Browsing by Subject "methane"

Northern peatlands are a large source of methane (CH4) to the atmosphere and can vary strongly depending on local environmental conditions. However, few studies have mapped fine-grained CH4 fluxes at the landscape-level. The aim of this study was to predict land cover and CH4 flux patterns in Pallastunturi, Finland, in a study area dominated by forests, peatlands, fells, and lakes. I used random forest models to map land cover types and CH4 fluxes with multi-source remote sensing data and upscaled CH4 fluxes based on land cover maps. The random forest classifier reliably detected the same land cover patterns as the CORINE Land Cover maps. The main differences between the land cover maps were forest type classification, misclassification between neighboring peatland types, and detection of sparsely vegetated areas on fells. The upscaled CH4 fluxes of sinks were very robust to changes in land cover classification, but shrub tundra and peatland CH4 fluxes were sensitive to the level of detail in the land cover classification. The random forest regression performed well (NRMSE 6.6%, R2 82%) and predicted similar CH4 flux patterns as the upscaled CH4 flux maps, despite predicting larger areas that act as CH4 sources than the upscaled CH4 flux maps. The random forest regressor also better predicted CH4 fluxes in peatlands due to added information about soil moisture content from the remote sensing data. Random forests are a good model choice to detect landscape patterns and predict CH4 patterns in northern peatlands based on remote sensing and topographic data.

Peatlands play an important role in the carbon cycle. Natural peatlands are in general sinks of carbon dioxide (CO2) and sources of methane (CH4), whereas drained peatland forests are CH4 sinks but their CO2 emissions increase compared to natural peatlands. Rotational even-aged forestry followed by ditch network maintenance (DNM) affect the water dynamics of the soil by increasing the water table level (WTL) first during clear-cut after which the WTL is lowered by DNM. Rising of WTL causes more anaerobic conditions and risk that CH4 sink turns into CH4 emissions. Lowering the WTL causes more aerobic conditions and strengthens the CH4 sink function but also increases CO2 emissions. In continuous cover forestry (CCF) where only part of the trees are removed, WTL would be naturally maintained. This could maintain CH4 sinks while lowering CO2 emissions by keeping the WTL at an adequate depth. Net emissions of CO2 and CH4 could be expected to follow the changes in CO2 and CH4 concentrations in soil. To understand the processes isotopic values can be used to interpret the production pathways of CO2 and CH4 since different pathways produce different isotope values. In this master’s thesis the aim was to study how the concentration of CO2 and CH4 as well as CO2 isotope values change in a peat soil and how partial harvest affects them. Gas samples were collected from the peat profile (5 – 65cm) at two different drained peatland forests, Lettosuo and Paroninkorpi, from control plots and partial harvested plots during 2019 and 2020. Samples were also collected from the moss layer. In addition, WTL, temperature of peat and O2 concentrations were measured. Concentrations and isotope values were analysed the laboratory with gas chromatography and isotope analyser (Picarro G2201-i). Water table level and temperature were generally higher in partial harvested areas than in control. Highest concentrations of both CO2 and CH4 were found in the deeper layers of the soil. Partial harvest had higher CO2 and CH4 concentrations in the deep layers (50 – 65cm) than control. The differences between partial harvest and control areas could be explained with the higher WTL in partial harvest. The measured isotopic values of CO2 indicated that most of the CO2 in the soil was derived from atmosphere or heterotrophic respiration and only <<20 % of CO2 was derived from CH4 oxidation. Even though both in control and in partial harvest the CH4 concentrations in the deep soil layers were high, the oxidation processes decrease the concentrations under the atmospheric CH4 concentration maintaining the CH4 sinks in both treatments. In partial harvest the CH4 sink is not in risk due to oxidation even though the WTL is higher. This should be verified with gas flux measurements.

