- Email: [email protected]
Chernobyl: eight years after
100~~
Third, and building on the preceding two paragraphs, we need a clearer understanding of the multidimensional concept of ‘rarity’l5Jh. Too often, analyses of the IUCN Red Data Books treat the category ‘rare’as if it were necessarily a class of endangerment. To the contrary, the fossil record suggests that some species can be persistently rare, yet not fall under the rubric of Caughley’s ‘small-population paradigm’. Caughley’s messages, as quoted or summarized above, obviously do not call for some Grand Unifying Theory. Nor do they call for theory in the sense of rigorous theorems or elaborately ‘realistic’ simulation models. Rather, they urge a somewhat different set of priorities in constructing a framework for discussing species’ conservation. He suggests less emphasis on elegant generalizations about minimum viable population sizes, and more focus on the many factors which cause populations to decline in the first place. But he recognizes ‘the inefficiency of case-by-case ecological investigations and recovery operations’“. What he envisions is a multifaceted codification of possible causes, a checklist of questions to ask. In calling for such a theory-based conservation biology, Graeme Caughley as in all else he did - saw the world as more than a collection of particularities, each system uniquely complicated and telling us little about any other; at the same time, he had a healthy distrust of
simple generalizations. like him.
We need more
References I
Caughley, G. (1976) in Theoretical Ecolog_y andApplications(May, R.M.,ed.). pp. 94-113, Blackwell Scientific Caughley, G. (1994)J Anim. Ecol. 63,215-244 Caughley, C. (1970) Ecology 51,53-72 Caughley, G. (1977) Analysis of Vertebrate Populations, John Wiley and Sons Caughley, G. (1981) in Problems in Principles
Management of Locally Abundant Wild Mammals (Jewel], P.A. and Holt, S., eds).
pp. 7-19, Academic Press 6 Basson, M., Beddington, J.R. and May, R.M. (1991) Math. Biosci. 104, 73-95 7 Milner-Gulland, E.J. and Beddington, J.R. (1993) Proc. R. Sot London Ser. B 252,29-37 8 Caughley, G. (1993) Conseru. Biol. 7,943-945 9 May, R.M. (1973) Stability and Complex@ in Model Ecosystems, Princeton University Press 10 Willis, K.J. (1993) Trends Ecol. Evol. 8,427-428 11 Hassell, M.P., Comins, H.N.and May, R.M. (1991) Nature 353,255-258 12 Sole, R.V., Bascompte, J. and Valls. J. (1992) I Theor. Biol 159,469-480 13 Hassell, M.P., Comins, H.N. and May, R.M. Nature (in press) 14 May, R.M. (1994) in Large Scale Ecology and Conservation Biology (Edwards, P.J., May, R.M. and Webb, N.R., eds), pp. 1-18, Blackwell Scientific 15 Rabinowitz, D., Cairns, S. and Dillon. T. (1986) in Conservation Biology (Soule, M.E., ed.). pp. 182-204, Sinauer 16 Prendergast, J.R., Quinn, R.M., Lawton. J.H., Eversham, B.C. and Gibbons, D.W.(1993) Nature 365,335-337
Chernobyl:eight years after Zhores A. Medvedev Zhores Medvedev is at 4 Osborn Gardens, MillHill,London, UK NW71DY.
