RD&D-Programme 2004 - SKB

The above work will be pursued in cooperation with the programmes for geochemistry and
hydrology and is dependent on the results of the surface hydrology measurements on the sites.
20.6 Terrestrial ecosystems
The terrestrial ecosystems – for example forest, agricultural land and mire – are characterized
by the fact that they normally have a groundwater table that always or usually lies just below the
ground surface. The dominant transport processes from the groundwater up to these systems are
root uptake, capillary force and the groundwater’s level fluctuations. Root uptake and accumulation
in biomass are, however, the most important processes for radionuclide transport to people
and other consumers. Mires and other wetlands are the special cases where the groundwater
table fluctuates around the level of the ground surface during most of the year, but otherwise
have properties similar to those of land types where the groundwater table is always below
ground level. General soil processes will therefore be dealt with in this section, and then forest
and wetlands as special cases.
Forest is the dominant ecosystem for the hypothetical sitings /20-47/ and can be a possible
recipient, see Figure 20-2. However, the results of studies of discharge of deep groundwater
from repository depth show that few streamlines end up in the forest, see section 20.5. Most
exit under streams and on the shorelines of lakes and seas, as well as in wetlands. The forest
has been the focus of several projects that have studied the fallout from Chernobyl, among
other things, see further /20-48/. Most studies have mainly been concerned with the short-term
consequences of radionuclide transport. Few calculations have been done of the migration
and accumulation of radionuclides from a deep repository in forest. An attempt was made in
the Forest Working Group of Biomass /20-49/. The most important long-term processes are
accumulation of nuclides in the soil profile and biological leaching processes that move nuclides
to biota. The upward transport of radionuclides from the groundwater table into the roots and
vegetation is also essential. The forest question is closely linked to near-surface hydrology and
Tree layer
Ash
Asp
Birch
Mixed forest
No tree layer (other)
No tree layer (forest)
Old pine
Old spruce
Unspec. young conifers
Young birch
Yoyng pine
Young spruce
Water
0 1,000 Metre
Figure 20-2. The forest in the Forsmark area after satellite image interpretation /20-47/.
280 RD&D-Programme 2004