Bo H. Svensson

Thawing sub‐arctic permafrost: Effects on vegetation and methane emissions

Ecosystems along the 0degreesC mean annual isotherm are arguably among the most sensitive to changing climate and mires in these regions emit significant amounts of the important greenhouse gas methane (CH4) to the atmosphere. These CH4 emissions are intimately related to temperature and hydrology, and alterations in permafrost coverage, which affect both of those, could have dramatic impacts on the emissions. Using a variety of data and information sources from the same region in subarctic Sweden we show that mire ecosystems are subject to dramatic recent changes in the distribution of permafrost and vegetation. These changes are most likely caused by a warming, which has been observed during recent decades. A detailed study of one mire show that the permafrost and vegetation changes have been associated with increases in landscape scale CH4 emissions in the range of 22-66% over the period 1970 to 2000.

Factors controlling large scale variations in methane emissions from wetlands

[1] Global wetlands are, at estimate ranging 115-237 Tg CH4/yr, the largest single atmospheric source of the greenhouse gas methane (CH4). We present a dataset on CH4 flux rates totaling 12 measurement years at sites from Greenland, Iceland, Scandinavia and Siberia. We find that temperature and microbial substrate availability (expressed as the organic acid concentration in peat water) combined explain almost 100% of the variations in mean annual CH4 emissions. The temperature sensitivity of the CH4 emissions shown suggests a feedback mechanism on climate change that could validate incorporation in further developments of global circulation models.

454 pyrosequencing analyses of bacterial and archaeal richness in 21 full-scale biogas digesters.

The microbial community of 21 full-scale biogas reactors was examined using 454 pyrosequencing of 16S rRNA gene sequences. These reactors included seven (six mesophilic and one thermophilic) digesting sewage sludge (SS) and 14 (ten mesophilic and four thermophilic) codigesting (CD) various combinations of wastes from slaughterhouses, restaurants, households, etc. The pyrosequencing generated more than 160,000 sequences representing 11 phyla, 23 classes, and 95 genera of Bacteria and Archaea. The bacterial community was always both more abundant and more diverse than the archaeal community. At the phylum level, the foremost populations in the SS reactors included Actinobacteria, Proteobacteria, Chloroflexi, Spirochetes, and Euryarchaeota, while Firmicutes was the most prevalent in the CD reactors. The main bacterial class in all reactors was Clostridia. Acetoclastic methanogens were detected in the SS, but not in the CD reactors. Their absence suggests that methane formation from acetate takes place mainly via syntrophic acetate oxidation in the CD reactors. A principal component analysis of the communities at genus level revealed three clusters: SS reactors, mesophilic CD reactors (including one thermophilic CD and one SS), and thermophilic CD reactors. Thus, the microbial composition was mainly governed by the substrate differences and the process temperature.

Clostridium ultunense sp. nov., a mesophilic bacterium oxidizing acetate in syntrophic association with a hydrogenotrophic methanogenic bacterium.

A syntrophic acetate-oxidizing bacterium, strain BST (T = type strain), was isolated from a previously described mesophilic triculture that was able to syntrophically oxidize acetate and form methane in stoichiometric amounts. Strain BST was isolated with substrates typically utilized by homoacetogenic bacteria. Strain BST was a spore-forming, gram-positive, rod-shaped organism which utilized formate, glucose, ethylene glycol, cysteine, betaine, and pyruvate. Acetate and sometimes formate were the main fermentation products. Small amounts of alanine were also produced from glucose, betaine, and cysteine. Strain BST grew optimally at 37 degrees C and pH 7. The G+C content of the DNA of strain BST was 32 mol%. A 16S rRNA sequence analysis revealed that strain BST was a member of a new species of the genus Clostridium. We propose the name Clostridium ultunense for this organism; strain BS is the type strain of C. ultunense.

In situ methane production from acid peat in plant communities with different moisture regimes in a subarctic mire

In situ methane production from acid peat in plant communities with different moisture regimes in a subarctic mire

Microbial oxidation of CH4 at different temperatures in landfill cover soils

Biological oxidation of CH(4) is an important constraint on the emission of this gas from areas, such as landfills to the atmosphere. We studied the effect of temperature on methanotrophic bacteria in three different landfill cover soils, incubated in the laboratory. In samples of a young cover, consisting of wood chips and sewage sludge, the phospholipid fatty acids (PLFAs), regarded as biomarkers for type I methanotrophs (16:1omega5t, 16:1omega6c, 16:1omega8c), primarily increased at low temperatures (5-10 degrees C). On the other hand, the PLFA marker for type II methanotrophs (18:1omega8c) was highly elevated only at 20 degrees C. These results suggest that temperature can determine the selection of methanotroph populations.