he Chernobyl accident in 1986 was much worse than the worst core meltdown scenario. It was a core explosion in which the uranium fuel rods were ruptured, destroyed and fragmented. A significant amount of dispersed nuclear fuel was ejected upwards and downwards. The first explosion at 01.23.40, 26 April 1986 was produced by a reactivity burst to about 100 times the full power of the RBMK-1000reactor. It was followed three seconds later by the second surge of power to about 440 times normal full power. The accident was a combination of human error with the reactor design defects which made possible a phenom-
T
enon later called ‘positive scram’, or increase of reactivity instead of decrease for a few seconds, when control rods moved down from their top, fully withdrawn positionlJ. At the time of the accident the reactor core had 1659 nuclear fuel assemblies, most of them from the first loading at the end of 1984. By 26 April 1986, reactor 4 had been in service for 865 days. The total mass of the uranium fuel in the core was 190.2tonnes. The total release of fission products (excluding inert radioactive gases) was initially estimated to be about 50 MCi,if the released radionuclides are decay-corrected to 6 May, when massive daily releases measured in megacuries were replaced by the escape of radionuclides measured in kilocuries. Recent recalculations based on the isotope composition of the melted core fuel inside the destroyed reactor indicate that
ISSUE
ESSAYS
the Chernobyl accident released about 170-185MCi, 3-4 times more than the initial Soviet estimate::. The underestimation was apparently due to the failure to register the size of the first radioactive plume created by explosive processes. The plume at this stage consisted mostly of large, medium and fine spent fuel particles (‘hot particles’) and was partly enriched in volatile radionuclides (Y ‘:(‘I, 13iCs) and inert gases. However, this largest plume was missed by the extensive Soviet radioactivity monitoring network. The nearest meteorology point provided with dosimeters and with air filters to determine radioactivity in air was in Chernobyl town, 14 km south of the power station. It was not operating at night. It did record the increased radioactivity at 0900 h during routine measurements. By this time the ‘explosion plume’ head was about 200250km west of the Chernobyl power plant, moving toward Poland over Pripyet Marshes, the largest swamp in Europe. This plume was also missed in Poland (where it arrived at night) and also on Sunday, 27 April in Sweden, Denmark and Finland. It was discovered only on Monday at the Forsmark nuclear power plant, north of Stockholm. By this time the plume was seriously diluted and it also had lost most of its hot particles, nearly all of which were larger than 20 micrometers in diameter. Hot particles later found in Poland were in the 100-500 micrometer range. Between the Polish border and Chernobyl the size and the density of the hot particle fallout were rising. Nearly 90% of the 30 km radius ‘exclusion zone’, which was later extended in a western direction to the village of Dolgy Les (65 km from Chernobyl and evacuated only at the end of May), was contaminated by the reactor fuel fragments of all possible sizes”. About one million square meters of topsoil around the plant was removed by bulldozers and treated as nuclear waste.
Radiationeffects on coniferous forests As early as May 1986, about 30 research institutes had set up research stations inside the heavily contaminated area around the Chernobyl power plant, from which the local population was already evacuated. The results of their studies, however, were considered classified until September 1990, when the first international conference on biological and radioecological aspects of the Chernobyl accident was organized in Chernobyl town and in the Zeleny Mys settlement just outside the ‘exclusion 30 km zone’. It was accidental luck that the explosion plume was blown in a westerly
100~~
ISSUE
ESSAYS
direction, where the nearest village was 25 km from the Chernobyl plant. All other directions from the plant were densely populated. The first village, Tolsty Les, which translates as ‘thick forest’ was sep arated from the plant by natural, mostly pine, forest. The trees in about 6 km2 of this forest were killed within several days of the accident. Doses of absorbed radiation on trees were later estimated in the range of 9000-11700rad (over 100Gy)s. This ‘killing zone’ was rather narrow (about 600m). Further along the plume axis, the height to which canopy was injured was decreasing; the same picture was observed at greater distances from the axis in southern and northern directions. This forest trapped several million curies of radioactive particles and played a buffer role. In 1987, this forest was cut by bulldozers and buried in specially-dug trenches as nuclear waste. However, in 1987-1991 the area of dying trees was growing, reaching 38 km2. About 120 km2 of pine forest in western and northern directions was classified later as a zone of medium damage, with an estimated absorbed dose in needles between 20 and 50 Gy6. Dead needles often contained microscopic ‘craters’ made by hot particles which burned through the waxen surfaces and were trapped inside needles. Herbaceous vegetation is more radioresistant than coniferous trees. Some species, particularly the natural population of Arabidopsis thaliana, an annual rosette plant, were selected for genetic studies’. It was expected that by comparing the frequency of different mutations in habitats with levels of radiation ranging from 0.02 to 240mRh-1 it would be possible to create ‘biological dosimeters’. These studies were also expected to reveal whether the habitat that was highly radioactive with fission isotopes led to
radioadaptation or selection of more radioresistant strains of plants.
