CLM20-2 full issue-1 - Flipbook - Page 27
A guide to conservation land management and greenhouse gas emissions
other agricultural operations that release GHGs,
but climate benefits will be offset to some extent
by the release of methane from the wetland,
especially during the early stages of rewetting, and
by any GHGs emitted through its management.
The specific climate benefits of rewetting these
organic soils will vary according to the depth
of the water table of the restored habitat, and
the type of wetland habitat that is allowed/
encouraged to develop. On organic soils, the
GWP100 is typically close to zero if the mean
annual water table is about 10cm below the soil
surface. If the water level is lower than this, the
habitat will cause warming due to drying out and
oxidation of peat, and if the water level is higher
than this, then the habitat will cause warming due
to the release of methane from the waterlogged
soil (e.g. Evans et al. 2021).
Creating wet woodland should provide the
greatest climate benefits per unit area through
keeping the soil wet enough to prevent oxidation
of the underlying peat, while also accumulating
carbon through growth of the trees, albeit with
some release of methane. There are, however,
limited opportunities to keep ex-arable and
agriculturally improved grassland on organic soils
sufficiently wet to do this. The next best option
climate-wise is to create swamp/fen, which has
an overall GWP100 close to zero – far lower than
the high warming effect of agriculturally drained
organic soil.
The least climate-beneficial freshwater wetland
creation options on organic soils are (re)creating
wet grassland and nutrient-rich waterbodies. On
organic soils, both habitats exert a far lower level
of warming than either arable or agriculturally
improved grassland, but unfortunately both
nevertheless still cause warming. This therefore
presents a conflict with conservation priorities,
given the high conservation importance of wet
grassland on organic soils, especially for breeding
birds such as snipe and black-tailed godwits (e.g.
Ausden & Bolton 2012), and for its other fauna
and flora. Meanwhile, areas of shallow, nutrientrich open water are obviously important for a
wide range of wetland wildlife.
Freshwater wetlands on mineral soil
There is less information available on changes
in the GHG flux resulting from creation of
The climate benefits of a 184ha intertidal habitatcreation scheme at Medmerry in West Sussex were
estimated at £3.3 million over 100 years, while
flood-risk management benefits were estimated at
£78 million. Nick Upton/Alamy Stock Photo
freshwater wetlands on mineral soils. The
climate benefits of this will, however, be far
lower than from creating wetlands on organic
soil, because it does not involve reducing the
large quantities of CO2 released from driedout organic soil. Despite this, creating swamp/
fen and lowland wet grassland on formerly
intensively managed arable on mineral soil will
still benefit the climate, due to the cessation or
reduction of emissions from farming activities,
and greater accumulation of organic matter
in the substrate than that which takes place in
arable soils (although this will again to some
extent be offset by the release of methane,
particularly in the case of creating swamp/
fen). There will probably be negligible climate
benefit from creating wet grassland on drained
improved/semi-improved grassland on mineral
soil, but there is little information on this.
Conservation Land Management Summer 2022 | Vol. 20 No. 2 25
