Periodic Reporting for period 4 - FluxWIN (The role of non-growing season processes in the methane and nitrous oxide budgets in pristine northern ecosystems)
Reporting period: 2024-10-01 to 2025-03-31
The response of the terrestrial biosphere to climate change is still largely unknown and represents a key uncertainty in climate change predictions. High latitude regions, including Arctic and boreal ecosystems, constitute a key component of the earth system due to significant soil carbon stocks. High latitude regions are net sources of methane (CH4) and nitrous oxide (N2O), but flux estimates disagree and further uncertainty is added due to a rapidly changing environment. Climate change effects are particularly strong during the non-growing season, altering the timing of spring snowmelt, fall freeze-up, and increasing winter temperatures. The changes have significant implications for biogeochemical cycles and ecosystem function across high latitude regions.
Despite growing evidence of the importance of non-growing season greenhouse gas emissions, few measurements have been made in pristine Arctic and boreal ecosystems. Non-growing season CH4 emissions can account for 10-100% of annual CH4 flux, while next to nothing is known about emissions of N2O during this period. Process-based models miss non-growing season emissions of CH4, underestimating them by 67% and annual emissions by 25%. This project identified controls and magnitudes of non-growing season CH4 flux in a boreal bog and showed that seasonal shifts in the processes underlying CH4 flux, particularly CH4 oxidation and plant transport, resulted in different spatial CH4 emissions than observed during the growing season. Fall emissions of CO2 and CH4 accounted for more than 20% of annual fluxes and ended with the formation of the snowpack. Emissions resulted partly from limited temperature sensitivity of ecosystem respiration in Sphagnum mosses. Ultimately, these result provided novel insights into greenhouse gas budgets and transform our understanding of fundamental earth system dynamics.
Despite growing evidence of the importance of non-growing season greenhouse gas emissions, few measurements have been made in pristine Arctic and boreal ecosystems. Non-growing season CH4 emissions can account for 10-100% of annual CH4 flux, while next to nothing is known about emissions of N2O during this period. Process-based models miss non-growing season emissions of CH4, underestimating them by 67% and annual emissions by 25%. This project identified controls and magnitudes of non-growing season CH4 flux in a boreal bog and showed that seasonal shifts in the processes underlying CH4 flux, particularly CH4 oxidation and plant transport, resulted in different spatial CH4 emissions than observed during the growing season. Fall emissions of CO2 and CH4 accounted for more than 20% of annual fluxes and ended with the formation of the snowpack. Emissions resulted partly from limited temperature sensitivity of ecosystem respiration in Sphagnum mosses. Ultimately, these result provided novel insights into greenhouse gas budgets and transform our understanding of fundamental earth system dynamics.
In the FluxWIN project, we investigated the seasonal variability fluxes of CO2, CH4, and N2O at a boreal bog and adjacent upland site in Finland. We instrumented a new automated chamber measurement site in the boreal bog, transitional dry bog, and upland forest, with 12 chamberss to measure CO2, CH4, and N2O fluxes and key ancillary data. These measurements ran from 2021 through the end of the project in 2025, although there are data gaps due to instrument failures and other difficulties. Data processing and quality control of this high-frequency chamber and environmental data were completed; data are archived on Pangaea.de. In addition, we measured CH4 fluxes using manual chambers in 2021 and 2022 from vegetation removal experiments to determine seasonal differences in methane (CH4) production, oxidation and plant transport in a boreal bog and effect on net CH4 emissions. Stable isotopes of CO2 and CH4 were also measured using both manual and automated chambers to better understand the processes resulting in methane emissions and as a proof of concept.
Capturing the spatial variability in CH4 fluxes and relative differences in CH4 production, oxidation, and transport was also a significant area of work during the project. We measured CH4 and CO2 fluxes on multiple field campaigns and expeditions, including Alaska 2021, Western Alaska 2023, Western Alaska 2024, Finnish Lapland 2022, mainly using both manual chambers. These measurements showed the spatial variability in CH4 emissions at many wetland sites, including ones affected by permafrost thaw. We also assessed the potential CH4 production across many different soils, including ones sampled in the expeditions, our boreal bog site, and earlier samples from Siberia by developing the instrumentation and protocol for soil incubations during the FluxWIN project. We applied this technique to look at interactions between carbon and nitrogen, the temperature response of respiration in the Sphagnum mosses, and how these affected CO2 and CH4 production under aerobic and anaerobic conditions. We looked more broadly at spatial variability in CH4 production, in well- and poorly- drained soils in Siberia, floodplains, permafrost soils on the north slope of Alaska, and finally a permafrost peatland thaw chronosequence in Finnish Lapland. To better interpret these data, we also used advanced microbial techniques (metagenomic sequencing) and to analyze functional metabolic pathway potentials as well as methanogen and methanotoph abundance from qPCR analysis.
