Secret life of streams

Co-leaders Jim Mitford-Taylor (left) and Shelby Stoneburner (right) sporting t-shirts sold by Ngā Kaimanaaki o te Waimapihi / Polhill Protectors for fundraising.

By Ham Davidson

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Flowing silently beneath Wellington are streams diverted through culverts and pipes on their way to the sea. Ham Davidson, Science Communication and Research Advisor for the Environmental Protection Authority, sheds some light on one of them and how it’s being protected.

After rolling down hills past bush reserves and wooden houses, bathing tūī and tickling the bellies of fishes, Wellington’s streams are diverted into pipes below the city for the rest of their journey out to sea.

Waimapihi Stream begins near the Zealandia ecosanctuary fence line and flows down through the Polhill Reserve to Aro Valley. There, it enters a culvert and flows under the city and out to the harbour. If you press your ear to the ground in Aro Street Park, you’re likely to hear it moving below.

Waimapihi Stream has become a key focus for the Polhill Protectors (Cap #44), or Ngā Kaimanaaki o te Waimapihi.  The first tīeke nest recorded outside of a sanctuary and on the mainland in 100 years was discovered in the Polhill Resserve in 2014, and this provided the impetus for the formation of the Aro Valley community group.

Since then, the Polhill volunteers have been committed to maintaining traplines, planting trees, managing invasive weeds, and restoring the native forest to its pre-colonisation state, for example, by bringing back podocarps and plants that provide stream shelter. The group run planting and weeding days to bring the Aro Valley community on board,and the local brewery provides liquid treats for the volunteers.

Nestled in the bush between the city and Zealandia in Karori, the Polhill Reserve has had a noticeable increase in birdlife over the past decade. Kākā, kōtare, robins and tīeke, among other guests, spill over from the ecosanctuary, where the 8.6 km predator-proof perimeter fence protects native species.

“Our kaupapa is co-existing with the people, the birds, and the bush peacefully – being responsible pet-owners, trapping pests, planting trees. We’re trying to lay down the welcome mat for these taonga travelling over the fence,” says co-leader Shelby Stoneburner. 

Co-founders of the Ngā Kaimanaaki o te Waimapihi/Polhill Protectors, Lisa and Geoff Whittle, pictured with their dog Phoebe and signage for keeping dog on-leash in the reserve to protect birds such as tīeke who nest near the ground.

The DNA of Waimapihi

Polhill Protectors were among the first participants in Wai Tūwhera o te Taiao – Open Waters Aotearoa, a community science programme run by the Environmental Protection Authority that involves taking water samples for environmental DNA analysis.

Environmental DNA, or eDNA, refers to all the tiny traces of genetic material that is left behind as living things pass through water or soil. A single litre of water from a stream will contain thousands of little pieces of DNA. Analysing these genetic breadcrumbs can build a picture of the biodiversity present at that time, and to help us visualise all the components of the ecosystem; big and microscopically small.

Ngā Kaimanaaki o te Waimapihi/Polhill Protectors took samples from four different waterways in the Polhill Reserve, including Waimapihi, to see what species might be benefiting from their efforts (or not, in the case of rats).

“We weren’t sure what to expect. We knew Waimapihi was slightly healthier than other urban streams nearby, but our only evidence for that was from watching the streams and spotlighting at night. When the eDNA results came through it was really magical. We found out there were ruru around, and banded kōkopu, even tuna (freshwater eels),” says co-leader Jim Mitford Taylor.

Lisa Whittle, a founder of Ngā Kaimanaaki o te Waimapihi/Polhill Protectors and tireless advocate for pest-free forests, says, “It was really exciting to find that tuna came all the way up from near Te Papa, under the streets, and up through the culvert here to Waimapihi. It’s amazing.”

See the sample results from Waimapihi

Explore the map

A satellite image of central Wellington suburbs, with the Waimapihi Stream and its tributaries indicated in green.

Fuelling the journey of discovery

The group have since formed a connection with mana whenua from Taranaki Whānui, learned the whakapapa, and shared the eDNA results with them.

It’s members  are troubled at the lack of protection for the stream after it leaves the reserve.  Once the Waimapihi stream enters the culvert beneath the city, it is legally considered stormwater.

“It’s hard for us to acknowledge that, doing all this work at the headwaters and then seeing it disappear and become unprotected,” says Lisa.

The group continue to share information about the waters of Waimapihi with their community and local council and have been looking into ways that the mana of the stream can be acknowledged beyond the culvert. Through Wai Tūwhera o te Taiao, they plan to do more eDNA monitoring and dig deeper into the secret life of these urban streams.

Ngā Kaimanaaki o te Waimapihi / Polhill Protectors Facebook page

Ngā Kaimanaaki o te Waimapihi / Polhill Protectors Instagram



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