Environmental Engineering Reference
In-Depth Information
shows typical remnants of natural mire types after
large changes in land use during the past few centu-
ries. The time period in which such land use changes
began may differ greatly, but the outcome is usually
similar.
that large drainage works in a landscape have frag-
mented the former regional fl ow systems into smaller
local cells. This fragmentation of hydrological systems
has resulted in signifi cant hydrochemical differences,
which can be observed even within a single small fen
(Wassen
et al
. 1996). In the Biebrza catchment in
eastern Poland, for example, the hydrochemical and
associated trophic gradients in the vegetation are still
very smooth and gradual over large distances (Wassen
et al
. 1996). This relative spatial uniformity is related
to slow but continous fl ow of groundwater in the mire
that keeps it saturated with mineral-rich groundwater.
Fen systems in the Netherlands resemble Polish fens
with respect to vegetation, but their hydrological
systems are much more variable. In areas with a large
precipitation surplus, drainage promotes
acidifi ca-
tion
in peatlands because calcium- and iron-rich
groundwater is replaced by rainwater (Schot
et al
.
2004). Such processes can even trigger bog formation,
when suffi cient precipitation water is present.
In order to compensate for water losses due to drain-
age, surface water is often supplied to agricultural
areas during summer. This artifi cial water supply tends
to reverse the natural fl uctuation pattern such that low
water levels occur in winter and spring and high water
levels occur in summer. Most of this water originates
from large rivers with much higher nutrient and sul-
phate content than groundwater. A higher nutrient
availability in the water leads to
eutrophication
. But
in organic soils, high sulphate levels may also trigger
eutrophication. This process is called
internal eutrophi-
cation
. Under anaerobic conditions, the availability of
alternative electron acceptors, such as sulphate, may
strongly stimulate the breakdown of organic matter
and increase the availability of nutrients (Smolders
et al
. 2006). During sulphate reduction, sulphide is
produced, which in relatively high concentrations is
toxic for most vascular plants (Lamers
et al
. 2002 ). In
most groundwater-fed fen soils, sulphide will not reach
toxic concentrations since it is chemically bound by
iron. When sulphide production, however, exceeds
the availability of iron, free sulphide concentrations
increase (Caraco
et al
. 1989). When iron availability in
the soil becomes limited, for instance when groundwa-
ter supply to the fen has stopped, phosphate concentra-
tions in the pore water can increase to high levels. Such
changes in nutrient cycling can be very harmful for
phosphorus - limited fens (Koerselman & Verhoeven
1995; Richardson 2008). In general, anoxic iron-rich
groundwater tends to slow down nutrient cycling,
16.3.1
Peat extraction
Peat extraction is responsible for circa 10% of global
mire losses, with new peat extraction sites being estab-
lished at a rate of 10 km
2
annually (Joosten & Clarke
2002). Countries with large peat extraction activities
for energy are Finland, Russia and Ireland. In Ireland,
in particular, this use of peat for energy is criticized
by national and international organizations because
burning peat is very ineffi cient as compared to burning
coal or gas. In other countries, like Germany, the Baltic
states and Canada, peat is primarily extracted as a raw
material for horticultural growing media. Even when
peatlands are no longer used for peat extraction, the
peat losses continue. Deeply drained peatlands suffer
from peat loss through shrinkage and mineralization
(Oleszczuk
et al
. 2008). This process may cause losses
as great as 2 - 3 cm yr
− 1
(Joosten 2009a) and trigger the
release of enormous amounts of greenhouse gases into
the atmosphere (ca. 40 kg of N
2
O ha
− 1
yr
− 1
and 10 t
ha
− 1
yr
− 1
of CO
2
; Armentano & Menges 1986 ). Alto-
gether, these processes have signifi cant impacts on
global greenhouse gas cycles. On a global scale, peat
losses due to agriculture, forestry and wildfi res amount
to circa 500 million tons of carbon per year (Joosten
2009b, see also Box 16.1 on Indonesian peatlands).
In contrast, global peat accumulation is estimated to
at least fi ve times less than that. This makes it clear
that global peatlands have switched from being car-
bon sinks to carbon emission sources (Couwenberg
et al
. 2010 ).
16.3.2 Indirect changes in
hydrological regimes
Most fens and bogs in north-western Europe have been
converted into intensively used agricultural land or
commercial forest plantations. These land use changes
have altered groundwater fl ow patterns and ground-
water composition, which of course has negative con-
sequences for remaining fens and bogs. Ecohydrological
research in Poland and the Netherlands has shown