Seasonal and Diurnal Methane Emissions From a Landfill and Their Regulation By Methane Oxidation

Rates of methane emission from a Swedish landfill, measured by chamber technique and permanent frames, ranged between 0.034 and 20 mmol CH4 m-2.h-1 on average. The emissions followed a seasonal pattern, with the highest fluxes occurring between September and May. Methane concentrations in soil also followed a seasonal pattern, with a marked decrease during summers. Using the means of methane emission rates from frost-free periods, a stepwise regression model was made, that could explain 95% of the variation. Soil temperature turned out to be the dominating factor, explaining 85% when transformed to a second-degree function. Methane emissions were negatively correlated with soil temperature, which strongly suggests that biological methane oxidation is an important regulating factor. The activity of methane-oxidizing microorganisms was greatest around 0.5-0.6 m depth in the soil profile, and moisture at this level enhanced emissions. The tendency for methane emissions to be higher at night was probably due to the inhibitory influence of low soil temperatures on methane-oxidizing microorganisms.

Depth distribution of microbial production and oxidation of methane in northern boreal peatlands.

The depth distributions of anaerobic microbial methane production and potential aerobic microbial methane oxidation were assessed at several sites in both Sphagnum- and sedge-dominated boreal peatlands in Sweden, and compared with net methane emissions from the same sites. Production and oxidation of methane were measured in peat slurries, and emissions were measured with the closed-chamber technique. Over all eleven sites sampled, production was, on average, highest 12 cm below the depth of the average water table. On the other hand, highest potential oxidation of methane coincided with the depth of the average water table. The integrated production rate in the 0–60 cm interval ranged between 0.05 and 1.7 g CH4 m −2 day− and was negatively correlated with the depth of the average water table (linear regression: r2 = 0.50, P = 0.015). The depth-integrated potential CH4-oxidation rate ranged between 3.0 and 22.1 g CH4 m−2 day−1 and was unrelated to the depth of the average water table. A larger fraction of the methane was oxidized at sites with low average water tables; hence, our results show that low net emission rates in these environments are caused not only by lower methane production rates, but also by conditions more favorable for the development of CH4-oxidizing bacteria in these environments.

A method of selective inhibition to distinguish between nitrification and denitrification as sources of nitrous oxide in soil

SummaryNitrapyrin and C2H2 were evaluated as nitrification inhibitors in soil to determine the relative contributions of denitrification and nitrification to total N2O production. In laboratory experiments nitrapyrin, or its solvent xylene, stimulated denitrification directly or indirectly and was therefore considered unsuitable. Low partial pressures of C2H2 (2.5–5.0 Pa) inhibited nitrification and had only a small effect on denitrification, which made it possible to estimate the contribution of denitrification. The contribution of nitrification was estimated by subtracting the denitrification value from total N2O production (samples without C2H2). The critical C2H2 concentrations needed to achieve inhibition of nitrification, without affecting the N2O reductase in denitrifiers, must be individually determined for each set of experimental conditions.

Biotic controls on CO2 and CH4 exchange in wetlands - a closed environment study

Wetlands are significant sources of the important greenhouse gas CH4. Here we explore the use of an experimental system developed for the determination of continuous fluxes of CO2 and CH4 in closed ecosystem monoliths including the capture of 14CO2 and 14CH4 following pulse labelling with 14CO2. We show that, in the ecosystem studied, ebullition (bubble emission) may account for 18 to 50% of the total CH4 emission, representing fluxes that have been difficult to estimate accurately in the past. Furthermore, using plant removal and 14C labelling techniques, we use the system to detail the direct influence of vascular plants on CH4 emission. This influence is observed to be dependent on the amount of vascular plants present. The results that may be produced using the presented experimental set-up have implications for an improved understanding of wetland ecosystem/atmosphere interactions, including possible feedback effects on climate change. In recent years much attention has been devoted to ascertaining and subsequently using the relationship between net ecosystem productivity and CH4 emission as a basis for extrapolation of fluxes across large areas. The experimental system presented may be used to study the complex relationship between vascular plants and CH4 emission and here we show examples of how this may vary considerably in nature between and even within ecosystems.