Radiation effects on fauna In the most contaminated area of about 40 km2west of the Chernobyl power plant, not only was the pine forest killed or damaged, but rodents perished as well. Along the axis of the initial plume, which was dropping hot particles, the dose rate at the soil level during spring and summer of 1986 was about 22Gy month-l for gamma and 860 Gymonth-1 for beta irradiations. In rodent communities around this ‘killingground’, there was a sharp reduction of the populations and some surviving animals developed many abnormalities in their internal organs. In 1986, the main contribution to the radiation level was from short-lived radionuclides (ls2Te, l311,l03Ru,140Be).In many places close to the damaged reactor, the doses were so high that they also inflicted radiation damage on the insect populations, which are generally highly radioresistant. From August 1986, a team of geneticists started to study the frequency of mutations in natural populations of Drosophila melanogaster at experimental sites at different distances and in different directions from the Chernobyl plant. The radionuclide composition of releases from the damaged reactor was changing over the lo-day ‘acute’ period and the character of contamination in different directions from the plant reflects this. The pattern of releases also reflects different physical processes inside the reactor: the initial powerful explosion which produced the plume over 2 km high, the subsequent graphite fire which produced smoke and hot-particles aerosol to a height of only a few hundred meters, and the final meltdown of the fuel (2-5 May
Fig. 1.1991, 4 km west of the Chernobyl plant. The pine forest died here In 1987; now the birch trees are also dying. Photo by Zhores A. Medvedev.
370
which increased the release of volatile radionuclides and mono-elemental very fine hot particles that were dispersed mostly to the south and east. The highly increased rate of mutations, particularly sex-linked recessive lethals, was ob served mainly at the beginning of this study in August 1986. In 1987 and following years, the mutation frequencies were much lower, which was explained not only by the reduced levels of radiation exposure, but also by the appearance of more radiation-resistant strains”. In aquatic ecosystems, serious changes were observed only in the man-made cooling pond of the Chernobyl plant. However, the contamination of this 22 km2 pond, south-east of the plant, was not high enough to damage the fish population. Fish muscles accumulated l37Csto levels high enough to make them unsuitable for consumption (up to 400-500 kBq kg-1 wet weight), but not high enough to inhibit growth and reproduction6.
The Chernobyl accident and the nuclear energy option for the CIS The post-Chernobyl climate of extreme radiophobia brought a moratorium on the construction of new nuclear power plants and the completion of those that were already under construction or even near completion. Only one working plant was actually closed down - the Armenian plant, consisting of two WER-440 pressurized water reactors (now the energy crisis in independent Armenia has made its population regret this action). Eleven remaining RBMK-1000and 1500 reactors were modified to improve their safety systems and continued to work. The Soviet nuclear energy programme was cancelled and the government opted to increase the production of oil, gas and coal. However, the production of oil peaked in 1988 and then started to decline rather sharply. Production of coal also started to decline in 1989. The resulting energy crisis apparently contributed to the collapse of the USSR. However, the postSoviet newly independent states found themselves in a different position. Russia, Kazakhstan, Turkmenia and Azerbaijan are self-sufficient in energy, whereas the others are highly dependent on the import of fuels. The worst energy crises developed in the Ukraine and Belarus, the two former Soviet republics which suffered most from the Chernobyl accident. Just when the late effects of the Chernobyl accident became apparent at first, in the rapid rise of thyroid cancers among children*O,there was also a significant change of attitude towards nuclear power. In 1992 the Russian and Ukrainian governments decided to complete the construction of some nuclear plants,
which were already close to final operational tests in 1986. In 1993, the first such project, the fourth block at the Balakovsky NPP on the banks of the Volga river, was inaugurated. This year, the third WER-1000 reactor will come into operation at the Kalinin NPP north of Moscow. One new WER-1000 reactor was completed and put into operation in the Ukraine, where 40% of all electricity supplies are now produced from nuclear power. The European country with the highest proportion of nuclear-generated electricity is now not France (72X), but Lithuania (90%). The Soviet militaryindustrial complex developed a conversion programme to adapt the naval reactors designed for ships and submarines to serve for civilian use in distant Siberian and Arctic locations, to which deliveries of oil are too expensive and possible only
during the very short summer. With the industrial output in Russia steadily declining over the last three years, the nuclear generation of electricity was probably the only branch of the economy that was growing in 1993-1994.
