B065-0005
Continuous High-Frequent Measurements of CO2, CH4 and N2O Fluxes in a Riparian Deciduous Forest:The Role of Hot Moments in 2.5 Year Period

Friday, 11 December 2020
Poster
Ulo Mander1, Alisa Krasnova2, Thomas Schindler2, Jordi Escuer-Gatius3, Mikk Espenberg2, Katerina Machacova4, Jaan Pärn2, Kuno Kasak2, Ulo Niinemets3 and Kaido Soosaar2, (1)University of Tartu, Institute of Ecology & Earth Sciences, Department of Geography, Tartu, Estonia, (2)University of Tartu, Department of Geography, Tartu, Estonia, (3)Estonian University of Life Sciences, Institute of Agriculture and Environmental Sciences, Tartu, Estonia, (4)Global Change Research Institute CAS, Department of Ecosystem Trace Gas Exchange, Brno, Czech Republic
Abstract:
The carbon and nitrogen budgets of temperate riparian forests are sensitive to interannual climatic variability. In turn, riparian forests are hot spots of greenhouse gas (GHG) fluxes in landscapes. Here we analyse data from the first long-term (Sept. 2017-Dec. 2019) continuous high-frequent study of soil emissions (automated chambers) and ecosystem (eddy-covariance, EC) fluxes of CO2, CH4 and N2O in a 40-year old riparian grey alder forest in Estonia. It is supported by a 1.5-year study of CH4 and N2O fluxes from tree stems (manual chambers).

Based on EC data, the forest is a sequester of CO2 (-5.6 kg C ha-1 y-1) and CH4 (-0.35 kg C ha-1 y-1) and emitter of N2O (0.3 kg N2O-N ha-1 y-1). Hot moments (Wet: Sept.-Nov. 2017, Dry with Drought Onset: May–July 2018, Freeze–Thaw: Feb. 2019, and Dry Minor: June 2019) play an important role in GHG fluxes. For ecosystem level fluxes of all three gases no hot moments were observed however, unlike several forests in the area, during the severe heat wave in summer 2018, the riparian forest continued sequester CO2. The Wet period was remarkable due to high CH4 emissions from stems – almost 100% of ecosystem (EC) level CH4 came from stems. Small N2O emission from stems was found in the Wet period. In contrast, soil N2O flux was mainly depending on hot moments: about 60% of all emissions came from these periods. Especially, during Drought Onset when soil water content (SWC) rapidly decreased, average flux reached >150 μg N2O-N m-2 h-1. In this period, we observed a very clear optimum related to SWC – N2O emission peaked at 50% SWC. During the Freeze–Thaw period, another hot moment of N2O, clear correlation was found with near-surface air temperature. Likewise, CH4 emission from stems in the Wet period showed an optimum at 75% SWC. Surprisingly, total N2O emission from the soil was about 5 times higher than that measured at the ecosystem level. For CH4 the EC level flux was coherent with the sum of soil and stem fluxes.

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