Subterranean ecosystems - Universidade de Évora

IAH 2007 XXXV Congress - Groundwater and Ecosystems Lisbon, Portugal
Landscape modelling for the assessment of a nuclear waste repository in
Sweden: Integration of hydrological and ecological modelling
Ulrik KAUTSKY, Sten BERGLUND, Jan-Olof SELROOS, Tobias LINDBORG
Swedish Nuclear Fuel and Waste Management Co. (SKB), Box 5864, SE-102 40 Stockholm, Sweden,
E-mail: ulrik.kautsky@skb.se, sten.berglund@skb.se, jan-olof.selroos@skb.se, tobias.lindborg@skb.se
ABSTRACT
The Swedish Nuclear Fuel and Waste Management Co. (SKB) currently investigates two sites in Sweden as
potential locations for an underground disposal of spent nuclear fuel. The site investigations cover geological,
chemical, hydrological and ecological factors. A strong emphasis has been put on the characterisation of
properties and processes affecting the water-born transport and the retention of radionuclides along flow paths
from repository depth (c. 500m below ground surface) to the surface, as well as the dispersal and accumulation
in the surface system. In the modelling performed to support the site descriptions and the safety assessments, a
wide range of hydrological tools have been utilised. These include tools primarily developed for modelling
groundwater flow in fractured rock, as well as hydrological modelling tools that handle surface and subsurface
flows, water uptake in vegetation and the interactions with the atmosphere. The couplings between the
hydrogeology, the near surface hydrology and the surface ecosystems have been especially important for this
integrated modelling.
We utilised a landscape approach where the different ecosystems were interconnected through
the surface hydrology (i.e., the surface water and near-surface groundwater flows) and the landscape was
subdivided by the catchments. Radionuclide transport was modelled in an evolving landscape starting from a
marine ecosystem over a coastal to a terrestrial landscape over a period of 20,000 years. The modelled
development of the landscape was affected by land uplift after the latest glaciations, sea-level changes, infilling
of lakes, and succession of vegetation. The terrestrial landscape includes lakes and rivers that successively
develop to mires and potential agricultural land. The discharge of groundwater from repository depth seems to
affect low-lying parts of the landscape primarily, which usually contain wetland ecosystems that can be used as
agricultural areas in the future.
In this paper, we focus on the description of the interconnection of the hydrological and
landscape modelling, and present results from characterisation and modelling performed to support the
assessment of potential radionuclide discharge from the rock to the surface ecosystems. Specifically, relatively
large-scale groundwater flow models extending well below repository depth are used to identify discharge areas,
and hence the potentially affected objects at the surface, whereas hydrological models with a more detailed
representation of the surface and near-surface processes provide direct inputs (e.g., residence times and water
balance components) to the modelling of transport in the surface system. At the surface the additional flows of
organic carbon are included in the modelling of fluxes that gives exposure to humans and the environment.
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