F.S. Chapin III H.A. Mooney is at the Dept of Biological Sciences. Stanford University, Stanford, CA 94305, USA;F.S. Chapin 111is at the Dept of Integrative Biology. University of California, Berkeley, CA 94720, USA.
he past few years have seen the development of earth system science, which has involved, among other things, learning how to operate at the boundaries of long-established natural science disciplines as well as how to scale information from local to regional and global spatial domains in order to understand the functioning of the earth as a system. This has been an exciting era - one that has engaged a large number of scientists and has resulted in new understanding and also new institutional arrangements at all levels, from educational systems to national research program development. The overarching theme of this development has been predicting the earth system response to global change, focusing first on climate change. We are now beginning to see greater attention being given to other dimensions of global change for which there is no question of their having impacts of regional and global significance’. These changes include those occurring through
T
Commission
5 Kozubov. G.M. and Taskayev. .A.l., eds (19W) Radiuzronnoy? licdei.st~‘@ nu KI1uo117y7~Lw c Raione Auclrrr IXI Chernobyfskor AES. llrai Dept of the Academy
6
Kryshev.
1.1..ed.
of Sciences of the USSR
( 1942)Rudrorc~ologirai
Nuclear Society International
of
Energy’s Team Analyses of the Chernobyl-4 Atomic Energy Station Accident Sequence, US Dept of Energy Adamov, E.O. et al. (1988) Atomnaya Energija 64(l), 24-29 Travis, J. (1994) Science 263, 750 Kashparov,
pp. 493-513.
Communities
Consequences of the Chernobyl 4ccrdent.
Anon. (1986) Report of the US Department
Demchuk,
ESSAYS
1-S October l!M/). of the European
References
V.V., Voytesekovich, V.A., Viktorova,
7 Abramov.
on Comparative Assessment of the Environmental Impact of Radionuclides Released during Three Major Nuclear Accidents’ Kyshtym, Windscale, Chernobyl (Luxembouq,
land use, biotic rearrangements and the changing composition of the atmosphere. Below, we briefly describe where some of these new directions are taking us in global change research. We refer readers to Refs 2-4 for detailed plans for future research in the response of terrestrial systems to global change related to the Global Change and Terrestrial Ecosystems (GCTE) core project of the International Geosphere-Biosphere Programme (IGBP). A synthesis of the early results of these programs can be found in a recent issue of Ambios.
Biodiversity and global change Two of the principal concerns of the ecological community during the past decade have been the loss of biodiversity and the consequences of global change. Those involved in these issues have represented disparate communities although the issues are clearly related. It is clear that these two communities are now coming together and that this marriage will produce new research direction+. Basically, earth system science is attempting to achieve an understanding of how the earth’s climate system interacts with global biogeochemical cycles. The principle arena of attention in biology has been at the ecosystem level and above. On the other hand, the past focus of biodiversity research has been on enumeration, monitoring and protection of biodiversity with a focus at the
I’. ,I.
(Moscow) 0.M
and
( 19921.Fr Tot k/ran
I IL’.
19-28
8
Taskaev. Al.. Testov. (1990) in B~olqc~l
the Consryuences (Abstracts
IO-18 September
Mys). p. 5. Academy
9 Zainullin,
Rakin. A.O.
of the USSR
VA.
E.N.. Generalova,
M V. and
(INE) kc Tot Emwon. 112.37-14
Kazakov, \:.S., Demidchuk. L.N. (1992,
V.C;.
1990. Zeleny
of Scienws
V.G.. Shevchenko.
Mjasnjankina,
10
B.V. and Zainullin,
ond Radiolog!cal Aspects of ot the Chrrnob~l Accident
of the First International
Conference.
N.V. and
Laptev, G.V. (1990) in Proceedings of.Seminar
V.I.. Fedorenko.
Shevchenko.
O.V.,
Future directions of global change research in terrestrial ecosystems H.A. Mooney
ISSUE
100~~
-__
E.P. and Astakhova.
