Browsing by Subject "GREENHOUSE-GAS FLUXES"

Sort by: Order: Results:

Now showing items 1-9 of 9
  • Heiskanen, Lauri; Tuovinen, Juha-Pekka; Räsänen, Aleksi; Virtanen, Tarmo; Juutinen, Sari; Lohila, Annalea; Penttilä, Timo; Linkosalmi, Maiju; Mikola, Juha; Laurila, Tuomas; Aurela, Mika (2021)
    The patterned microtopography of subarctic mires generates a variety of environmental conditions, and carbon dioxide (CO2) and methane (CH4) dynamics vary spatially among different plant community types (PCTs). We studied the CO2 and CH4 exchange between a subarctic fen and the atmosphere at Kaamanen in northern Finland based on flux chamber and eddy covariance measurements in 2017-2018. We observed strong spatial variation in carbon dynamics between the four main PCTs studied, which were largely controlled by water table level and differences in vegetation composition. The ecosystem respiration (ER) and gross primary productivity (GPP) increased gradually from the wettest PCT to the drier ones, and both ER and GPP were larger for all PCTs during the warmer and drier growing season 2018. We estimated that in 2017 the growing season CO2 balances of the PCTs ranged from -20 g C m(-2) (Trichophorum tussock PCT) to 64 g C m(-2) (string margin PCT), while in 2018 all PCTs were small CO2 sources (10-22 g C m(-2)). We observed small growing season CH4 emissions (<1 g C m -2 ) from the driest PCT, while the other three PCTs had significantly larger emissions (mean 7.9, range 5.6-10.1 g C m(-2)) during the two growing seasons. Compared to the annual CO2 balance (-8.5 +/- 4.0 g C m(-2)) of the fen in 2017, in 2018 the annual balance (-5.6 +/- 3.7 g C m(-2)) was affected by an earlier onset of photosynthesis in spring, which increased the CO2 sink, and a drought event during summer, which decreased the sink. The CH4 emissions were also affected by the drought. The annual CH4 balance of the fen was 7.3 +/- 0.2 g C m(-2) in 2017 and 6.2 +/- 0.1 g C m(-2) in 2018. Thus, the carbon balance of the fen was close to zero in both years. The PCTs that were adapted to drier conditions provided ecosystem-level resilience to carbon loss due to water level drawdown.
  • Tupek, B.; Minkkinen, K.; Pumpanen, J.; Vesala, T.; Nikinmaa, E. (2015)
  • Riutta, Terhi; Korrensalo, Aino; Laine, Anna M.; Laine, Jukka; Tuittila, Eeva-Stiina (2020)
    Vegetation and hydrology are important controlling factors in peatland methane dynamics. This study aimed at investigating the role of vegetation components, sedges, dwarf shrubs, and Sphagnum mosses, in methane fluxes of a boreal fen under natural and experimental water level draw-down conditions. We measured the fluxes during growing seasons 2001-2004 using the static chamber technique in a field experiment where the role of the ecosystem components was assessed via plant removal treatments. The first year was a calibration year after which the water level draw-down and vegetation removal treatments were applied. Under natural water level conditions, plant-mediated fluxes comprised 68%-78% of the mean growing season flux (1:73 +/- 0:17 gCH(4) m(-2) month 1 from June to September), of which Sphagnum mosses and sedges accounted for one-fourth and three-fourths, respectively. The presence of dwarf shrubs, on the other hand, had a slightly attenuating effect on the fluxes. In water level drawdown conditions, the mean flux was close to zero (0:03 +/- 0:03 gCH(4) m(-2) month(-1)) and the presence and absence of the plant groups had a negligible effect. In conclusion, water level acted as a switch; only in natural water level conditions did vegetation regulate the net fluxes. The results are relevant for assessing the response of fen peatland fluxes to changing climatic conditions, as water level drawdown and the consequent vegetation succession are the major projected impacts of climate change on northern peatlands.
