Fjölrit RALA - 15.06.2004, Side 128

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. 104
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