[APWG] Gorse could be destroying the quality of the country's water and action must be taken now to rid the country of the noxious weed

[Marc Imlay]

Does this work in New Zealand relate to any of our weeds? Thanks.

 

Marc

 

 

Gorse a threat to water quality 

The Marlborough Express | Friday, 2 February 2007

Gorse could be destroying the quality of the country's water and action must
be taken now to rid the country of the noxious weed, says a senior scientist
involved in a Rotorua study on the weed. 

Dr Guna Magesan, a senior scientist with Ensis, the unincorporated joint
venture between Crown Research Institute Scion in Rotorua, and Australia's
CSIRO, said gorse could be having a greater effect on nitrate levels than
originally thought. 

Nitrate is one of the major nutrients that damages water quality. 

It stimulates algal and weed growth in lakes and rivers which can cause the
water to be unsafe for drinking and swimming and can make it an unsuitable
habitat for fish. 

Lakes are particularly sensitive to nitrate, making this research important
to the clean up of Rotorua lakes. 

"Nitrate is a huge issue and millions of dollars have been spent trying to
reduce it. 

"The main blame has always gone to farmers, but our findings indicate that
gorse may also contribute significantly," Dr Magesan said. 

"The government is currently doing nothing to control gorse growth. 

"Yet if funding isn't made available our waterways will only become more
degraded by out-of-control gorse." 

But the effect of gorse on Marlborough water is not known. 

Marlborough District Council rural services manager Alan Johnson said the
council could not really carry out water quality monitoring throughout the
district to determine nitrate problems. 

Gorse was prolific throughout the district, but nitrate levels were not seen
as a big problem. 

Marlborough was different from the Waikato, where runoff into lakes was not
flushed away as in rivers, Mr Johnson said. 

Currently in most of Marlborough gorse must be controlled within 10m of a
boundary if your neighbour is controlling it. 

Gorse was difficult to control and it would be impossible to legislate for
landowners to control all the gorse on their property. 

Mr Johnson said gorse was beneficial in that it was a nitrogen fixer and was
a good host species for some plants, so it had positive effects as well as
negative. 

He said he would watch the study with interest. 

Dr Magesan's study, which was funded by Environmental Bay of Plenty, is the
first to focus on the role gorse has on water quality and the results have
surprised even him. 

"We found that nitrate leaching from gorse was extremely high in some cases.


"For example, samples taken from a gorse area on a farm had nitrate levels
of 16 parts per million, compared with 1ppm for the control area on the same
land. 

"Our results indicate that gorse is a serious problem for our waters. 

"What makes that even worse is that gorse is a fast growing species and has
already taken over 900,000ha of the country," Dr Magesan said. 

Dr Magesan and his team are in the final year of the three year project, and
hope to expand the research to the rest of the country. 

He said it would be important to look out how soil type and climate impacted
nitrate leaching from gorse. 

"Gorse is prolific throughout New Zealand, so if our findings are replicated
in other areas then New Zealand has a major issue on its hands." 

Gorse was declared a noxious weed in New Zealand in 1900 and government
subsidies were given to farmers to eradicate the weed until 1984, but the
battle against the growth of the weed was never won. 

"Gorse is a hard weed to get rid of. 

"It is fast growing, can live for 46 years in New Zealand, and seeds can
remain in the soil for up to 30 years. 

"It would be a massive undertaking to rid the country of gorse, but if we
are serious about saving our water, it is something we might have to do." 

As well as extending the project to the rest of New Zealand, Dr Magesan said
that his team hoped to explore alternative methods for destroying gorse and
slowing down growth. 

 

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