Fróðskaparrit - 01.01.1998, Page 247

FLOGSÁÐFRØÐILIGAR OG GRÓÐRARLIGAR BROYTINGAR f SAMBANDI
VIÐ BOTNSETING AV SAKSUNARVATNSØSKU í FØROYUM
253
HAGAMÝRA: percentages
Fig. 8. Pollen and spore diagram ofselected taxafrom the Saksunarvatn ash zone, Hagamýra. Percentage values
are expressed as TLP minus alien AP. Total identifiable palynomorph concentrations exclude alien AP.
Mynd 8. Flogsáð- og grókomstrikumynd av úrvaldum taxa úr saksunarvatnsøskuøkinum í Hagamýru. Virði í
prosentum eru lýst sum TLP minus fremmant AP. I samanløgdu palynomorfkonsentratiónunum, sum kunnu
eyðmerkjast, er fremmant AP ikki tikið við.
proximately pre-ash levels close to the up-
per boundary of the ash, whereas total pa-
lynomorph concentrations remain de-
pressed, does suggest that vegetational
and/or flowering changes were taking place
in the pollen cachment area of Hagamýra.
The subsequent increases in total paly-
nomorph concentrations from 204.5 cm
(i.e. well above the ash zone), are still at
somewhat reduced levels from those in the
gytjja below the ash (Fig. 7). Although the
clayey gyttja here may have accumulated at
a faster rate than the gyttja beneath the ash,
leading to reduced palynomorph concen-
trations, the percentage data are showing
marked changes which probably reflect
changes in catchment vegetation.
Environmental change
The full length of the pollen profde (188-
269 cm; Fig. 7) displays sharp falls in
Cyperaceae, Caltha palustris-type and
Rumex acetosa above the upper margin of
the ash layer and increases in taxa such as
Pinus sylvestris, Poaceae, Apiaceae and
Huperzia selago. Although the values for
Isoetes echinospora above the ash are sim-
ilar to those immediately below its basal
margin (Fig. 8), the subsequent disappear-
ance of the taxon is notable. In terms of per-
centage pollen representation, the post-ash
sustained decline in Betula pollen is possi-
bly related to the ash-fall.
The adverse fortunes of Cyperaceae and
Caltha palustris-type may be due to wetter
habitats becoming ‘choked’ with ash as
runoff focused tephra-laden material into
stream channels and pools. Rumex acetosa
may have suffered from its frequent occur-
rence in damp habitats including stream-
sides. Alterations in water chemistry and
translucence in the former lake basin of
pre-peat Hagamýra, probably resulted in
the eclipse of Isoetes echinospora and
Myriophyllum alterniflorum. Poaceae, Api-
aceae, Botrychium lunaria and Huperzia