:2’oturr, 359.L’l-22
species level. Concerns are now developing about the status of biodiversity at multiple levels of integration - genes to landscapes - and furthermore there is growing recognition that biodiversity may have important consequences for ecosystem processes. An unresolved issue is whether the diversity of organisms (independent of their traits) influences ecosystem processes. Species may differ within and between communities in properties that affect ecosystem and global processes such as productivity. nutrient cycling and fluxes of carbon. water, energy and trace gases between the ecosystem and the atmosphere. Although there has been great international concern about the extinction of species, ecologists have begun only recently to ask what is the ecosystem significance of this loss of biodiversity. There are several views on this question, one being that each species is like a rivet on an airplane so that the loss of each species increases the probability of catastrophic change in ecosystem processes. An alternative viewpoint is that some ecosystem processes (e.g. the cycling of carbon and nutrients) can be carried out effectively by a relatively small number of species, and that other species are in some sense redundant or less necessary for maintaining the rates of these processes. A third perspective is that diversity serves as insurance against change in system function if a species is lost. Therefore, species properties would affect ecosystem processes primarily when an ecosystem is responding to environmental change, rather than under steady-state conditions. These different perspectives have led to debates about
Third, and building on the preceding two paragraphs, we need a clearer understanding of the multidimensional concept of ‘rarity’l5Jh. Too often, analyses of the IUCN Red Data Books treat the category ‘rare’as if it were necessarily a class of endangerment. To the contrary, the fossil record suggests that some species can be persistently rare, yet not fall under the rubric of Caughley’s ‘small-population paradigm’. Caughley’s messages, as quoted or summarized above, obviously do not call for some Grand Unifying Theory. Nor do they call for theory in the sense of rigorous theorems or elaborately ‘realistic’ simulation models. Rather, they urge a somewhat different set of priorities in constructing a framework for discussing species’ conservation. He suggests less emphasis on elegant generalizations about minimum viable population sizes, and more focus on the many factors which cause populations to decline in the first place. But he recognizes ‘the inefficiency of case-by-case ecological investigations and recovery operations’“. What he envisions is a multifaceted codification of possible causes, a checklist of questions to ask. In calling for such a theory-based conservation biology, Graeme Caughley as in all else he did - saw the world as more than a collection of particularities, each system uniquely complicated and telling us little about any other; at the same time, he had a healthy distrust of
simple generalizations. like him.
We need more
References I
Caughley, G. (1976) in Theoretical Ecolog_y andApplications(May, R.M.,ed.). pp. 94-113, Blackwell Scientific Caughley, G. (1994)J Anim. Ecol. 63,215-244 Caughley, C. (1970) Ecology 51,53-72 Caughley, G. (1977) Analysis of Vertebrate Populations, John Wiley and Sons Caughley, G. (1981) in Problems in Principles
Management of Locally Abundant Wild Mammals (Jewel], P.A. and Holt, S., eds).
pp. 7-19, Academic Press 6 Basson, M., Beddington, J.R. and May, R.M. (1991) Math. Biosci. 104, 73-95 7 Milner-Gulland, E.J. and Beddington, J.R. (1993) Proc. R. Sot London Ser. B 252,29-37 8 Caughley, G. (1993) Conseru. Biol. 7,943-945 9 May, R.M. (1973) Stability and Complex@ in Model Ecosystems, Princeton University Press 10 Willis, K.J. (1993) Trends Ecol. Evol. 8,427-428 11 Hassell, M.P., Comins, H.N.and May, R.M. (1991) Nature 353,255-258 12 Sole, R.V., Bascompte, J. and Valls. J. (1992) I Theor. Biol 159,469-480 13 Hassell, M.P., Comins, H.N. and May, R.M. Nature (in press) 14 May, R.M. (1994) in Large Scale Ecology and Conservation Biology (Edwards, P.J., May, R.M. and Webb, N.R., eds), pp. 1-18, Blackwell Scientific 15 Rabinowitz, D., Cairns, S. and Dillon. T. (1986) in Conservation Biology (Soule, M.E., ed.). pp. 182-204, Sinauer 16 Prendergast, J.R., Quinn, R.M., Lawton. J.H., Eversham, B.C. and Gibbons, D.W.(1993) Nature 365,335-337
Chernobyl:eight years after Zhores A. Medvedev Zhores Medvedev is at 4 Osborn Gardens, MillHill,London, UK NW71DY.
