Cleaner ponds, with the help of a floating garden
By Esther Goh,
A murky pond beside Auckland's busy Northern Motorway is at the centre of an environmental trial to produce cleaner water with the help of a garden growing on a floating island.
Photo: NZTA
The pond, located near Silverdale, 40 kilometres north of Auckland, is being used to catch stormwater runoff from nearby State Highway 1.
It is now
home to what is known environmentally as a floating vegetated island
(FVI) – a hydroponic mat-like platform that allows plants to grow on its
surface while their roots dangle into the water for nourishment.
The initiative is being spearheaded by the NZTA's
Auckland Motorway Alliance.
Plants growing on the floating wetland have been selected for their extensive mass of roots,
an important factor in filtering polluted water. Their diet
includes contaminants found typically in a motorway environment, according to the AMA's stormwater asset manager, Peter
Mitchell – oils,
zinc, chromium and copper, the residue of tyres, brake linings and fuel
flushed into the pond when it rains.
"It doesn't sound the tastiest of diets, but the plants on the FVI are
flourishing," Mitchell said. "How well they adapt to the 'diet' will
help us discover if there is a way to improve on the work we're already
doing to clean up water in the ponds."
The Auckland Motorway Alliance was established by the NZTA four years
ago to maintain and operate 220 kilometres of motorway – a role that
also includes environmental accountabilities. It is responsible for the
highest concentration of stormwater ponds in New Zealand.
Steve Mutton, the NZTA's acting state highway manager for Auckland and Northland, said the trial fits with a key NZTA objective to make better use of the country's existing transport system.
"In the next few
years, there will be more than 100 stormwater treatment ponds besides
Auckland's motorways. If the result of this trial is positive, we could
retrofit other stormwater ponds to help improve the city's landscape and
reduce the environmental impact of transport," Mutton sad.
The stormwater pond at Silverdale has been split in two –
environmentalists describe it as bifurcation – for the trial. On one
side lies the FVI and on the other, the
stormwater remains untreated. The split allows environmentalists to see
how effectively the floating island helps improve water compared to the
standard stormwater pond.
Auckland University's Dr Elizabeth Fassman said the two-year trial
should provide scientific clues leading to long-term environmental
benefits.
Comments
Daph
good to know that the government cares for our environment and find ways to help improve it.
Maurice Kiely, Chow:hill
It's similar to schemes I have seen in the US in the treatment of 'black waste' from buildings - what's of interest is the life-span of the plant material and ultimate means of 'disposal' of plant material after uptake of contaminants ie is the intention the material then goes to a specialist landfill?
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