The clear separation of the parameters into the groups of Table 1
can be used as decision support in terms of ranking of remediation
measures on the catchment scale. This analysis indicates that the
focus of remediation measures should focus on the catchment area
of the Saale, if Hg pollution should be reduced. Conversely, the
catchment area of the Mulde would be in the focus in the case of
Cd pollution remediation in the River Elbe.
The influence on the variation of dissolved, colloidal and particulate
concentrations (Figs. 4 and 5) within the total sample was in
agreement with results of Baborowski et al. (2007) regarding the
transport of dissolved (group 1, Table 1) and particulate (group 2,
Table 1) substances in the River Elbe. This is mainly due to their
biogeochemical properties. In the former study, Ni, As and U were
mainly transported in dissolved form (55–80%), whereas the dissolved
proportion of metals with geogenic origin (Fe, Pb, Al) was
negligible. As already discussed with respect to the drivers for
the formation of groups (Table 1), U concentrations are diluted
during flood events, due to their stable pollution level in the catchment
area. The temporarily increased colloidal proportions of U
with increasing discharge can be explained by interaction of drainage
water entries from former mining areas with river water
(Furrer et al., 2002).
The comparable variation of sub-fractions of group 3 and 4
(Table 1) (tributaries Mulde and Saale) seems to be affected by several
factors. Both tributaries were intensively used by mining and industry in the past. Their morphological conditions differ from
the River Elbe. In contrast to the tributaries, the Elbe is freeflowing
in its middle reach. Flow and matter transport here are
mainly influenced by groyne fields. In the tributaries, a large reservoir
in the upper stretch of the River Mulde and several lock- and
weir systems in the upper stretch of the River Saale act as sediment
traps. This is probably the reason for the similar distribution pattern
of the sub-fractions of both rivers. The similarity of the results
regarding the dissolved proportion of elements within the total
fraction in 2005 and 2006 suggests comparable conditions in terms
of sources, transport and fate of metals in the catchment area of the
Middle Elbe. This is an important point regarding the suitability of
the method as tool to assess pollution trends in a catchment area.