| A review of current knowledge and available data covering the stable isotope composition of
groundwater in Norway is presented. Furthermore, the future challenge of obtaining
systematic background datasets and of integrating isotopes into the mainstream of
hydrogeological observation programmes is discussed. I will summarize our experiences
gained from different preliminary studies and will try to identify relationships to existing
datasets, historical registrations, and networks on precipitation data.
The study of transient effects in hydrological cycles is highly topical as these
are supposed to provide means for investigating the effects of climate change and
increasing human activities. From a hydrogeological point of view, is critical to establish
suitable tools for the large scale observation of changes in groundwater recharge and
depletion, their likely controls, and the expected nature of responses to changing
climate, urbanization and other human activities. In this context, stable isotopes
(δ18O and δ2H of water) can provide an expedient instrument to investigate the
general hydrological setting, connections, and pathways of various scale aquifer
systems. However, we are up to now missing an expedient background dataset
on hydrogeological and hydrological stable isotopes observations for mainland
Norway.
Against this background, during years 2010 and 2011 the Geological Survey of Norway
(NGU) organized two nation-wide sampling campaigns on the stable isotope composition of
modern groundwater. These pilot studies aimed to obtain a first overview about the data
ranges and natural variations to be expected. We used stations from the existing Norwegian
Groundwater Monitoring Network (Landsomfattende Grunnvannsnett, LGN) to collect
samples of groundwater at 55 different locations throughout Norway. As a main characteristic
of these two datasets, all δ18O and δ2H values of the “LGN series” were well correlated and
plotted close to the global meteoric water line. This essentially documents the in principal
exclusively meteoric origin of these waters, and indicates that the LGN groundwaters
investigated shared the same type of origin: (i) evaporation from the ocean, and (ii) isotopic
enrichment by rainout (continental effect). Conversely this also indicates that other
processes (re-evaporation, admixture of water with a different genesis, etc.) did not have
significant influence in this dataset. In parallel, two more detailed local application
studies have been conducted in unconsolidated glaciofluvial aquifers in S-Norway
(eastern part of the Gardermoen / Øvre Romerike Aquifer in Akershus county,
and glaciofluvial deposits at the Granli waterworks of Kongsvinger in Hedmark
county). In these investigations, detailed vertical profiles obtained with multi level
sampling devices displayed systematic vertical evolution of groundwater isotopic
composition, and it is demonstrated how an extended local dataset can enable to discuss the
discrimination between different groundwater / surface water influences, and supports the
planning of groundwater exploitations and groundwater water resources management. |