The water of Iijoki river is in midsummer at very low level - like in many others rivers in the North.
In the time of spring flood the water level is many meters higher, and will slip over riverbanks
to the ow-lying mires and forests.
Rapids are important particularly in winter: this is the place, where the river receives oxygen and ligth.
Dick snow- and ice cover forestalls the connections between the air and water...
The waters especially in middle part of North Finland are brown colored because of humus coming from mires.
Characteristics of northern waters are:
-There is a lot of water because the terrain is quite even, the climate is moist and there is a lot of water from the melting snow. In Finland there are over 188 000 lakes (area over 0,05 hectares), so of the total area of Finland the lakes cover about 10%.
- In the north there are a lot of rivers and the frequency of lakes is the most dense there, too.
- Waters are not rich in nutrition, especially phosphorus and nitrogen are minimum factors. The amount of organisms in these kinds of lakes is small but they are often very good fishing places.
- In Lapland there are more clear waters than in the rest of Finland (less swamps so there is less humus in the water). In southern (southern parts of Lapland and in Ostrobothnia) waters are often humus rich because there are more swamps. (see picture above - even the ice cover is brown).
- The average depth in Lapland is about 5 meters but there are shallow lakes and ponds, too. They can freeze all the way to the bottom that can cause an oxygen deficiency during the winter. That’s not very common in the north because the waters are mainly nutrient poor and there isn’t much life (and the life there is, is very slow during the winter).
- The water of lakes mixes up twice a year: autumn and spring circulation.
All 18 largest lakes in Europe are situated in North Europe (see the table!).
Long rivers in Northern Europe are more common in farther south.
The northern part of the Gulf of Bothnia is like a lake because the content of salt is so small. There are only some green algae, few bigger algae and few halophytes. In shallow shores the breakers aren’t able to destroy the vegetation, but it brings decomposing matter to the shore and the shore vegetation get more nutrients. Shore moves upward from the sea (almost one meter in hundred years). The primary succession of vegetation is very clear: the sedge zone of water shore develops in to bush- and forest vegetation. On the islands about 200 years old can grow abot 70 different plant species, depending on the dispersion capacity of species and the area of island.
Two limnological types: eutrophic and oligotrophic lakes
Water in the eutrophic lakes is troubled, the vegetation is flourishing and there exist many plant species. Wide and tall bulrush (Schoenoplectus lacustris) -, reed (Phragmites australis) - and horsetail (Equisetum fluviatile) -populations are growing on the shores. Further away you’ll find waterlilies and pond-lilies and few submerged plants, too. The eutrophic lakes are common in Southern Finland, but rare in the north.
There are a little nutrients in the water of oligotrophic lakes, and the water is often very clear. The sedge (Carex) -populations are common.
As well oligotrophic are lakes where the water is brow, so called dystrophic lakes. The dystrophic lakes are common all over in Finland and particularly in the central Northern Finland where the peatbogs are abundant. The most common are horsetail (Equisetum fluviatile) -dominated lakes.
The shore zones are quite similar to those in the seashores of Gulf of Bothnia. (See picture!). The littoral zone of lakes is often the most diversified/polymorphic part of the lake. The landshore (geolitoral zone) is narrow.
(Above): Characteristics of river scenery is often an enlargement of river with sedge shores,
which looks like
a lake (in the picture Carex rostrata).
The river banks can be high and steep;
during years the river has ‘corroded’ deeper in to gravelled ground
and the flowing water
has made the river banks steeper. The lowest forests (deciduous forests)
are quite fertile because of the silt that flood brings.
Where the flood doesn’t reach there are pine
and dwarf shrub dominating forests.
-Picture from the Kitka-river (Kuusamo).
(Above): Peat-covered shores are common in the north.
Here e.g. dwarf birch (Betula nana) and slender sedge (Carex lasiocarpa).
