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Te Ipukarea Society: Wetlands, our giant sponges

Saturday February 08, 2020 Written by Published in Environment

World Wetlands Day was celebrated this week. This recognises the important habitat wetlands provide for plants and animals that have adapted to these watery environments, including insects, fish and birdlife. 

 

A wetland is any land area that is saturated with water, either permanently or seasonally such as marsh and swamps.  Your taro patch is a wetland! 

In the Cook Islands we are lucky to have four types of wetlands:

•        Freshwater marshes and swamps: on Rarotonga, Mangaia, Atiu, Mitiaro and Mauke.

•        Permanent freshwater lakes: Lake Tiriara on Mangaia, Lake Tiroto on Atiu, and Lake Rotonui and Lake Rotoiti on Mitiaro.

•        Tidal salt marsh: at Ngatangiia Harbour on Rarotonga.

•        Mountain streams: on Rarotonga.

The most common use of the freshwater swamps is for the cultivation of taro. Cultivation methods include raised taro beds (pa’i taro), taro swamp (repo tavari) or irrigated taro terraces (such as those found in the Takuvaine and Tupapa valley streams).

The cultivation of taro in wetlands is very important to our food security in the Cook Islands, particularly in the Pa Enua.  

A number of wetland plant species are also used in traditional Maori medicine, such as mauku vai (water grass), ta’uri’au and tamore.

Rarotonga also has the only remaining tidal salt marsh in the country – the Aroko Salt Marsh in Ngatangiia. This salt marsh is different to freshwater swamps where we grow our taro, as the area is covered by salt water during high tide.

The Aroko Salt Marsh provides habitat for certain marine species found nowhere else in the Cook Islands such as the koiti raukura (fiddler crab), and provides shelter and safe hatchery conditions for lagoon fish species.

Wetlands do some of their best work in reducing pollution entering our lagoon. They effectively “clean” water that is contaminated by soil, fertilisers and septic effluent. Acting as a natural filter, wetlands prevent pollutants such as nitrates and phosphates from entering the lagoon. 

Wetlands also do an important job of retaining water, a bit like a giant sponge.  By slowing down the water moving over the surface of the land to the lagoon, it reduces the impact of floods.  Flooding like the recent severe episodes in Avatiu were far less frequent or severe back in the days when the wetlands were intact.

Unfortunately, our Cook Islands wetlands have been shrinking for decades due to development and conversion into agricultural land.  

A permit from National Environment Service must be obtained for any works in a wetland. This includes clearing, dumping, paving, reclamation and removal of trees, or the erection of any building or structure in a wetland.

An Environmental Impact Assessment is also required should any environmental impacts be anticipated. 

Perhaps a ra’ui to protect the filling in of wetlands could be useful? Just as ra’ui are placed on lagoon areas, wetland areas are also vitally important to the health of our islands and people.

It is important to recognise the value of these ancient wetlands and the role they play not only in providing food, but in filtering our pollution, providing a home for biodiversity and preventing flooding.  If you are considering filling in a taro patch or other form of wetland, please think again!

 

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