4 April, 2006
Broom project aims to shed more light on dirty lakes
Research is underway in the Taupo region to investigate the impact that nitrogen from sources other than fertilisers and
animals, such as leguminous weeds, may be having on our waterways.
A long-term project is being undertaken by researchers from Ensis, the joint forces of Crown Research Institute Scion,
based in Rotorua, and Australia's CSIRO.
Ensis Environment Science Leader for Waste Management, Dr Guna Magesan says it is the first time this issue has been
researched by Ensis.
"Everyone is aware of the negative impact that farming and animal run-off is having on some waterways, however little
research has been undertaken to investigate the nitrogen contribution from leguminous weeds such as broom," says Mr
Magesan.
"It is well known that broom fixes nitrogen. But at this stage we are not sure how much nitrogen can be accumulated in
plants and how much it releases through litter fall and decomposition," he says.
In order to find what is happening under field conditions, experiments will be undertaken by Tim McLay, the head of
science at Reporoa College. Mr McLay was recently awarded a Teacher Fellowship by the Royal Society of New Zealand to
spend 12 months at Ensis.
The research will be undertaken at a number of sites in the Lake Taupo region. Some smaller projects will also be
developed for science students at Reporoa College.
The initial research involves digging a one metre deep pit at each field site and analysing the soil profile to
determine drainage.
"We will insert a number of suction cup samplers to collect soil water samples at one metre depths.
"We need to determine how quickly the nitrogen is moving. If it progresses slowly then the plant roots will stop most of
it getting into the soil water; however if it moves quickly, that means that larger quantities will be reaching the
waterways," says Mr McLay.
"We will concentrate initially on nitrate movement, the mobile form of nitrogen that passes through soil, as it is
important to learn how much leaching occurs. In addition, we don't know whether the nitrate is making its way to the
waterways and if so, what the quantity of nitrate might be."
Dr Magesan says it is important that as much as possible is learned about the pathways that lead to nitrogen and
phosphorus entering the lake.
"Leaching and surface runoff of nutrients from pastoral agriculture forms a large part of the nutrient load on Lake
Taupo. The research will help us understand the impact of broom near our lakes and streams, so we can plan around it,"
he says.
Mr Magesan says he is confident the research will shed more light on ways of reducing nitrate leaching.
ENDS