Full-text - Norsk entomologisk forening

Norwegian stoneflies 1/ 217
Area 7. South Varanger
In South Varanger, studies were carried out
in two widely separated areas (Fig. 4): the
Pasvik area and the Korpfjell area. The
Pasvik area is situated in the northern part
of the Sub-Alpine and Boreo-Montane subzone,
while the Korpfjell area lies in the
upper part of the Sub-Alpine belts, where
it is close to the arctic vegetation zone
(Sjiirs 1963).
Area description
Ten streams and five lakes in the Pasvik
area, and three streams and two lakes in the
Korpfjell area were investigated.
The whole area belongs to the Precambrian
'Baltic shield', but there are differences in
the Pasvik area. Around Spurvvann in the
north-west, there are younger formations
with intrusions of basic rocks. The Quarternary
deposits are mainly moraine material
(Boyum 1970).
The climate is less continental than
the Kautokeino area, but precipitation is
low (below 400 mm a year). The Korpfjell
area has the highest oceanity factor.
The south-eastern parts of Pasvik consist
mostly of boggy areas at an altitude of
between 50 and 100 m a.s.l. In the west, the
landscape is somewhat higher, with heights
of about 200 m a.s.l. In the north-west it is
even higher (about 300 m). The area investigated
on Korpfjell lies between 200 and
260 m a.sJ.
Most of the Pasvik area is covered by
coniferous forest. Along the streams and
rivers there is often a dense fringe of willow.
In the north-west there are areas which lie
on the border of the Sub-Alpine belt. There
is also here a great deal of willow along the
streams, especially in the lower parts. The
flora is also described by Kalheber & Tobias
(1971).
On Korpfjell, birch woodland predominates
around Korpvann, while above this and along
the streams willow dominates.
Stream descriptions
The Pasvik area is dominated by the River
Pasvik, which forms the border between
Norway and the USSR. The river comes from
lake Enare in Finland and is mainly slowflowing,
with sand and gravel substrata.
Fig. 11. Stream at Ivargammevann in Pasvik.
Riffles, with substrata of larger stones, occur
occasionally. Most of the streams in this area
drain into the River Pasvik. The substratum
of these is mostly large stones (Fig. 11), but
there are also some streams with finer substrata
of gravel and sand such as Gjokbekken
(stream 4) and Skjellbekken (stream 7).
In the Korpfjell area only three streams
were investigated. They all had a mixed substratum
of stones, gravel and sand. Measurements
of hardness and pH were made on
several occasions. Values of pH around 7.0
were common in the Pasvik area (see also
Boyum 1970), and the lowest recorded was
6.6. Calcium hardness varied generally between
1 and 2 mg Ca+ + 11. The highest
values were recorded in Storkilden, pH 7.4
and 3.0 mg Ca+ + 11 and a stream flowing
from Spurvvann, pH 7.1 and 3.4 mg Ca++/1.
On Korpfjell, Oterbekken had pH 6.5 and
1.7 mg Ca + + 11 and Bannebekken pH 6.7
and 2.2 mg Ca+ +11.
Stonefly fauna
In South-Varanger 24 species were recorded,
23 in Pasvik and 15 at Korpfjell,
Table IX.
At Korpfjell two of the 15 species were
taken in lakes and 13 in streams. The total
number of species taken in lakes in area 7 was
13, the highest in Norway.
The dominating carnivorous species in the
Pasvik area is Diura bicaudata, which was
taken in great numbers in lakes. lake outlets
and streams. Next to Diura bicaudata in
abundance was the omnivore Isoperla obscura