Reducing pressure on Auckland’s estuaries

Auckland is built right on top of a vulnerable ecosystem that's under threat. The University of Auckland's Diana LaScala-Gruenewald asks what we can do to help

At 6pm tonight, Auckland, Wellington and Christchurch will join cities around the world in Climathon, a 24-hour global event that brings together innovators, entrepreneurs, students and professionals to brainstorm solutions to climate change challenges. Participants will select a local problem, work towards a solution for a full day, and share their ideas with city stakeholders.

One climate change challenge of relevance to New Zealand, and to Auckland in particular, is estuarine health. Everyone knows that Auckland is a city on the sea, and that its economy and culture rely on access to clean and healthy coastal waters. But Auckland is also built right on top of a very special and vulnerable kind of ecosystem called an estuary. 

What is an estuary?

Most broadly, an estuary is a place where fresh and salt water meet. In Auckland city, for example, the Tamaki River empties into the sea through the Tamaki Estuary, and the Whau River does the same through the Whau Estuary. These transition zones are natural filters that trap sediment and break down pollutants, resulting in clearer, cleaner coastal waters.

Estuaries are also one of the most productive ocean habitats. They are home to unique plants and animals that are adapted to withstand the changes in temperature, salt content and sediment content that are par for the course inside an estuarine environment. Shellfish and marine worms thrive in estuaries, helping to clear the water and bottom of organic particles. Birds, sharks, eels and over 30 species of commercial fish use estuaries as nursery habitats, arriving annually to feed and breed.

Estuaries under threat

It’s clear that estuaries play an important role in cleaning coastal waters and supporting biologically and commercially valuable plants and animals. Unfortunately, these ecosystems are also threatened by expanding agriculture and urbanisation. Their natural abilities to trap sediment and break down pollutants can be overwhelmed by excessive soil and toxins in the water, resulting in low oxygen and high sediment conditions that are dangerous to estuarine plants and animals.

If Aucklanders of the future want to continue to swim in clear coastal waters, sunbathe on clean beaches, watch exotic, native birds and catch fish with their children, we must not add to the climate change equation by increasing sedimentation.

Where does all this sediment come from? New Zealand’s soil is soft and fine, and it requires the dense and deep mats of roots produced by native plants to hold it in place, especially through rainy winters. When these plants are cleared for any reason, the soil tends to slip and run into waterways.

Early Māori burnt down coastal forest in northern New Zealand to farm, increasing the amount of sediment in estuaries, approximately 700 years ago. The rate of vegetation clearance increased with the arrival of European settlers. Now, the rate of sediment accumulation in estuaries, or sedimentation, is 10 times higher than it was before the arrival of Europeans. Poorly considered practices in agriculture, mining, forestry and construction have resulted in sedimentation that threatens the health of our estuaries and the animals and plants that live there.

What can we do?

Auckland currently has a clean and green reputation, but its environmental success is in part due to its relatively small population. As Auckland expands, it must consider how to do so sustainably. Estuarine health must be part of that calculation. Climate change will increase pressure on our coastal systems, with higher water temperatures stressing our native organisms and stronger, more frequent storms battering our coastlines. If Aucklanders of the future want to continue to swim in clear coastal waters, sunbathe on clean beaches, watch exotic, native birds and catch fish with their children, we must not add to the climate change equation by increasing sedimentation.

Auckland will expand in the coming years. The population will grow, and agriculture and infrastructure will grow to support it. We can’t change that. What we can change is how that population is housed, transported and fed. I challenge participants in this year’s Auckland Climathon to consider legislation and innovation that can reduce sedimentation pressure on the city’s estuaries, and give them the best shot of survival in the face of climate change.

Can you help our journalists uncover the facts?

Newsroom is committed to giving our journalists the time they need to uncover, investigate, and fact-check tough stories. Reader donations are critical to buying our team the time they need to produce high-quality independent journalism.

If you can help us, please donate today.


Newsroom does not allow comments directly on this website. We invite all readers who wish to discuss a story or leave a comment to visit us on Twitter or Facebook. We also welcome your news tips and feedback via email: Thank you.

With thanks to our partners