The radiobiogical effects on scots pine trees (pinus sylvestris) in the chernobyl exclusion zone.
Dear Editors: AS A contribution to the interesting paper by Yoschenko et al. (2011), I report here the results of a sampling performed 20 years ago in the Chernobyl exclusion zone. From 27 April to 2 May 1991, a seminar on ‘‘Radioecology and Countermeasures’’ was organized in Kiev by the Soviet Branch of the International Union of Radioecology. In the framework of the seminar, I participated in a visit to the exclusion zone with a collection of many samples (Cigna 1991). In particular, I got a pine tree less than 1 m high and a very small one (about 10 cm high) grown in an experimental field from a seed, which became irradiated at the time of the accident. Both plants were immediately transplanted in my garden in North Italy. The small pine showed at first some morphological changes with many apical branches, but after some years it started to develop regularly just as nonirradiated pine trees. In March 1996, the younger plant was about 50 cm high and the older one about 1.5 m high (Fig. 1). The growth of both plants developed regularly (Fig. 2), and at present the younger plant is now about 9 m high with a slimmer trunk, while the other older pine, which was already grown up at the time of the accident, is about 7 m high. The diameter at breast height is 17 cm for the younger plant (about 20 y old) and 23 cm for the
CHRONIC IRRADIATION OF SCOTS PINE TREES (PINUS SYLVESTRIS) IN THE CHERNOBYL EXCLUSION ZONE: DOSIMETRY AND RADIOBIOLOGICAL EFFECTS
To identify effects of chronic internal and external radiation exposure for components of terrestrial ecosystems, a comprehensive study of Scots pine trees in the Chernobyl Exclusion Zone was performed. The experimental plan included over 1,100 young trees (up to 20 y old) selected from areas with varying levels of radioactive contamination. These pine trees were planted after the 1986 Chernobyl Nuclear Power Plant accident mainly to prevent radionuclide resuspension and soil erosion. For each tree, the major morphological parameters and radioactive contamination values were identified. Cytological analyses were performed for selected trees representing all dose rate ranges. A specially developed dosimetric model capable of taking into account radiation from the incorporated radionuclides in the trees was developed for the apical meristem. The calculated dose rates for the trees in the study varied within three orders of magnitude, from close to background values in the control area (about 5 mGy y−1) to approximately 7 Gy y−1 in the Red Forest area located in the immediate vicinity of the Chernobyl Nuclear Power Plant site. Dose rate/effect relationships for morphological changes and cytogenetic defects were identified, and correlations for radiation effects occurring on the morphological and cellular level were established.
Lake Muzahi, Rwanda: limnological features and phytoplankton production
Lake Muhazi, a small lake of Rwanda (East Africa) was studied from 1986 to 1990. A dramatic decrease of the catch of Oreochromis niloticus (350 T y−1 in the fifties vs 30 T y−1 in 1982) suggested a loss of productivity or overfishing. In the same period, other ecological changes occurred: the submerged macrophytes regressed and there was a decrease in Secchi depth (0.65 m in 1987 vs 1.5 m in the fifties). Compared to other lakes of the same area, the plankton production seemed low. The results of the present study characterize lake Muhazi as a shallow lake with a rather unstable diurnal stratification and with slight differences in mixing regime between its eastern, deepest part and its western, shallowest part. Secchi disk depth does not vary seasonally to a large extent. The water has a rather high mineral content (conductivity of about 500 µS cm−1 at 25 °C) and low concentrations of dissolved N and P, except in the hypolimnion, where NHinf4sup+-N can be high.Two species, Microcystis aeruginosa and Ceratium hirundinella, account for most of the phytoplankton biomass, which is about 50–80 mg chlorophyll a m−2 in the euphotic zone, usually with little seasonal variation. Daily gross production estimates amount to about 6 to 9.5 g O2 m−2 d−1 with a significant difference between the two parts of the lake. Data on C:N and C:P ratio in the phytoplankton suggest that some N deficiency might occur in the eastern part. Moreover, the Zm:Zc ratio could also lead to rather low net production rates (0.21–0.25 d−1 for a mixed layer of 4 m)In conclusion, the primary production of lake Muhazi is medium for African lakes and the hypothesis that decreased planktonic production could account for a reduced fish production should be discarded. Whereas the present yield of the fishery is only 20 kg ha−1 y−1, the yield estimated from primary production ranges between 46 and 64 kg ha−1 y−1. This could be reached through proper management. Finally, some hypotheses are given to explain the ecological changes which occurred in the lake.