​Later this month Nelson City Council will begin trialling a biological method to treat the ongoing issues with weeds and algae that have, for many years, afflicted the Tahunanui Stormwater Detention Pond, also known as the Modellers Pond.

The trial will use Diatomix (a diatom fertilizer), in an effort to create a more stable environment in the stormwater detention pond, with the aim of reducing the filamentous algae and aquatic weeds.

The trial is being implemented with the support of the Modellers Pond Project Group, which includes representatives from Council, the Modellers Society and the Tahunanui Business Association.

Works and Infrastructure Committee Chair and Project Group member Cllr Stuart Walker says “This is an approach that has worked effectively in similar situations in Australia. Research indicates that it may provide a suitable solution and all members of the working party are enthusiastic about the trial.”

Sport and Recreation Committee Chair and Project Group Member, Cllr Tim Skinner says, “There could be real environmental benefits to this approach. For a start, we are using a biological control for a biological problem, rather than using chemicals to manage the water quality and consequentially, the ecosystem of the pond.”

The trial will last between 3 – 18 months depending on results. The pond water will be monitored throughout the trial and signage will be placed at the pond to advise the public if they should avoid water contact at any stage. 
How it works

Sometimes referred to as “nature’s best water cleaners”, diatoms are micro-organisms found in waterways that generate oxygen.

The trial involves the use of nano-silica mixture called Diatomix. Only diatoms feed on silicates, making this non-toxic product the perfect food source for these micro-organisms.

While diatoms are thriving on the nutrient boost from Diatomix, other less desirable forms of algae (filamentous etc.) are starved out.

Conducting the trial will determine if using Diatomix is suitable for the long-term stability and health of the stormwater detention pond.