Fjölrit RALA - 15.06.2004, Side 128

GIS for the geochemistry of surface waters in Northeastem Iceland
Marin Ivanov Kardjilov1, Siguröur Reynir Gíslasson2, Guörún Gísladóttir1 and
Árni Snorrason3.
'Department of Geology and Geography, University of Iceland. 2Science Institute, University of Iceland.
3Hydrological Service of the National Energy Authority, Iceland.
Land surface hydrologic processes play an important role in the global water cycle. Besides
the study of the precipitation, the definition of the water dissolved and suspended fluxes and
water chemical composition has recently meteorology, digital weather and flood prediction
models, mitigation of the hydro- geological risks and studies of climate dynamics.
gained increasing attention in hydrology, agronomy,
The overall goal of this study is to use GIS (Geographic Information Science) to distribute
spatially and to visualise the geochemistry of the surface waters of selected rivers in
Northeastem Iceland. These rivers were chosen because: 1) enormous database for the
dissolved constituents exists (Gislason et al. 2003) 2) they drain almost exclusively
basalt/basaltic glass catchments, 3) they experience limited but variable biological activity, 4)
they drain catchments of variable glacier cover and 5) they are unpolluted.
The mnoff map of Iceland by Haukur Tómasson (1982) was used for spatial modelling.
The dissolved river water data for the period of 1998-2003 was taken form Gíslason et al
(2003). There is a conspicuous relationship between the concentration of most dissolved
constituent and the discharge of the rivers, and the relationship changes from one catchment
to another. This reflects probably the age of rock, glacier cover, vegetation etc. This
relationship has been described by power functions (Gíslason et al. 2003). In the present
study, the concentration versus discharge relationship is cast in terms of mnoff rather than
discharge. Runoff is simply the discharge at the sampling spots divided by the catchment area
above the samphng spot. Within each catchment, mnoff is the dominant variable for the
variation in chemical concentration. This provides the opportunity to use mnoff maps, to
spatially distribute river water concentration data, and makes it possible to predict surface
water concentration anywhere within the catchment. The first dissolved constituents
distributed spatially, are the one that stem only from weathering of rock; alkalinity and silica.
Other dissolved major constituents, such as Na, Ca, Mg, S and K originate both from
weathering of rock and precipitation. Before they are spatially distributed, they are corrected
for what was brought in with precipitation, using their Cl-ratio and assuming that all dissolved
C1 in the river water is brought in by precipitation.
The spatially distributed values provide opportunity to study relationships between the
geochemistry of the surface water and the geographic distributed phenomena such as age,
slope, vegetation cover etc.
This study is the first attempt to use GIS to distribute spatially and to visualise dissolved
constituents within the river catchments in Iceland. Later, this approach can be used to create
atlas of geochemistry of surface waters in Iceland. Furthermore, user-friendly Intemet based
GIS has been developed for these catchments. This GIS approach makes it possible to create
limitless number of maps and spatial queries.
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