2.
ESTONIAN WATER RESOURCES AND THEIR STATUS
The freshwater supply of Estonia consists of surface
water and groundwater. There are more than 1,200 lakes and 420 rivers and brooks
in Estonia. Most of them are small water bodies sensitive to pollution. Surface
water bodies are fed from precipitation. The amount of precipitation in Estonia
is between 500 and 850 mm per year, the average of many years being 670 mm.
Evaporation is on average 450 mm per year and the rest of water drains into
water bodies or filters into the soil, thus increasing the groundwater
resources. The volume of groundwater resources varies greatly by regions.
Uplands, especially the Pandivere Upland, are the main catchment areas for
groundwater resources. Local catchment areas are situated mostly in the regions
of limestone projections as well as in sand and gravel ridges. The best arable
lands lie often in these areas.
The natural protection of groundwater depends on the
thickness and structure of residual soil. The other important factors are the
soil and subsoil relief, tectonic faults and karst formations. Quarries and even
small excavations can influence the level of protection significantly. As a
rule, in settlements and on fields groundwater is less protected than in natural
areas, e.g. forests and swamps. Plants growing in natural areas utilise most of
the nitrogen compounds in the soil and that is why only a small amount of them
leach into groundwater. The most environmentally friendly and cost-effective way
of increasing the plant production is to spread it on agricultural land.
By intensive crop cultivation mineral fertilizers are
used to raise the productivity of plants. Fertilizers and pesticides, if used in
great amounts, are dangerous both to the environment and human.
Fertilizers, which are not absorbed by plants during the
vegetation period, will be transferred from the soil into surface or
groundwater. The same goes for manure, if spread in winter: when snow melts,
most of the nutrients in manure will filter together with melting waters into
the brooks, ditches or lakes adjacent to the fields. In the water body, these
nutrients cause excessive growth of plants and overgrowing. In winter the amount
of oxygen may decrease in such water bodies and that in its turn may reduce the
diversity of life.
For human health it is harmful to drink water rich in
nitrates. As far as domestic animals are concerned, nitrates are not so harmful
for their health, but these substances can damage the quality of stock-farming
products. To protect groundwater and surface water in regions of intensive
agriculture, nitrate sensitive zones shall be determined. Nitrate sensitive zone
is a zone where because of the land application of fertilizer, the content of
nitrate ion in groundwater has exceeded or may exceed 50 mg/l or where surface
water bodies have been eutrophied, or where the danger of eutrophication exists.
The level of pollution with nitrates of both surface and
groundwater is higher in Central, Western and Northern Estonia. However,
recently the situation has improved as agricultural production has diminished,
although in some places, the amount of nitrates is still quite high in subsoil
groundwater.
Local pollution is in most cases caused by human
negligence. Careless handling of liquid fuels, lubricating oils, pesticides or
liquid fertilizers (slurry, urine) is the most dangerous. Ownerless storages of
fertilizers and chemicals as well as toxic chemicals or their packaging, which
have been left in the nature, represent a significant danger. Animal husbandry
can also cause great danger of water pollution if management of manure has not
been organised in an environmentally sound manner.
