Rit (Vísindafélag Íslendinga) - 01.06.1976, Page 80

of each point of sampling are obtained from the topographic maps,
a total of nine sheets, published by Landmælingar Islands in the
years 1967—1972, scale 1:250 000. The samples are arranged in
such a way that all samples on each map sheet are grouped to-
gether within the table. Within each map sheet the sampling points
are listed with increasing latitude, whereas all samples with the
same latitude are listed with increasing longitude. All the sampling
points listed in Table II in the Appendix are shown on Fig. 19 as
filled circles. In cases where there is only a circle the water is
believed to originate as precipitation in the immediate surround-
ing area. In other cases a line has been drawn from the sampling
point into the middle of the expected recharge area.
In many cases it is difficult to prove the validity of the surmise
that a water source originates as precipitation in a certain recharge
area. Circumstances may make it very likely that the water source
in question comes from a certain recharge area although this can-
not be proved. In such cases, however, where different water
sources, believed to originate in the same recharge area, all have
similar SD-values, it seems a valid conclusion that the water sources
in question all originate in this particular recharge area. The cold
springs and surface streams listed in Table 7 are a good example
of this procedure. Hydrogeological conditions point towards a local
origin of all these som-ces. And since all sources in the same dis-
trict have approximately the same öD-value, which also agrees with
the mean ðD-value of the precipitation, apparently our prediction
about the local origin of these samples has been right. Two other
examples may be mentioned. Three cold springs, of which two are
located on the northem and one on the westem slope of the moun-
tains of SkarðsheiSi in Southwest Iceland, have ðD = — 58.5%0,
5d = — 60.2%0 and ðD = — 61.6%0 respectively. Since all these
sources are believed to have their recharge area in the mountains
of Skarðsheiði, it seems very likely that the mean ðD-value of the
precipitation on Skarðsheiði is close to ðD = — 60%0. Four water
sources on the eastern slope of the mountains of Dyngjufjöll, in the
eastem part of central Iceland, are thought to have their recharge
area in Dyngjufjöll. In spite of the fact that these sources are cold
springs at different altitudes and they also differ in water tempera-
ture, they all have very similar deuterium content, ðD = — 93.6%0,
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