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ŠUMARSKI LIST 13/2005 str. 187     <-- 187 -->        PDF

B. Vrbek. 1. Pilaš. T. Dubravac: LYSIMETRIC MONITORING OF SOIL WATER QUALITY IN THE FOREST ... Šumarski list -SUPLEMENT (2005). 165-185
(LI00) show the prevalence of cations over anions.
The soils still have good buffer capacity.


Despite the still good function and acid neutralisation
in the soil, the fine tiny roots and the ground vegetation
in the forest may already be threatened. There
are evident changes. The surface soil layers in the range
of pedunculate oak and common hornbeam in


northwest Croatia show acidification trends due to the
already unacceptable levels of contamination.


Further trends in matter depositions and the condition
of the Croatian forest ecosystems can only be determined
with detailed, several-year-long measurements
with the lysimetric method.


CONCLUSIONS


According to the data of precipitation measurements
in the forest of pedunculate oak and common
hornbeam, lower average liquid quantities in mm were
measured under the crown cover than in the open. The
precipitation quantity measured under the crown was


81.17 % in relation to the control site in the area of
Cesma. For the area of Pokupsko and Šiljakovina the
quantity was 89.12 % in relation to the control site, and
in the area of Repaš it was 80.22 % in relation to the
control site. According to the 1997 measurements, interception
accounted for approximately 10.9-19.8 % in
an older forest of pedunculate oak and common hornbeam
in northwest Croatia.
The results of cation and anion analyses show that it
is not enough to measure only the concentration of individual
elements in the solution. Rather, the quantity
should be reduced to g/m2 or kgha´in order to gain an
insight into the quantity of depositions and leaching in
a forest ecosystem.


According to statistical analysis, the highest amounts
of chlorine were found in lysimeters at a depth of
10 and 100 cm in the area of Pokupsko basin and Šiljakovina.
Česma and Repaš follow.


In all the sites, the highest amounts of S04-S reached
lysimeters at 10 cm in depth. In this respect, Repaš
takes the lead, followed by Cesma and Pokupsko.
Increased sulphur was also recorded in lysimeters at
100 cm in depth in the area of Pokupsko and Česma,
and less so in Repaš.


An increase in N03-N was the highest in lysimeters
at a depth of 10 cm in the area of Česma and Pokupsko,
and in the control plot in Repaš. Slightly lower increases
were found in lysimeters at 100 cm and the samples


under the crowns. The increase relates mainly to nitrates,
since they are leached from the soil into the groundwater.


Sodium and chlorine contents were the highest in
lysimeters at 100 cm in depth in the Pokupsko-Siljakovina
area. The increase is manifold in comparison with
all the other measuring sites and plots.


On average, the quantities of potassium were the
highest in lysimeters at 10 cm in depth in Česma and
slightly lower in the Pokupsko and Repaš areas. In Repaš,
most potassium was found in the control measuring
point and in the samples under the tree crowns.


The highest average quantities of calcium were
found in the area of Česma, in lysimeters at 100 cm in
depth, which can be attributed to a higher quantity of
CaC03 in the deeper soil profile layers.


The highest magnesium content was found in lysimeters
at a depth of 100 cm, followed by lysimers at a
depth of 10 cm in Česma. Somewhat lower increase
was found in Pokupsko-Šiljakovina, while in Repaš,
the increase was recorded in the control plot and in the
forest.


According to the calculated ion difference in %, the
poorest soil buffer capacity was recorded in the area of
the Pokupsko basin with Šiljakovina, and then in the
Česma watershed. In these areas, acids penetrated the
lysimeters at 10 cm deep. The measuring sites below
the tree crowns and the control measure site also showed
a negative prefix. The Repaš area did not show negative
ion difference in lysimeters; therefore, they are
sufficiently buffer active to neutralise acids deposited
via dry and wet depositions in the community of pedunculate
oak and common hornbeam.