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sloping downward from the Agelerbroek northwards, so that floodwater from
that area would flow into the Ottershagen area. By allowing flooding also to take
place in the Agelerbroek, diaspores could be carried northward in the flood-
water. These restoration measures will create potential for development of
floodplain areas typical for medium-sized (stream order 3-4) streams with their
characteristic gradients in sediment deposition and create opportunities for water
resource managers to discharge water in these areas to prevent flooding in
economically vital areas. Hence this case study demonstrates how the OLU
approach can increase the awareness of resource managers to the importance of
spatial processes and connectivity in landscapes and, if properly applied, can lead
to more long-term successful restoration projects.
Conclusions
Studies comparing different methods to establish reference conditions, such as
spatial typology, predictive models, palaeo-reconstruction and historical and
contemporary data are encouraging. More comprehensive studies are, however,
needed to quantify better the uncertainties associated with different approaches.
Somewhat disconcerting is the finding that spatial typologies (probably the most
common approach used by European member states in implementing the WFD)
are significantly poorer at partitioning biological variance than model-based
approaches. Furthermore, there is now a growing awareness that the reference
condition is not static or as previously presumed, oscillating around long-term
means, but showing monotonic climate-driven trends. Hence approaches that
explicitly include interannual variability in weather and/or long-term trends in
climate, such as modelling approaches that include predictor variables like
number of degree-days and hydrological variables should be given greater
consideration. Along these lines, studies focussed on trying to disentangle the
effects of short-term climatic events such as the influence of interannual NAO
oscillations from long-term climate-driven trends would be of interest.
Predicting the effects of global change on freshwater ecosystems is complicated,
and there is now an increased understanding that complexity increases many-fold
as ecosystems already affected by anthropogenic stress now experience and
respond to the effects of climate change. How ecosystems respond to the effects
of multiple stressors is currently under debate. Nevertheless, it is clear that
managers need to consider the importance of how multiple stressors may affect
ecosystem structure and function of aquatic ecosystems if management endeavours
are to be successful. Restoration measures such as the use of woody debris are
considered a cost-effective approach to increase habitat complexity and improve
hydromorphology in streams. However, more robust statistical designs, including
multiple restored, unrestored and reference sites and several years of study both
before and after intervention are needed to better understand the short- and
long-term effects of this and other types of restoration.
Importantly, connections between restored sites and their surroundings, both
in terms of dispersal of organisms and flows of water and solutes, deserve more
consideration in future restoration projects. Furthermore, the scale of restoration
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