  • Mathijssen, Paul J. H.; Kahkola, Noora; Tuovinen, Juha-Pekka; Lohila, Annalea; Minkkinen, Kari; Laurila, Tuomas; Väliranta, Minna (2017)
    Data on past peatland growth patterns, vegetation development, and carbon (C) dynamics during the various Holocene climate phases may help us to understand possible future climate-peatland feedback mechanisms. In this study, we analyzed and radiocarbon dated several peat cores from Kalevansuo, a drained bog in southern Finland. We investigated peatland succession and C dynamics throughout the Holocene. These data were used to reconstruct the long-term atmospheric radiative forcing, i.e., climate impact of the peatland since initiation. Kalevansuo peat records revealed a general development from fen to bog, typical for the southern boreal zone, but the timing of ombrotrophication varied in different parts of the peatland. Peat accumulation patterns and lateral expansion through paludification were influenced by fires and climate conditions. Long-term C accumulation rates were overall lower than the average values found from literature. We suggest the low accumulation rates are due to repeated burning of the peat surface. Drainage for forestry resulted in a nearly complete replacement of typical bog mosses by forest species within 40 years after drainage. The radiative forcing reconstruction suggested positive values ( warming) for the first similar to 7000 years following initiation. The change from positive to negative forcing was triggered by an expansion of bog vegetation cover and later by drainage. The strong relationship between peatland area and peat type with radiative forcing suggests a possible feedback for future changing climate, as high-latitude peatlands may experience prominent regime shifts, such as fen to bog transitions.
  • Marushchak, M. E.; Friborg, T.; Biasi, C.; Herbst, M.; Johansson, T.; Kiepe, I.; Liimatainen, M.; Lind, S. E.; Martikainen, P. J.; Virtanen, Tarmo; Soegaard, H.; Shurpali, N. J. (2016)
    Methane (CH4) fluxes were investigated in a subarctic Russian tundra site in a multi-approach study combining plot-scale data, ecosystem-scale eddy covariance (EC) measurements, and a fine-resolution land cover classification scheme for regional upscaling. The flux data as measured by the two independent techniques resulted in a seasonal (May-October 2008) cumulative CH4 emission of 2.4 (EC) and 3.7 gCH(4) m(-2) (manual chambers) for the source area representative of the footprint of the EC instruments. Upon upscaling for the entire study region of 98.6 km(2), the chamber measured flux data yielded a regional flux estimate of 6.7 gCH(4) m(-2) yr(-1). Our upscaling efforts accounted for the large spatial variability in the distribution of the various land cover types (LCTs) predominant at our study site. Wetlands with emissions ranging from 34 to 53 gCH(4) m(-2) yr(-1) were the most dominant CH4-emitting surfaces. Emissions from thermokarst lakes were an order of magnitude lower, while the rest of the landscape (mineral tundra) was a weak sink for atmospheric methane. Vascular plant cover was a key factor in explaining the spatial variability of CH4 emissions among wetland types, as indicated by the positive correlation of emissions with the leaf area index (LAI). As elucidated through a stable isotope analysis, the dominant CH4 release pathway from wetlands to the atmosphere was plant-mediated diffusion through aerenchyma, a process that discriminates against C-13-CH4. The CH4 released to the atmosphere was lighter than that in the surface porewater, and delta C-13 in the emitted CH4 correlated negatively with the vascular plant cover (LAI). The mean value of delta C-13 obtained here for the emitted CH4, 68.2 +/- 2.0 %, is within the range of values from other wetlands, thus reinforcing the use of inverse modelling tools to better constrain the CH4 budget. Based on the IPCC A1B emission scenario, a temperature increase of 6.1 degrees C relative to the present day has been predicted for the European Russian tundra by the end of the 21st Century. A regional warming of this magnitude will have profound effects on the permafrost distribution leading to considerable changes in the regional landscape with a potential for an increase in the areal extent of CH4-emitting wet surfaces.
  • Minkkinen, Kari; Ojanen, Paavo; Penttilä, Timo; Aurela, Mika; Laurila, Tuomas; Tuovinen, Juha-Pekka; Lohila, Annalea (2018)
    Drainage of peatlands is expected to turn these ecosystems into carbon sources to the atmosphere. We measured carbon dynamics of a drained forested peatland in southern Finland over 4 years, including one with severe drought during growing season. Net ecosystem exchange (NEE) of carbon dioxide (CO2) was measured with the eddy covariance method from a mast above the forest. Soil and forest floor CO2 and methane (CH4) fluxes were measured from the strips and from ditches with closed chambers. Biomass and litter production were sampled, and soil subsidence was measured by repeated levellings of the soil surface. The drained peatland ecosystem was a strong sink of carbon dioxide in all studied years. Soil CO2 balance was estimated by subtracting the carbon sink of the growing tree stand from NEE, and it showed that the soil itself was a carbon sink as well. A drought period in one summer significantly decreased the sink through decreased gross primary production. Drought also decreased ecosystem respiration. The site was a small sink for CH4, even when emissions from ditches were taken into account. Despite the continuous carbon sink, peat surface subsided slightly during the 10-year measurement period, which was probably mainly due to compaction of peat. It is concluded that even 50 years after drainage this peatland site acted as a soil C sink due to relatively small changes in the water table and in plant community structure compared to similar undrained sites, and the significantly increased tree stand growth and litter production. Although the site is currently a soil C sink, simulation studies with process models are needed to test whether such sites could remain C sinks when managed for forestry over several tree-stand rotations.