The intensification of milk production has increased the size of farms and reduced the use of pastures in recent decades worldwide. The interest in farm animal welfare and the climate impact of dairy products is growing. Offering dairy cows full-time pasture access has declined, but there are other possibilities to provide outdoor access for dairy cows. The aim of this study was to evaluate the effects of two outdoor management systems on the feeding behaviors and productivity of lactating dairy cows. This study was conducted at the University of Helsinki research barn’s freestall and adjacent pastureland in Viikki. The experimental design was a replicated 3x3 Latin square. Twenty-seven Ayrshire cows were divided into nine squares. During the experiment, cows went through three 21-day periods. Cows in squares were assigned to the following treatments: partial access to pasture with sufficient forage for grazing (pasture), partial access to pasture without grazeable forage (paddock), and indoor confinement. Milk yield and ECM were greater in the paddock than in the pasture treatment. Part-time grazing led to an energy deficit because pasture cows had the lowest milk yield. Outdoor access reduced the content of saturated fatty acids and increased the content of monounsaturated fatty acids in milk. Pasture cows spent 30% of their outdoor time eating and paddock cows 27%. Paddock cows used 15% of their total eating time eating TMR and 12% attempting to graze. Pasture cows ruminated the most between 12:00 a.m. and 6:00 p.m., and indoor cows ruminated more than outdoor cows between 7:00 a.m. and 5:00 p.m. Outdoor cows ruminated more than indoor cows from 6:00 p.m. to 11:00 p.m. The cows on the pasture produced less methane per day than the paddock cows. However, methane production in g/kg ECM was not different among groups. According to this study, grazing seems to be a motivating activity for dairy cows. Providing TMR outdoors can be beneficial for the welfare of dairy cows because it enables a choice between feeds and helps to maintain milk yields. Partial outdoor access changed the diurnal pattern of rumination but not the total time used for rumination. There were no differences in milk’s polyunsaturated fatty acid contents between treatments, but eating fresh grass modified the cow’s milk to be healthier.

Global warming caused by the warming effect of greenhouse gases (GHGs) induces permafrost thaw, which could alter Arctic ecosystems from prominent carbon sinks to potential sources of GHG emissions when polar microorganisms become metabolically more active and have access to carbon compounds that were previously largely unavailable. Polar microbes can have significant contributions to the growing emissions of carbon dioxide (CO2), methane (CH4) and nitrous oxide (N2O) and therefore, studies on their metabolism are important. The aim of my study was to investigate polar microbial community composition and diversity as well as functional potential that was related to GHG-cycling in a subarctic environment with genome-resolved metagenomics. Soil cores were collected at the Rásttigáisá fell that is located in Northern Norway. After DNA extraction, ten mineral soil samples were sequenced. Metagenome-assembled genomes (MAGs) were reconstructed using either the combination of human-guided binning and automatic binning or human-guided binning only. Taxonomy was assigned to the MAGs and the functional potential of the MAGs was determined. I recovered dozens of good-quality MAGs. Notably, the MAGs from the mostly unknown phyla Dormibacterota (formerly candidate phylum AD3) and Eremiobacterota (formerly candidate phylum WPS-2) were reconstructed. There were MAGs from the following bacterial phyla as well: Acidobacteriota, Actinobacteriota, Chloroflexota, Gemmatimonadota, Proteobacteria and Verrucomicrobiota. In addition to the bacterial MAGs, MAGs from the group of ammonia-oxidizing archaea were recovered. Most of the MAGs belonged to poorly studied phylogenetic groups and consequently, novel functional potential was discovered in many groups of microorganisms. The following metabolic pathways were observed: CO2 fixation via the Calvin cycle and possibly via a modified version of 3-hydroxypropionate/4-hydroxybutyrate cycle; carbon monoxide oxidation to CO2; CH4 oxidation and subsequent carbon assimilation via serine pathway; urea, ammonia and nitrite oxidation; incomplete denitrification as well as dissimilatory nitrate reduction to ammonium. My study demonstrates how genome-resolved metagenomics provides a valuable overview of the microbial community and its functional potential.

