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Forestry-drained peatlands in the boreal region are currently undergoing restoration in order to bring these ecosystems closer to their natural (undrained) state. Drainage affects the methane (CH4) dynamics of a peatland, often changing sites from CH4 sources to sinks. Successful restoration of a peatland would include restoration of not only the surface vegetation and hydrology, but also the microbial populations and thus CH4 dynamics. As a pilot study, CH4 emissions were measured on two pristine, two drained and three restored boreal spruce swamps in southern Finland for one growing season. Restoration was successful in the sense that the water table level in the restored sites was significantly higher than in the drained sites, but it was also slightly higher than in the pristine sites. The restored sites were surprisingly large sources of CH4 (mean emissions of 52.84 mg CH4 m-2 d-1), contrasting with both the pristine (1.51 mg CH4 m-2 d-1) and the drained sites (2.09 mg CH4 m-2 d-1). More research is needed to assess whether the high CH4 emissions observed in this study are representative of restored spruce mires in general. [ABSTRACT FROM AUTHOR]

The problem of model complexity has been lively debated in environmental sciences as well as in the forest modelling community. Simple models are less input demanding and their calibration involves a lower number of parameters, but they might be suitable only at local scale. In this work we calibrated a simplified ecosystem process model (PRELES) to data from multiple sites and we tested if PRELES can be used at regional scale to estimate the carbon and water fluxes of Boreal conifer forests. We compared a multi-site (M-S) with site-specific (S-S) calibrations. Model calibrations and evaluations were carried out by the means of the Bayesian method; Bayesian calibration (BC) and Bayesian model comparison (BMC) were used to quantify the uncertainty in model parameters and model structure. To evaluate model performances BMC results were combined with more classical analysis of model-data mismatch (M-DM). Evapotranspiration (ET) and gross primary production (GPP) measurements collected in 10 sites of Finland and Sweden were used in the study. Calibration results showed that similar estimates were obtained for the parameters at which model outputs are most sensitive. No significant differences were encountered in the predictions of the multi-site and site-specific versions of PRELES with exception of a site with agricultural history (Alkkia). Although PRELES predicted GPP better than evapotranspiration, we concluded that the model can be reliably used at regional scale to simulate carbon and water fluxes of Boreal forests. Our analyses underlined also the importance of using long and carefully collected flux datasets in model calibration. In fact, even a single site can provide model calibrations that can be applied at a wider spatial scale, since it covers a wide range of variability in climatic conditions. [ABSTRACT FROM AUTHOR]

We built an automatic chamber system to measure greehouse gas (GHG) exchange in forested peatland ecosystems. We aimed to build a system robust enough which would work throughout the year and could measure through a changing snowpackin addition to producing annual GHG fluxes by integrating the measurements without the need of using models. The system worked rather well throughout the year, but it was not service free. Gap filling of data was still necessary. We observed problems in carbon dioxide (CO2) flux estimation during calm summer nights, when a CO2 concentration gradient from soil/moss system to atmosphere builds up. Chambers greatly overestimated the nighttime respiration. This was due to the disturbance caused by the chamber to the soil-moss CO2 gradient and consequent initial pulse of CO2 to the chamber headspace. We tested different flux calculation and measurement methods to solve this problem. The estimated flux was strongly dependent on (1) the type of the fit (linear and polynomial), (2) the starting point of the fit after closing the chamber, (3) the length of the fit, (4) the speed of the fan mixing the air inside the chamber, and (5) atmospheric turbulence (friction velocity, u*). The best fitting method (the most robust, least random variation) was linear fitting with the period of 120-240 s after chamber closure. Furthermore, the fan should be adjusted to spin at minimum speed to avoid the pulse-effect, but it should be kept on to ensure mixing. If nighttime problems cannot be solved, emissions can be estimated using daytime data from opaque chambers. [ABSTRACT FROM AUTHOR]

