Sunday, August 14, 2022

Wetland guidelines released following four-year project

Seven years ago, Gray and Marilyn Baldwin decided to construct a wetland on their farm to future proof it against impending environmental legislation and the industry’s changing social licence.

It developed into a four-year project aiming to improve the knowledge of wetland design and performance for Waikato farmers.

After two years of delays due to covid restrictions, the project’s final field day was held where the Wetland Practitioner Guide – Wetland Design and Performance Estimates was released.

The project received funding and support from the Waikato River Authority (WRA), DairyNZ, NIWA, Opus, Hill Laboratories and Waikato Regional Council.

Its total cost was $150,000 with the WRA funding half and the rest coming from the other involved parties.

The wetland was then built on the 713 hectare farm, just south of Putaruru. 

It covers 0.85ha, has more than 12,000 native plants and has a 52ha catchment area close to the Ngutuwera Stream and Pokaiwhenua/Karapiro catchment.

Key to the project was the monitoring of waterflows and contaminant concentrations entering the wetland by NIWA scientists so they could monitor its performance.

That monitoring showed it removes about 60% of nitrogen (N), 70% of sediment and 20% of phosphorus (P) from the water it receives.

“Our farm is located in the Upper Karapiro catchment, which is one of the more sensitive ones in the Waikato region, as it drains into the Karapiro,” Gray Baldwin said.

“We want to improve local waterways and we see the wetland as being important to the whole catchment. It is a taonga.”

Gray said the most challenging part of constructing the wetland was ensuring the area itself was level, which was necessary to ensure water travelled through the wetland as slowly as possible to allow time for any contaminates to be filtered.

Its location was also important. 

It borders the farm’s main race, meaning all the effluent from the cows travelling to and from the dairy shed was captured.

It also had three natural seepage areas on the surrounding hills that aid the filtering of nutrients prior to them entering the wetland.

The family are pleased to see biodiversity in the area improving and native birds flourishing.

“We have had a good increase in wildlife. We do get frog noises, my late father-in-law came down here one day and got great delight on his face when he saw a pair of pied stilts. He said he had not seen pied stilts on this farm for two decades,” Marilyn said.

“It’s something pretty special. It does something for the staff too on the farm, to go past the wetland is very cool.”

The Baldwins’ wetland is one of 11 case studies published in the new guidelines.

“My late father-in-law came down here one day and got great delight on his face when he saw a pair of pied stilts. He said he had not seen pied stilts on this farm for two decades.”

Marilyn Baldwin
Waikato dairy farmer

These showed that as wetlands increase from 1-5% of a catchment area, sediment removal typically increases from 50-90%, N removal increases from 25-52% in warmer zones of New Zealand and 18-38% in cooler zones of New Zealand and P removal increases from 25-48%.

DairyNZ general manager for sustainable dairy Dr David Burger said as farmers increasingly look to protect and develop wetlands, advice is often sought on how to design wetlands to maximise their performance.

“We know that wetlands have lots of potential for reducing an environmental footprint and biodiversity and all of those cultural values and we know at a principal level, its about capturing that water, slowing it down and letting all of the bugs do the work.”

But installing one was also not so simple to undertake on a working dairy farm, a point Marilyn makes.

While she loves having the wetland, there are realities in maintaining it. 

“This is a working farm and it takes time, it takes money and it needs staff and all of those three things are difficult at times,” she said.

There was always ongoing work. 

In the past two months, they planted a further 1500 cabbage trees, she said.

Burger said the scientists learned a lot from the project, coping with years where there was both flooding and drought.

“The learnings have been absolutely significant. We’ve learned a lot about wetland design around the performance of this wetland and we have had a lot of real-time sensors on this wetland monitoring flows and trends and have learned a lot about how they function.”

From that perspective, the project had been a success, he said.

“We’ve got some real science and some real numbers around how the wetland performs.”

NIWA’s principal scientist aquatic pollution Dr Chris Tanner said the guidelines are designed for practitioners, but also provide evidence for farmers and councils of wetland effectiveness in removing contaminants.

“The estimates are based on over 20 years of New Zealand study and international field-scale monitoring and modelling studies. Estimates were then refined, tested and endorsed by a technical advisory group supporting the project.”

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