he Chernobyl accident in 1986 was much worse than the worst core meltdown scenario. It was a core explosion in which the uranium fuel rods were ruptured, destroyed and fragmented. A significant amount of dispersed nuclear fuel was ejected upwards and downwards. The first explosion at 01.23.40, 26 April 1986 was produced by a reactivity burst to about 100 times the full power of the RBMK-1000reactor. It was followed three seconds later by the second surge of power to about 440 times normal full power. The accident was a combination of human error with the reactor design defects which made possible a phenom-
T
enon later called ‘positive scram’, or increase of reactivity instead of decrease for a few seconds, when control rods moved down from their top, fully withdrawn positionlJ. At the time of the accident the reactor core had 1659 nuclear fuel assemblies, most of them from the first loading at the end of 1984. By 26 April 1986, reactor 4 had been in service for 865 days. The total mass of the uranium fuel in the core was 190.2tonnes. The total release of fission products (excluding inert radioactive gases) was initially estimated to be about 50 MCi,if the released radionuclides are decay-corrected to 6 May, when massive daily releases measured in megacuries were replaced by the escape of radionuclides measured in kilocuries. Recent recalculations based on the isotope composition of the melted core fuel inside the destroyed reactor indicate that
ISSUE
ESSAYS
the Chernobyl accident released about 170-185MCi, 3-4 times more than the initial Soviet estimate::. The underestimation was apparently due to the failure to register the size of the first radioactive plume created by explosive processes. The plume at this stage consisted mostly of large, medium and fine spent fuel particles (‘hot particles’) and was partly enriched in volatile radionuclides (Y ‘:(‘I, 13iCs) and inert gases. However, this largest plume was missed by the extensive Soviet radioactivity monitoring network. The nearest meteorology point provided with dosimeters and with air filters to determine radioactivity in air was in Chernobyl town, 14 km south of the power station. It was not operating at night. It did record the increased radioactivity at 0900 h during routine measurements. By this time the ‘explosion plume’ head was about 200250km west of the Chernobyl power plant, moving toward Poland over Pripyet Marshes, the largest swamp in Europe. This plume was also missed in Poland (where it arrived at night) and also on Sunday, 27 April in Sweden, Denmark and Finland. It was discovered only on Monday at the Forsmark nuclear power plant, north of Stockholm. By this time the plume was seriously diluted and it also had lost most of its hot particles, nearly all of which were larger than 20 micrometers in diameter. Hot particles later found in Poland were in the 100-500 micrometer range. Between the Polish border and Chernobyl the size and the density of the hot particle fallout were rising. Nearly 90% of the 30 km radius ‘exclusion zone’, which was later extended in a western direction to the village of Dolgy Les (65 km from Chernobyl and evacuated only at the end of May), was contaminated by the reactor fuel fragments of all possible sizes”. About one million square meters of topsoil around the plant was removed by bulldozers and treated as nuclear waste.
Radiationeffects on coniferous forests As early as May 1986, about 30 research institutes had set up research stations inside the heavily contaminated area around the Chernobyl power plant, from which the local population was already evacuated. The results of their studies, however, were considered classified until September 1990, when the first international conference on biological and radioecological aspects of the Chernobyl accident was organized in Chernobyl town and in the Zeleny Mys settlement just outside the ‘exclusion 30 km zone’. It was accidental luck that the explosion plume was blown in a westerly
100~~
ISSUE
ESSAYS
direction, where the nearest village was 25 km from the Chernobyl plant. All other directions from the plant were densely populated. The first village, Tolsty Les, which translates as ‘thick forest’ was sep arated from the plant by natural, mostly pine, forest. The trees in about 6 km2 of this forest were killed within several days of the accident. Doses of absorbed radiation on trees were later estimated in the range of 9000-11700rad (over 100Gy)s. This ‘killing zone’ was rather narrow (about 600m). Further along the plume axis, the height to which canopy was injured was decreasing; the same picture was observed at greater distances from the axis in southern and northern directions. This forest trapped several million curies of radioactive particles and played a buffer role. In 1987, this forest was cut by bulldozers and buried in specially-dug trenches as nuclear waste. However, in 1987-1991 the area of dying trees was growing, reaching 38 km2. About 120 km2 of pine forest in western and northern directions was classified later as a zone of medium damage, with an estimated absorbed dose in needles between 20 and 50 Gy6. Dead needles often contained microscopic ‘craters’ made by hot particles which burned through the waxen surfaces and were trapped inside needles. Herbaceous vegetation is more radioresistant than coniferous trees. Some species, particularly the natural population of Arabidopsis thaliana, an annual rosette plant, were selected for genetic studies’. It was expected that by comparing the frequency of different mutations in habitats with levels of radiation ranging from 0.02 to 240mRh-1 it would be possible to create ‘biological dosimeters’. These studies were also expected to reveal whether the habitat that was highly radioactive with fission isotopes led to
radioadaptation or selection of more radioresistant strains of plants.
