Wetland wise - all about wetlands

If you have a wetland on your property and are interested in looking after it, this guide is for you.

Read on and you’ll find out how to restore wetlands – whether as a habitat for native plants and animals, as an attractive part of your property, or as a way to clean up your water supply.

If you’re interested in creating a new wetland, this guide may also provide some useful pointers.

What is a wetland?

The term ‘wetland’ covers habitats where the land is covered in, or saturated by, water for at least some of the time.

Wetlands occur in areas where surface water collects or where underground water seeps through to the surface. They include swamps, bogs, marshes, gumlands, saltmarshes, mangroves and some river, lake and stream edges.

Wetland on the Pouto Peninsula with Lake Humuhumu in the background.

Why wetlands are important

In the past, many people did not recognise the true value of wetlands and consequently nearly all of them have been converted to pasture or urban use. Wetlands help prevent flooding and improve water quality, as well as providing the necessary habitat for a number of unique species of plants and animals. Conserving and restoring wetlands will provide many benefits to the wider environment.

A giant ‘sponge’
Wetlands act as a giant sponge, helping to soak up water and improve water quality. Plants in wetlands slow the flow of water off the land so that, in times of flood, more can be absorbed into the soil and taken up by the plant life. In summer, stored water is slowly released from wetlands, maintaining water flows.

Overseas studies have found that peak flood levels can be reduced by 60-80% in catchments with one third of their area in lakes or wetlands.

Cleansing the system
Bacteria in wetlands’ damp soils contribute to cleaner water by absorbing and breaking down about 90% of the nitrogen contained in farm run-off (such as in fertilisers, chemicals and animal wastes). This cleaner water prevents nuisance algal blooms and is better for livestock and wildlife. Plants also trap waterborne sediment, preventing silt entering streams and harbours.

A food source
Wetlands are among the most productive places on Earth, providing an enormous food source for fish, birds and other animals. They absorb large amounts of water and nutrients from outside sources and contain micro-organisms (fungi and bacteria) which efficiently decompose and recycle nutrients.

A cultural treasure
Wetlands are also important to Māori, featuring in the history and culture of many hapū. Wetland plants are traditional materials for clothing, mats, medicine and dyes. Wetland animals, especially tuna (eels), are valuable food sources.

Taikirau wetland Motatau.

Wetland types in Northland

The Northland region has eight main types of wetlands:

  • Bogs
  • Fens
  • Salt marshes
  • Swamps
  • Marshes
  • Gumlands
  • Seepages
  • Ephemeral (seasonal) wetlands

Bogs
Bogs are very rare and precious in the Northland region. Fed only by rainfall, they are low in fertility and are acidic. They are home to a variety of specialist plant life, with the wettest dominated by sphagnum moss. In Northland, bogs are home to the nationally threatened mudfish species. Drier bogs support a variety of plants including sedges, rushes, umbrella ferns and manuka.

Fens
These are the rarest type of wetland. They are largely infertile, like bogs, but because they also receive runoff from surrounding land, they have areas of fertility. They usually have higher biodiversity than other wetland types.

Salt marshes/coastal wetlands
Estuaries (including salt marshes and mangroves) are the most productive of all wetlands and are especially rich in animal life. Many coastal fisheries depend on estuaries as fish spawning grounds.

Swamps
Most wetlands on private land are swamps. They are fertile because they receive runoff from surrounding land which brings silt and organic matter. Swamp water levels fluctuate seasonally and most swamps are in valley bottoms.

Typical swamp plants include raupo, purei (Carex sedges) and harakeke (flax). The organic matter these plants produce encourages large populations of aquatic invertebrates and birds.

Shallow water – lakes, ponds, dune lakes and rivers
Open water is not strictly a wetland type, but it is often associated with shallow water margins surrounded by wetland vegetation. These areas are important water bird and native fish habitat.

Northland is home to more than 400 dune lakes. These lakes within old sand dune systems are often dynamic, with fluctuating water levels and shorelines that are often being changed by shifting sand dunes. Dune lakes are home to a large diversity of native plants and animals, including the rare freshwater fish, the dwarf inanga, which
is only found in some dune lakes in Northland.

Northland has some of New Zealand’s most pristine dune lakes.  Dune lakes, especially on the Poutō Peninsula, are often associated with huge marsh wetlands.

Marshes
These are on flood plains associated with rivers, or next to lakes.  At times they are flooded and at other times they are dry. Marshes sometimes have tall trees such as kahikatea, swamp maire and pukatea which have adapted to living with their roots in waterlogged soil.

