Look North for a deeper picture of decomposition
FluxWIN The role of non-growing season processes in the methane and nitrous oxide budgets in pristine northern ecosystems
The soil in northern ecosystems may freeze in Winter, yet recent research shows that decompositional processes can still continue during the colder months. Researchers in the FluxWIN project are taking gas flux measurements throughout the year, aiming to gain deeper insights into the processes behind Winter emissions of greenhouse gases, as Dr Claire Treat explains. A lot of studies on the carbon cycle and greenhouse gas emissions have been conducted during the growing season in Summer when plants are active, yet less attention has been paid to the Winter months. Extrapolations to the cold season have been based on our understanding of these growing season processes, yet earth system models of carbon emissions tend to break down over the Winter months, for reasons that are not fully understood. “We don’t really understand why the models don’t work, whether it’s something to do with the physical soil properties for example, or representations of the soil dynamics,” says Dr Claire Treat, a researcher at the Alfred Wegener Institute in Germany. As the head of the ERC-funded FluxWIN project, Dr Treat is looking at greenhouse gas emissions both in the growing season and also outside it, reflecting a recent shift in perspective. “Over the past 15 years or so it’s been found that soil microbes can be active at colder temperatures than modellers - who parameterise soil decomposition processes had previously realised,” explains Dr Treat.
Greenhouse gas budgets The nature of soil thermodynamics means that the surface of the soil can freeze before the layer underneath, so decompositional processes can in fact continue into the Winter. This may then affect the greenhouse gas budget, a topic that Dr Treat and her colleagues in the project are investigating. “One of the questions we’re looking at is whether the freezing of
unaffected by human activity. “They haven’t been used for agriculture, and they haven’t been logged recently,” continues Dr Treat. “We plan to conduct several campaigns over the Winter and Spring, and take measurements over some longer periods over the course of a year. We’re very interested in the transition between Spring and Summer when plants are starting to come out.”
This high-frequency greenhouse gas analyser lets us measure pretty small fluxes of both methane and nitrous oxide. Our focus really is on carbon dioxide and methane, and also on this nitrous oxide component. the soil surface is enough to impede oxygen diffusion into the soil and make it anaerobic, and then turn a site that wouldn’t normally produce methane into a site where oxygen is sufficiently depleted that it does,” she outlines. Researchers are taking measurements at several ecosystems on the Siikenava II site in Finland, a location which has been relatively
This research involves using automated chambers to take the measurements throughout a whole year, without the need for a researcher to be physically present. Measurements are collected throughout the day at 6 hour intervals, providing researchers with a wealth of data. “These chambers are essentially like a gas sampling mechanism. They are highly portable,
The FluxWIN project investigates how greenhouse gas emissions and soil processes change throughout the year. In summer, warm soil temperatures and plant activity stimulate the production of methane (CH4) and net uptake of carbon dioxide (CO2). In the fall and spring, larger than expected emissions of CO2 and CH4 have been observed despite cooler soil temperatures and lack of plant activity. These periods are a focus of the project.
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EU Research
Project Objectives
The importance of non-growing season greenhouse gas fluxes to annual budgets in pristine northern terrestrial ecosystems is growing in awareness. Greenhouse gas (GHG) fluxes during the non-growing season and freeze-thaw dynamics are still underrepresented and may be a reason why current process-based models predict inadequate annual methane (CH4) and nitrous oxide (N2O) budgets. FluxWIN is therefore investigating ecological and biogeochemical processes in global carbon (C) and nitrogen (N) cycles during the non-growing and shoulder seasons by combining high-frequency greenhouse gas measurements, biogeochemical monitoring and process-based modeling.
Automated, robotic chambers capture greenhouse gas emissions throughout the year. Here they are measuring CO2, CH4, and N2O exchange from a dry bog site.
Project Funding and can be used to take measurements for quite a long time” says Dr Treat. The chambers are being used together with a high-frequency gas analyser which is far more sensitive than the traditional gas chromatograph, enabling Dr Treat and her colleagues to detect smaller fluxes than was previously possible. “This highfrequency greenhouse gas analyser lets us measure pretty small fluxes of both methane and nitrous oxide (N2O). Our focus really is on carbon dioxide (CO2) and methane, and also on this N2O component,” she continues. “We have some preliminary measurements which we’re currently analysing, and we’re also planning the second year of measurements.” The project also has an experimental component, with PhD students working on experiments both in the field and the laboratory. The aim here is to tease out the processes underlying methane emissions during the cold season, particularly relating to methane production and oxidation. “These are the two main processes that contribute to the methane flux. We’re planning to do a comparison next Summer with data from another site much further north, in Finnish Lapland, that has some permafrost,” explains Dr Treat. A model has been developed to explain these processes, which Dr Treat plans to test using data from several sites. “The idea is to make sure that this model will work at Siikenava II, then we intend to test it at some other sites and assess whether it includes the right mechanisms. We have data from some long-term monitoring sites, such as Svalberg, and the Samoylov island station in the Lena River Delta in Siberia,” she says. “The idea is to investigate whether these mechanisms are important for climate models and models of the carbon cycle.”
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Climate models This research holds wider relevance in terms of refining complex climate models and understanding how the climate is likely to evolve in future as more permafrost thaws at northerly latitudes. The project will make an important contribution in this respect, with the establishment of measurement infrastructure at Siikenava II set to provide more data. “This will allow us to test and develop new instrumentation to improve methane flux measurements in particular,” stresses Dr Treat. However, the more immediate goal in the project is to build a deeper understanding of what controls these Winter emissions. “Is it related to some of these physical processes happening in the soil? Is it to do with the freeze-thaw dynamics, like the formation of an ice layer, that maybe results in anaerobic soil? Or is it changes in soil moisture dynamics, or soil biogeochemistry?” says Dr Treat. “It would be very exciting to identify a new mechanism. We should be able to have a complete annual budget of greenhouse gas emissions for a range of boreal sites, which will be very valuable.” Researchers have a pretty good handle on the amount of greenhouse gases that are released during the Summer, but if emissions during Winter and the transition to the colder months turn out to be higher than previously thought then this would dramatically change the overall picture. “If emissions during Winter, Spring and the shoulder seasons contribute an additional 20 percent on top of the growing season budget, then the picture looks very different,” points out Dr Treat.
This project has received funding from the European Union’s Horizon 2020 research and innovation programme under the Grant Agreement No. 851181
Project Partners
• University of Helsinki • University of Eastern Finland
Contact Details
Project Coordinator, Claire Treat Alfred Wegener Institute Helmholtz Center for Polar and Marine Research Telegrafenberg A45 14473 Potsdam T: +49(331)58174 5412 E: claire.treat@awi.de W: https://www.awi.de/en/about-us/ organisation/staff/single-view/claire-treat.html
Dr Claire Treat
Dr Claire Treat is Junior Research Group Leader for Permafrost Region Greenhouse Gas Fluxes at the Alfred Wegener Institute. Her research focuses on the response of greenhouse gas fluxes to environmental changes resulting from various factors, such as climate warming and permafrost thaw.
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