New Zealand's estuaries 'in hot water'

The health of New Zealand's estuaries is on the decline, and climate-induced heat waves mean they are quite literally 'in hot water'

Wading in amongst scratchy branches, sticky mud and ocean water might not be everyone's cup of tea, but for Karin Bryan it's a favourite pastime.

Estuaries are her happy place.

"I wouldn't have said that 15 years ago. Fifteen years ago I had never walked in a mangrove in my life," she says.

But Bryan's happy place isn't as cheerful lately. With climate change driving up sea levels and ocean temperatures, New Zealand's 300-plus estuaries are in trouble - a big problem considering their vital role in protecting the environment.

"There are a lot of species that aren't doing very well at the moment, and it can be very difficult to determine what's exactly causing them not to be well, whether it's the habitat decline, whether it's disease, whether it's predation.

"But certainly adding these really, really hot summer temperatures onto that is going to cause an added stress," she says.

Bryan says it's difficult to know what the worst-case outcome could look like, because there are so many moving parts, but one thing that's really thrown a spanner in the works are sudden events that seem to happen out of the blue.

"We really had focused on these slow onset events... like temperature in the summer getting gradually warmer, the sea level getting gradually higher, but we haven't focused enough on these episodic events - things like Cyclone Gabrielle - those kind of things that really just reset everything," she says.

Another issue worrying Bryan is some of the projects on the Fast-Track Approvals Act list.

"What really worries me about it is there are a lot of things that have already gone through the Environment Court that have gone back on [the list].

"I get that we need to make the economy stronger so then we can learn to care for the environment or put money into caring for the environment, but there's a balance and we're tracking that balance very quickly to something that's becoming quite destructive on our environment."

(The Detail approached the Minister for Infrastructure, Chris Bishop, for comment. His office sent a generic response but didn't address Bryan's concerns.)

The latest issue plaguing estuaries are short-lived, sudden heatwaves, which is Bryan's next research topic.

"If you had an understanding of what the probability of a heat wave occurring in your estuarian system [is], you could think a little bit more about how to create a more resilient ecosystem in that estuary," she says.

Being able to better predict these heat waves won't mean damage can be prevented, but Bryan says it will provide a head-start in rebuilding and restoration.

But a lot of the damage in estuaries is man-made, with the removal of native forest, urban development and roadworks increasing land erosion, which has increased the rate of sedimentation in estuaries.

A higher sedimentation rate means an estuary gets shallower more quickly and the species living in it slowly die. The health of the estuary itself deteriorates and eventually will dry out completely.

Bryan says humans get a lot of benefit from estuaries, and caring for them is important.

"The environment, and estuaries included, they clean our oceans, they help keep fish species healthy... and we don't really realise that, and so by degrading our estuaries over time, we're degrading that environmental capital that we had.

"I think it's a bit like getting into debt, and not really figuring out how you're managing your mortgage and how you're going to manage your retirement. You don't stop and think about it every day, but one day you will have to retire and you will need that money, and one day we will need to rely on our environment in a way that we never have before and it just won't be there."

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