The NIWA unit measures eddy co-variance – in this case the exchange of carbon dioxide between the atmosphere and pasture immediately upwind.
The science agency’s research at Lauder is part of a broader CarbonWatch NZ project, which includes researchers Landcare Research, Waikato University and GNS Science, looking at greenhouse gas exchange in forests, pasture and urban environments.
NIWA scientist Dr Sara Mikaloff-Fletcher said the Lauder tower will help answer key questions about the amount of carbon absorbed or emitted by pasture.
It is the first time NIWA has fixed a flux tower beside its other atmospheric monitoring units, some of which are fixed on towers up to 10 metres tall.
Once data is brought together with measurements across the country and models, NIWA hopes to reveal important insights on the balance between daytime photosynthesis and night-time respiration from the soil and plants.
Importantly for farmers, its set to be a research tool as agriculture soon faces reporting greenhouse emissions at farm scale.
NIWA, Landcare Research and Waikato University have previously collected a large amount of data at tests farms around the country.
Mikaloff-Fletcher said once data from Lauder is compared to other test sites it will be easier to understand how, where and why greenhouse gas emissions are absorbed or emitted in particular areas.
“We have all these individual sites that tell us something important locally.
“The idea is to bring them together and analyse them together across all of the people in New Zealand who are doing this work and to be able to use them to inform a national-level model of what’s going on.”
One of the most pressing inquiries is a comparison of carbon exchange on intensively-managed pasture, like an irrigated farm, with low-intensity pasture.
There is some evidence to suggest intensively-managed, irrigated pasture is a low-level source to the atmosphere.
“But there’s been at least one paper published in NZ that suggests it could be a sink.”
Mikaloff-Fletcher said the Lauder data will form part of research to give a clear picture of what pasture is doing in NZ’s carbon cycle and fill in some gaps about how different types of land-management practices, over large scale, can impact NZ’s net carbon loss.”
Farm boundaries are irrelevant to gas movements and biological processes so NIWA will now be able to use the flux tower, other on-site monitoring equipment and data to better understand the content and movement of well-mixed air over an area, say, as large as central Canterbury.
NIWA will establish a new atmospheric monitoring site in the area, which is dominated by irrigated farms, most of them dairy, arable or mixed livestock farms.
During some wind conditions the new greenhouse gas observation site will sample air flows from the sea that have moved across pasture, Mikaloff-Fletcher said.
“You have air that’s travelling all across a landscape before arriving at an observatory station. And now, instead of one paddock, you see quite a broad perspective. So, we’re also going to bring in these atmospheric measurements in places where you have a dominance of particular types of land use.”
Local wind is only one factor in atmospheric research. High resolution atmospheric models allow scientists to account for the movement of air for several days before arriving at the observing station.
Using NIWA weather models researchers released carbon dioxide particles from observing stations and those carbon dioxide particles basically ride the wind backward in time, to describe all the places that the air came from, to inform that measurement. It’s telling you where the wind’s been, basically, before it arrived at your station, over several days.”
Mikaloff-Fletcher said all types of atmospheric measurements will continue to be important for NIWA research, not least because eddy co-variance sites can be installed only on flat land.
The observations in the atmosphere need elevation so NIWA can measure well-mixed air that has moved across large areas of land. The heights of the towers varied, based on what land is available for a site and the natural height of the landscape.
“One of the quite cool things about the atmospheric measurements is that one of the big unanswered questions for NZ is what’s going on in the hill country.
“Our atmospheric greenhouse gas measurements can sample air coming from the hill country as well as flat lands.”
Atmospheric data from test sites around the country are filling in those knowledge gaps, she said.
