Wetlands
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3 min read
Wetlands on farms serve as nature's kidneys, filtering out nitrates, trapping sediment and phosphorus, and reducing faecal bacteria from runoff, improving water quality. This page advises you on protecting and managing these essential ecosystems. It suggests fencing wetlands to guard them from livestock and planting to increase nitrate uptake and wildlife habitat. Rules regarding wetlands were updated in 2020, so check with your regional council before commencing any activities. Constructed wetlands can also be an effective solution. For severe nitrate removal, a concern is pollution swapping, but this page concludes that the likelihood is low.
Protecting, restoring and creating wetlands on-farm can reduce nutrient losses, decrease the impact of floods and provide a valuable habitat for native plants and animals.
Wetlands act as the kidneys of the environment, and can remove significant amounts nitrate from runoff through denitrifying bacteria and uptake by plants, markedly improving the quality of water leaving the wetland. They also trap sediment and phosphorus and reduce faecal bacteria.
As one of the most biologically diverse ecosystems, wetlands provide a valuable home for native plants and animals.
Identifying and protecting wetlands on your farm
Wetlands include anything from small on-farm swamps and seeps, to large, regionally recognised areas.
New Zealand has lost 90 percent of its wetland areas from drainage. Protecting even small wetlands on farm adds a lot of value to the environment.
Wetland rules and regulations
Your regional council may have requirements for works within wetlands. The National Environmental Standards for Freshwater also introduced a number of rules relating to wetlands in 2020. Before undertaking any activity within or near to an existing wetland you should check these rules. You can also seek advice from your regional council.
In December 2022 the Government announced changes to freshwater regulations surrounding wetlands. These changes go some way to addressing concerns raised by DairyNZ in our submission during the 2021 consultation - view submission here.
Wetland maintenance activities (such as weed and pest control) are provided for, if the activities prevent the deterioration or preserve the existing state of a wetland. Check with your regional council on what this means in practice.
What you can do with wetland areas on your farm
Fencing wetlands will protect them from stock and allow them to perform to their maximum benefit, reducing the amount of nitrate, phosphorous and sediment entering waterways, improving stock management, protecting land from flood damage and providing a habitat for native wildlife.
Planting wetlands will add further benefit by increasing the uptake of nitrate, trapping more sediment before it enters waterways and increasing the habitat available for wildlife. For more information on what to plant and planting methods, visit the planting page.
Funding and technical guidance on wetlands
Some regional councils offer funding for the development of wetlands. We recommend you contact your regional council before you start work to find out what funding is available.
DairyNZ has been working with NIWA and a technical working group comprising representatives from regional and central government, the dairy sector and non-government organisations, to agree on a set of design principles and performance estimates for constructed wetlands, and develop a wetland design practitioner guide.
With support and input from DairyNZ, NIWA has also produced guidelines for constructed wetland treatment of pastoral farm run-off. The guidelines cover general aspects of sizing and siting a wetland, construction, plant selection, wetland effectiveness, and maintenance.
Based on these technical guidelines, DairyNZ will prepare practical resources to support landowners who wish to design and install constructed wetlands on their property.
Do constructed wetlands designed to remove nitrate lead to pollution swapping?
Microbial denitrification is the key process by which nitrogen is removed in well-established wetlands. In this process naturally occurring denitrifying bacteria and fungi typically found in wet soils and decomposing vegetation convert nitrate in water into harmless atmospheric nitrogen gas (N2) as part of their respiration process.
However, when this process is incomplete, nitrous oxide (N2O) – a potent greenhouse gas – can be produced. DairyNZ commissioned AgResearch to review the likelihood of nitrous oxide being produced from constructed wetlands and other denitrifying bioreactors and they concluded “The results of our review suggest that the potential for pollution swapping in wetlands and denitrifying bioreactors is unlikely”.
A farmer's perspective on managing wetlands
In the video below Waikato farmer John Hayward explains the benefits of managing wetlands and his passion for being both environmentally friendly and productive.
Articles
- Wetlands secret ingredient to future water quality (20 March 2018)
- Science shows riparian plantings are keeping streams clean (9 August 2017)