It is necessary actively seek effective ways to reduce agricultural emissions so that the proportion of agricultural greenhouse gas emissions in total national emissions does not increase. The aim of this study was to evaluate with carbon footprint calculators different options for reducing greenhouse gas emissions of dairy production and the carbon footprint of energy-corrected milk. The scenarios included the changes in the dietary concentrate proportion, the proportion of grass in cultivation, the digestibility of roughage and the level of milk production. In addition, the effect of temperature on methane emissions from manure was examined. Data of a dairy farm located in Central Ostrobothnia from year 2020 were utilized in the study. The assessment was carried out by using the carbon footprint calculator developed by the European Commission and the Valio Carbo® environmental calculator. According to the results of both calculators, the effect of the changes in the concentrate proportion in the diet on the carbon footprint of milk was very small. Reducing the proportion of concentrate in the diet reduced total emissions. Reducing the proportion of rapeseed meal in feeding reduced total emissions more than reducing the proportion of barley. Increasing the proportion of grass in cultivation reduced the carbon footprint of milk and the total amount of greenhouse gas emissions with both calculators. According to the European Commission carbon calculator, increasing grass yield and also increasing the proportion of grain in cultivation reduced the carbon footprint of milk and the total amount of greenhouse gas emissions. With Valio Carbo® environmental calculator, increasing the proportion of grain in cultivation increased the carbon footprint of milk and the total emissions. According to European Commission calculator, the total emissions and the carbon footprint of milk decreased when the digestibility of roughage decreased. The increase of milk production level also clearly reduced the carbon footprint of milk with both calculators. However, the change in the milk production level had only a small effect on the amount of emissions produced. Reducing the conversion factor describing the effect of temperature on methane formation from slurry reduced the carbon footprint of milk. The decrease in the conversion factor reduced the emissions from the manure system by 51.3 percentage and reduced the milk carbon footprint from 1.21 to 1.15 kg CO2e/kg ECM. In conclusion, there are many feasible opportunities to reduce the carbon footprint. The most effective ways to reduce total emissions at farm level are to increase the proportion of grass in cultivation and to increase the yield of grass. Raising the milk production level effectively reduces the carbon footprint, but in the future the calculations must take into account that the dry matter intake is higher as the milk yield increases. The main differences between the calculators are currently in the coefficients they use. When comparing the results given by the calculators, it is important to note that the calculation principles cannot fully take into account the possible opposite effects of different factors. The results should be looked critically with a caution that the results given by different calculators are not directly comparable.

Environmental factors are important tools in constructing methane flux models and estimations. Among the abiotic factors, plants and their functional groups have been noted to have significant effect on methane fluxes for three reasons. First, the vegetation community compositions express their abiotic environmental factors that affect not only the plants, but also local methanogen and methanotroph communities. Second, the vegetation itself might produce methane emissions and have a direct effect on methane balance. Third, the plant functional groups and species have differences in their chemical and physical properties that support different methanogen communities and therefore have an indirect impact on methane fluxes. In this study, methane fluxes of different plant communities were observed during one growing season in northern boreal catchment area in Muonio. Study focuses to determine the link between methane fluxes and abiotic and biotic environmental factors in different vegetation types. Closed chamber technique was used to measure methane and carbon dioxide fluxes from 23 plots every two weeks in period of June-August. Environmental data, such as moisture, temperature species composition etc. were collected from the plots. Vegetation types for each plot were determined via ordination analysis. Linear mixed-effects regression model and generalized additive model were applied and compared to observe the relationships of methane and environmental factors in different vegetation types. Dataset was divided into four vegetation types in clustering analysis: wet fen, pine bog, spruce swamp and forest. The greatest amount (average 5959 µg/m²/h) and biggest range (standard deviation 5285 µg/m²/h) of methane emissions were observed on wettest fen-like study sites. Peatland types in general acted as net methane sources. The driest, forest-like vegetation type acted as a net methane sink. The amount (average -107 µg/m²/h) and range (standard deviation 117 µg/m²/h) of methane fluxes were very moderate in comparison to peatland types. These effects intensified towards the climax of growing season. The most significant environmental factors were mostly abiotic on driest study sites and the whole plant biomass was more significant biotic methane flux regulating factor than plant functional groups. On wetter study sites, the role of abiotic factors decreased, and plant functional group increased. Graminoids were linked to bigger methane emissions especially on wetter study sites. Forest mosses and different shrub types seemed to have a link with lower methane emissions or methane absorption. The effect of other plant functional groups on methane fluxes varied more, and their role remains unclear. None of the environmental factors could estimate the methane flux alone, and the methane budget seems to be a sum of multiple variables in each vegetation type. The role of plant functional groups varied in different vegetation types and was dependent on surrounding vegetation. More research is needed to get better tools to estimate methane balance and to understand the underlying mechanisms in climate and environmental change.