In addition to the scientific insights generated with the chamber work, this FluxWIN work also formed the basis for technological developments. We tested several novel CH4 sensors for application in wetland conditions, including their sensitivity to temperature, methane, and biogenic VOCs in synergetic activities with other EU and ERC projects. We developed a software tool for the processing and quality control of automated chamber data as well as gap-filling methodology and developed methodology to upscale our plot-level chamber measurements to the landscape scale using UAS-derived land cover classifications. Finally, using our developed expertise in chamber methods and measurements from Siikaneva, we conducted a survey of experts to assess researchers implementation of chamber methods and quantify the effects of researchers decisions during data processing on flux data. These showed strong variation among researchers that can contribute substantially to difficulties comparing CH4 flux values among different research groups.
Together, these achievements showed important insights into the seasonality of CH4 cycling in boreal wetland ecosystems. We also developed insights into landscape-scale controls on methane and CO2 cycling following permafrost thaw using experimental incubations, field measurements, and data synthesis and review.
Capturing the spatial variability in CH4 fluxes and relative differences in CH4 production, oxidation, and transport was also a significant area of work during the project. We measured CH4 and CO2 fluxes on multiple field campaigns and expeditions, including Alaska 2021, Western Alaska 2023, Western Alaska 2024, Finnish Lapland 2022, mainly using both manual chambers. These measurements showed the spatial variability in CH4 emissions at many wetland sites, including ones affected by permafrost thaw. We also assessed the potential CH4 production across many different soils, including ones sampled in the expeditions, our boreal bog site, and earlier samples from Siberia by developing the instrumentation and protocol for soil incubations during the FluxWIN project. We applied this technique to look at interactions between carbon and nitrogen, the temperature response of respiration in the Sphagnum mosses, and how these affected CO2 and CH4 production under aerobic and anaerobic conditions. We looked more broadly at spatial variability in CH4 production, in well- and poorly- drained soils in Siberia, floodplains, permafrost soils on the north slope of Alaska, and finally a permafrost peatland thaw chronosequence in Finnish Lapland. To better interpret these data, we also used advanced microbial techniques (metagenomic sequencing) and to analyze functional metabolic pathway potentials as well as methanogen and methanotoph abundance from qPCR analysis.
In addition to the scientific insights generated with the chamber work, this FluxWIN work also formed the basis for technological developments. We tested several novel CH4 sensors for application in wetland conditions, including their sensitivity to temperature, methane, and biogenic VOCs in synergetic activities with other EU and ERC projects. We developed a software tool for the processing and quality control of automated chamber data as well as gap-filling methodology and developed methodology to upscale our plot-level chamber measurements to the landscape scale using UAS-derived land cover classifications. Finally, using our developed expertise in chamber methods and measurements from Siikaneva, we conducted a survey of experts to assess researchers implementation of chamber methods and quantify the effects of researchers decisions during data processing on flux data. These showed strong variation among researchers that can contribute substantially to difficulties comparing CH4 flux values among different research groups.
Together, these achievements showed important insights into the seasonality of CH4 cycling in boreal wetland ecosystems. We also developed insights into landscape-scale controls on methane and CO2 cycling following permafrost thaw using experimental incubations, field measurements, and data synthesis and review.
This project pushed our understanding about the key controls of methane fluxes during the cold season at both the small scale to the very large scale. At the small scale, we developed new hypotheses about the key role of microtopography and plant transport in wetlands controlling the seasonal pattern of methane emissions, which were previously unknown. At the very large scale, we developed new hypotheses about the role of landscape scale features related to geomorphology and history in controlling CH4 fluxes. These are novel outcomes from the FluxWIN Project, and both results were unexpected. Secondly, the FluxWIN team pushed the chamber flux methodology to reach beyond the current state of the art through several key innovations. We did this by quantifying researcher bias in flux measurements, a critical step toward enabling reliable intercomparison across studies. We showed that this bias caused by researcher decisions can add 20-30% variability in fluxes to the same measurement dataset. Next, we successfully deployed a mobile, automated chamber system in a remote, off-grid location during the 2024 West Alaska expedition for 10 days demonstrating its feasibility in challenging field conditions. Third, in synergy with other projects, we conducted several proof-of-concept study and calibration of low-cost methane sensors in a real-field application, paving the way for more accessible and scalable greenhouse gas monitoring.