Radiation effects on fauna In the most contaminated area of about 40 km2west of the Chernobyl power plant, not only was the pine forest killed or damaged, but rodents perished as well. Along the axis of the initial plume, which was dropping hot particles, the dose rate at the soil level during spring and summer of 1986 was about 22Gy month-l for gamma and 860 Gymonth-1 for beta irradiations. In rodent communities around this ‘killingground’, there was a sharp reduction of the populations and some surviving animals developed many abnormalities in their internal organs. In 1986, the main contribution to the radiation level was from short-lived radionuclides (ls2Te, l311,l03Ru,140Be).In many places close to the damaged reactor, the doses were so high that they also inflicted radiation damage on the insect populations, which are generally highly radioresistant. From August 1986, a team of geneticists started to study the frequency of mutations in natural populations of Drosophila melanogaster at experimental sites at different distances and in different directions from the Chernobyl plant. The radionuclide composition of releases from the damaged reactor was changing over the lo-day ‘acute’ period and the character of contamination in different directions from the plant reflects this. The pattern of releases also reflects different physical processes inside the reactor: the initial powerful explosion which produced the plume over 2 km high, the subsequent graphite fire which produced smoke and hot-particles aerosol to a height of only a few hundred meters, and the final meltdown of the fuel (2-5 May
Fig. 1.1991, 4 km west of the Chernobyl plant. The pine forest died here In 1987; now the birch trees are also dying. Photo by Zhores A. Medvedev.
370
which increased the release of volatile radionuclides and mono-elemental very fine hot particles that were dispersed mostly to the south and east. The highly increased rate of mutations, particularly sex-linked recessive lethals, was ob served mainly at the beginning of this study in August 1986. In 1987 and following years, the mutation frequencies were much lower, which was explained not only by the reduced levels of radiation exposure, but also by the appearance of more radiation-resistant strains”. In aquatic ecosystems, serious changes were observed only in the man-made cooling pond of the Chernobyl plant. However, the contamination of this 22 km2 pond, south-east of the plant, was not high enough to damage the fish population. Fish muscles accumulated l37Csto levels high enough to make them unsuitable for consumption (up to 400-500 kBq kg-1 wet weight), but not high enough to inhibit growth and reproduction6.