Methane is a powerful greenhouse gas that is released to the atmosphere in many ways from natural sources. While wetlands are seen as major sources, open water systems, including small boreal lakes, should also be considered when estimating methane emissions locally and globally. Methane is produced the sediments and has several oxidation processes and emission pathways. In this master’s thesis, the sediments of Lake Pääjärvi, southern Finland, were studied using two different porewater sampling methods to analyze methane concentrations and geochemical properties of the porewater. The sampling methods, the Rhizons filter and the cut syringe method, were both performed to total of five sampling sites. A sediment profile was made from two locations, PAME1 and PAME2, and single sampling at 10 cm depth from the other sites. The sampling sites were located on different parts of the lake at depths of 3–16 m. Additionally, the water column was sampled for methane and water quality, and sediment for grain size, organic matter, and the C:N-ratio. As a result, the sampling methods were successful, and the sediment profiles and the sites could be compared. While there was difference in the methane concentrations, reliability of the methods was not concluded. The Rhizons filter method gave higher methane concentrations in only one sampling site, whereas the cut syringe was dominant in all others. Influential factors on the differences could be the use of different sampling cores, or the different duration of sampling between the sampling sites. The sulfate-methane transition zone was recognized from the depth of 4.5–6.5 cm in PAME1 and circa 3 cm in PAME2. The only sediment feature that coincided with high methane concentrations was larger grain size, although the variation between sampling sites was not large. The methane concentrations in the epilimnion were higher than near the sediment-water interface, which suggested that the methane in Lake Pääjärvi originates mainly from the catchment area and not from the sediments.

Experimental warming provides a method to determine how an ecosystem will respond to increased temperatures. Northern peatland ecosystems, sensitive to changing climates, provide an excellent setting for experimental warming. Storing great quantities of carbon, northern peatlands play a critical role in regulating global temperatures. Two of the most common methods of experimental warming include open top chambers (OTCs) and infrared (IR) lamps. These warming systems have been used in many ecosystems throughout the world, yet their efficacy to create a warmer environment is variable and has not been widely studied. To date, there has not been a direct, experimentally controlled comparison of OTCs and IR lamps. As a result, a factorial study was implemented to compare the warming efficacy of OTCs and IR lamps and to examine the resulting carbon dioxide (CO2) and methane (CH4) flux rates in a Lake Superior peatland. IR lamps warmed the ecosystem on average by 1-2 oC, with the majority of warming occurring during nighttime hours. OTC's did not provide any long-term warming above control plots, which is contrary to similar OTC studies at high latitudes. By investigating diurnal heating patterns and micrometeorological variables, we were able to conclude that OTCs were not achieving strong daytime heating peaks and were often cooler than control plots during nighttime hours. Temperate day-length, cloudy and humid conditions, and latent heat loss were factors that inhibited OTC warming. There were no changes in CO2 flux between warming treatments in lawn plots. Gross ecosystem production was significantly greater in IR lamp-hummock plots, while ecosystem respiration was not affected. CH4 flux was not significantly affected by warming treatment. Minimal daytime heating differences, high ambient temperatures, decay resistant substrate, as well as other factors suppressed significant gas flux responses from warming treatments.