Nitrous oxide (N2O) fluxes were measured fortnightly to monthly with manual chambers in 2004-2008 and hourly with automatic chambers during the snow-free seasons of 2007 and 2008 in a sedge fen in northern Finland. The fluxes were generally low, varying from −45 to 37 µg N2O-N m−2 hour−1 (negative fluxes indicating uptake of N2O from the atmosphere into the soil) and showing large spatial and temporal variation. Slightly higher emissions were observed in winter than in summer. On an annual scale, the fen acted as a N2O source. The annual balances showed a clear decreasing trend from 1.1 kg N ha−1 year−1 (= 12.2 µg N m−2 hour−1) in 2004 to zero balances in 2007 and 2008. Two potential reasons for the decreasing mean flux were (i) a decreasing atmospheric N deposition during the snow-free season, and (ii) a rising water-table level (WTL), which restricts the availability of oxygen in the peat and therefore favours the formation of molecular nitrogen (N2) instead of N2O by the denitrifying microbes. The measurements conducted with the automatic chambers during the snow-free season showed a positive exponential relationship between the N2O flux and the temperature in 2008, but not in 2007. Similarly, a unimodal relationship with the WTL was found in 2008, with maximum fluxes observed when the WTL was about 4 cm above the fen surface. No diurnal variation in N2O fluxes measured by automatic chambers was found. The fluxes measured by the manual or automatic chambers were similar in magnitude, but different in their temporal pattern. The daily N2O concentration at a depth of 0.15 m in the peat was always lower than the ambient atmospheric concentration, indicating that at this depth the atmospheric N2O was consumed. Together with the observed negative flux rates this suggests that microbial N2 production is a significant part of the N cycle in this fen. [ABSTRACT FROM AUTHOR]

Fluxes of greenhouse gases (GHG) carbon dioxide (CO2), methane (CH4) and nitrous oxide (N2O) were measured during a two month campaign at a drained peatland forest in Finland by the eddy covariance (EC) technique (CO2 and N2O), and automatic and manual chambers (CO2, CH4 and N2O). In addition, GHG concentrations and soil parameters (mineral nitrogen, temperature, moisture content) in the peat profile were measured. The aim of the measurement campaign was to quantify the GHG fluxes before, during and after thawing of the peat soil, a time period with potentially high GHG fluxes, and to compare different flux measurement methods. The forest was a net CO2 sink during the two months and the fluxes of CO2 dominated the GHG exchange. The peat soil was a small sink of atmospheric CH4 but a small source of N2O. Both CH4 oxidation and N2O production took place in the top-soil whereas CH4 was produced in the deeper layers of the peat. During the thawing of the peat distinct peaks in CO2 and N2O emissions were observed. The CO2 peak followed tightly the increase in soil temperature, whereas the N2O peak occurred with an approx. one week delay after soil thawing. CH4 fluxes did not respond to the thawing of the peat soil. The CO2 and N2O emission peaks were not captured by the manual chambers and hence we conclude that automatic chamber measurements or EC are necessary to quantify fluxes during peak emission periods. Sub-canopy EC measurements and chamber-based fluxes of CO2 and N2O were comparable, although the fluxes of N2O measured by EC were close to the detection limit of the EC system. We conclude that if fluxes are high enough, i.e. greater than 5-10 μgNm-2 h-1, the EC method is a good alternative to measure N2O and CO2 fluxes at ecosystem scale, thereby minimizing problems with chamber enclosures and spatial representativeness of the measurements. [ABSTRACT FROM AUTHOR]

Methane (CH4) fluxes from drainage ditches and adjoining strips between the ditches were measured in fall 1995 at a drained mire in Finland. The fluxes were measured at different mire sites usingstatic chambers (diffusion and plant-mediated transport) and inverted funnels (ebullition). The emissions (chamber measurements) of CH4 from drainage ditch bottoms, ditch sides, and strips between ditches ranged from 0 to 595 mg.m- 2.d-1, from 0 to 78 mg.m- 2.d-1, and from -3 to 33 mg.m- 2.d-1, respectively, The ebullition of CH4 from ditches was rather small, ranging from 3 to 37 mg CH4.m-2.d- 1, which was less than 10% of the CH4 flux measured by the chambers. As the proportion of ditches of the total peatland area is rather small, the inclusion of methane fluxes from ditches would not considerably change the previous estimates of the effect of drainage on the greenhouse gas balance of Finnish peatlands. [ABSTRACT FROM AUTHOR]