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ŠUMARSKI LIST 13/2005 str. 183     <-- 183 -->        PDF

B. Vrbck, I. Pilaš, T. Dubravac: LYSIMETRIC MONITORING OF SOIL WATER QUALITY IN THE FOREST ... Šumarski list -SUPLEMENT (2005), 165-185
INTRODUCTION


Persistent soil acidification through dry and wet depositions
gives rise to a series of secondary consequences,
such as the dissolution of heavy toxic metals and
nutritive materials and their transformation into a liquid
phase (soil solution), which then penetrates the
groundwater. Not only is the capacity of drinking water
thus diminished, but other side effects also occur. In
certain climatic conditions and areas, the quality and
quantity of water that percolates through a forest ecosystem
towards groundwater should be tested, since
groundwater is generally used as water supply. This issue,
studied in detail by Brechtel (1991) and Leh-
n a r d t et al. (1983), is particularly important in case of
soils with a lower buffer capacity (e.g. soils on acid parent
substrates), Ulrich (1982). Many authors claim
that forest soil acidification, which is directly related to
lowered pH values and increased Al3+ concentrations
in the soil solution, is the most responsible factor in forest
damage and decline in many areas.


Lysimeters are devices that monitor movement of
water through the soil and water percolation through a
particular soil volume. These instruments measure the
quality of soil solutions and materials that reach the
soil through precipitation and are further percolated into
groundwater or flow laterally across the impermeable
soil horizon. The word lysimeter is derived from


the Greek words "lisis", meaning dissolution and "metrom",
meaning measurement.


This term can be applied to any instrument that monitors
the quantity and quality of soil water that passes
through the soil solum or moves laterally along a slope.
In the beginning, lysimeters were used to measure the
components of soil water balance - evapotranspiration
(Sraka 1996), as well as changes in the reserves of
physiologically active water. They were also used to
determine excessive water in the soil - percolation into
groundwater. Since the end of the 20lh century lysimeters
have increasingly been used to study the chemical
percolate content in the soil profile. Ebermayer
(1879) was among the first to use lysimeters to measure
water movement through undisturbed forest soil. A
normal soil solution contains 100-200 different soluble
complexes, many of which contain metal cations
and organic matter (Sposito 1989). In Croatia, lysimetric
research into liquid soil phase lagged behind
that in Europe. This segment of pedology received impetus
only some ten years ago (lysimetric pedology).
The application of lysimetric techniques in forest conditions
is still insufficiently treated in specialist papers.
This issue has been dealt with by Vranković et al.
(1991), Vrbek (1992, 1993, 2000, 2002), Vrbek and
Pilaš (2000,2001).


METHODS OF WORK


The sample plots in which research was conducted
were set up in a typical community of pedunculate oak
and common hornbeam. This community is not exposed
to flooding, but in winter the soil is saturated with water.
The community inhabits raised terrains and micro-elevations
in drained terrains. This type of community generally
encompasses pedunculate oak forests on the highest
terrains in the Croatian lowland areas. According to
Raus et al. (1992), the community of pedunculate oak
and common hornbeam (Carpino betuli-Quercetum roboris,
Anić 1956/emed. Rauš 1969), which continues on
floodplain forests of pedunculate oak, narrow-leaved
ash and black alder in lower areas and on forests of sessile
oak and common hornbeam in higher positions, is
characterised by a broad ecological amplitude. This is
reflected in the highly diverse and typical layer of ground
vegetation. The community takes up a belt between
110 and 120 m above the sea.


The quality of soil liquid phase and deposited matter
was monitored in sample plots (Table 1).


A system of small plastic lysimeters was installed
for the purpose of monitoring percolating soil water
(Figure 1).


The lysimeters, filled with 96 % pure quartz sand
and equipped with special filters, separate the percolate
from the soil particles. The instruments were installed
at two depths in the pedological profile: 10 cm deep
below the humus horizon and 100 cm deep in the mineral
soil part.


Up to 6 plastic rainfall gauges and 6 plastic funnels
were placed diagonally below the tree crowns in each
plot.


Three rainfall gauges and three funnels were installed
in control sites in the open space outside the influence
of vegetation (bulk).


CATION AND ANION ANALYSIS


The chemical liquid content was analysed in the Sta


precipitation: S042"- ions, NO3"- ions were determined
te Hydrometeorological Office. CI-, S042--S, N03~-N, spectrophotometrically (Perkin Elmer Lambda-1 specNH4-
N, Na´, KT, Ca" and Mg/+ ions were determined. trophotometer), NH4+- ion and Cl"-ion were determi


Standard and typical analytical methods were used to ned with the ionselective electrode method (ORION identify
small quantities of substances in water and Microprocessor ionanalyser, model 901), while metal