Wetlands

Wetlands are ‘in between’ areas – they are permanently or intermittently wet areas on the margins of drier land or along the margins of water bodies like lakes, rivers or the sea. The wet conditions create unique ecosystems – from the underlying substrates to the plants and animals specially adapted to live in them.

Repo (wetlands) are part of this beautiful landscaped narrative between wai and whenua.

Cheri van Schravendijk-Goodman

In between doesn’t mean small or unimportant – wetland systems like Kopuatai Peat Dome cover nearly 10,000 ha, and Southland’s Awarua-Waituna wetlands spread over 20,000 ha.

Unfortunately, these systems represent a fraction of the wetlands that once covered Aotearoa New Zealand. Prior to human arrival, nearly 10% of the land cover was wetlands. Over the past 150 years, 90% of wetlands have been drained or have deteriorated. Agricultural and urban areas now cover what were once diverse ecosystems and areas of cultural, economic and spiritual significance for tangata whenua.

As a society, we have gained a greater understanding of repo – their cultural values and the ecosystem services they provide – and work is under way to restore repo throughout Aotearoa.

Freshwater wetlands

The main freshwater wetland types in Aotearoa are bogs, fens, swamps and marshes. Wetland types are usually determined by the amount of water and where it comes from. Water flows influence nutrient availability and the types of vegetation the wetland can host.

Bogs get all of their water from rain, so they don’t receive the nutrients that groundwater and surface water often deliver to other types of wetlands. Bogs are continuously wet – the water table is close to the surface, and this creates poorly aerated and acidic conditions. Plant material doesn’t fully decay in these conditions, so peat slowly accumulates. Bogs have unique ecosystems with mosses, lichens, rushes and carnivorous plants. Peat bogs in the Waikato are home to the tiny, endemic insect called Fred the Thread.

Fens also have a peat substrate. Fens are located on slight slopes or at the edges of bogs so they are fed by both rain and groundwater, which provides extra nutrients. Fens tend to be wet, with the water table just below the surface, but there can be dry patches too. Vegetation includes tussock grasses, sedges, mānuka and tall herbs.

Swamps are fed by both surface water and groundwater so they get regular influxes of nutrients. Swamps often form in valley floors, basins, deltas and plains so they have standing water that can be fairly deep. Vegetation includes raupō, sedges, rushes, harakeke and trees such as kahikatea, pukatea, swamp maire and tī kōuka (cabbage tree).

Marshes are the most nutrient rich of the freshwater wetlands. Marshes are located alongside rivers, lakes and other marginal areas. They have seasonal water fluctuations, which means they can be dry in summer but wet in winter. Vegetation includes rushes, grasses, sedges and herbs.

Aotearoa also has some uncommon wetland types including geothermal wetlands and plutonic wetlands. Plutonic wetlands form in caves and underground streams. There isn’t enough light for plants to grow, so the ecosystem includes fungi, microbes, insects and fish.

Marine wetlands

Estuaries are the wetlands that form between the land and the sea where freshwater mixes with saltwater. Estuarine wetlands include marshes, seagrass meadows, mudflats and mangrove forests. These are some of the most productive ecosystems in the world.

Defining wetlands

Although ecologists like to create labels, wetlands don’t always fit into discrete categories. Wetland systems can have different types of repo within them. Whangamarino Wetland, located in the Waikato region, is a combination of peat bog, swampland and open water. There can be quite a bit of variation within wetlands, and if environmental conditions change, the ecosystems the wetland supports will change too.