Xuefei Li, Maarit Raivonen, Tiia Grönholm, Timo Vesala
Boreal wetlands are one of the largest pools of organic carbon on Earth. At present, up to 30% of the Earth's organic carbon is thought to be contained in the Boreal peat deposits. This massive storage, however, seems to become more and more unstable as climate change gains pace.
Apart from accumulating carbon thanks to plant photosynthesis, natural wetlands affect the global greenhouse gas balance by emitting methane (CH4). They are the largest single CH4 source into the atmosphere. Processes leading to CH4 emissions from wetlands are generally known, but their relative contributions, trends and controls often remain obscure. With the prospects of drastic global changes becoming realistic, it is of capital importance to forecast the dynamics of peatland carbon storage and CH4 emissions in this context. We study peatland - atmosphere interactions with a range of measurements and modelling approaches, the key combination aimed at disentangling the complexity of those ecosystems.
Siikaneva fen & bog: Ensemble of ecosystem measurements
We approach different aspects of the peatland - atmosphere interactions at the biggest South Finnish natural mire of Siikaneva. Two measurement stations are operating currently in the fen (Figure 1) and bog (Figure 2) areas of the wetland; both have EC setups for measuring the turbulent fluxes of energy, CO2, H2O and CH4, and a set of meteorological and soil measurements. We closely interact with the University of Eastern Finland, who perform a range of ecological measurements, including e.g. vegetation sampling and monitoring and chamber measurements of the greenhouse gas fluxes. The Siikaneva stations' infrastructure is being constantly developed.
Rinne et al. (2007) quantified the total annual emission from the Siikaneva fen to be 12.6 g m-2. They also showed that, most of the year, the emissions are driven by the temperature of peat below the water table and that most of the emissions are produced during the snow-free period. Peltola et al. (2013) tested the performance of four methane gas analysers at the Siikaneva fen and recommend to use the RMT-200 fast response methane gas analyser (Los Gatos Research, USA). A comparison of the Siikaneva-2 eddy-covariance CO2 flux with the plant-scale photosynthesis can be found in Korrensalo et al. (2017).
Nummela: Greenhouse gas balance of a constructed urban wetland
Wetlands are constructed in the urban areas primarily as mitigation tools to reduce rapid changes in water balance and to improve water quality in local waterways. The Nummela Gateway -wetland is located within a 550 hectare stream watershed, in the catchment of Lake Enäjärvi in Vihti, Southern Finland. The vegetation and water quality within the wetland has been monitored since its establishment in 2010. In January 2013 an intensive measurement campaign was started to study the GHG balance using eddy covariance flux measurement of heat, CO2, H2O and CH4, and a set of meteorological measurements. A time series of CH4 flux is show in Figure 4.
See also the Urban Oases.
Mukhrino: First eddy-covariance measurements at a West Siberian middle taiga bog
West Siberia houses some of the vastest wetlands of the world, by scale comparable only with those of Canada. However, a large fraction of the Siberian wetland diversity remains unexplored due to remoteness of many areas and underdeveloped infrastructure. Measurements at the Mukhrino field station (60°54’ N, 68°42’ E, Figure 3) were initiated in 2015 jointly with the Yugra State University. The station equipment is similar to that in the Siikaneva stations. In the 2015-2016 growing seasons, the measurements of CO2 and energy fluxes were brought out. These results have been already published in Alekseychik et al. (2017). Net uptake of 196 gC m-2 over the May-August period was observed in 2015. Installation of a CH4 sensor is planned.
Modelling methane emissions from wetlands
Magnitude of the methane emissions depends on how much methane is produced in the anaerobic soil zone of a wetland, and how much of it gets destroyed by oxidizing microbes before it escapes into the atmosphere. There are several routes for the methane to move upwards: it can diffuse within the soil matrix, it can move through wetland plants that have their roots in the methane-rich soil water, and it can accumulate into bubbles that are released into the atmosphere when the conditions allow it (Figure 5). Via plants and possibly also ebullition, methane bypasses the oxidation.
We are working on a model of methane production, oxidation and transport in boreal peatlands called HIMMELI. A publication detailing the HIMMELI model structure and comparison against measurements has been recently published in GMD (Raivonen et al., 2017). The model parameters have been calibrated using Markov Chain Monte Carlo (MCMC) method (Susiluoto et al., 2018). In addition, HIMMELI has been used in ebullition modelling comparison study published in BG (Peltola et al., 2018).
The model will be included in the global biosphere model JSBACH that is part of the MPI Earth System Model. We also will utilize the model for analysing the methane fluxes observed at our own peatland sites.
Global Vegetation Modelling Group, Max Planck Institute for Meteorology (MPI), Hamburg
Department of Forest Sciences, UHEL
Finnish Meteorological Institute
Prof. Eeva-Stiina Tuittila, Aino Korrensalo, University of Eastern Finland
Dr. Ilkka Korpela, Department of Forest sciences, UHEL
Dr. Janne Rinne, Department of Physics, UHEL
Prof. Elena Lapshina, Yugra State University
Figure 1: General view of the Siikaneva-1 fen site. Photo by Pavel Alekseychik.
Figure 2: General view of the Siikaneva-2 bog site. Photo by Pavel Alekseychik.
Figure 3. General view of the Mukhrino Field Station. The EC tower and one of the meteorological stations can be seen on extreme right. Photo by Nina Filippova.
Korrensalo, A., Alekseychik, P., Hájek, T., Rinne, J., Vesala, T., Mehtätalo, L., Mammarella, I. and Tuittila E.-S. (2017) Species-specific temporal variation in photosynthesis as a moderator of peatland carbon sequestration. Biogeosciences 14:257-269.
Peltola O, Mammarella I, Haapanala S, Burba G, Vesala T (2013) Field intercomparison of four methane gas analyzers suitable for eddy covariance flux measurements. Biogeosciences 10:3749-3765.
Aurela M, Lohila A, Tuovinen J, Hatakka J, Riutta T, Laurila T (2009) Carbon dioxide exchange on a northern boreal fen. Boreal Environ.Res. 14:699-710.
Rinne J, Riutta T, Pihlatie M, Aurela M, Haapanala S, Tuovinen J, Tuittila E, Vesala T (2007) Annual cycle of methane emission from a boreal fen measured by the eddy covariance technique. Tellus Ser.B-Chem.Phys.Meteorol. 59:449-457. 10.1111/j.1600-0889.2007.00261.x
Haapanala S, Rinne J, Pystynen K, Hellen H, Hakola H, Riutta T (2006) Measurements of hydrocarbon emissions from a boreal fen using the REA technique. Biogeosciences 3:103-112.