A Taonga in our hands: The Future of Ahuriri Estuary

[As published in March/April BayBuzz magazine.]

Unlike many other estuaries in New Zealand, Ahuriri has not yet reached the point of no return. So the establishment of a tributaries catchment group, and a statutory committee charged with protecting it, may have come in the nick of time. 

The Ahuriri Estuary – a tidal river mouth fed by tributaries from a diverse catchment that takes in rural and urban areas, and connects to a shallow lagoon – is facing a series of challenges that threaten its future. These problems have been growing and compounding over a century, to the point where today, this local treasure is struggling to maintain its equilibrium. 

It’s a long body of water with fresh water and salty areas, varying depths and a wide range of animal and plant life. In particular, migratory birds that fly from Alaska and the Arctic every year to feed, including the much-revered Godwit, or Kuaka. Te Whanganui ā Orotū, as it is called in Māori, meaning the Great Estuary of Orotū, (an ancestor) is classified as a nationally significant Wildlife Refuge. 

Everything from sediments and farm chemicals, untreated storm water pollution, invasive species, to topographical changes have had or are having an impact on this important habitat. 

According to HB Regional Council’s chief scientist, Anna Madarasz-Smith, many of New Zealand’s estuaries face challenges, and some have reached a tipping point – meaning that, while it’s possible for them still to reach a state of health, the natural equilibrium has changed permanently. 

With twenty years experience working with the estuary, she says Ahuriri has yet to reach that tipping point. 

“We’ve known about the estuary’s challenges for a number of years … in 1991 the first joint management plan was pulled together by the Department of Conservation, Napier City Council, Hastings District Council and Hawke’s Bay Regional Council – and it was only ever in draft. 

“There is a very long history with the earthquake and human interventions, drainage, the creation of farmland, the expressway and all of those things that chip away. So, the estuary is in a state of decreased health and we have some challenges in the way that it functions, from greenhouse sequestration, to filtering water for cleaning and transforming nutrients. It’s not doing too well … we need to be focussing.” Because the challenges are multi-factoral, the approach to tackling them must also be broad, she says. 

But Angie Denby, chair of the Ahuriri Estuary Protection Society, which has been around since the early 80s, says that it has been the collective lack of action that has had the biggest impact of all on the estuary. Until very recently, ownership of the estuary’s management was scattered across various councils and government departments, and getting them to work together was an uphill battle, she says. 

Te Komiti Muriwai o te Whanga Ahuriri Estuary and Catchment Committee 

This is all set to change as a result of the 2022 Crown settlement with the Ahuriri Hapū, and the formation of a trust set up to receive the proceeds, Mana Ahuriri. The settlement includes a Crown directive for a statutory committee to be created for the care and protection of the estuary.

Te Komiti Muriwai o te Whanga, a co-governance entity with Napier City Council as the administrating body, will now take the lead on all projects and initiatives for the protection and health of the estuary. It is charged with preparing and approving a management plan for the estuary and catchment.

Chaired by Mana Ahuriri, it is made up of representatives from NCC (Annette Brosnan), HDC (Tania Kerr), HBRC (Hinewai Ormsby) and DOC. Anna Madarasz-Smith is on the technical advisory group for Te Komiti (some appointments may change, at the time of writing Te Komiti was still finalising names).

Te Kaha Hawaikirangi, who has just taken over as chair of Mana Ahuriri and consequently co-chair of Te Komiti, says that it has engaged a consultant (PWC) to support it in the development of the plan and has begun hosting wānanga and workshops.

A final plan is legislatively required by March 2025. However Te Kaha tells BayBuzz that the goal is to have it completed this year, with community consultation, so as to align with councils’ LTP planning.

Any recommended actions that fall out of this process will have teeth.

“When it’s finalised it must be implemented. That’s the reason why we have all these partners around the table – so that we are on the same waka and going in the same direction.”

The principles and values associated with the plan have been mapped out and eventually the plan will be harmonised with TANK and any other council plans that overlap with it, so that there is no ambiguity. 

“Our plan will be focussed on the restoration and the mauri of the estuary.”

