Wetlands and Nutrient Capture

In March 2010 we looked at a Hawke’s Bay Regional Council trial using floating wetlands to remove nutrients in a catchment in Central Hawke’s Bay. A year on we follow up on the results of the trial and look at the progress of other wetland initiatives in the region.

Floating wetlands are wetland plants growing in a buoyant mat on the surface of the water. The plant roots hang down beneath the floating wetland and provide a large surface area for the growth of beneficial micro-organisms (biofilm) that can enhance nitrogen removal.

Because the plants are floating, they are forced to take their nutrients from the water rather than from the sediments.

The floating wetlands are an innovative approach that makes use of the well-known water purifying effects of natural wetlands.

Despite high hopes this trial – on a small stream in the Tukipo catchment – it hasn’t worked out. This item will discuss the reasons – which include – too rapid a water flow for the roots and biofilm to absorb nitrogen.

Subsequent to this trial large scale floating wetlands have been introduced in the Bay of Plenty – on lakes – where they are proving to be highly effective.

The trial was on council owned land in the Tukipo catchment. The floating wetland had been constructed in Oct 2009 and when RD filmed, it had been in place in the Tukipo stream for 6 months.

The Tukipo has the poorest water quality in the Ruataniwha Plains, and its catchment is landlocked on the floodplain and therefore doesn’t benefit from flushes produced by storm events in the mountains. It is surrounded by intensive farming.

Measurements had showed that there were high loadings of dissolved nitrogen in the trial waterway.

A conventional wetland to strip out nutrients would have needed to be 15,000 square metres in size, and would have required significant earthworks and tree clearing.

The floating wetland required minimal earthworks in comparison and it was thought it might be cheaper to maintain.

The floating wetlands are designed to strip out 90% of the nitrogen and 15% of the phosphorus from the water in our trial, which is taking 12 months to collect all the data.

Instead of 15,000 square metres, the floating wetland was only 750 square metres in size.

The mat has Carex and rush plants plugged into it.

At the time the HBRC thought that floating wetlands had the potential, along with farming best practices, to be a significant contributor to cleaning up our water.

Stephen Cave says the mat is currently still in place but the carex has been trimmed back.

The HBRC has a Regional Landcare Scheme. It is designed to help Hawke’s Bay landowners and the community to develop more sustainable land use systems and to protect areas of biodiversity. Among RLS initiatives is support for wetland protection.

Prior to 2003 the HBRC regional council’s funding for wetlands was directed to ‘council owned’ wetlands such as Pekapeka Swamp and Lake Tutira…..

In July 2003 Council introduced a separate programme to assist individual farmers to protect wetlands on their properties based on the gains that could be made through protecting and enhancing wetlands on private property.

The councils decided that protecting threatened wetlands remnants and enhancement of areas with potentially high wetland habitat values is easier when they work alongside individual owners.

The idea was to promote sustainable land use initiatives and protect and enhance biodiversity.

Council approved an initial $50,000 to help facilitate ‘on farm wetland’ projects per year. The grants are capped at $5000 per property per year.

The funding can be used for :

• The establishment of retirement fencing

• Weed removal

• The provision and establishment of native plants

• Deepening and or the creation of open water habitat

• The provision of a compensatory alternative water supply

Applications are treated in order of receipt until each year’s grant allocation is expended,

The scheme does not apply to:

• Landscape or aesthetic enhancement

• Properties less than six hectares in size.

The on farm wetland initiative has proved very popular and fully subscribed. On the basis of this the allocation for on farm wetlands was increased to $75,000 two years later. ( Where does funding for that sit now ?)

Since the category was introduced, the regional land care scheme has funded 138 projects on no fewer than 110 properties. Projects have ranged from the creation of large ‘lake’ areas costing over $100,000 to small retirement and planting projects. When combined with landowner contributions, the total value of these projects exceeds $1.3 million.

What makes an ‘on farm’ wetland eligible?

The wetland must be on private or multiple owned property and it must contain native wetland plants.  It must display actual or potential ecological values for wildlife and it must have the potential to interact with and contribute to the biodiversity of an area.  No covenant is required.  The grant is not generally for an existing water supply dam. (NB. The decision whether to provide grant assistance by exception in such cases is to be based on an assessment of the “ecological values” of the dam at the time of grant application.)

Maximum grants for any one wetland will not exceed $5,000.   Only one wetland per farm is eligible for grant each year.   The grant rate is up to 50% of the cost of the restoration and protection works.   Currently the total grant available is $100,000 per year. This may change from year to year.  Wetlands are selected, based on their relative value, until the grant is used for that year.