ABSTRACTS / RESUMES - Comitato Glaciologico Italiano

draining south-east part of the most industrialised area
in Poland - Silesian Upland. The surveyed rivers: Biala
Przemsza, Sztola and Chechlo, receive mine waters from
the greatest lead and zinc mines in Poland, at Bukowno
and Trzebinia. 2 m 3/s, 1.3 m 3/s and 0.5 m 3/s of mine waters,
respectively, is dumped into these rivers, the amounts
accounting for 50%,990/0 and 60 % of their mean annual
discharge.
Samples of the bottom sediments were taken at 11-18 sites
along investigated river courses, at each site in three crosssections
situated in meander loops, pools and riffles (Chechlo
River) or in braided reaches (Sztola River). Six grab
samples were taken in characteristic points of cross-sections
in the deepest points, channel bars, at the banks (below
and above the water table) and on floodplain. Grain
size distribution of the sediments was determined and the
Zn, Cd, Pb, Ni, Cu, Mn, Fe and Ag concentrations in fractions
< 1 mm and < 0.063 mm were analysed using flame
AA spectroscopy. Additionally, the X-ray analysis of selected
samples was performed.
The heavy metals present in a solid phase are basically associated
with fine particles (especially < 0.063 mm) transported
from mines. Accumulation of the material coming
from mines changes both the concentration of heavy metals
and the content of silt and clay fractions in bed sediments'
so it is easy for identification in sand-bed channels.
Among factors controlling accumulation of heavy metals in
the investigated channels the four are well seen; i.e. the
density and size of transported particles, channel morphology,
river flow amplitude and water stage.
On relatively short reaches immediately below outlet of
mine waters, the highest concentrations of Zn, Cd, Pb and
Ag in cross profiles occur in the deepest points of crosssections
and on channel bars, whereas the lowest ones at
the banks. Observed regularity can be explained by the effect
of mechanical sorting; light particles of dolomite being
washed away by a strong current and dense particles of
sphalerite and galena, leaving behind. These particles of
heavy minerals are transported as a bed load. The reversed
distribution occurs along reaches where heavy metals present
in a solid phase are transported in suspension. There,
the highest concentrations of heavy metals in fraction