Wetlands
Biodiversity
To many people the word ‘wetlands’ conjures up images of marshy swamps filled with tall rushes. But the
term refers to a range of vastly different habitats which make up some of the most interesting and productive
environments in New Zealand. Wetlands can include bogs and swamps, coastal estuaries, braided rivers,
marshes, puddles and margins of lakes, streams, rivers and even the moist hollows among sand dunes
known as dune slacks – in other words a place where the ground is always, sometimes or occasionally wet!
Unfortunately, wetlands are among the world’s most threatened habitats and in New Zealand only about 10
percent of our wetlands remain. This makes them very special places indeed.
A rich habitat
We now have a better understanding of the role
that wetlands play in reducing the severity of
floods, recharging groundwater, filtering water and
contributing generally to the health of our environment.
Wetlands, in their natural state, create a rich and
diverse habitat for a huge array of native plants and
animals, including hundreds of bird and invertebrate
species. Many species, such as whitebait/ïnanga
need wetland areas for part of their life cycle. Other
unique species, like mudfish/köwaro, are endangered
due to the vast reduction in their habitat.
Birds that live in wetlands range from the secretive
bittern/matuku, which is well camouflaged and often
unseen, to the kakï/black stilt, which is one of the
world’s rarest wading birds and lives only in the
Poutu dune lakes P. Anderson Mackenzie Basin in South Canterbury.
RD&I Hamilton
Published by
Department of Conservation
Christchurch
2006
NS0027
An extraordinary range of migratory birds also take
advantage of New Zealand’s wetlands. One example
is the Eastern bar-tailed godwit/kuaka which breeds
in Siberia and migrates to New Zealand, arriving in
October. This remarkable bird feeds constantly while
mudflats are exposed in order to build up enough
energy to fly home.
Specialised plant species include the bladderwort
(Utricularia monanthos), which gets nitrogen from
microscopic insects through bladders on its roots,
and the forked sundew (Drosera binata), which uses
sticky hairs to trap insects. A number of orchid species
thrive in a wet environment, even growing in open
water. Some of these orchids are very rare, such as the
swamp orchid, Pterostylis micromega.
Forms of spongy mat plants are also extremely
important in wetlands, particularly in the way they help
to create peatland by trapping sediment which then
builds up soil. This process occurs over thousands of
years and the resulting peatlands are often extremely
old.
In estuaries and wet coastal areas there are hundreds
and thousands of dependent crustaceans, birds, fish
and plants. In our more unique freshwater ecosystems
there are 36 known varieties of fish and hundreds of
aquatic and semi-aquatic invertebrates, some of which
are specialised for geothermal systems and extreme
environments.
Where are they?
Australasian bittern/matuku
M. F. Soper
Although they are much reduced in extent, wetlands
still occur in a number of places throughout New
Zealand. This country has more than 70 major
river systems, 770 lakes and at least 73 significant
freshwater wetlands. In addition, there are numerous
estuaries and coastal wetlands containing tidal
mudflats, sand systems and mangrove habitats.
Some wetlands are so significant that they have been
listed under the Ramsar Convention, an international
agreement for the conservation and wise use of
wetlands. The aim of the convention is to prevent the
loss of the world’s wetland habitats.
Threats
Baron dragonflies mating
P. Schilov
Human activity
Many wetlands have been damaged or destroyed
completely by drainage, roading, building and farming.
Some people view wetland modification as a positive
form of development because they perceive wetlands
to be wasteland. However, draining, channelling,
flood control, and land reclamation all change these
rare habitats, and affect the species that live in them.
Often land is cleared and drained right to the edge
of wetland margins, which harms intermediate areas.
Once wetland water levels have been modified,
these areas can also become susceptible to invasion
by exotic weeds (e.g. willows and Glyceria). Flax/
harakeke, snails, fernbirds/mätätä and brown duck/
päteke are now rare in many areas because their semiwetland habitat no longer exists. The land area taken
may seem small at the time, but it adds to a large total.
Aquatic pests
Ahuriri wetlands
Ahuriri wetlands
Weeds and algae can clog a waterway, changing its
nature entirely. Unfortunately, in recent years aquatic
pests like the waterweed hornwort have dramatically
expanded their range and there have been new
arrivals like the alga didymo. These pests are most
readily spread on fishing gear and boats or kayaks
which are transported from one waterway to the next.
It is essential for lake and river users to clean their
equipment before leaving a waterway to ensure it is
free from contamination.
Pest fish can also do a great deal of damage to our
waterways. Fish like koi carp and gambusia can stir
up sediment and increase nutrient levels and algal
concentrations. Pest fish also compete with native
species for food, contribute to erosion, prey on native
fish species and their eggs and remove aquatic
plants. These fish are spread both accidentally and on
purpose.
Pollution and other threats
Accidents involving hazardous substances can do
great damage to wetlands but so too can a build-up of
nitrates from sewage, storm water runoff and farming.
Fire is another threat to wetlands, particularly during
dry seasons and the harvesting of sphagnum moss
for horticultural use is another way that wetlands are
reduced.
What can you do?
Minimising pollution and damage to wetlands is
something we can all think about and do no matter
what our recreational or business interest. For
example:
•
Landowners and farmers can fence stock off from
vulnerable waterways and lake edges.
•
Anglers and trampers can take care not to
transport weeds from one location to another
via their boots and gear (all fishing gear, boats
and trailers should be thoroughly cleaned before
leaving a waterway and travelling to the next).
•
Car and 4WD owners should stick to formed roads
and avoid travelling in boggy terrain.
•
The proper resource consents and authority should
be sought before extending roads, draining land or
modifying water courses.
•
Any sightings of new waterweeds or pest fish
should be reported to the local authority.
•
•
Never empty aquarium contents into a waterway.
Be careful with fire. Although wetlands are by their
very nature wet, in dry conditions the upper layers
of a wetland can be completely destroyed by fire,
ruining for many years the nature of that habitat
and creating an environment for weeds like the
Australian hakea plant, gorse and wattle.
For more information
Contact your local DOC office or visit the DOC website
at www.doc.govt.nz
Check out: www.ramsar.org and
www.nzfreshwater.org.