Large contribution of boreal upland forest soils to a catchment‐scale CH<sub>4</sub> balance in a wet year

Lohila, Annalea; Aalto, Tuula; Aurela, Mika; Hatakka, Juha; Tuovinen, Juha‐Pekka; Kilkki, Juho; Penttilä, Timo; Vuorenmaa, Jussi; Hänninen, Pekka; Sutinen, Raimo; Viisanen, Y.; Laurila, Tuomas

doi:10.1002/2016gl067718

Cited by 54 publications

(57 citation statements)

References 35 publications

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“…However, the emission peaks at Lettosuo were relatively small when compared to upland mineral soil forest sites, where emissions of up to 3.7 mg CH 4 m −2 h −1 have been observed in wet conditions (e.g., Savage et al, 1997;Lohila et al, 2016). Similarly, the maximum hourly uptake in summer at Lettosuo was rather similar to the fluxes reported for the above-mentioned upland forests (from −50 to −120 µg CH 4 m −2 h −1 at Lettosuo vs. −40 to −80 µg CH 4 m −2 h −1 at upland forests).…”

Section: Emission Peakssupporting

confidence: 71%

“…The average annual uptake in boreal upland forests typically varies from about 100 to 500 mg CH 4 m −2 yr −1 Dutaur and Verchot, 2007;Lohila et al, 2016), but also annual net emissions from upland forests have been reported (e.g., Sundqvist et al, 2015;Lohila et al, 2016). Thus, the net annual CH 4 exchange measured at Lettosuo (excluding the ditches) was well within the typical range of the average CH 4 sinks reported for boreal upland forests.…”

Section: Ch 4 Exchange Dynamics In a Peatland Forest 421 Annual Balmentioning

confidence: 99%

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Methane exchange at the peatland forest floor – automatic chamber system exposes the dynamics of small fluxes

et al. 2017

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Abstract. We measured methane (CH 4 ) 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 CH 4 fluxes by 10-45 % as compared to exponential regression. However, the use of exponential regression with small fluxes (< 2.5 µg CH 4 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 CH 4 flux: the forest floor acted as a CH 4 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 CH 4 m −2 h −1 . CH 4 emission peaks were observed occasionally, mostly in summer during heavy rainfall events. Diurnal variation, showing a lower CH 4 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 CH 4 exchange varied from −104 ± 30 to −505 ± 39 mg CH 4 m −2 yr −1 among the six chambers, with an average of −219 mg CH 4 m −2 yr −1 over the 2-year measurement period.

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Section: Emission Peakssupporting

confidence: 71%

Section: Ch 4 Exchange Dynamics In a Peatland Forest 421 Annual Balmentioning

confidence: 99%

Methane exchange at the peatland forest floor – automatic chamber system exposes the dynamics of small fluxes

et al. 2017

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“…The methane consumption rate was also dependent on the available soil water, soil temperature and nutrient availability. Although not addressed in that model, it should be noted that if the soil water content increases enough to inhibit the diffusion of oxygen, the soil could become a methane source (Lohila et al, 2016). This transition can be rapid, thus creating areas that can be either a source or a sink of methane depending on the season.…”