Radiomethane (14CH4) is a radioactive isotopologue of methane known to be emitted from nuclear facilities. As methane is a potent greenhouse gas and measuring the concentration of carbon-14 in a methane sample gives information about the origin of the sample, it is important to be able monitor 14CH4. The state-of-the-art method for radiomethane measurements is accelerator mass spectrometry, but optical methods have also been proposed due their affordability and suitability for field measurements. Radiomethane has already been measured with optical methods, but usually indirectly by first combusting it to carbon dioxide – direct measurement of radiomethane with optical methods would require spectroscopic information, and the first absorption spectrum of radiomethane was measured only in the year 2019. In this thesis, the exploration of the CH-stretching vibrational band ν3 of 14CH4 is continued: Total of 43 lines with 17 new lines have been measured and assigned with improved accuracy. Furthermore, the widths of the lines have been studied in detail for the first time and a simple model to estimate the 14CH4 line positions to aid possible future research on radiomethane is presented. The measurements were conducted with photoacoustic spectroscopy using frequency modulation techniques and a mid-infrared continuous-wave optical parametric oscillator (OPO) as a light source. The OPO frequency was referenced to a wavelength meter and the frequency scanning (measuring over an absorption line) was executed with a proportional–integral–derivative controller in LabVIEW. The novel results presented in this thesis are useful for possible future applications in quantitative analysis of radiomethane, and the results are also relevant for fundamental research as radiomethane is the last naturally occurring isotopologue of methane that has not yet been extensively studied with optical methods.

Pristine mires are an important carbon storage, but after drainage, the carbon is released from the peat through aerobic decomposition. In Finland, half of the original mire area has been drained, mainly for forestry purposes. Majority (83 %) of the drained area is suitable for forestry. Out of the forestry-suited drained peatlands, the nutrient-rich forestry drained peatlands emit high amounts of CO2 due to high aerobic decomposition as nutrient-rich conditions are favourable for decomposing bacteria. Rewetting of these nutrient-rich peatlands could offer a solution for halting the CO2 emission, but the CH4 emission increases after rewetting. The studies show differing results of CH4 emission from nutrient-rich rewetted peatlands. There are studies reporting both high and low emission of CH4 from nutrient-rich peatlands, and differing studies on how the emission evolves in time. This thesis focused on three variables that could affect the CH4 emission: time from rewetting, water level and site type. There were 27 different study sites at 8 locations. These sites were rewetted 3 to 28 years prior to measurements and represented nutrient-rich tree-covered peatlands (Rhtkg, Mtkg, Ptkg). Ptkg was the least nutrient-rich site type in the study. The CH4 flux was measured with a chamber method from July to November of 2021. Water level was monitored with loggers and manual measurements. The data was analysed with linear regression and analysis of variance, depending on the independent variable. Mean CH4 fluxes were used to compare sites with each other. The results show that water level affects the CH4 emission at statistically significant level. When water level is deeper than 10cm below ground level, the CH4 emission is low. One site differed from this trend and despite the high water level, the CH4 emission was close to zero. Time from rewetting did not affect CH4 emission at statistically significant level, but there was a visible trend of older rewetted peatlands emitting less than more recently rewetted ones. This finding was contradicting to the literature as it was supposed that the more recently rewetted peatlands emit less CH4. Out of site types, the Mtkg2 and Rhtkg site types emitted most, but there was no statistical significance. When analysed with using both the water level and site type, there were statistical differences between site types. When comparing mean CH4 emissions from nutrient-rich (Rhtkg+Mtkg) and least nutrient-rich (Ptkg) peatlands at the same water level, the Ptkg sites emitted less, but not at a statistically significant level. The findings indicate that, when rewetting a nutrient-rich tree-covered peatland, it should be done so that the water-level does not rise above 10cm, but this is very difficult or impossible to regulate. Restoration process and how it develops is difficult to foresee and the end-result might differ. Research on CH4 emissions from rewetted nutrient-rich peatlands and what affects it is increasingly important as CH4 affects the climate change in the near future.