Periodic Reporting for period 4 - FluxWIN (The role of non-growing season processes in the methane and nitrous oxide budgets in pristine northern ecosystems)
Periodo di rendicontazione: 2024-10-01 al 2025-03-31
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.
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.