Wetlands, even if cover a relatively small fraction of Earth’s surface, play an important role in global carbon cycle. They are the main terrestrial source of methane (CH4), but due to anaerobic conditions they accumulate significant part of captured in photosynthesis carbon dioxide (CO2). Due to the progressive climate change these ecosystems are exposed to different climate-inducted extreme events. One of them are fires that can significantly affect the carbon-storage potential of the wetlands.
In this study we analyze the impact of a great fire on one of the largest mid-European wetlands in Biebrza Valley (northeastern Poland) on the CO2 net ecosystem exchange (NEE). Over 5,500 ha of landscape of the Biebrza National Park burned down during this event in April 20-25, 2020. In the north-east edge of the core of this fire, there was an eddy-covariance measurement site, where greenhouse gas fluxes (CO2, CH4, H2O) had been continuously recorded since 2013. The measurement system suffered to some extent, but flux measurements were resumed after repair works in approximately 2 weeks. Almost the entire source area of eddy-covariance system was affected by the fire. Thus, post-fire measurements show the dynamics of NEE for an ecosystem recovering from a fire.
In the flux measurements period (2013-2020) the studied ecosystem was affected not only by the above fire event but also by severe droughts in 2015 and 2018-2020. In consequence in non-fire years the annual totals of CO2 flux followed the mean ground water table level (WTL) and spanned from -990 gCO2∙m-2∙yr-1 (CO2 sink) in the wettest year to +1020 gCO2∙m-2∙yr-1 (CO2 source) in the driest year 2019. However, even taking into account the influence of WTL and temperature fluctuation we observed clear impact of the spring fire on CO2 exchange. Shortly after the fire, in May, the wetland was in average a source of CO2 (positive monthly total of NEE), which had not happened before even in the driest years. However, already in the second half of May, the absorption of CO2 began to predominate over the emissions. From the mid-June to the end of July we observed very intensive growth of plant cover and exceptionally strong absorption of CO2, much higher than in other years with similar thermo-hydrological conditions. Consequently, the total CO2 flux in the post-fire period (May-December) was negative, while in remaining dry years the strong emission of CO2 was observed for the same part of year.
Acknowledgements: Funding for this research was provided by the National Science Centre, Poland under project UMO-2020/37/B/ST10/01219. The authors thank the authorities of the Biebrza National Park for allowing the continuous measurements in the area of the Park.
How to cite: Fortuniak, K., Pawlak, W., and Siedlecki, M.: Dynamics of net CO2 exchange in the wetland ecosystem recovering from a fire , EMS Annual Meeting 2021, online, 6–10 Sep 2021, EMS2021-115, https://doi.org/10.5194/ems2021-115, 2021.