Jökull - 01.12.1988, Síða 46

Chloride in groundwater (in ppm Cl").
Fig. 5. The chloride content of the groundwater is indicative of the chemical content of the precipitation, but
locally increased by influx of geothermal water.
Mynd 5. Klóríðinnihald í grunnvatni á fyrst og fremst rót sína að rekja til efnainnihalds úrkomunnar.
Blöndun við jarðhitavatn veldur staðbundinni aukningu í klóríðinnihaldi.
Explanations / Skýringar:
Isolines of chloride in groundwater in ppm Cl— / Jafngildislínur klóríðs í grunnvatni íppm Cl—.
amounts to 30 - 40 % in the abundantly watered
southem lowlands, but it may be considerably
higher in the dry northeastem part of the country.
The marine component is easily recognized in the
chloride content. In the southem lowlands it is 10 -
20 ppm in the groundwater, but in the rain shadows
on the northem side of the glacier Vatnajökull it is
below 1.5 ppm. The evapotranspiration taken into
account, the potential evapotranspiration is con-
sidered to be equal or even exceed the precipitation,
the mean chloride content in the precipitation must
have been below 1 ppm. This low concentration in
the groundwater and the regular decrease in chloride
with distance from the coast corresponding to the
meteorological conditions hardly leaves any space
for a noticeable dissolution of chloride from the
rocks. The chloride content in the cold groundwater
(3 - 6 °C) can therefore with a minimal error be
regarded as an indicator of the marine component
(Fig. 5).
The marine component then appears to be strong
close to the coast, the chloride content being 10-60
44 JÖKULL, No. 38, 1988