Wetland Management

Posted on April 30, 2014

Wetlands offer an enormous amount of ecological and economic benefits if well-managed and protected. It just makes sense!

Wetlands are home to a wide range of plant species, aquatic creatures, and bird life. Many of these unique, natural habitats are located on agricultural land, making farmers the primary custodians.

Wetlands play a valuable role in filtering pollutants out of stormwater runoff and groundwater. They help to maintain healthy waterways, minimise nitrogen levels, and prevent algal blooms and nuisance weed growth.

Unfortunately though, a large number of New Zealand’s wetlands have been damaged or destroyed over the last century.

Ecological Benefits

Wetlands are effectively gigantic filtering sponges. They are sometimes described as the kidneys of the landscape as they slow the flow of water off land into waterways, and in times of flood, absorb water into the organic wetland soils. In summer, stored water is released slowly to maintain water flows, providing a more balanced habitat for stream life.

Wetland plants trap water borne sediment, cleaning up water before it enters rivers and streams. In the right conditions, bacteria living in damp wetland soils and on the roots of the plants, can convert up to 90% of the nitrogen from farm run off into nitrogen gas, which is then released into the atmosphere. This helps prevent algal blooms and nuisance weed growth in the waterways.

Managing wet areas, seeps and swamps on the farm:

  • Improves water quality by filtering sediment, faecal bacteria, nitrogen and phosphorus run off and by removing soluble nitrogen from run off and resurfacing groundwater. In some soils, managed wetlands are the most effective solution to reducing the amount of nitrogen reaching waterways.
  • Enhances biodiversity and provides habitat for eels, native fish, birds and insects.
  • Reduces stock losses from bogging and allows for better stock management.
  • Helps to reduce flood peaks and maintain summer water flows.

Managing wet areas, seeps and swamps at the headwaters of catchments, will have the most impact on water quality downstream. Management of wetlands is particularly important in areas where high nitrogen levels in groundwater have been identified as a problem or where downstream waterways are known to be particularly sensitive to excessive nitrogen levels.

Once nitrogen has found its way into groundwater, it can only be treated where the groundwater reappears at the surface (ie at springs, wetlands and seeps). Maintaining these wet areas and their grasses and rushes is essential to remove nitrogen from emerging groundwater. If there is plenty of organic matter and reasonable water retention time, most of the nitrogen will be removed by plant uptake.

Management of wetlands

For wet areas to remain effective as filters they:

  • Must remain wet for all or most of the year. Many wet areas on farms have already been drained. To improve water quality these areas must remain wet.
  • Must be fenced off from stock. Most sedges, rushes and flax are palatable to stock. These plants must be protected as they have an important role in slowing flow, filtering water, and providing a carbon source for the bacteria that remove nitrogen. Cattle pugging will also reduce the ability of wet areas to absorb water.
  • Require plantings. Native sedge grasses, raupo, rushes, and flax grow well in wetland areas. Manuka, Kanuka, Cabbage trees and Kahikatea grow well on the dryer margins of the wetland area.

Wetland areas can also be used to retain nitrogen loaded water run off from farm tracks and from other farm drainage systems.

In general, wetland areas offer limited feed value during the winter and spring so are better fenced off at least, during those months. Wetlands can establish well during the winter but they need to be fenced off from stock. If the wetland is difficult to fence with post and batten fencing, consider using permanent or even temporary electric fencing.

Economic Benefits

On a purely economic basis, the capital outlay of draining a wetland might appear cheaper than fencing it off and completing plantings. The downside is that a resource consent may be required, there is a risk that the drain won’t flow well while there may be a need for ongoing drainage maintenance.

The better option in the long-term would be to fence off and plant the wetland – saving time and money in drainage maintenance, and stock management and health. At the same time, the wetland will be preserved and enhanced, adding value to the property. Furthermore, some of New Zealand’s wetland species, such as Manuka, are proving to provide significant economic benefits, making planted wetlands a potential source of alternative income for the landowner.

Other economic benefits for fencing off wetlands include:

  • Reducing Liver Fluke infestation.
  • Not wasting fertilizer on wetland areas.
  • Reducing flood peaks and maintenance of summer water flows.

Sustainable Dairying Water Accord

The Sustainable Dairying Water Accord is putting in place certain measures to preserve wetlands. These measures include:

  • 100% exclusion of dairy cattle from wetlands identified as significant by 31 May 2014*
  • 100% exclusion of dairy cattle from additional wetlands within 3 years of them being identified as significant by a regional council.

* Wetlands that were identified by a regional council as being significant at or before 31 May 2012.

For further information please refer to: www.dairynz.co.nz/page/pageid/2145866853?resourceld=790