Environmental Engineering Reference
In-Depth Information
because surface water or rainwater may replace the
groundwater. In the long run, however, the increased
influence of nutrient-rich surface water will result in
increased plant productivity (Koerselman
et al.
1990)
whereas a replacement with acidic rainwater will lead
to acidification of the top soil (van Diggelen
et al.
1994). Both processes result in completely altered
vegetation composition but it may take up to several
decades before the effects are clearly visible. The
relative importance of these processes depends to a
high degree on the local situation.
conservation; see Chapter 1 in this volume. Existing
natural values, both of pristine mires (8100 ha) and
species-rich semi-natural grasslands (3600 ha), will
be strictly protected and managed. Reclaimed polder
areas will be partly reflooded (37,000 ha) to develop
into eutrophic swamps and partly managed in an
environmentally friendly manner (139,000 ha). Also part
of the infiltration area (111,000 ha) will be managed
in an environmentally friendly manner. Inevitably
the implementation of such a large plan takes con-
siderable time. Whereas the conservational part of the
plan will be implemented for the greater part before
2005 this is certainly not the case with the restora-
tion part. In the largest river valley, that of the
River Peene, 2800 ha of the planned 19,000 ha were
restored by 2000, 8 years after the start. The main
reasons for this slow progress are economic. The estim-
ated costs of the project amount to a130.5 million for
an implementation period of 20 years (Landesregierung
Mecklenburg-Vorpommern 2000; see www.um.mv-
regierung.de).
During the second half of the 1990s plans for the
restoration of the Everglades, in Florida, USA, were
beginning to emerge. Not only has the surface of the
Everglades decreased dramatically in historic times but
there are also large hydrological problems in the
remaining part due to a reduction of the incoming
water flow by 70%. About 7.5 million m
3
are diverted
to the Atlantic Ocean instead of entering the reserve.
Consequently, water shortage occurs, not only in the
reserve but in the public water supply of Miami as
well. A so-called comprehensive plan was presented
to the US Congress in July 1999 and consisted of
a combination of over 200 projects. Interestingly,
these are less focused on increasing the size of the
reserve than on restoration of the hydrology. Topics
to be dealt with are quantity, timing, quality and dis-
tribution. The end point has not been decided upon
yet but 50% of the restoration goals should be
achieved by 2010. Total costs are estimated to
amount to $7.8 billion, $1.4 billion of which have been
made available by the signing of the Everglades
Restoration Act in December 2000. State and federal
sponsors must return to Congress every 2 years to get
new projects authorized as the restoration moves for-
ward (see www.evergladesplan.org).
A somewhat different approach is followed in the
development of the
Ecologische HoofdStructuur
(EHS;
3.6 Landscape restoration
Human impact on the landscape has been enormous,
not only on the spatial distribution of organisms
but especially also on the conditions that enable their
occurrence. If one wants to reverse this process and
especially if this should be done in a sustainable
way, one should pay attention to the spatial context
in particular (Hobbs & Morton 1999). This implies that
restoration of complete landscapes gives the best
chances for long-term survival of self-sustaining
ecosystems. In practice this occurs very little, mainly
because of practical and financial constraints. The first
attempts are, however, being carried out.
The spatial relation between wetlands and regional
hydrology made it clear relatively early on that land-
scape restoration is unavoidable for rehabilitating
degraded systems. Most cases concern riverine systems,
especially in dry areas where the effects of human
actions are most clearly visible, for example in the
western USA (Kentula 1997). Typically such processes
are now in the planning phase. Elaborate techniques
to analyse causes of degradation and to evaluate
alternative restoration scenarios are now being
developed (van Diggelen
et al.
1995, Kershner 1997)
and sites are being prioritized.
An example of restoration of one of the largest
wetlands is the plan for a
c
.290,000 ha lowland river
landscape in the state of Mecklenburg-Vorpommern
(north-east Germany). The goal of this plan is to
re-establish functioning river valleys, including the most
relevant parts of the infiltration areas. The concept con-
sists of a combination of plans for true restoration
(re-establishment of a former situation), rehabilitation
(re-introduction of certain ecosystem functions) and
