Periodic Reporting for period 2 - FluxWIN (The role of non-growing season processes in the methane and nitrous oxide budgets in pristine northern ecosystems)
Période du rapport: 2021-10-01 au 2023-03-31
The FluxWIN project addresses the measurement gap for winter, spring and fall CO2, CH4, and N2O measurements that was earlier noted for 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%. To develop new baseline measurements of the annual exchange for the three major greenhouse gases, the FluxWIN project installed a new automated flux chamber measurement system at a pristine bog and upland forest site in boreal Finland (see picture; https://www.awi.de/en/science/geosciences/permafrost-research/research-focus/permafrost-region-greenhouse-gases.html ) consisting of 12 chambers, 9 transparent and 3 opaque. We are measuring greenhouse gas fluxes and other key environmental data year-round since 2021. This comprehensively equipped field site offers great opportunities for testing new sensors and methods in a controlled and well-studied system with a reliable environmental reference baseline.
To understand what key biogeochemical processes differ between the growing season and the rest of the year, we are using complementary field measurements, laboratory experiments, data synthesis and process-based modelling. The field measurement results from our site in boreal Finland have shown that freeze-thaw dynamics in the spring and fall can affect the measured fluxes. The laboratory results and data synthesis have quantified rates of methane and CO2 production at low temperatures for not only the FluxWIN sites but also for permafrost sites in Siberia. This illustrates whether process rates in the permafrost ecosystems are similar to other ecosystems. This comparison to permafrost-affected ecosystems is of particular interest since permafrost regions are very remote and it is therefore difficult to maintain an automated chamber system for accurate annual GHG budgets. The process-based modelling approach allows us to extrapolate our measurements both over longer time periods (2011-2021) and over broader spatial scales. The overall impact is to shift the paradigm from “nothing happens outside of the growing season” to “capturing non-growing season processes is key to understanding ecosystem dynamics.” Ultimately, results will provide novel insights into greenhouse gas budgets and transform our understanding of fundamental earth system dynamics.
The FluxWIN project team has completed eight expeditions to Finland for site setup, measurement, and sample collection. All together, we have more than one full year of additional experimental-based measurements that will let us test for seasonal differences in the rates of CH4 production, oxidation, and transport. We conducted four laboratory experiments to test key process rates at low temperatures with samples from our main field sites as well as other permafrost sites across the pan-Arctic. These two project parts have provided significant training opportunities for students in both field and laboratory methods, resulting in 3 completed Masters Theses with several more in progress. We have also made progress on the modelling work package in order to test hypotheses of the processes controlling growing and non-growing season CH4 fluxes. We have the preliminary modelling results for the period 2011-2022 and are working on model calibration and evaluation using independent datasets from project collaborators. In addition, the FluxWIN project team work has resulted in 14 related peer-reviewed publications and 4 conference presentations related to polar regions biogeochemistry. Overall, progress is better than expected due to severe corona-related delays restricting project setup and travel to the field site that we encountered since the beginning of the project in 2020.