Groups like the protection society and the catchment group will be stakeholders in this consultation.

Protection Society Denby says, “[The trust are] getting their group set up and terms of reference together. I understand the trust has a lot of ideas and will be reaching out to groups like ours. Everyone will have their own interests, but I feel optimistic that having Mana Ahuriri at the head will put conservation and the environment at the forefront of everything.” 

An uphill battle for the estuary

Like Madarasz-Smith, Denby and the Protection Society have long been working to monitor and organise for the health of the Ahuriri Estuary. The protection society was founded in 1981 when Napier city council was intending to build a marina in the estuary where the Pandora Pond is now.

“There has always been the challenge of recreation vs conservation, and there probably always will be,” she says.

This summer the society has been keeping an eye on the birds that nest on the spit in Pandora Pond, where they have witnessed much destruction. “People riding trail bikes through the nests, children throwing eggs, others throwing gravel at the nests. We even got to the point of letting the police know this was happening because it is an offence under the Wildlife Act.”

Along with people, pests are also an issue. Stoats, weasels and cats come for bird eggs and babies, and so trappers work at the Southern Marsh where many birds gather. Wader bird numbers are counted twice yearly by Birds NZ, but not all the various birds that live there are counted.

“The really ubiquitous issues that are cosmopolitan around the estuary are sediments, the physical bounding of the estuary, and nutrients,” says Madarazs-Smith. 

By physical bounding, she means room for the estuary to be an estuary. 

“[The estuary is impacted by] the land we reclaimed and drained, and then the stop banks we built … as the sea level rise comes in, these intertidal habitats that are so important don’t have anywhere to go. I liken it to breathing, it needs to inhale and exhale with the tidal cycle.”

Sediment

While sediment is a massive problem for estuaries throughout the country, Ahuriri is having particular issues with sediment brought down in Cyclone Gabrielle. Because of the force of the water, residual sediment in the system continues to trickle down, and based on previous floods elsewhere, it’s estimated that it may continue to come down for up to seven years, she says.

“Anywhere that you have disrupted sediment that doesn’t have a cover holding it together, it has a potential to come through anytime it rains. People will have noticed that the rivers are turning brown very quickly.”

The fine mud clogs up all the holes in the sand, which like everything else needs to breath, and it can turn black and emit a smell like rotten eggs because of the lack of oxygen. “You can get a die off of anything underneath.”

Synthetic fertilisers

Phosphorous and nitrogen are both problems for Ahuriri, with phosphorous the bigger of the two. What it does is make microscopic plants in the water grow, but too much can cause algal blooms and this affects water clarity. If the sunlight can’t filter down to the sediment at the bottom, many of the estuary’s transformational properties are sabotaged, while dissolved oxygen crashes and the environment can’t support the needs of sea life, says Madarasz-Smith.

Tube worm

This creature builds coral like structures that displace other life in the estuary because of how massive these can become. “It’s been in the estuary since the 1990s and not posed much of a problem, and then in about 2011 it just took off and we have a massive biomass of it. It has taken advantage of the estuary’s challenges. It would have flourished because of the nutrients creating algal blooms and then builds these massive reef-like structures,” she says.

HBRC mechanically removed 600 tonnes of it over a few years, and has recently brought in expertise from the Cawthron Institute for management options.

Stormwater

Since New Zealand doesn’t treat any of its stormwater, everything that runs off the road and into the drains, including pollutants, goes into our waterways. But in the case of Napier, fully 75% of the city’s stormwater is released into the estuary. When there is really heavy or prologued rain, the council has consent to release sewerage into the estuary as well. 

Napier’s Deputy Mayor, Annette Brosnan, who is also deputy chair of Te Komiti, has been working for years to improve the city’s stormwater drains, and has had modelling done based on over five years of water quality testing across the network.

“When I came into government I tried to get Napier’s waterways and drains planted up with riparian planting. But we couldn’t just plant the drains, we needed to do a stormwater model around what plants would work, what the capacity issues were, what sediments and toxins were in different parts of the network. That’s now been done and is being peer reviewed.” 