Section: Soil Uptakementioning

confidence: 99%

The global methane budget 2000–2012

Saunois

Bousquet

Poulter

et al. 2016

Earth Syst. Sci. Data

948

733

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Abstract. The global methane (CH 4 ) budget is becoming an increasingly important component for managing realistic pathways to mitigate climate change. This relevance, due to a shorter atmospheric lifetime and a stronger warming potential than carbon dioxide, is challenged by the still unexplained changes of atmospheric CH 4 over the past decade. Emissions and concentrations of CH 4 are continuing to increase, making CH 4 the second most important human-induced greenhouse gas after carbon dioxide. Two major difficulties in reducing uncertainties come from the large variety of diffusive CH 4 sources that overlap geographically, and from the destruction of CH 4 by the very short-lived hydroxyl radical (OH). To address these difficulties, we have established a consortium of multi-disciplinary scientists under the umbrella of the Global Carbon Project to synthesize and stimulate research on the methane cycle, and producing regular (∼ biennial) updates of the global methane budget. This consortium includes atmospheric physicists and chemists, biogeochemists of surface and marine emissions, and socio-economists who study anthropogenic emissions. Following Kirschke et al. (2013), we propose here the first version of a living review paper that integrates results of top-down studies (exploiting atmospheric observations within an atmospheric inverse-modelling framework) and bottom-up models, inventories and data-driven approaches (including process-based models for estimating land surface emissions and atmospheric chemistry, and inventories for anthropogenic emissions, data-driven extrapolations). . Top-down inversions consistently infer lower emissions in China (∼ 58 Tg CH 4 yr −1 , range 51-72, −14 %) and higher emissions in Africa (86 Tg CH 4 yr −1 , range 73-108, +19 %) than bottom-up values used as prior estimates. Overall, uncertainties for anthropogenic emissions appear smaller than those from natural sources, and the uncertainties on source categories appear larger for top-down inversions than for bottom-up inventories and models.The most important source of uncertainty on the methane budget is attributable to emissions from wetland and other inland waters. We show that the wetland extent could contribute 30-40 % on the estimated range for wetland emissions. Other priorities for improving the methane budget include the following: (i) the development of process-based models for inland-water emissions, (ii) the intensification of methane observations at local scale (flux measurements) to constrain bottom-up land surface models, and at regional scale (surface networks and satellites) to constrain top-down inversions, (iii) improvements in the estimation of atmospheric loss by OH, and (iv) improvements of the transport models integrated in top-down inversions.

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“…The Webb-Pearman-Leuning (WPL) correction (Webb et al, 1980) was applied when applicable (Laurila et al, 2005). More details of the measurement systems and data post-processing are given in previous studies (Aurela et al, 2009;Laurila et al, 2005;Lohila et al, 2016;Peltola et al, 2013;Rinne et al, 2007). For this study, the half-hourly averages were further averaged to daily fluxes to match the time resolution of the model.…”

Section: Field Measurementsmentioning

confidence: 99%

Importance of vegetation classes in modeling CH4 emissions from boreal and subarctic wetlands in Finland

Raivonen

Alekseychik

et al. 2016

Science of The Total Environment

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• CH 4 emission from Finnish wetlands was simulated by CH4MOD wetland .• We recalibrated the vegetation parameters of graminoids, shrubs and Sphagnum.• Simulated CH 4 variations agreed well with the eddy-covariance observations. • Annual CH 4 emissions were reasonably simulated in different years and sites.• Parameterization of different vegetation process was essential in long-term CH 4 estimates. Boreal/arctic wetlands are dominated by diverse plant species, which vary in their contribution to CH 4 production, oxidation and transport processes. Earlier studies have often lumped the processes all together, which may induce large uncertainties into the results. We present a novel model, which includes three vegetation classes and can be used to simulate CH 4 emissions from boreal and arctic treeless wetlands. The model is based on an earlier biogeophysical model, CH4MOD wetland . We grouped the vegetation as graminoids, shrubs and Sphagnum and recalibrated the vegetation parameters according to their different CH 4 production, oxidation and transport capacities. Then, we used eddy-covariance-based CH 4 flux observations from a boreal (Siikaneva) and a subarctic fen , which was consistent with the observations (7-22 g m −2 yr −1 G R A P H I C A L A B S T R A C T a b s t r a c t a r t i c l e i n f o). However, there are some discrepancies between the simulated and observed daily CH 4 fluxes for the Siikaneva site (RMSE = 50.0%) and the Lompolojänkkä site (RMSE = 47.9%). Model sensitivity analysis showed that increasing the proportion of the graminoids would significantly increase the CH 4 emission levels. Our study demonstrated that the parameterization of the different vegetation processes was important in estimating long-term wetland CH 4 emissions.

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Large contribution of boreal upland forest soils to a catchment‐scale CH₄ balance in a wet year

Cited by 54 publications

References 35 publications

Methane exchange at the peatland forest floor – automatic chamber system exposes the dynamics of small fluxes

Methane exchange at the peatland forest floor – automatic chamber system exposes the dynamics of small fluxes

The global methane budget 2000–2012

Importance of vegetation classes in modeling CH4 emissions from boreal and subarctic wetlands in Finland

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Large contribution of boreal upland forest soils to a catchment‐scale CH4 balance in a wet year

Cited by 54 publications

References 35 publications

Methane exchange at the peatland forest floor – automatic chamber system exposes the dynamics of small fluxes

Methane exchange at the peatland forest floor – automatic chamber system exposes the dynamics of small fluxes

The global methane budget 2000–2012

Importance of vegetation classes in modeling CH4 emissions from boreal and subarctic wetlands in Finland

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Product

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Large contribution of boreal upland forest soils to a catchment‐scale CH₄ balance in a wet year