Browsing by Subject "Carbon"
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(2023)Northern peatlands are important carbon storing ecosystems, contributing to carbon cycle as sinks and sources. The two most important greenhouse gases in the carbon cycle are carbon dioxide (CO2) and methane (CH4). The study area of this work consists of two sloping fens in the Kuusamo area. from which the peat geochemistry and peat properties (peat stratigraphy, ash content, and bulk density) are studied. In addition, the chronology, carbon-nitrogen ratio, carbon content, and carbon accumulation are studied in the Puukkosuo from the three sampling sites. In the characterization of peat geochemistry, Puukkosuo in the dolomitic rock area and Suvisuo in the volcanic rock area were divided into different geochemical zones based on the cluster analysis. The paludification in the Puukkosuo area has started around 10 000 years ago, and the accumulation of peat have been ongoing in the whole peat basin after 1000 years. The geochemical zones in the Puukkosuo can be divided into five different groups, from which the deepest part of the peatland basin can be separated due to the high heavy metal concentrations in the oldest peat. Most of the bulk peat is differentiated into alternating groups, from which the changes in the peat nutrients are recorded. The margins of the Puukkosuo are separated based on the geochemical properties. The top part of the northwestern edge can be characterized as high concentrations of atmospheric origin elements, whereas the effect of the nearby road can be noted in the concentrations of the top part of the southeastern edge. The amount of carbon accumulated has varied throughout the development of Puukkosuo, and the highest rates are recorded in the lower part of the peat profiles in all study sites. Highest carbon-nitrogen -ratios are recorded near the basal peat samples especially in the deepest part of the Puukkosuo. The long-term carbon accumulation differs from the other long-term averages in the boreal zone. The largest differences were recorded in the deepest part of the basin in the long-term carbon accumulation rates during the Early Holocene. The respective value in the Puukkosuo is four times higher (60 g m-2 yr-1) in contrast to others. During the Late Holocene the long-term carbon accumulation rates correspond to the other average values in the boreal peatlands (25 g m-2 yr-1).
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(2023)Boreal peatlands are major constituents of the global carbon (C) and water cycles and therefore important climate regulators. These cycle dynamics are strongly determined by plant phenology (e.g., vascular plant photosynthesis and seasonality) and evapotranspiration (ET), next to other abiotic factors. While it is evident that climate change affects these networks of interactions, it is only poorly understood to what extent, as site-specific empirical evidence over multiple decades is lacking. This study investigates the role of phenology (leaf area index: LAI) for peatland C (net ecosystem exchange: NEE) and water fluxes (ET and water table: WT) by combining inter-annual and seasonal observations at the ecosystem level, in Siikaneva fen, Finland (2005-2007, 2014-2022). Interactions with temperature (T), vapor pressure deficit (VPD), photosynthetically active radiation (PAR) and rain were included and tested with various statistical methods (trend- and correlation-analysis, commonality analysis, time lag testing, stepwise multiple-regression, and structural equation modelling). Significant trends were found for LAI (increasing) and WT (decreasing), suggesting ongoing changes in the ecosystem (climate change signal). Within this system LAI provided substantial effects on NEE, less so on ET. These relationships differed seasonally: the greenup season showed the strongest effects of LAI on NEE and ET (and other interactions). However, e.g., PAR and VPD became more relevant for NEE and ET in the later seasons. A time lag analysis suggested that effects (e.g., LAI on NEE) can be delayed at the scale of weeks. Inconclusive evidence was found for the LAI effect on ET and WT (via ET). It is assumed that ET is a limited measure to differentiate between evaporation (E) and transpiration (T) by leaves or the ground, as they might cancel each other out. A shading of increasing LAI over the season might shade moss-ET (and photosynthesis). The applied methods provided complementary information with differing suitability to reveal certain parts of complex network dynamics. A consistent, while seasonally changing, importance of plant phenology for peatland NEE can be concluded. Phenology showed clear correlation with ET, however, the effect size could not be quantified conclusively. Future studies should partition E and T or incorporate the contribution of mosses to both ET and NEE for a more comprehensive understanding. Collectively, this study highlights the role of phenology for peatland C and water fluxes and provides evidence for climate change induced alterations of biotic-abiotic interactions at the ecosystem scale.
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(2024)In this thesis, fossilized teeth of herbivores from four sites in Western Mongolia (Altanteel, Chono-Kharyakh, Oshin-Boro-Udzyur-Ula and Khrigis Nur) are examined for their stable carbon and oxygen isotope record. The fossils date to the Late Neogene period (ca. 10-3 Ma). The aim of the thesis is to reconstruct the palaeoclimate and palaeoenvironment of Western Mongolia during the Late Neogene using the isotopic records obtained from the fossilized teeth. The enamel of fourteen teeth from Rhinoceros, Equids, and a possible Giraffid was sampled and analyzed for δ13C and δ18O-values. The analyses were conducted using well-established methods with Isotope Ratio Mass Spectrometry. The stable carbon isotopes (13C and 12C) can be used to determine, the types of plants that these animals consume. Plants can be categorized into three groups based on their photosynthesis pathways. This study focuses on the C3 -plants, typically found in moister environments, and the C4-plants, which thrive in dry conditions. Specific δ13C-values have been established for these groups: –34‰ to –24‰ for C3-plants, and –20‰ to – 9‰ for C4. The δ13C-values obtained from the teeth of herbivores can be compared to these limits, allowing evaluation of the mammals’ diets (whether they consisted of C3 or C4-plants). If C3 plants dominate the die, this would indicate a moister climate, and likely a forested environment. Conversely, the presence of C4 plants would suggest grassland areas with more arid climatic conditions. The stable oxygen record in the teeth relates to the δ18O-composition of meteoric water in the area. Analysing δ18O-values facilitates the reconstruction of the mean temperatures of the habitats and allows for a comparison of climatic factors affecting precipitation and temperature over time. The stable carbon and oxygen records are compared to reconstruct the climate and environment of Western Mongolia during the Late Neogene. The results suggest an increase in the δ13C-values over time, which indicating a shift in the animals’ diets towards a more drought-stressed C3 and C4 plant-based one. The δ18O-values, on the other hand, remain stable and do not indicate a change in temperature during the Late Neogene. Comparing both the δ13C- and δ18O- values with studies conducted in China indicates a gradual aridification in Western Mongolia and China during the Late Neogene. However, the temperatures did not change significantly, although there were most likely alternating cooler and warmer periods during the time span of 10-3 Ma.
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