Groundtruth has provided a crucial role in the construction of a wetland on Kaiwaiwai Dairy Farm. Data from the project shows the wetland is efficiently removing nitrogen from drainage water and improving water quality in Wairarapa Moana.

By working with landowners, Greater Wellington Regional Council and with the help of funding from the Ministry for the Environment’s ‘Fresh Start for Freshwater’ Clean-Up Fund, a number of nutrient loss mitigation strategies have been put in place on a number of farms in the Lake Wairarapa catchment. These have improved the quality of water entering Lake Wairarapa and enhanced biodiversity across farmland and the edge wetlands.

Wetland areas are extremely useful in restoring water quality. Contaminants such as nitrogen and phosphorus enter waterways through groundwater, surface runoff and direct application. Left unchecked these nutrients feed algal growth which degrades water quality. In a wetland, anaerobic bacteria in the sediment convert the nitrate-nitrogen in the water to nitrogen gas which is then released into the atmosphere. This is known as denitrification.

A wetland has been constructed adjacent to a remnant Kahikatea stand which is being restored. Earthworks have transformed a traditionally wet 0.75 ha of pasture to a wetland with about 0.5 ha of open water. The balance of the area is planted banks. The design is unique in that the area actually comprises of three separate wetlands providing a serpentine flow path of water down 6m wide bays. These bays run back and forth across the area to slow down water flow, maximise residence time and water treatment. The wetland is well vegetated to give good dispersion and even flow through the majority of wetland and minimise channelisation or dead-zones.

 Take a look, watch the video at –

Results – for detailed results on water quality changes through the wetland read more (PDF 372.62 KB).