NORSK ENTOMOLOGISK TIDSSKRIFT - Norsk entomologisk forening

The Tana often floods as early as mid-May,
and the inundations are usually over before
mid-June.
Flooding is seldom accompanied by ice­
drifting on the Gaula, the Namsen, Saltdals­
elva, and Malselva. This only happened on the
Namsen on 3 March 1948 and 9 February
1960, and on the Gaula on 1 May 1966 (water
level at Gaulfoss 6.7 m). Along these rivers the
thaw in the lowland is usually complete
before is has commenced in the mountains.
On the Tana in Finnmark, drifting of ice
usually occurs at the same time as the spring
floods, because of simultaneous thawing over
a wide range within the watercourse.
The temperature in the Gaula during the
spring flood in 1965 was 7-8°C, in Mfilselva
in June 1966 8·9°C, and on 2 June 1967 it
was 6°C. These temperatures were measured
in the rivers. In backwaters the temperature
at Rundhaug, 2 June 1967, was higher, up to
12°C, but as the river rapidly rose the
temperature decreased, and finally the tem­
perature differences were negligible.
THE EFFECT OF INUNDATION
THE EFFECT OF INUNDATIONS
119
Investigation of fauna during and after inunda­
tions
I. Investigations during rising water level
on MiUselva (Rundhaug) 2-3 June and
22-23 June 1967
On both occasions, the river rose rapidly
from a moderate to a high level during the
night. The surface layer of the zones up to
1 m above the water's edge was investigated.
Sample 1-1 (Table II), 2 June 1967: Sandy
places without vegetation. Lower lying sandy
places submerged.
Samples 1-2 (Table II), 2 June (1-2, A) and
22 June 1967 (1-2, B and C): Gravelly slopes
without vegetation, mostly elevated.
Samples 1-3 (Table 1I), 2 June (1-3, A) and
22 June 1967 (1-3, B): Strongly sloping, gravel­
ly declivity, ending above in a dense grassy
mat. Most of the lower lying gravelly sites
submerged. None of the species listed in the
table were taken from the same sites at low
water level.
Table 11. Coleoptera collected in Samples / /-3 by time-catch. The figures give the number o[specimens;
ifestimated, the abundance per m 2 is given in brackets
Sample I-I 1-2, A 1-2, B 1-2, C 1-3, A 1-3, B
Collecting time (mins.) 15 26 20 14 40 20
Dyschirius septentrionum Munst. 1 (0.3)
Bembidion dlffici/e Mtsch. 1 (0.2)
B. /apponicum Zett. 2 2 (0.6) 1 (0.4) 1 (0.5) 2 (0.4) 1 (0.4)
B. petrosum Geb\. I 25 (7.2) 21 (7.9) 10 (5.4) 83 (15.6) 18 (6.8)
B. prasinum Dft. 1 (0.3) 2 (1.2) 3 (0.6) 2 (0.8)
B. schueppe/i Dej. 5 (1.5) 1 (0.4)
B. virens Gyl\. I (0.2)
Agonum [u/iginosum Panz. 1 (0.4)
Geodromicus p/agiatus F. 2 (0.8)
Stenus [uscipes Gr. 1 (0.4)
S. strandi Bck. 2 (0.4)
Oxypoda proceru/a Mnh. 1 (0.2)
Hypnoidus pu/che//us L. 2
H. rivu/arius Gyl\. 2 (0.4)