- tion close to 40 Ci kmB2 for 13’Cs, contamina- tion concentrations in accumulative land- forms are twice as high as the accepted norms. Thus contamination should be monitored in these areas. Figure 1 shows that ‘clean’ buck- wheat in farms can be produced only at a soil contamination level of less than 15 Ci kmP2. Spatial forecast of meadow grasses based on contamination (Fig. 2) and a geochemical landscape map can be seen in Fig. 3.

Geochemical landscape analysis of the con- taminated areas in the western part of the Bryansk region has indicated landscapes and objects that are of primary importance for long- term radioecological monitoring, as follows:

( 1) In polesje landscapes: (i) natural and semi-natural vegetation and soils of supera- queous landscapes of H-Fe class (bottomland meadows, especially those used for haymaking

and grazing); (ii) green mosses and bilberries, the bark of trees in woodlands, especially in H- Fe class subordinate landscapes; (iii) vegeta- tion and waters of the supra-aquatic moor and peat bogs (H-Fe class), including flood waters in spring.

(2 ) In moraine landscapes: (i) tine earths in topsoils of arable lands; (ii) topsoils of cul- tivated transitional and accumulative landscapes.

( 3 ) For both landscape types and their tran- sitional variants: (i) litter, humic and illuvial horizons (especially for 90Sr) of sandy pod- zolic soils in autonomous conditions (H-class); (ii) natural vegetation and soils of swamps (H-Fe class).

Terrace side bottomland meadows in polesje are believed to be the primary indicators of the lateral water migration of the Chernobyl radionuclides, especially 90Sr, and lichens in all landscapes serve as long-term indicators of radionuclide contamination caused by the pri- mary deposition. Finally, it should be men- tioned that monitoring of radionuclide accu-

Fig. 1. Forecast of buckwheat contamination with ‘)‘Cs (in comparison with accepted contamination level, 199 1).

E.M. Korobova, V.G. Linnik / Landscape and Urban Planning 27 (1993) 91-96 95

0 density of contamination, C’S’~’ (Ci km’)

Russian boundary

settlements

Fig. 2. Density of contamination with 13’Cs. (Data are from the Hydrometeorological Service.)

kBq/kg

~2.5 2.5-7 7-21 21-40 >40

with high variability of accumulation

Fig. 3. Forecast of the maximal 13’Cs content in meadow grasses (transfer coefficients after Loshchilov et al., 1990).

mulation in local landscapes is of particular significance for those areas with medium con- tamination, where conditions for a local or

temporary dangerous increase in radioactive element bioaccumulation could exist in some landscapes.

96 E.M. Korobova. V.G. Lmnik / Landscapeand Urban Planning 27 (1993) 91-96

Conclusions

( 1) Landscape and geochemical features have played an important role in the deposi- tion and further spatial redistribution of global and Chernobyl artificial radionuclides.

(2 ) Landscape and geochemical analyses make it possible to produce a spatial structural model of environmental factors responsible for element migration in the parent rock-soil- water-plant system and food chains. This is helpful for a regional monitoring strategy, spa- tial extrapolation of the monitoring results, and decision-making on land use and other sub- jects by regional and local authorities in the areas contaminated by Chernobyl radio- nuclides.

approach is valid as a monitoring strategy in any other region with aerial contamination.

Acknowledgements

The authors are much obliged to N.I. Vol- kova and V.K. Zhuchkova for the landscape map created for the study area.

References

Khitrov, L.M., Korobova, E.M. and Linnik, V.G., 199 1. Geo- chemical-landscape and radioecological mapping of the USSR areas with Chernobyl radioactive contamination (the main principles of the working project). SCOPE RADPATH. RE. 36.9 1, Essex University, UK, April 199 1,

24 PP. Korobova. E.M. and Korovjakov, P.A., 199 1. Landscape and

geochemical approach to drawing up a soil distribution profile for Chernobyl radionuclides in distant areas. Proc. Seminar on Comparative Assessment of the Environment Impact of Radionuclides Released During Three Major Nuclear Accidents: Kyshtym, Windscale, Chernobyl. Luxemburg, l-5 October 1990. IURA, pp. 309-326.

Kvasnikova, E.V., 1993. Creation of the maps of Cs-137 con-

( 3 ) Short-term monitoring aimed at evalu- ation of the contaminated area shortly after the aerial contamination should take into account such geochemical landscape features as land- form and the type of vegetation cover. In all landscapes, lichens serve as long-term indica- tors of primary deposition.

(4) It is proposed that long-term environ- mental monitoring of vast areas be carried out in the main types of the contaminated geo- chemical landscapes with due regard to-the enchanced bioaccumulation of radionuclides in superaqueous and accumulative landforms, as well as their concentration in marsh waters rich in soluable organic matter.

( 5 ) Geochemical landscape analyses for monitoring purposes are demonstrated in the example of the Russian areas most contami- nated with radionuclides (in the Bryansk re- gion). It is shown that landscape structures should be taken into account in the calculation of transfer coefficients in food chains.

( 6 ) The proposed geochemical landscape

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