CLM20-2 full issue-1 - Flipbook - Page 24
A guide to conservation land management and greenhouse gas emissions
Rewetting drained peatlands not only prevents the release of large quantities of CO2, but also benefits wildife,
and can reduce flood risk and the discoloration of drinking water. Wayne HUTCHINSON/Alamy Stock Photo
It may come as a surprise that undamaged,
near-natural bogs (i.e. undegraded blanket bog
and lowland raised mires) exert only a small
cooling effect per unit area. Undamaged bogs
sequester carbon very slowly but, importantly,
have been doing so over a long period of time
and have thereby accumulated large quantities
of carbon in their peat. The big climate issue
regarding these bogs is that, once artificially
drained, they release large quantities of CO2 back
into the atmosphere through oxidation of the
dried-out peat.
Saline wetlands
The components of the GHG flux of high-salinity
lagoons and intertidal habitat differ again from
those of freshwater wetlands. First, wetlands
with a salinity of more than about half that
of sea water release little or no methane (e.g.
Poffenbarger et al. 2011). Moreover, intertidal
habitat accumulates carbon through two
mechanisms. The first is by way of saltmarsh
plants, seagrass, algae and cyanobacteria taking
up CO2 from the atmosphere via photosynthesis,
with a proportion of the carbon from this
accumulating in vegetation and estuarine
sediment. The second is through the accumulation
in estuarine sediment of particulate carbon that
has been transported to the estuary along rivers.
Saltmarsh produces a greater cooling effect per
unit area than mudflat, because its vegetation
sequesters significant quantities of carbon. There
is little information on the GHG flux of highsalinity lagoons, but they will probably have less
of a cooling effect than saltmarsh or mudflat,
particularly because they do not accumulate
organic matter in sediment at such a high rate.
The only type of conservation management
that commonly takes place in intertidal areas is
grazing of saltmarsh by domestic livestock. This
grazing will again reduce the rate that carbon
accumulates in the vegetation and subsequently
in estuarine sediment, while the livestock will also
release methane. Grazing, by reducing vegetation
height, also reduces the rate that sediment is
trapped among the vegetation (e.g. Andresen
et al. 1990), although this sediment and the
carbon within it should nevertheless accumulate
elsewhere in the coastal system.
Ways to benefit both the climate
and wildlife
The greatest possible benefits to both wildlife and
the climate per unit area can be provided through
rewetting drained blanket bogs and lowland
raised mires, and especially by (re)creating
various types of semi-natural habitat on formerly
intensively managed farmland. Far smaller
benefits for the climate might also be achieved
by modifying ongoing conservation management
22 Conservation Land Management Summer 2022 | Vol. 20 No. 2
