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ŠUMARSKI LIST 7-8/2021 str. 24     <-- 24 -->        PDF

to be statistically reliable. The reason for this is that the measurements are made in such a way to ensure the same measurement conditions each time (geometry of the sample, measurement time, the same detector and calibration).
Calculation elimination of radioactive decay impact – Računska eliminacija utjecaja radioaktivnog raspada
Given the large time gap between the first and second sampling and measurements (2003 and 2004) on the one hand, and the third sampling and measurements (2017) on the other hand, it could be assumed that the measured activity of 137Cs in the third measurement, due to the half-life of 137Cs, would be lower for about a quarter than in the samples from 2003 and 2004. The law of radioactive decay is well known and allows the calculation of radionuclide activity at any point in time. Therefore, it is possible to eliminate the influence by computation of radioactive decay for the measurement of 2017, in a way that all of the measured activity of 137Cs in the samples from the three measurements, recalculate for the date of July 1, 2003 allowing the comparison of the first and second measurements, and for July 1, 2016, when approximately one half-life of 137Cs has expired since the contamination (1986). All samples were computationally analyzed in the described manner, and the results for all samples were shown and interpreted in total (as an arranged pair of values for July 1, 2003 and July 1, 2016), ensuring that the interpretation of results of the difference between recalculated value of the third sampling and the first and second sampling can be  exclusively attributed to geochemical processes that occur in the environment over time (given that the impact of radioactive decay is eliminated by calculation).
RESULTS AND DISCUSSION
REZULTATI I RASPRAVA
Distribution of 137Cs and 40K in the tissues of silver fir – Distribucija 137Cs i 40K u tkivima obične jele
Distribution results of 137Cs in the tissues of silver fir (Abies alba Mill.) refer to the peak shoots and needles, the rings, the bark and cambium and root, and to reviewed comparative presentation of results in all silver fir sampled tissues.
Distribution of 137Cs in the peak shoots and needles of silver fir – Distribucija 137Cs u vršnim izbojcima i iglicama obične jele
Figure 1 shows the distribution of 137Cs activity in silver fir trees shoots of different heights and ages in all three sampling years, showing also the distribution according to the age of shoots (and not to the calendar year).
Comparison of age sequences of 137Cs activity in shoots of silver fir (Figure 1) for individual height between two years (2003 and 2004), using the non-parametric test for related samples (“Wilcoxon matched pairs test”), shows that the values of 2004 are statistically significantly (p = 0.05) higher at altitudes of 8 and 16 m than those in 2003, while at the 25 m difference between the two was not statistically significant. This could be interpreted as a result of an increase in the photosynthesis intensity, which is in the fir, as coniferous species, present throughout the year and of the trees metabolism level during the growing period, leading to a temporary accumulation of 137Cs in the shoots.
Figure 2 show the distribution of 137Cs in silver fir needles at different heights and different age in three sampling years.