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SUMMARY
The effect of pollution on the
fauna of two thermal rivers in
Iceland
by Gísli Már Gíslason
Institute of Biology, University of Iceland,
Grensásvegur 12, Reykjavík
The thermal rivers, Varmá in Mosfells-
sveit district, about 15 km north-east of
Reykjavík, and Varmá in Ölfus district,
aboul 40 km east of Reykjavik were studied.
Both are run-off rivers, partly fed by hot
springs (Figs. 1 and 2). Both flow through
relatively densely populated areas, with
sewage from 700 people entering into
Varmá in Mosfellssveit and from 1450
people in Varmá in Ölfus. Both receive
pollution from livestock, greenhouses and
wool washing factories. Varmá in Mosfells-
sveit occasionally receives large quantities of
hot (80°C) water from a hot water pumping
station, and Varmá in Ölfus receives
effluents from a salmon rearing station
(Table I).
Several changes occur in physical and
chemical properties of the rivers down-
stream (Figs. 3 and 4), such as a rise in
temperature, especially in Varmá in Mos-
fellssveit below the hot water pumping
station on 2 Febr. 1977, when the overflow of
hot water was discharged into the river.
Specific conductance and pH increase
downstream, mainly below the wool
washing factories.
Pollution clearly affected the fauna in
these two rivers (Figs. 5 and 6). Greatest
number of species was found above the
populated areas, and it decreased down-
stream. First to disappear were 'Frichoptera
larvae and Capnia vidua (Plecoptera), but an
increase in Chironomidae and Oligochaeta
was found in the sewage pollution. Down-
stream of the wool washing factory in
Varmá in Mosfellssveit, hardly any animal
was found, with the exception of amphipods
in the estuary. Below the main sewage entry
in Varmá in Ölfus, the numbers of Lymnaea
peregra, oligochaetes and predators (Hydra-
chnellidae, Helobdella stagnalis) increased.
The two rivers are on the list of preserved
areas published by the Nature Conservation
Council of Iceland (Gardarsson 1975, 1978)
due to the value they have as unique rivers
in Iceland. It is not possible to return the
rivers to their original state, but some sug-
gestions are made to improve their condi-
tion.
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