Environmental Engineering Reference
In-Depth Information
area. This requires stakeholder participation. With-
out that support, fen rehabilitation is almost unachiev-
able because of confl icting land use claims from
farmers, foresters, city dwellers and so on (Klimkowska
et al
. 2010b ).
One of the largest rehabilitation projects in the world
is the well-known project in the Florida Everglades
(Kadlec 2009 ), where large - scale hydrological meas-
ures are being executed to reinstate insofar as possible,
the original fl ow patterns of this large fen system.
Much effort is given to reduce phosphorus loading to
the protected fen areas of the Everglades National
Park. A substantial amount of phosphorus stems from
agriculture, and therefore this sector should logically
contribute substantially to the cost of rehabilitation. If
farmers do not meet the goals of phosphate reductions,
as formulated in
Best Management Practices
, they are
required to pay extra taxes to the state of Florida. The
total cost of the actions intended to maintain and
restore the ecological character of the Everglades is
currently estimated at more than US$10 billion, and
the fi gure is rising (Kadlec 2009).
tion for drinking water and industrial use - should
ideally be addressed simultaneously and in an inte-
grated fashion.
Not all terrestrialization fens need management.
In oligotrophic lakes, small bog hummocks or low-
productive fen vegetation can develop soon after the
formation of a fl oating mat of reed or large sedges. In
eutrophic lakes, terrestrialization can lead to monocul-
tures of reed (
Phragmites australis
) with little value for
nature conservation. In such cases, cutting can reduce
the vitality of the reed and increase biodiversity.
Summer mowing reduces the vitality of
Phragmites
more than winter mowing (van Diggelen
et al
. 1996 ).
Excavating new peat ponds is a measure to restart the
terrestrialization process to provide new habitats for
rare and endangered fen species (Beltman
et al
. 2001 ).
Excavation should be practised only when the new peat
ponds can be supplied with very clean water, preferably
groundwater.
16.4.4
Rehabilitation of spring mires
Most degraded spring-mire systems can no longer be
restored since the original peats and sediments have
disappeared and the water discharge sites have shifted
to lower sections of the spring system and cannot be
directed upwards. The replacement communities, con-
sisting of plant and animal species adapted to low tem-
peratures and constantly fl owing water, are also highly
endangered in western Europe (Wolejko
et al
. 1994 ).
Rehabilitation measures should aim at stabilizing
water outfl ow in springs and preventing pollution in
infi ltration areas. When the discharge of groundwater
has diminished or the spring water has been polluted
in surrounding infi ltration areas, the most obvious
measure is to protect the direct catchment areas and
abolish drainage and fertilization practices. In efforts to
rehabilitate a severely damaged spring mire complex
(6 ha) in the Sernitz region of north-eastern Germany
(Koska & Stegmann 2001), several measures were
taken concurrently to raise the water table. Measures
included (1) constructing a series of wooden dams in
the largest drainage ditches, (2) completely fi lling
ditches with peat, (3) refl ooding parts of the mire with
spring water and (4) perforating the impervious gyttja
layers at the base of the mire. The best results were
obtained with complete fi lling of drainage ditches.
Flooding parts of the mire with spring water that had
16.4.3
Restoration of terrestrialization fens
In western Europe, terrestrialization fens in lake areas
are often the last refuge for nutrient-poor fen plants
that were once widespread in natural groundwater-fed
fens. With increasing eutrophication of surface waters,
the lakes also became polluted and, as a consequence,
nutrient-poor fen species in the terrestrialization fens
have become rare (van Wirdum
et al
. 1992 ). Restoring
such nutrient-poor fens has to start with improving
the water quality of the lakes in which the fens occur.
Technical solutions, such as sewage treatment plants,
can decrease nutrient concentrations. In densely pop-
ulated areas, however, sewage treatment may not be
suffcient, since nutrients from diffuse sources may
enter a protected nature area via canals or via ground-
water fl ows from surrounding agricultural areas. A
proper way to deal with the complex relationships in
the water systems and human exploitation of water
(e.g. for drinking water, navigation and tourism) is
integral water management. In other words, all the
interrelated hydrological problems in a watershed -
including pollution of underwater sediments, local
and regional input of pollutants, shoreline manage-
ment, water level management, groundwater extrac-
