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■ SUMMARY
Terrestrial influence ön the biota in
ICELANDIC RIVERS
Chemical composition in rivers is determined by
the geology, topography and vegetation cover in
the catchment areas (fig. 7, table 1). This seems
to determine the productivity of the rivers in the
catchment areas as indicated by catch of salmon
and density of benthic invertebrates. Catchment
areas of Icelandic rivers are described and fluc-
tuations of nutrients (figs 8 and 9). Rivers origi-
nating in lakes and from areas with extensive
cover of vegetation produced much more Atlan-
tic salmon (Salmo salar) than rivers originating
from barren areas, which only produced few
salmon or none (fig 10). Organic matter dril'ting
downstream from river headwaters determined
species composition of benthic communities.
Filter-feeding blackfly larvae (Simulium
vittatum) dominated lake outlets (fig. 11),
whereas algae-grazing chironomids dominated
rivers without lake influence (fíg 12). Glacial riv-
ers have the lowest density and diversity of
benthic invertebrates of all river groups (fig. 13).
The study is supported by the Research Council
of Iceland (Science Fund), the Research Fund of
the University of Iceland and the Framework of
EU (Environment and Climate) to the project
AASER (Contract ENV-CT95-0164).
PÓSTFANG HÖFUNDa/AuTHORS'ADDRESSES
Hákon Aðalsteinsson
Orkustofnun / National Energy Authority
Grensásvegi 9
IS-108Reykjavík
ha@os.is
Gísli Már Gíslason
Líffræðistofnun Háskólans / Institute of
Biology, University of Iceland
Grensásvegi 12
IS-108Reykjavík
gmg@rhi.hi.is
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