8.7.2 Management of Organic Soils
for Conservation, Biodiversity Protection,
Carbon Sequestration, and Catchment
Hydrological Protection
Maintaining Organic Soils in their natural state has a number
of important benefits, including biodiversity protection,
carbon sequestration, absorbing flood waters, and maintaining stream flows during drier periods. In order to maintain Organic Soils, to prevent loss of carbon dioxide to the
atmosphere, and to keep the water holding capacity of
wetlands intact, the peat material needs to be protected from
fire, and also from drainage.
The biodiversity value of wetland ecosystems in New
Zealand includes 27 species of protected birds, rare mud
fish, long-finned eels, insects, and a number of threatened
plants. However, simply fencing such areas off is not sufficient to maintain all their values. Invasive plants are a threat
in many wetland areas containing Organic Soils, willows
and some invasive grasses (such as ‘reed sweet grass’,
Glyceria maxima) have overtaken large areas of wetlands in
both the North and South islands. While efforts to control
willows, using herbicides, have proven reasonably successful (though somewhat unsightly for some years as the dead
trees take a long time to break down), no practical way to
deal with some weeds has been identified. If weeds are
invading it is best to remove a small infestation early, rather
than wait until it becomes a major problem.
Activities on adjacent land that cause lowering of water
tables are a problem in maintaining areas of Organic Soils.
There are many examples around New Zealand where
drainage of adjacent farmland may threaten the viability of a
wetland. For example, in the Waikato region drainage on
farms near the peat lakes (Sect. 8.3.2) has led to lowering of
water tables, biodegradation, and consolidation of the peat,
and thus lowering the lake level as well. Several lakes near
Ohaupo, and two lakes north of Hamilton, have been drained
and completely lost since the 1930s as a result of drainage of
neighbouring land. Thus, drainage of the peatlands surrounding peat lakes needs to be carefully managed to prevent drainage and further loss of the unique Waikato peat
lakes. It is important to develop understanding and
co-operation between neighbours for wetlands to be
protected.
Fire is an ever-present threat to Organic Soils, destroying
vegetation, combusting the organic soil material, and
releasing CO 2 into the atmosphere. Once started, fires in peat
may be very difficult to extinguish. Peat fires have been
known to smoulder for years, with potential to break out as a
spreading fire if conditions become favourable (hot, dry
windy conditions when water tables are seasonally low).
While fires occasionally occur through natural causes, such
as lightning strikes (evident as charcoal fragments in the peat
records back through time), fires in peatland have become
more common due to both deliberate and accidental human
activities.
Peat fires were a regular occurrence in the farmed peatlands of the Waikato in the early-mid-twentieth century
(https://teara.govt.nz/mi/video/27060/peat-fire). In days past,
burning to clear vegetation and sparks from steam engines
were common causes of fires, along with careless disposal of
cigarettes. In 2011, a fire in the Rukuhia Peat near Hamilton
was started by sparks from welding repairs on a railway line.
The natural vegetation of peatlands is somewhat adapted to
fire. Research by Bruce and Bev Clarkson, among others,
has shown that over decades the vegetation will slowly
recover to pre-fire conditions. However, repeated fire will
undoubtedly gradually degrade the peat resource and fire has
a detrimental impact on wildlife, which for threatened plants
or animals could be devastating. On the other hand, some
early and mid-successional species, including some orchids,
benefit from an occasional fire to provide them with habitat.
Overall, people need to be particularly vigilant to ensure that
no fires are started in or near areas of Organic Soils.
Increased inflow of sediments and nutrients from surrounding farmland can adversely impact the conservation
values of wetlands by changing the soil conditions to favour
invasive plants. While over time many wetlands gradually
naturally infill and change, such processes may be greatly
enhanced by inputs of runoff from surrounding farmland. In
the area of the Whangamarino wetland in the Waikato there
have been long-running differences over management of the
wetland between farmers who want water tables lowered,
conservationists who want to maintain natural conditions,
and regional council flood management programmes. The
flood management works divert (potentially nutrient and
sediment rich) flood water into the wetland area to protect
property downstream by lowering the flood peaks in the
Waikato River. The issues are complex and proving difficult
to resolve.
Carbon dioxide is lost to the atmosphere when plants or
organic materials are biodegraded or burned; conversely,
carbon is sequestered (or locked up) away from the atmosphere when plant material is preserved in a peatland.
