prilagođeno pretraživanje po punom tekstu

ŠUMARSKI LIST 7-8/2021 str. 31     <-- 31 -->        PDF

after the Chernobyl accident on Medvednica (Sljeme) and Lovrenčić et al. (2008) in Gorski Kotar in which they monitored the dynamics of l37Cs movement on a monthly basis throughout the year and found higher 137Cs activities in the bark of fir and heartwood during the growing season, when the trees were physiologically more active. The previous results of the two studies suggest that silver fir is a good model species for 137Cs biomonitoring because they behave similarly in different habitats, although this claim would need to be extended to more localities.
Relationship between 40K and 137Cs activities in trees and soil – Odnos aktivnosti 40K i 137Cs u drveću i tlu
To understand the possible explanations of long-term presence of 137Cs in the forest ecosystem, this study, measuring concentration levels of 137Cs activity in the tissues of silver fir and soils near sampled trees, also covered the level of 40K activity, trying to explain the relationship between 40K and 137Cs activities in trees and soil, considering that the two isotopes are homologous. Research (Lovrenčić et al. 2008) also confirms that 137Cs is involved in physiological processes in a similar way as potassium, since these two elements are homologous. Their activity is inversely proportional to the age of the needles and twigs, that is, the highest is in the youngest tissue sections. The soil characteristics play a key role in the transfer of 137Cs, based on their texture, ability to exchange cations and organic matter content. Clay soils accumulate 137Cs and it was found that if the proportion of clay in the soil is higher, the 137Cs activity in the soil is also increased, because its sorption is conditioned by clay minerals (Kruyts and Delvaux 2002, Stauton et al. 2002). The content of K+ in the soil can cause the collapse of the extended interlayers (Rigol et al. 2002), because in this case the 137Cs is binding within the interlayer and is blocked, and unavailable for transfer processes. Potassium availability is strongly associated with sorption and desorption processes, as well as fixations that take place in the soil (Đurđević 2014). Previous research on the relationship of 40K and 137Cs in soils has been primarily related to measuring and determining the distribution and level of 137Cs activity in soils after the Chernobyl and Fukushima accidents (Smolders et al. 1997, Rochon et al. 1998, Gerzabek 1996, Zhu and Smolders 2000, Kruyts and Delvaux 2002; Kaunisto et al. 2002; Zibold et al. 2009). Their importance was highly related to dealing with the consequences that occurred after the entry of 137Cs in the environment and taking measures to secure food production and animal farming, but also protect forest ecosystems.
The study of distribution of 137Cs in the trees of silver fir (Abies alba Mill.) from Lika is based on three occasions within the interval 2003 - 2017 which included field ring samples of trees with three heights (separated on the bark and growth rings), roots, needles, peaks of shoots, and soils near felled trees, and after laboratory processing of collected samples in the gamma spectrometer, statistical analysis and interpretation of the data obtained, resulted in the following conclusions:
1. Following  the results of previous researches in a similar but wider area (which was limited to 137Cs activity in soil and honey, Barišić et al. 2018), this study confirmed long-term contamination of Lika forest ecosystems with radioactive precipitation that had entered the Vrhovine area by remote atmospheric transport after the nuclear tests and the Chernobyl nuclear power plant accident, which manifested itself in measurable 137Cs concentrations in plant tissues at least three decades after contamination.
2. Throughout the observed period (2003 - 2017), the variability of 137Cs distribution in the tissues of silver fir trees decreased continuously. The reason for this was on one hand radioactive decay (about 26% in all tissues during the observed period), while on the other hand it was due to the gradual elimination of 137Cs from tree tissue, mostly through dead bark, and needles, which caused a decrease in 137Cs activity during the observed period up to 96% in needles, peak shoots and fir rings (in relation to the recalculated values, after elimination of the influence of radioactive decay).
3. The highest 137Cs activity of silver fir tissues were measured in peak shoots and needles, and significantly lower activity in other tissues, regardless of the time of year. The conclusion is that the main elimination pathways of 137Cs are needles typically several years old and which the tree gradually sheds throughout the year.
4. In the soil habitat of the silver fir 137Cs migrated deeper, towards the root, and thus become biologically available.
5. The recorded concentration of 137Cs and 40K are statistically significant correlations for the total sample, and separately for the needles sample. These results (given that no statistically significant negative correlation was observed, while a significant positive correlation can still be interpreted by a random process) suggest that the tree does not distinguish between these two homologous elements.
6. The results of the research (the first of its kind in Croatia focused on the edificatory tree species tissue) contribute to the understanding of future of 137Cs that entered the tissue of edificatory tree species in the forest ecosystem, as well as its distribution in time and space, which (especially in comparison with rare similar research in the world) complements the emergence of the 137Cs biogeochemical cycle in the environment (especially in forest trees).
Many thanks Ph.D. Delko Barišić, Ph.D., Full Professor Oleg Antonić, Full Professor Nikola Kezić and Matija