Water Quality in Slovenia - Agencija RS za okolje

S U R F A C E W A T E R S
In the years 2003 to 2006, the monitoring network consisted of monitoring sites in lakes and monitoring
sites at the lakes’ inflows and outflows. The sampling of lakes was carried out at selected depths along
the water column. The monitoring programme was primarily adjusted to monitor eutrophication,
which is the main problem in most natural and artificial lakes of the Temperate Zone on a carbonate
geological layer, to which all lakes and reservoirs in Slovenia also belong. In the lakes and their inflows,
the status of nutrients and general physico-chemical parameters were primarily monitored. Analyses
of pollutants, heavy metals and pesticides were only carried out in some inflows and outflows where,
taking into account the pressures in the catchment area, an increased concentration of individual
pollutants in water was to be expected. The lakes were evaluated according to OECD criteria (33),
which classify the lakes into five trophic categories, based on the average annual concentration of
total phosphorus and nitrogen, the average annual and minimum transparency, and the average
annual and maximum concentration of chlorophyll-a. Other pressures that have to be taken into
consideration in the ecological status classification of lakes or the ecological potential of artificial
reservoirs as required by the Water Framework Directive, were not evaluated while an appropriate
methodology is still in the course of preparation. Among biological quality elements, the status of
phytoplankton, macrophytes, phytobenthos and benthic invertebrates was monitored. In the years
2003 to 2006 the final assessment of lake status was made according to the status of phytoplankton
(one of the OECD criteria), which is expressed by the average and maximum annual concentration
of chlorophyll-a. The sampling of macrophytes, phytobenthos and benthic invertebrates was carried
out at selected sites in the shore zone according to new methodology, adapted for the assessment
of the ecological status of lakes. A detailed programme outlining the monitoring of water quality for
each individual lake is presented in the annual Programme for monitoring the quality of lakes (32).
Lake Bled
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