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ŠUMARSKI LIST 13/2005 str. 185     <-- 185 -->        PDF

B. Vrbek, I. Pilaš, T. Dubravac: LYSIMF.TR1C MONITORING OF SOIL WATER QUALITY IN THIi FQRF.ST Šumarski list SUPLEMFNT (2005). 165-185
via throughfall. The quantities for NH4*-N in the lysimeters
are lower than in the control site and in the forest,
the potassium quantities are lower than in the forest,
the NO3" -N are equal to the quantities in the forest,
and lower than in the control site, and all other
substances (Na+, Ca2+, Mg2t, CI" S042" -S) are several
times higher.


After calculating ion differences in % (ID) in the five
plots representing each area, the obtained results
had positive and negative prefixes. In the nature, under
a balanced status and ideal conditions, ion differences
(ID) should be in balance. Of the five plots, three showed
a higher anion input than cation input in the samples
from surface lysimeters. These arc plots 23 and 36
(Pokupsko and Šiljakovina), and plot 6 (Česma in the
Čazma area). More anions than cations were also recorded
in the control sites in plots 15, 25 and 36. These
data do not correspond to the data from lysimeters,
because this also depends on the soil buffer capacity in
the observed plots.


The average pH values of liquids vary from 5.73 to


5.97 in the open, and from 5.42 to 6.24 below the
crowns. The lowest pH values were found in lysimetric
samples, where pH varied from 4.86 to 5.49 (Table 11).
According to Brechtel and Vukorcpa (1991), the
differences in depositions within forest ecosystems, in
comparison with control sites, may be attributed to the
fact that, as a rule, sulphur depositions in the form of
sulphate are 3 to 4 times higher in forest ecosystems
than in the open. The difference for chlorides is 1-5 to
3 times higher. For nitrates and ammonia the differences
are 1.5 to 2.5 higher, while the deposition of hydrogen
ion itself is 2^1 times higher.


An increase in almost all cations and anions below
the tree crowns in relation to the open area in mgL"´
was recorded in the area of Repaš. Apart from nitrates
and ammonia, the quantity of some substances in the
lysimeters was several to ten times higher in comparison
with the control samples. Throughfall and stem-
flow increase the concentration of particular substances,
which leads to their increase in the forest soil. Oak
trees contribute to increased concentrations more than
hornbeam trees, but this could also be due to the differences
in sample concentrations.


DISCUSSION


The quality and quantity of liquids in the plots under
the crown shelter (throughfall), of the percolate in
the soil (lysimetric water) and of precipitation in the
control site (open space free of vegetation) were monitored
in the vegetation period from April to October.
About 54.5 to 56.5 % of precipitation was intercepted
in the vegetation period in relation to the whole year.
Precipitation in the form of snow outside the vegetation
period was not sampled and analysed, and neither
were rain, hoarfrost or similar. Data shown in the tables
contain only one part of about 56 % of the substances
arriving via dry and wet depositions. Precipitation flowing
down the branches and stems in the leafless period,
as well as the deposited substances, acidify the soil
in the stem base as well as the stem bark.


Tables 4-9 show total cation and anion quantities in
kgha"´ in the five main plots per sampling site for the
whole vegetation period from April to October. Figures
(Figure 3-14) show total quantities in kgha"1 in each
plot separately for cations and anions. The summary Table
10 and Figure 15 show the real condition of the cation
and anion input of the 5-plot average in kgha"´ in all
parts of the forest ecosystem, in the control site and in
the soil. In the vegetation period, annual depositions in
the forest community of pedunculate oak and common
hornbeam bring about 16.77 kgha"´ of nitrogen compounds
(N03-N+NH4-N), 1.29 kgha"´ of Na, 9.87 kgha"´
of Ca, 3.67 kgha"´ of Mg, 33.67 kgha"´ of K, 6.95 kgha"´
of CI and 4.73 kgha"´ of S04-S. According to the results,
depositions of nitrogen compounds were higher than


those of sulphur. In the last thirty years, nitrogen input
in Europe has increased from 3^4 87 kgha"´ per year to
10-20 kgha"´ per year. According to data by Komle novi
ć (1988), nitrogen input of 10 to 40 kgha"´ represents
critical contamination of a forest ecosystem. Excess
nitrogen stimulates the growth of the leaf mass and
slows down the lignification process, as well as negatively
affects the development of the root system and mycorrhizae.
This results in disturbed nutrition and reduced
plant resistance to drought and low temperatures
(K o m 1 e n o v i ć et al, 1997). In their research in beech
and spruce forests in Switzerland, Fluckinge r and
Brau n (1993) measured bulk depositions of 10 to


12 kgha"1 year"´ N (NH4-N) in the open in lowland parts,
and of 13 to 20 kgha"´ year"´ N in pre-mountainous parts.
In forest stands of beech and spruce these values arc
higher and amount to about 25 kgha"´ year"´. In northern
Italy U g o 1 i n i et al. (1993) report on nitrogen depositions
from 10-14 kgha"1 year"´ to 20 kgha"´ year"´, depending
on a sampling site (geographical area, altitude,
exposure etc.). In their research of similar problems in
Denmark, Nguyen etal.(\990) state that acids in precipitation
are unequally represented per measuring sites
due to different air transport of S02 and NOx by wind,
clouds etc. The severity of rain and the size of raindrops
play a vital role here. The principal causes of wet deposition
acidification in Europe are sulphur (H2S04) and
nitric acid (HN03). The transformation of NOx in HNO,
is faster than the transformation of S02 in H2S04.