However, within wetlands some biodegradation continues in
anaerobic conditions and results in the release of methane
(CH 4 ), which is also a greenhouse gas. Work by Dave
Campbell and others has shown that the undisturbed
Kopouatai restiad peat bog has relatively high overall rates
of carbon sequestration (from about 135 to 250 g C
128
8 Organic Soils
for Conservation, Biodiversity Protection,
Carbon Sequestration, and Catchment
Hydrological Protection
Maintaining Organic Soils in their natural state has a number
of important benefits, including biodiversity protection,
carbon sequestration, absorbing flood waters, and maintaining stream flows during drier periods. In order to maintain Organic Soils, to prevent loss of carbon dioxide to the
atmosphere, and to keep the water holding capacity of
wetlands intact, the peat material needs to be protected from
fire, and also from drainage.
The biodiversity value of wetland ecosystems in New
Zealand includes 27 species of protected birds, rare mud
fish, long-finned eels, insects, and a number of threatened
plants. However, simply fencing such areas off is not sufficient to maintain all their values. Invasive plants are a threat
in many wetland areas containing Organic Soils, willows
and some invasive grasses (such as ‘reed sweet grass’,
Glyceria maxima) have overtaken large areas of wetlands in
both the North and South islands. While efforts to control
willows, using herbicides, have proven reasonably successful (though somewhat unsightly for some years as the dead
trees take a long time to break down), no practical way to
deal with some weeds has been identified. If weeds are
invading it is best to remove a small infestation early, rather
than wait until it becomes a major problem.
Activities on adjacent land that cause lowering of water
tables are a problem in maintaining areas of Organic Soils.
There are many examples around New Zealand where
drainage of adjacent farmland may threaten the viability of a
wetland. For example, in the Waikato region drainage on
farms near the peat lakes (Sect. 8.3.2) has led to lowering of
water tables, biodegradation, and consolidation of the peat,
and thus lowering the lake level as well. Several lakes near
Ohaupo, and two lakes north of Hamilton, have been drained
and completely lost since the 1930s as a result of drainage of
neighbouring land. Thus, drainage of the peatlands surrounding peat lakes needs to be carefully managed to prevent drainage and further loss of the unique Waikato peat
lakes. It is important to develop understanding and
co-operation between neighbours for wetlands to be
protected.
Fire is an ever-present threat to Organic Soils, destroying
vegetation, combusting the organic soil material, and
releasing CO 2 into the atmosphere. Once started, fires in peat
may be very difficult to extinguish. Peat fires have been
known to smoulder for years, with potential to break out as a
spreading fire if conditions become favourable (hot, dry
windy conditions when water tables are seasonally low).
While fires occasionally occur through natural causes, such
as lightning strikes (evident as charcoal fragments in the peat
records back through time), fires in peatland have become
more common due to both deliberate and accidental human
activities.
Peat fires were a regular occurrence in the farmed peatlands of the Waikato in the early-mid-twentieth century
(https://teara.govt.nz/mi/video/27060/peat-fire). In days past,
burning to clear vegetation and sparks from steam engines
were common causes of fires, along with careless disposal of
cigarettes. In 2011, a fire in the Rukuhia Peat near Hamilton
was started by sparks from welding repairs on a railway line.
The natural vegetation of peatlands is somewhat adapted to
fire. Research by Bruce and Bev Clarkson, among others,
has shown that over decades the vegetation will slowly
recover to pre-fire conditions. However, repeated fire will
undoubtedly gradually degrade the peat resource and fire has
a detrimental impact on wildlife, which for threatened plants
or animals could be devastating. On the other hand, some
early and mid-successional species, including some orchids,
benefit from an occasional fire to provide them with habitat.
Overall, people need to be particularly vigilant to ensure that
no fires are started in or near areas of Organic Soils.
Increased inflow of sediments and nutrients from surrounding farmland can adversely impact the conservation
values of wetlands by changing the soil conditions to favour
invasive plants. While over time many wetlands gradually
naturally infill and change, such processes may be greatly
enhanced by inputs of runoff from surrounding farmland. In
the area of the Whangamarino wetland in the Waikato there
have been long-running differences over management of the
wetland between farmers who want water tables lowered,
conservationists who want to maintain natural conditions,
and regional council flood management programmes. The
flood management works divert (potentially nutrient and
sediment rich) flood water into the wetland area to protect
property downstream by lowering the flood peaks in the
Waikato River. The issues are complex and proving difficult
to resolve.
Carbon dioxide is lost to the atmosphere when plants or
organic materials are biodegraded or burned; conversely,
carbon is sequestered (or locked up) away from the atmosphere when plant material is preserved in a peatland.
However, within wetlands some biodegradation continues in
anaerobic conditions and results in the release of methane
(CH 4 ), which is also a greenhouse gas. Work by Dave
Campbell and others has shown that the undisturbed
Kopouatai restiad peat bog has relatively high overall rates
of carbon sequestration (from about 135 to 250 g C
128
8 Organic Soils