Journal cover Journal topic
Biogeosciences An interactive open-access journal of the European Geosciences Union
Biogeosciences, 14, 1947-1967, 2017
https://doi.org/10.5194/bg-14-1947-2017
© Author(s) 2017. This work is distributed under
the Creative Commons Attribution 3.0 License.
Research article
10 Apr 2017
Methane exchange at the peatland forest floor – automatic chamber system exposes the dynamics of small fluxes
Mika Korkiakoski1, Juha-Pekka Tuovinen1, Mika Aurela1, Markku Koskinen2, Kari Minkkinen2, Paavo Ojanen3, Timo Penttilä3, Juuso Rainne1, Tuomas Laurila1, and Annalea Lohila1 1Finnish Meteorological Institute, Atmospheric Composition Research, P.O. Box 503, 00101 Helsinki, Finland
2University of Helsinki, Department of Forest Sciences, P.O. Box 27, 00014 University of Helsinki, Finland
3Natural Resources Institute Finland, Viikinkaari 4, 00790 Helsinki, Finland
Abstract. We measured methane (CH4) exchange rates with automatic chambers at the forest floor of a nutrient-rich drained peatland in 2011–2013. The fen, located in southern Finland, was drained for forestry in 1969 and the tree stand is now a mixture of Scots pine, Norway spruce, and pubescent birch. Our measurement system consisted of six transparent chambers and stainless steel frames, positioned on a number of different field and moss layer compositions. Gas concentrations were measured with an online cavity ring-down spectroscopy gas analyzer. Fluxes were calculated with both linear and exponential regression. The use of linear regression resulted in systematically smaller CH4 fluxes by 10–45 % as compared to exponential regression. However, the use of exponential regression with small fluxes ( <  2.5 µg CH4 m−2 h−1) typically resulted in anomalously large absolute fluxes and high hour-to-hour deviations. Therefore, we recommend that fluxes are initially calculated with linear regression to determine the threshold for low fluxes and that higher fluxes are then recalculated using exponential regression. The exponential flux was clearly affected by the length of the fitting period when this period was  <  190 s, but stabilized with longer periods. Thus, we also recommend the use of a fitting period of several minutes to stabilize the results and decrease the flux detection limit. There were clear seasonal dynamics in the CH4 flux: the forest floor acted as a CH4 sink particularly from early summer until the end of the year, while in late winter the flux was very small and fluctuated around zero. However, the magnitude of fluxes was relatively small throughout the year, ranging mainly from −130 to +100 µg CH4 m−2 h−1. CH4 emission peaks were observed occasionally, mostly in summer during heavy rainfall events. Diurnal variation, showing a lower CH4 uptake rate during the daytime, was observed in all of the chambers, mainly in the summer and late spring, particularly in dry conditions. It was attributed more to changes in wind speed than air or soil temperature, which suggest that physical rather than biological phenomena are responsible for the observed variation. The annual net CH4 exchange varied from −104 ± 30 to −505 ± 39 mg CH4 m−2 yr−1 among the six chambers, with an average of −219 mg CH4 m−2 yr−1 over the 2-year measurement period.

Citation: Korkiakoski, M., Tuovinen, J.-P., Aurela, M., Koskinen, M., Minkkinen, K., Ojanen, P., Penttilä, T., Rainne, J., Laurila, T., and Lohila, A.: Methane exchange at the peatland forest floor – automatic chamber system exposes the dynamics of small fluxes, Biogeosciences, 14, 1947-1967, https://doi.org/10.5194/bg-14-1947-2017, 2017.
Publications Copernicus
Download
Short summary
We measured methane exchange rates at the forest floor of a nutrient-rich drained peatland in southern Finland. The forest floor acted mainly as a small methane sink, but emission peaks were occasionally observed during spring and rainfall events. The strength of the sink correlated best with groundwater level and soil temperatures at 20 and 30 cm depths. Diurnal variations were also observed but they were caused by changes in ambient wind speed and not by biological processes.
We measured methane exchange rates at the forest floor of a nutrient-rich drained peatland in...
Share