Environmental Engineering Reference
In-Depth Information
16.1
INTRODUCTION
In this chapter, we discuss restoration of damaged
mires worldwide, but with a particular focus on Europe.
We will fi rst describe some pristine mire types that can
serve as a source of information and inspiration for
restoration projects. However, they are not necessarily
the appropriate
reference systems
for all
ecological
restoration
projects (e.g. those in densely populated
areas whose hydrological systems have often been irre-
versibly changed). Accordingly, we will also discuss
rehabilitation
prospects of mire remnants within
strongly human - infl uenced
landscapes
(see also
Chapter 5). The vegetation of such mire remnants may
resemble that of natural mires, but
hydrologically
such systems are very different. The vegetation compo-
sition of relic mires can sometimes be used as a refer-
ence in rehabilitation projects.
Mires
are peatlands where peat is currently being
formed (Joosten & Clarke 2002). A
peatland
is land with
peat, that is, with a superfi cial layer of partially decom-
posed organic material that is at least 20-30 cm thick.
Mires are ecosystems that produce peat and include
bogs
and
fens
. Bogs are mires raised above the sur-
rounding landscape and solely fed by precipitation,
especially rainwater, whereas fens are situated in
depressions and, in addition to precipitation, they are
also fed by ground- or surface water. Bogs are always
acidic (pH < 4.2; Siegel
et al
. 2006), whereas fens are
often base-rich or slightly acidic or neutral (pH > 5.5;
Succow 1988; Wheeler
et al
. 2002 ).
Along with the term 'mires', we will also use the
generic term
wetland
to describe any area of land that
is sometimes or always covered by shallow water, and
supports vegetation adapted to saturated soil condi-
tions. A wetland may or may not be a peatland; it can
also occur on mineral soil.
It is estimated that on a world scale the natural
extent of mires was more than 4 000 000 km
2
(Joosten
& Clarke 2002 ), of which 2 500 000 km
2
is situated in
North America and Siberia (Plate 16.1). Human
exploitation has altered 500 000 km
2
in such a way
that peat accumulation has been stopped. Mire losses
are highest in Europe (>50%) due to intense human
population pressure and the climatic suitability for
both agriculture and forestry. Losses are particularly
great in western and southern Europe, where less than
10% of the natural mire area has remained (Joosten &
Clarke 2002). About 80% of the mire losses here are
related to agriculture and forestry. Finland and Russia
in particular have drained large areas of peatland for
forestry (50 000 km
2
and 38 000 km
2
, respectively);
this accounts for more than half of the global destruc-
tion of mires for forestry (Joosten 2009a). In most
eastern European countries, between 10% and 50% of
the former mires remain. In South America and Africa,
peat losses are low in absolute values, but that is
because these continents do not have large stocks of
peat. In Africa, for instance, some 140 000 km
2
was
originally present, but 20% of that is now already lost
(Joosten 2009b). In South America, losses amount to
10%, but peat extractions are expanding, particularly
in Tierra del Fuego (Argentina and Chile), where
unique bogs have developed with a cover of only one
Sphagnum
species (
S. magellanicum
).
16.2
UNDISTURBED MIRE SYSTEMS
The classifi cation of mires is based mainly on species
composition, often supported by stratigraphical and
palaeo - ecological data (Brinson 1993 ; Gr ΓΌ nig 1994 ).
Succow and Joosten (2001) integrated hydrological
features with the genesis of mires and linked that to
nutrient status and vegetation composition. Here we
focus on the following fi ve types: rainwater-fed bogs,
groundwater-fed percolation fens, terrestrialization
fens, spring fens and fl oodplain fens.
16.2.1
Rainwater-fed bogs
Bogs are fed by rainwater although some peripheral
parts - the so-called lagg zone - can be infl uenced by
water from surrounding areas that has been in contact
with mineral soil (Plate 16.2a). Most bog systems origi-
nate from lakes and groundwater-fed mire systems,
over which a developing rainwater lens allows
Sphag-
num
moss species to grow. In this way,
Sphagnum
' escapes ' the infl uence of groundwater and may form
a domed-shape peat body that grows above the imme-
diately surrounding area. Groundwater fl ow to the bog
system remains essential for the functioning of the bog
system by keeping water levels stable. The living top
layer of a bog consists of a loosely structured layer,
called
acrotelm
(Ingram 1983). It consists of living
mosses (predominantly
Sphagnum
species), intermin-
