Wetlands

Today, 90 per cent of New Zealand’s original wetlands have been lost, with many of the remaining wetlands degraded by weed invasion, stock access, modifications and barriers to fish migration. The ongoing grazing and drainage of wetlands for urban and rural development is further reducing this scarce habitat type and introduced species continue to invade these areas.

Wetland types

Example of a wetland (Crown Copyright: Department of Conservation: Te Papa Atawhai, n.d.)

Wetlands are very diverse, which may explain the broad definitions provided for them within international treaties and the RMA. They vary in wetness, fertility, acidity and salinity. They are influenced by a range of factors including different landforms, substrates, hydrology and vegetation.

Wetland types are varied and the type of wetland plays a key role in the variety of fauna and flora found within each habitat. The following table describes wetland types in New Zealand, and details of their distinctive features. 1963

Bogs

Bogs are low in nutrients, poorly aerated and usually acidic due to being almost constantly water-logged. All the water in bogs comes from rain, which means they do not benefit from the nutrient-laden water flowing from neighbouring or underlying soils. Bogs support a wide range of plants and animals including moss, lichens, rushes, orchids, silver pine and fernbirds. A rare moth is found inbogs in the Waikato. Bogs can be found in Southland, Westland, the Chatham Islands and in the Waikato. 

Fens

Fens are marginally higher in nutrient content than bogs. They are enriched by ground water inflow carrying minerals from adjacent soils. They have a peat substrate (the partly decomposed remains of plants and animals which form in wet, oxygen-poor sites). They are able to support a range of vegetation which includes tussock, manuka, tangle ferns and Baumea sedges. Fens are found on minor slopes or on the edges of raised bogs.

Swamp

Swamps are much richer in nutrients than bogs and fens, so they can be highly fertile. They benefit from both ground and surface water inflow, carrying nutrients and sediments from adjacent land. A wide variety of plants can be found in swamps including sedges, rushes, reeds, bullrush (raupo), flax and manuka. A number of forest trees live in swamps such as kahikatea, pukatea and cabbage trees (tī kōuka). Swamps tend to be found in low lying areas such as basins, valley floors, deltas and plains. Examples of large swamps can be found at Whangamarino in the Waikato and at Mangarakau in Golden Bay. 

Geothermal Wetlands

Geothermal wetlands are created by hot water and mud flowing from thermal streams, hot springs and geysers. The fern Cyclosorus is commonly found in New Zealand’s geothermal wetlands. Excellent examples of geothermal wetlands are found in the Waikato and Bay of Plenty regions.

Lacustrine Wetlands

Lacustrine wetlands are connected to lakes and ponds. Vegetation in these wetlands includes aquatic plants, algae, floating ferns and herbs. Tall reed-like plants such as club rushes, raupo and giant rushes may occur closer to the edges.

The characteristics of lakes associated with lacustrine wetlands vary. Some are of peat origin, like Lake Serpentine in the Waikato. Others are associated with sand dunes, like Lake Wainamu, in west Auckland. They also exist on the margins of lagoons, such as Lake Ellesmere in Canterbury, and are found on the margins of impounded rivers, such as the Waikato hydro lakes. In addition, they are found near volcanoes, such as at Lake Tarawera, and near glaciers, such as those at Tekapo and the Nelson Lakes. 

Riverine Wetlands

As the name suggests, riverine wetlands are connected to flowing water in rivers and streams. The unique braided river systems of the South Island provide temporarily wet areas. Birds, such as black stilts, feed in these areas. Swampy backwater sections occur behind river levees. Algae are supported on wetland beds and submerged aquatic plants are abundant. Good examples include the Buller River in Nelson and Ahuriri River in Canterbury. The Waihou River Blue Springs in the Waikato region is an example of abundant submerged plants being supported in riverine wetlands.

Plutonic Wetlands

This type of wetland is found mainly in limestone caves and underground streams. Caves in lava tubes also support this form of wetland, as do aquifers. Plant life cannot be sustained due to a lack of light. However, fungi, microbes, insect larvae and some species of fish live there. Such wetlands are best viewed on guided cave tours such as in Waitomo and Takaka.

Wetland ecosystem services

Wetlands provide a number of ecosystem services:

Role

Importance

Water Storage

  • Slow rate of discharge and moderate peak surges
  • Protect land from floods
  • Reduce effects of storm runoff and seasonal flooding
  • Assist with groundwater recharge which in turn feeds high quality water to lakes, rivers and streams

Buffer between land and sea

  • Provide shoreline protection along margins of lakes and streams
  • Can absorb action of waves or currents
  • Secure sediment, preventing erosion and reducing accumulation of deposits in neighbouring waterways, reducing the need for flood and stormwater control structures

Filter Pollutants

  • Help to improve quality of water
  • Allow toxins and nutrients to settle out
  • Plants take up a proportion of the nutrients, whilst other contaminants may be transformed into a less harmful substance

High Social Appeal

  • High aesthetic value
  • Opportunities for education, tourism, scientific research and recreation

Cultural Importance

  • Regarded by Māori as taonga (having much cultural and spiritual significance)
  • Provide important traditional resources, medicinal supplies and food

Carbon Sink

  • Healthy wetlands can be highly effective carbon sinks, absorbing between two and five tonnes of carbon per hectare

Threats

Over 90 per cent of New Zealand’s wetlands have been drained or filled over the last 150 years. Some of New Zealand’s most threatened natural ecosystems  now include lowland wetlands and bogs. Over half of the remaining freshwater wetlands are on privately owned land.

  1. National Wetland Trust of New Zealand

Last updated at 1:55PM on February 25, 2015