A wetland developed by Federated Farmers members Gray and Marilyn Baldwin on their Putaruru dairy farm has become something of a ‘poster child’ for how wetlands can help manage a farm’s environmental footprint and boost biodiversity.
The farm was chosen as the venue for the launch of a new NIWA-DairyNZ resource aimed at helping farms with wetland design and performance.
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 wetlands can significantly reduce nutrient and sediment losses on farms. They also provide habitat for birds and fish, improve biodiversity and help create an attractive farm environment,” David said.
According to Landcare Research, more than 90% of New Zealand’s wetlands were lost in the past 150 years. As of 2019, the North Island had only 4.9% of its original wetlands left.
The wetland that the Baldwin Family Trust began establishing in 2015, with funding from the Waikato River Authority, features as a case study in the ‘Wetland Practitioner Guide – Wetland Design and Performance Estimates’.
The Baldwin’s 713 hectare, 850 cow dairy farm is in the South Waikato’s Upper Karapiro catchment, which drains directly into Lake Karapiro.
“We want to improve local waterways and we see the wetland as being important to the whole catchment. It is a taonga,” Gray Baldwin said.
The Baldwins recognised in 2014 that pressure for environmental stewardship of the land and society’s interest in what dairy farmers were doing was only going to increase. They also realised that if they got in early, there was a better chance of help with work establishing a wetland.
The Waikato River Authority, DairyNZ, NIWA, Opus, Hill Laboratories, and Waikato Regional Council worked together with the Baldwin Family Trust on the project. The aim was to improve knowledge of wetland design and performance and share this with Waikato farmers and the community.
Consultation and engineering was vital in getting the foundations of the wetland system correct and a component of the development where the Waikato River Authority funding proved integral.
“When water comes in from off the farm, rather than coming in through a narrow channel we wanted it to spread out amongst all the rushes and the sedges which do the good work of denitrifying the water and cleaning it up. Getting that GPS perfectly level was a big part of the cost,” Gray said.
The wetland now captures runoff from 45ha of surrounding farmland and the race. Altogether including some of the smaller natural seepage wetlands on the sides of the hill, it services an 81ha catchment.
Over 12,000 native plants were planted at the site by local community groups.
The family is pleased to see biodiversity in the area improving and native birds flourishing.
With funding from DairyNZ, NIWA scientists monitored water flows and contaminant concentrations to assess the Baldwin’s wetland performance.
Despite its relatively small size (around one percent of the farm catchment area), good design and extensive planting means the wetland removes around 60 percent of nitrogen, 70 percent of sediment and 20 percent of phosphorus from the water it receives.
The new guidelines highlight that as wetlands increase from one to five percent of a catchment area:
- sediment removal typically increases from 50 to 90 percent
- nitrogen removal increases from 25 to 52 percent in warmer zones of New Zealand
- nitrogen removal increases from 18 to 38 percent in cooler zones of New Zealand
- phosphorus removal increases from 25 to 48 percent.
The guidance is the result of a four-year project between DairyNZ and NIWA, with input from many other organisations, including regional councils and Fish and Game NZ.
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.”
Dr Burger said farmers who are interested in constructing wetlands can contact an environmental consultant to work through the new guidance. Farmers should also seek regional council advice on consents and any assistance available.
Fish & Game has welcomed the new NIWA-DairyNZ resource.
“New Zealanders are becoming far more aware of the important role wetlands play in ‘taking care of water,’ from recharging groundwater and augmenting flows, and filtering runoff pollution,” New Zealand Fish and Game Council Chair Ray Grubb said.
“Wetlands are vital for wildlife because they provide valuable habitat for both native and valued introduced species. Healthy wetlands are also crucial in helping to minimise the impact of weather events like floods and droughts, which too many New Zealand communities are unfortunately all too familiar with.”
The Wetland Practitioner Guide – Wetland Design and Performance Estimates covers:
- wetland performance, design, sizing, siting, and costs
- selecting and establishing plants, and wetland maintenance
- wetland case studies from across New Zealand.
The guidance is supported by twelve regional councils, Fish & Game NZ and the Waikato River Authority. It can be downloaded at www.dairynz.co.nz/wetlands