The Chernobyl accident and the nuclear energy option for the CIS The post-Chernobyl climate of extreme radiophobia brought a moratorium on the construction of new nuclear power plants and the completion of those that were already under construction or even near completion. Only one working plant was actually closed down - the Armenian plant, consisting of two WER-440 pressurized water reactors (now the energy crisis in independent Armenia has made its population regret this action). Eleven remaining RBMK-1000and 1500 reactors were modified to improve their safety systems and continued to work. The Soviet nuclear energy programme was cancelled and the government opted to increase the production of oil, gas and coal. However, the production of oil peaked in 1988 and then started to decline rather sharply. Production of coal also started to decline in 1989. The resulting energy crisis apparently contributed to the collapse of the USSR. However, the postSoviet newly independent states found themselves in a different position. Russia, Kazakhstan, Turkmenia and Azerbaijan are self-sufficient in energy, whereas the others are highly dependent on the import of fuels. The worst energy crises developed in the Ukraine and Belarus, the two former Soviet republics which suffered most from the Chernobyl accident. Just when the late effects of the Chernobyl accident became apparent at first, in the rapid rise of thyroid cancers among children*O,there was also a significant change of attitude towards nuclear power. In 1992 the Russian and Ukrainian governments decided to complete the construction of some nuclear plants,
which were already close to final operational tests in 1986. In 1993, the first such project, the fourth block at the Balakovsky NPP on the banks of the Volga river, was inaugurated. This year, the third WER-1000 reactor will come into operation at the Kalinin NPP north of Moscow. One new WER-1000 reactor was completed and put into operation in the Ukraine, where 40% of all electricity supplies are now produced from nuclear power. The European country with the highest proportion of nuclear-generated electricity is now not France (72X), but Lithuania (90%). The Soviet militaryindustrial complex developed a conversion programme to adapt the naval reactors designed for ships and submarines to serve for civilian use in distant Siberian and Arctic locations, to which deliveries of oil are too expensive and possible only
during the very short summer. With the industrial output in Russia steadily declining over the last three years, the nuclear generation of electricity was probably the only branch of the economy that was growing in 1993-1994.
F.S. Chapin III H.A. Mooney is at the Dept of Biological Sciences. Stanford University, Stanford, CA 94305, USA;F.S. Chapin 111is at the Dept of Integrative Biology. University of California, Berkeley, CA 94720, USA.
he past few years have seen the development of earth system science, which has involved, among other things, learning how to operate at the boundaries of long-established natural science disciplines as well as how to scale information from local to regional and global spatial domains in order to understand the functioning of the earth as a system. This has been an exciting era - one that has engaged a large number of scientists and has resulted in new understanding and also new institutional arrangements at all levels, from educational systems to national research program development. The overarching theme of this development has been predicting the earth system response to global change, focusing first on climate change. We are now beginning to see greater attention being given to other dimensions of global change for which there is no question of their having impacts of regional and global significance’. These changes include those occurring through
T
Commission
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land use, biotic rearrangements and the changing composition of the atmosphere. Below, we briefly describe where some of these new directions are taking us in global change research. We refer readers to Refs 2-4 for detailed plans for future research in the response of terrestrial systems to global change related to the Global Change and Terrestrial Ecosystems (GCTE) core project of the International Geosphere-Biosphere Programme (IGBP). A synthesis of the early results of these programs can be found in a recent issue of Ambios.
Biodiversity and global change Two of the principal concerns of the ecological community during the past decade have been the loss of biodiversity and the consequences of global change. Those involved in these issues have represented disparate communities although the issues are clearly related. It is clear that these two communities are now coming together and that this marriage will produce new research direction+. Basically, earth system science is attempting to achieve an understanding of how the earth’s climate system interacts with global biogeochemical cycles. The principle arena of attention in biology has been at the ecosystem level and above. On the other hand, the past focus of biodiversity research has been on enumeration, monitoring and protection of biodiversity with a focus at the
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species level. Concerns are now developing about the status of biodiversity at multiple levels of integration - genes to landscapes - and furthermore there is growing recognition that biodiversity may have important consequences for ecosystem processes. An unresolved issue is whether the diversity of organisms (independent of their traits) influences ecosystem processes. Species may differ within and between communities in properties that affect ecosystem and global processes such as productivity. nutrient cycling and fluxes of carbon. water, energy and trace gases between the ecosystem and the atmosphere. Although there has been great international concern about the extinction of species, ecologists have begun only recently to ask what is the ecosystem significance of this loss of biodiversity. There are several views on this question, one being that each species is like a rivet on an airplane so that the loss of each species increases the probability of catastrophic change in ecosystem processes. An alternative viewpoint is that some ecosystem processes (e.g. the cycling of carbon and nutrients) can be carried out effectively by a relatively small number of species, and that other species are in some sense redundant or less necessary for maintaining the rates of these processes. A third perspective is that diversity serves as insurance against change in system function if a species is lost. Therefore, species properties would affect ecosystem processes primarily when an ecosystem is responding to environmental change, rather than under steady-state conditions. These different perspectives have led to debates about