Environmental Engineering Reference
In-Depth Information
topsoil in dry years (Price 1998). Increasing ground-
water levels in surrounding agricultural areas will
improve the restoration success in the bog remnants
considerably, but this is an option only when these
drained areas can be purchased, or otherwise com-
pensation can be arranged for the relevant farmers or
landowners.
Experimental research has shown that good restora-
tion results can be achieved when the peat either swells
up to the newly created water table or becomes
buoyant, in both cases creating a favourable substrate
for
Sphagnum
mosses. Floating of
Sphagnum
vegetation
is usually caused by high methane production from
underlying substrates (Lamers
et al
. 2002 ; Tomassen
et al
. 2003). Buoyancy of
Sphagnum
mats is stimulated
when poorly humifi ed
Sphagnum
peat is still present
(Tomassen
et al
. 2004), or when slightly or somewhat
calcareous groundwater enters the peat base, thus
stimulating decomposition (Malmer & Wall é n 1993 ;
Smolders
et al
. 2003 ). Some fi eld experiments are pres-
ently underway in which small amounts of lime are
added to the peat before rewetting and less degraded
peat from other areas is added in order to stimulate
decompostion processes and methane production (van
Duinen
et al
. 2011 ).
2003). Carbon dioxide in bogs is derived mainly from
decomposition processes. As a result, carbon dioxide
concentrations are highest just above the inundated
peat soils. Therefore, shallower waters will present not
only more favourable light conditions but also higher
carbon dioxide concentrations for submerged
Sphag-
num
. Once submerged or fl oating
Sphagnum
species
have established, a structure may be formed on which
true bog species can establish and form a new func-
tional acrotelm. Key species for acrotelm development
are
Sphagnum magellanicum
,
S. papillosum
,
S. imbrica-
tum
,
S. fuscum
and
S. rubellum
. These typical ' hummock '
and 'lawn' species are usually very slow colonizers
compared to the wetter 'hollow' species such as
S. cus-
pidatum
and
S. fallax
. Introduction of key species in
carpets dominated by hollow species or on bare sub-
strates appears to be very successful, indicating that
the main constraint is colonization (Smolders
et al
.
2003 ).
Several recent studies suggest that in the fi rst stages
of peat regeneration,
Sphagnum
plants may also need
support from tussock-forming species, such as
Eriopho-
rum vaginatum
, or from perennial species such as rela-
tively tall
Carex
species that can form many erect
shoots, without shading the
Sphagnum
plant too much
(Ramseier
et al
. 2009). In Canada, mulching with
straw has been used for protection against evapotran-
spiration losses and to provide a support structure for
young
Sphagnum
plants (Rochefort
et al
. 1995 ).
High a tmospheric N d eposition
Limpens
et al
. (2003) showed that high atmospheric N
deposition (30 - 35 kg of N ha
− 1
yr
− 1
) reduces the growth
of rainwater - fed
Sphagnum
species and favours the
growth of
Molinia caerulea
and
Betula pubescens
. Above
18 kg of N ha
− 1
yr
− 1
Sphagnum
species cannot take up
all the NH
4
+
from the soil solution and the nitrogen
becomes available for vascular plants, which start to
shade the
Sphagnum
plants, thereby reducing their
growth considerably.
16.4.2 Rehabilitation
of groundwater-fed fens
Repairing the hydrological regime of a wetland is more
complex than just raising water levels. In groundwater-
fed fens, in particular, increasing water levels may lead
to
acidifi cation
when the discharge of base-rich
groundwater cannot be reinstated. Therefore, success-
ful management of groundwater-fed fens should be
approached at a broader scale that includes the
landscape-scale management of groundwater systems.
Not only quantitative aspects are important but also
qualitative aspects. Leaching of nitrate to the ground-
water, for instance, can cause large-scale mobilization
of sulphate from geological pyrite or gypsum deposits
and the immobilization of ferrous iron (Smolders
et al
.
2010 ). A
landscape - scale approach
often implies chang-
ing land use in the entire surrounding catchment
Low d issolved o rganic c arbon c oncentrations
Initial stages of bog formation usually consist of a
dense vegetation of submerged or fl oating
Sphagum
species, like
Sphagnum cuspidatum
or
S. fallax.
Carbon
dioxide availability is crucial to the growth of sub-
merged
Sphagnum
species (Smolders
et al
. 2001 ). In
general, such species are only able to reach buoyancy
when carbon dioxide concentrations in the pore water
(i.e. the water fi lling the spaces between grains of sedi-
ment) are higher than 500 μ mol l
− 1
(Smolders
et al
.