  • Laine, Merjo Piia Päivikki; Rütting, Tobias; Alakukku, Laura Elina; Palojärvi, Ansa; Strömmer, Rauni Hannele (2018)
    No-till is considered an agricultural practice beneficial for the environment as soil erosion is decreased compared to ploughed soils. For on overall evaluation of the benefits and disadvantages of this crop production method, understanding the soil nutrient cycle is also of importance. The study was designed to obtain information about gross soil nitrogen (N) process rates in boreal no-tilled and mouldboard ploughed spring barley (Hordeum vulgare L.) fields after autumn harvesting. In situ soil gross N transformation process rates were quantified for the 5 cm topsoil in 9 days' incubation experiment using N-15 pool dilution and tracing techniques and a numerical N-15 tracing model. Gross N mineralization into ammonium (NH4+) and NH4+ immobilization were the most important N transformation processes in the soils. The gross mineralization rate was 14% and NH4+ immobilization rate 64% higher in no-till than in ploughing. Regardless of the faster mineralization, the gross rate of NH4+ oxidation into nitrate (NO3-) in no-till was one order of magnitude lower compared the ploughing. The results indicate that the no-tilled soils have the potential to decrease the risk for NO3- leaching due to slower NH4+ oxidation.
  • Nemitz, Eiko; Mammarella, Ivan; Ibrom, Andreas; Aurela, Mika; Burba, George G.; Dengel, Sigrid; Gielen, Bert; Grelle, Achim; Heinesch, Bernard; Herbst, Mathias; Hörtnagl, Lukas; Klemedtsson, Leif; Lindroth, Anders; Lohila, Annalea; McDermitt, Dayle K.; Meier, Philip; Merbold, Lutz; Nelson, David; Nicolini, Giacomo; Nilsson, Mats B.; Peltola, Olli; Rinne, Janne; Zahniser, Mark (2018)
    Commercially available fast-response analysers for methane (CH4) and nitrous oxide (N2O) have recently become more sensitive, more robust and easier to operate. This has made their application for long-term flux measurements with the eddycovariance method more feasible. Unlike for carbon dioxide (CO2) and water vapour (H2O), there have so far been no guidelines on how to optimise and standardise the measurements. This paper reviews the state-of-the-art of the various steps of the measurements and discusses aspects such as instrument selection, setup and maintenance, data processing as well as the additional measurements needed to aid interpretation and gap-filling. It presents the methodological protocol for eddy covariance measurements of CH4 and N2O fluxes as agreed for the ecosystem station network of the pan-European Research Infrastructure Integrated Carbon Observation System and provides a first international standard that is suggested to be adopted more widely. Fluxes can be episodic and the processes controlling the fluxes are complex, preventing simple mechanistic gap-filling strategies. Fluxes are often near or below the detection limit, requiring additional care during data processing. The protocol sets out the best practice for these conditions to avoid biasing the results and long-term budgets. It summarises the current approach to gap-filling.
  • Laine, A.M.; Mäkiranta, P.; Laiho, R.; Mehtätalo, L.; Penttilä, T.; Korrensalo, A.; Minkkinen, K.; Fritze, H.; Tuittila, E-S (2019)
    Abstract Northern peatlands form a major soil carbon (C) stock. With climate change, peatland C mineralization is expected to increase, which in turn would accelerate climate change. A particularity of peatlands is the importance of soil aeration, which regulates peatland functioning and likely modulates the responses to warming climate. Our aim is to assess the impacts of warming on a southern boreal and a sub-arctic sedge fen carbon dioxide (CO2) exchange under two plausible water table regimes: wet and moderately dry. We focused this study on minerotrophic treeless sedge fens, as they are common peatland types at boreal and (sub)arctic areas, which are expected to face the highest rates of climate warming. In addition, fens are expected to respond to environmental changes faster than the nutrient poor bogs. Our study confirmed that CO2 exchange is more strongly affected by drying than warming. Experimental water level draw-down (WLD) significantly increased gross photosynthesis and ecosystem respiration. Warming alone had insignificant impacts on the CO2 exchange components, but when combined with WLD it further increased ecosystem respiration. In the southern fen, CO2 uptake decreased due to WLD, which was amplified by warming, while at northern fen it remained stable. As a conclusion, our results suggest that a very small difference in the WLD may be decisive, whether the C sink of a fen decreases, or whether the system is able to adapt within its regime and maintain its functions. Moreover, the water table has a role in determining how much the increased temperature impacts the CO2 exchange. This article is protected by copyright. All rights reserved.