ESTONIAN ENVIRONMENTAL REVIEW 2009

6.4.5. Status of lakes
The ecological status of lakes was assessed on the basis
of biological and physico- chemical quality indicators. In
the process, the status of fish was not taken into account
as the determination of class boundaries for fish is still
in progress.
On the basis of the rating, most Estonian lakes are in the
“good” or “moderate” status (figure 6.14). The so-called 2/3
rule was used to assess the status of lakes. According to this
rule, at least one quality indicator was to be used from each
biological quality element and physico-chemical general
conditions. The number of quality indicators used had to
be at least seven, with all of the indicators having equal
weight. The status rating is assigned to the status category
of 2/3 of the indicators. Some of the quality indicator values
may indicate a quality lower than that of the combined
rating, but the number of such quality indicators should
not exceed 1/3 of the total number of indicators.
The ecological status of Lake Peipsi and Lake Pskov
has worsened in recent years. This is above all due to
eutrophication from excessive phosphorus load. The percentage
of blue-green algae with respect to all algae has
increased in the summer months, while diatom biomass
has decreased. Algal toxin concentrations in water have
repeatedly exceeded the permitted limit values for bathing
water. Due to the proliferation of algae, fish spawns have
become muddy and fish reproduction conditions have
worsened. Overall, the ecological status of Lake Peipsi was
rated moderate and that of Lake Pskov, poor.
The ecological status of Narva reservoir has remained
relatively stable in this decade. For the most part, the
reservoir’s ecosystem behaves similarly to the northern
part of Lake Peipsi. In the last few years, a rise in both
phosphorus and nitrogen concentrations has been observed
in Narva reservoir. Phytoplankton concentrations have
also increased – especially blue-green algae biomass and
chlorophyll a concentrations – as a result of which the
ecological status of the reservoir was rated moderate.
The indicators for the status of Lake Võrtsjärv depend
significantly on the lake’s water level, which in recent
years has been quite low. For this reason, the water quality
and status of the phytoplankton in this water body were
assessed on the basis of data for the last 10 years. The
combined rating of the ecological status of Lake Võrtsjärv
on the basis of phytoplankton, macrophytes and water
quality was deemed good. The major fluctuations in the
water level of recent years make it difficult to distinguish
between natural and anthropogenic changes and thus
reduce the reliability of the rating.
Status of smaller lakes. The existing data made it possible
to assess the status of 152 small lakes J (figure 6.14,
map 6.7). Of the lakes assessed, 17 were in high status, 76
were in good status, 50 were in moderate and 9 were in
poor status. The status of macrophytes in Estonian lakes
is the poorest indicator. Regarding water quality it can
be said that on the basis of nitrogen, over half of the lakes
were in moderate or worse condition, while on the basis of
phosphorus, slightly over 20% of the lakes were in moderate
or worse status. Of the largest lakes, Ülemiste, Maardu
and Harku in Harju County were in moderate condition,
as were Kaiavere in Jõgeva County and Vagula and Tamula
lakes in Võru County. The condition of Veisjärv in Viljandi
County is poor.
high
good
moderate
poor
100
80
60
40
20
%
0
Viru
Peipsi
Võrtsjärve
Harju
Matsalu
Pärnu
Läänesaarte
Pandivere
Mustjõe
Figure 6.14. Ecological status of small lakes in Estonia, 2004–2008. The number indicates the number of lakes in the given status class.
Data: EEIC.
Read more:
• Advanced WISE water map viewer.
[WWW] http://www.eea.europa.eu/themes/water/mapviewers/
advanced-wise-viewer/
• Estonian Environment Information Centre website.
[WWW] http://www.keskkonnainfo.ee/
index.php?lan=EN&sid=2&tid=2 (state of environment)
• Ministry of the Environment website.
[WWW] http://www.envir.ee/67250 (water)
104
J
Small lakes – all lakes besides Peipsi, Pskov and Võrtsjärv.