Gumlands
Gumlands may not appear to be wetlands as they are at the top of hills and are dry most of the time. However, hard pan soils formed under old kauri forests mean that the drainage is very poor, so they are wet in winter. They contain unique shrubland communities and, because they are infertile, share many species with bogs. These are very rare now as most have been cleared or developed.

Seepages
These are places on slopes were water comes to the surface, often as small springs. They are common, but are seldom fenced, looked after or appreciated.

Ephemeral wetlands
Seasonal or ephemeral wetlands are areas where water ponds in winter and dries up in summer. This gives rise to short, turf-like vegetation. The most common ephemeral wetlands are in coastal dunes where they are known as dune slacks.

Unique wetland wildlife

Wetlands support an immense variety of animals, some of which are very rare.

Most of New Zealand’s wetland animals are not found anywhere else in the world. They include fernbirds, New Zealand dabchicks, New Zealand scaup and paradise shelducks. Mudfish are also unique. Pateke (brown teal) are now restricted to two small populations on the east coast of Northland and Great Barrier Island.

Animals that can only live in wetlands face an uncertain future through habitat loss and/or damage. Many, like the Australasian bittern, pateke and short-jawed kokopu, are now endangered.  Conservation and restoration programmes help to provide the habitat they need and ensure these wildlife survive into the future.

Wetland birds

The size and diversity of wetlands in an area determines the diversity of birdlife that can be supported.

Bird Habitat requirement
Spotless crake, marsh crake and Australasian bittern
These secretive birds feed in permanently shallow water under flax and other wetland plants. They build nests under sheltering sedges, such as purei and occasionally among stands of shrubs, such as manuka.
North Island fernbird
Fernbirds prefer wetlands with dense ground cover under a selection of shrubs and small trees like manuka. Northland is the stronghold for fernbirds.
Pied stilt Pied stilts feed on worms and insects in temporary winter pools in paddocks and permanent wetlands. They nest in scattered clumps of rushes.
New Zealand scaup
New Zealand scaup prefer deep, open and clear water with abundant invertebrates (insects, worms and snails). They nest in dense wetland vegetation such as raupo and purei.
Grey duck, New Zealand shoveler and grey teal
These birds prefer shallow water around the edges of a pond or lake. They need open water to moult in safety, away from predators.
New Zealand dabchick and Australasian little grebe New Zealand dabchick and Australasian little grebe feed in deep, open water but build their nests on floating rafts of vegetation among reeds.
Tui, waxeye and kukupa
These birds visit wetlands at certain times to feed. Tui and waxeye feed on nectar-producing plants like harakeke (flax). Kukupa (wood pigeons) visit wetlands to feed on fruiting trees like kahikatea.
Pateke
(brown teal)
The endangered pateke feed in damp, short pasture, and in seepage areas, shallows of ponds and estuaries. They nest among dense clumps of sedges and rushes, usually near water. Pateke prefer to roost beside the deep water of ponds, streams or estuaries, usually beneath large trees.

Focus on fish

Many of New Zealand’s native freshwater fish live in wetlands for some or all of their lives – such as short-fin and long-fin eels, inanga and banded kokopu. These fish also journey to and from the sea using a corridor of estuaries, rivers, streams and drains. This watery pathway must be kept intact if they are to complete their lifecycles successfully.

In contrast, the black mudfish and endangered Northland mudfish spend all their lives in wetlands, drains or weed-filled creek beds.  During dry spells, they have an extraordinary ability to burrow deep into mud or under logs and hibernate for months at a time.  This means they can occupy seasonal wetlands not accessible to other fish.

Banded Kokopu (Photo: Rowan Strickland)

Whitebait

The juveniles of many of our native fish, such as banded and shortjawed kokopu, inanga and koaro – are collectively known as ‘‘whitebait’’. Their eggs hatch in autumn and the larvae are washed out to sea. Six months later they make the hazardous return journey as juveniles. Most of the whitebait fishery catch is inanga.

Juvenile kokopu and koaro can travel large distances upstream, even climbing damp rocks beside steep waterfalls, until they reach sheltered streams and wetland habitats.

Insects and other creatures

Although birds are the most visible component of wetlands, other animals like invertebrates (such as insects, snails, crustaceans and worms), amphibians (frogs) and reptiles (lizards, etc) also live there. Typical wetlands can have hundreds of rarely seen insect species, all of which form an integral part of the food web.

Large native dragonfly (Photo: DOC).