Water Quality in Slovenia - Agencija RS za okolje
Water Quality in Slovenia - Agencija RS za okolje
Water Quality in Slovenia - Agencija RS za okolje
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32<br />
W A T E R Q U A L I T Y I N S L O V E N I A<br />
Cerknica Lake<br />
The <strong>in</strong>termittent Cerknica Lake is a very unique aquatic ecosystem that does not share any common<br />
characteristics with permanent lakes. Due to its great water level fluctuation and the large metabolic<br />
role of marsh plants, there is almost no eutrophication. The results of monitor<strong>in</strong>g show that the<br />
pollutants, especially heavy metals from <strong>in</strong>dustrial plants <strong>in</strong> the catchment area of the Cerknica Lake,<br />
do not exceed the limit values prescribed <strong>in</strong> the Decree of chemical status of surface waters (Table<br />
1). At the monitor<strong>in</strong>g site Stržen - Dolenje jezero, the chemical status was good <strong>in</strong> 2005, but <strong>in</strong> 2006,<br />
it was bad due to the exceeded concentration of detergents, which <strong>in</strong>dicates a problem with the<br />
unregulated discharge of municipal wastewaters.<br />
Velenje Lake<br />
Velenje Lake was formed <strong>in</strong> the vic<strong>in</strong>ity of the Thermal Power Plant Šoštanj, as the terra<strong>in</strong> above the<br />
abandoned part of the lignite m<strong>in</strong>e sank and was flooded. In 2006 it was <strong>in</strong>cluded <strong>in</strong> the national lake<br />
quality monitor<strong>in</strong>g for the first time. Velenje Lake could be classified as a hypereutrophic lake, on the<br />
basis of the average concentration of total phosphorus (120 μg/L) and the average concentration of<br />
nitrogen (1500 μg/L), but the analysis of phytoplankton and the average concentration of chlorophylla<br />
(2.7 μg/L) <strong>in</strong>dicated a productivity characteristic of little to moderately charged lakes with nutrients.<br />
The primary production <strong>in</strong> Velenje Lake is probably limited by the presence of other substances, which<br />
are <strong>in</strong> <strong>in</strong>creased amounts present <strong>in</strong> the lake. In comparison with other lakes, a high average annual<br />
concentration of sulphates (594 mg/L), chlorides (41.2 mg/L) and potassium (51.6 mg/L) especially<br />
stand out <strong>in</strong> Velenje Lake. The average concentration of sulphate is 3.9 times higher than the limit<br />
value for the chemical status accord<strong>in</strong>g to the Decree of chemical status of surface waters (7), which<br />
classifies Velenje Lake as one with a bad chemical status.<br />
Šmart<strong>in</strong>sko Lake, Slivniško Lake, Perniško Lake, Ledavsko Lake and<br />
Gajševsko Lake<br />
All reservoirs <strong>in</strong> north-eastern <strong>Slovenia</strong>, i.e. Šmart<strong>in</strong>sko Lake, Slivniško Lake, Perniško Lake, Ledavsko<br />
Lake and Gajševsko Lake are, under all OECD criteria, eutrophic to hypereutrophic lakes with a high<br />
concentration of total phosphorus and nitrogen. All these reservoirs are shallow, silty and overloaded<br />
with fish. Chemical analyses of <strong>in</strong>flows show that, besides high trophic status, the chemical status could<br />
also be problematic <strong>in</strong> some of these reservoirs. Namely, <strong>in</strong> the <strong>in</strong>flows of Šmart<strong>in</strong>sko Lake, Perniško<br />
Lake and Ledavsko Lake, <strong>in</strong>creased concentrations of pesticides and heavy metals were occasionally<br />
measured, exceed<strong>in</strong>g the limit values specified <strong>in</strong> the Decree of chemical status of surface waters (7).<br />
Due to low sampl<strong>in</strong>g frequency, the calculation and evaluation of chemical status of <strong>in</strong>flows are not<br />
possible. The contents of pollutants exceed<strong>in</strong>g the limit values are presented <strong>in</strong> Table 8.<br />
Šmart<strong>in</strong>sko Lake Ledavsko Lake