NZ’s new plan for clean water

Radar technology is to be employed in a $13.7 million New Zealand research project to determine how forests impact water flow and quality.

P-band radar, which the research team says was developed by the Jet Propulsion Lab at space agency NASA, will help them measure underground moisture levels in New Zealand forests.

It is part of a five-year Forest Flows programme headed by Scion, the Crown Research Institute, which aims to find out more about what happens to water in forests and the implications for downstream water quality and availability.

The programme will also look at what degree forests “trap” nitrate and prevent it from leaching into New Zealand’s rivers, streams and other waterways.

Part of the motivation is to create a model for future land management decisions as climate change leads to more periods of flooding and drought.

Programme leader Dean Meason says existing data is out of date: “There was a lot (forest hydrological research) in the 1960s and 1970s but we now have a population of around five million (compared to around three million then) while the area of land in commercial forestry was half of what it is now.

“Forests are increasingly seen as a competitor for water by downstream users,” he says. “This perception is likely to increase with the One Billion Trees Programme (through which the government is targeting the planting of one billion trees by 2028).

“But we hope to turn this thinking around and prove how strategically situated forests can improve water resources, reduce the impact of flooding and increase water flow during dry periods. This will ensure New Zealanders have a sustainable water supply and a reliable source of high-quality drinking water.”

Meason says the technology being used is “a game-changer”. The P-band radar, for example, will be operated from a plane, can measure moisture to a depth of 1.5m and “means we will be able to scan entire forests”.

His team will also use other airborne remote sensing technology - lidar and hyperspectral imagery - to create detailed forestry maps and ground-based wireless network technology to measure, among other factors, a tree’s water use and water-borne nitrate levels.

Research is expected to get under way by the middle of this year at selected sites on the West Coast of the South Island, Canterbury, Wairarapa, Northland and one other location yet to be determined. Most of the work will be carried out in radiata pine stands and other exotic and native species.

Meason says there have been many questions raised about whether forests are taking water away from other land uses; whether radiata pine (which makes up 89 per cent of New Zealand’s commercial forests) uses up 100 per cent of summer rainfall; whether it is better to plant natives; what locations are the most suitable for planting.

“Now we want a better understanding of how much rainfall is stored within a forest and to what degree it is released,” he says. “Our aim is to protect primary sector productivity at the same time as improving water quality and allowing for future urban and rural demands for water.

“It will determine whether some tree species and forest types are better at flood mitigation than others and identify planted forests with the potential to be passive water reservoir systems; we envisage new forests could be used as low-cost water storage alternatives to dams.”

Commercial forests cover 1.7m hectares in New Zealand while indigenous or native forests make up 6.3m hectares, according to Stats NZ figures.

Working with stakeholders including iwi, central and regional government, landowners and industry, the Forest Flows programme is a collaboration with a number of New Zealand and overseas organisations. In New Zealand they include NIWA (National Institute of Water and Atmospheric Research), XERRA (Earth Observation Institute), the University of Auckland and the University of Waikato.

International collaborators include Virginia Tech, the Universities of Massachusetts and Southern California and Remote Sensing Solutions (US), Whitegum Forest and Natural Resource (Australia), MVArc , a forestry research group based in Portugal  and ARAUCO, a wood and forestry company in Chile.

Associate Professor Kevin Maguire of Virginia Tech’s department of Forest Resources and Environmental Conservation says as climate change threatens more periods of flooding and drought, there is increasing attention on the ways that land management decisions impact water quality in the future.

“The issues we’re looking at in New Zealand are applicable anywhere,” he say. “What happens in forests and how water is used has huge implications for water quality and availability.”

Maguire - whose comments were included in a Virginia Tech press release earlier this month - says it is also important to understand how nitrogen is transported and how it reacts with the soil.

“Researchers will use isotopic ‘tracers’ in the water and in nitrogen to measure the movement of water and nutrients through a forest system. It’s a little like putting a flag or a tracker on a molecule of water or an atom of nitrogen and seeing where it goes.”