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Source: NIWA – National Institute of Water and Atmospheric Research

The Filamentous Algae Nutrient Scrubbers (FANS) trials are testing the capability of native algae to filter contaminants such as nitrogen and phosphorus from farm runoff.

The project centres on gently sloping floways, or channels, which convey drainage water from the surrounding paddocks through dense stands of native algae.

The Oedogonium, Spirogyra, Rhyzoclonium and Cladophora algae used in the trials all come from nearby streams.

As the drainage water flows down the channel, the algae convert dissolved nitrogen and phosphorus into biomass which is harvested periodically.

The harvested algae can be used as natural fertiliser or animal fodder. Other uses are also being explored by the research team and iwi partners.

Water samples are taken at the channel inflow and outflow points every week to assess the nutrient concentrations before and after treatment.

NIWA Water Quality Scientist Dr Jason Park, who is leading the project, says monitoring indicates the FANS systems can produce more than 16 tonnes of algal biomass in four months.

This points to removal of about 370kg of nitrogen and 75kg of phosphorus from the waterway per hectare, per year.

“We expect the biomass production and nutrient removal will more than double in the upcoming summer.”

Data collected from the trials will help determine the level of nutrients FANS systems can remove over a range of conditions.