Because of this NCC has a good understanding of what contaminants there are and which areas they are in. The highest levels of heavy metals are found in the industrial areas, but are found throughout the network. 

Impact on migratory birds

That’s a lot of problems for an estuary to handle, so what is the impact on birdlife?

Godwits fly from Alaska and spend nine days in the air and use all their energy to get here – they can’t land on water at any point. When they arrive they’re close to death and need to feed. Ahuriri estuary is like a gas station for them.

Madarasz-Smith says that in order to support these migratory birds, the estuary needs to have healthy shellfish beds and worms, so when it isn’t in the best of health, the birds can’t feed well. The estuary’s biodiversity not only underpins the health of these migratory birds but also Hawkes Bay’s fisheries. 

This problem was underlined in a recent UN report on the state of the world’s migratory species. Almost 50% of species registered under the Convention of the Conservation of Migratory Species of Wild Animals are experiencing a decrease, with over one-fifth of them facing the risk of extinction. The primary dangers to migratory species are overexploitation and habitat loss caused by human activities.

Associate Professor Phil Battley, Zoology and Ecology Group, Massey University, says that, “Our bar-tailed godwits, red knots and other species that migrate across hemispheres may rely on very few stopover sites, and habitually use the same places year after year. Their continued existence needs these sites to be protected.”

Ahuriri Tributaries Catchment Group

Another important group working on the health of the estuary is the local catchment group, formed about 18 months ago by a group of individual landowners. The group is working to improve land management and farming practices to improve water quality in the tributaries flowing into the estuary, and it has been making some very good progress. 

Like the Protection Society, the catchment group will be a community stakeholder for Te Komiti, and in fact, Wiremu and Tipene Cottrell of Mana Ahuriri are members of the group, says chair Robert Pattullo.

“We call ourselves the Ahuriri Tributaries Catchment Group and we are a very special case to be honest. We are quite small, covering from Bay View, around the foot hills into Poraiti and down into Taradale. It might be 10,000 to 12,000 hectares. Bigger catchment groups span 200,000 hectares. 

“And within that, there are only about half a dozen significant farming landowners, and then there are some smaller blocks. But there are also lots of lifestyle blocks. There could be up to 1,000 of those. We’re doing some analysis on that.”

The catchment also includes residential and commercial land, including the airport, port, Pan Pac, and the Pandora industrial area. “We all flow into the estuary,” Pattullo says. 

As a result, the catchment group has representatives from across the board with varying expertise, not just pastoral farmers, and is co-chaired by soil scientist Phil Schofield. It includes freshwater ecologist Keiko Hashiba, representatives from the local marae, and many others.

A year ago the group went through the process of becoming a charitable trust, which enabled them to apply for $8,000 funding from the Red Cross to run some events after Cyclone Gabrielle. This helped them introduce themselves to the community, as well as help out some of the lifestyle blocks that were devastated in the storm, he says.

Mini-freshwater plans

Pattullo says they also received $10,000 from Westpac, a nationwide Landcare grant, that was used to assist lifestyle block owners that had properties under 20ha, and are therefore not required to be compliant with the government’s freshwater rules.

“But they really are all part of our estuary catchment. So we are running a pilot we call ‘mini-freshwater environmental plans’, which involves going out to these blocks and introducing ourselves with a modelled free water plan from the Landcare Trust.” Every landowner with a mini-freshwater plan gets $500 to buy plants for riparian planting along water ways or hillside stabilisation. “That is special to our catchment because we have lots of these small block owners, and we are going to be able to do about 30 of those a year, and we’ve done about 12 already.”

The catchment group is also mapping these lifestyle blocks to identify key areas for improvements in land and water management, because freshwater is impacted by the sediment washed off the hills.

More recently the catchment group has been working with the Ministry for Primary Industries, and secured $600,000 in funding over four years to employ coordinators and carry out more significant freshwater water testing and special projects, such as making improvements to Wharerangi Stream. Others will be developed as they go along.

What about the farmers?

