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ŠUMARSKI LIST 5-6/2004 str. 59     <-- 59 -->        PDF

M. Popijač. I. Sclctković. M. Volncr, I. Lovrcnčić. D. Barišić. N. Kczić: DINAMIKA KRETANJA ... Šumarski list br. 5-6. CXXVI1I (2004), 269-277
properties of plants and trees must be observed in light of new damage to
forests caused by atmospheric pollution which is manifested in three different
ways: a) through the direct impact of atmospheric pollutants on leaves and
assimilation, b) by intake of substances into the soil by dry or wet deposition
and its impact on physiological processes in subsoil and external portions of
forest trees, and c) by indirect damage due to climate change and increased
sensitivity of trees to extreme climatic, edaphic and biotic conditions. The
level of radioactivity that contaminated the Republic of Croatia in the form of
radioactive fallout has been estimated at 5.2 x 1015 Bq, which is approximately
0.28 % of the total activity released from the reactor at Chernobyl.
Cesium behaves and is distributed in an organism in a manner similar to
potassium (Baratta, 1994). The speed of cesium´s vertical migration in uncultivated
soil depends on several factors, such as soil type, its mineral composition,
pH, organic matter content, hydrogeological processes, and geochemical
processes. On the forest floor, the primary source of137Cs is the surface
organic layer (Kruyts, Delvaux, 2002). Plants take in microconstituents,
including radionuclides, in two ways: indirectly through their roots from the
soil, and directly by sedimentation of radionuclides on leaves or flowers.
Out of all potassium isotopes, only potassium -40, or 40K, is radioactive,
i.e. it is a naturally-occurring primordial radionuclide with a half-life of
1.26 x 109 years. 4"K is one of the most widespread natural radioactive elements,
as it accounts for approximately 1 % of the total number of all atoms
formed in the earth s crust and its activity is easily and reliably measured.
In this research we want to contribute to knowledge of the dynamics of
movement and the fate of model pollution of forest ecosystems, so the movement
of Cs and " K on various parts of silver fir trees (Abies alba) on the
slopes of Sljeme was analyzed for the period from 1997 to 1999. Apex tips, or
needles, bark and heartwood from the silver fir were taken as samples. l37Cs
and 4"K activity were established using the gamma-spectrometry method. In
all samples analyzed, 40K and 137Cs activity had crossed into the apex tips and
young needles. Increase in Cs and 4"K activity in fir needles from the older
to the younger apex sections did not exhibit a linear trend. We compared the
dynamic of´Cs and 4"K movement in the needles, bark and heartwood by
month in each of the three years. The l37Cs and4n K activity trend is increasing
from older to younger sections in all parts. Similarly, we can say that activity
is greatest in the tree bark in comparison to other tested samples. In each
month in 1997, 1998 and 1999 (twelve months per year), the movement of
cesium and potassium in the fir trees on Sljeme Mountain was measured.
Samples of needles, bark and heartwood were always taken from the same
trees.
The results presented indicate the importance of monitoring l37Cs dynamics,
because this research shows and confirms that the cesium recorded after
Chernobyl is still in the ecosystem. This model of the dynamics of movement
137Cs and the link between this movement in relation to the physiological functions
of the trees have facilitated more clear and accurate monitoring of other
negative consequences which occur in forest ecosystems and have a negative
impact on the development of trees, in this case the silver fir.
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