“And then there is the phosphorous that comes off the farms, and the biodiversity in the streams. We’ve always seen freshwater kōura and eels in our streams, but Gabrielle was pretty hard on them to be honest. They are coming back now. We do that with eDNA water testing to find out what species were there and enhance that and if they’re not there, then we need to find out.”

Pattullo says farmers are under no illusion that those of them on the Western side of the estuary will be in for some home truths in regards to the phosphorous, sediment and e coli that are coming out of their farming operations. The estuary is getting shallower and warmer, and there is a multiplying effect taking place, he says.

“If you don’t know, you don’t know how to improve,” he says.

There are about half a dozen farms in the 400ha plus category, all sheep and beef, also a little bit of horticulture and viticulture around Bay View, and on some of the tributary flats there is cropping.

“We are not engaging directly with the larger farmers at this stage. In time, when the freshwater farm plans and the TANK plan is finally confirmed and run out [that might happen]. We are not going to stand up and say we are experts.” But the group will continue to consult with farmers as part of the catchment, as they are doing lots of important land stabilisation work, he says.

Catchment groups by their nature will lead to more environmentally sound practices, he says. 

Those may in some instances include regenerative practices, which many farmers and lifestyle block owners are beginning to experiment with across the country. Such practices could aid in holding up sediment and runoff into the estuary and because catchment groups are led by community and volunteers, examples of good practice are often shared. “It’s enormously fulfilling. it makes your community a great place to live in.”

Future regional park and water treatment centre

The final piece in the puzzle is dealing with Napier’s stormwater issues, both in terms of treatment at source so that it doesn’t flow into the estuary, and as a protection against floodwaters.

Annette Brosnan is leading the charge on plans for the Ahuriri regional park and constructed wetlands and water treatment facility on 284ha of farmland owned by NCC on one side of Prebensen Drive, opposite Parklands. The idea is more than just a solution for storm and floodwaters, it will be a community space, a cultural storytelling centre, a home for wildlife.

The link back to Te Komiti and its developing plan, is that the park’s development will be consistent with the objectives, policies and guidance that they give, says Brosnan.

“It borders the channel of the estuary, from the Pond and Embankment Bridge that goes up into the foothills and there is currently a stop bank and a cycle way that goes along it. The vision for the park is to transform it into a stormwater system that treats the water before it goes into the estuary – that’s the primary purpose. A step forward as a council to how we treat the environment.”

Brosnan has worked for five years to get the park into the NCC long term plan, and has succeeded in setting up the council’s first co-governed joint committee – half Mana Ahuriri and half NCC and HBRC.

“In the first one to 10 years we have got $40 million to work on storm water diversions and the creation of the park, a ten-year project. And then for the 20 years after, we have a further $20 million to work on catchment improvements, outfall improvements and water quality. So we have a 10-to-30 year plan to treat 75% of the city’s stormwater through the park,” Brosnan says.

NCC has recently appointed a consortium to work with the community and council on the master plan. The vision is ambitious and includes things like sediment traps, wetland treatment systems that can strip different contaminants out, a big amphitheatre-like public space that will double as stormwater retention in high flood or rain events, education centres, cultural storytelling, biodiversity links back into the city and habitat for protected species. This means there will be both publicly accessible areas and others that won’t be.

“I think in ten years’ time we will certainly have this park well-established and then a further twenty years of investment, which will including planting up the tributaries, including Napier’s stormwater drains and waterways, with riparian planting.”

Caretaking into the future

Anna Madarasz-Smith says that a decade is a fair assessment for how long before we start seeing improvements in the health of the estuary and its tributaries, but ultimately 50, 75 or 100 years will be needed.

“That’s where we should be looking. We might see some changes in water quality aspects in the next 6-to-8 years, but we can’t determine natural variability from changes in management within short time cycles, that’s why long-term monitoring is so important.”

But she is very hopeful because finally the work has begun. It’s guided by science that has already been done to identify what the problems are and the scale of them. And most importantly, the collective responsibility needed is now in play. 

“We have common understanding that there is an issue and a common understanding to resolve it. That has been a progression from over twenty years. Iwi have always been trying to enhance it, as have the Protection Society. But now we have everyone on that waka.”