Assessing the ecosystem carbon storage in two subarctic areas: Phytomass and soil organic carbon stocks at Abisko in Sweden and Utsjoki in Finland
Independent thesis Advanced level (degree of Master (Two Years)), 30 credits / 45 HE creditsStudent thesis
Carbon is stored in natural Earth system reservoirs such as the crust, the atmosphere, the soil, the ocean and the phytomass, and naturally fluctuates in between these pools at different time-scales. However, due to human activities such as burning of fossil fuel and deforestation has the organic carbon content in the atmosphere in the form of CO2 increased by a third over the last century, triggering a climate warming. Increased air temperatures have the capability to further alter the carbon cycle, hence the size of and the fluctuations between reservoirs. Current concerns regarding permafrost regions is the thawing of permafrost making organic matter available for decomposition, during which carbon is released to the atmosphere as greenhouse gases, acting as a positive feedback to the warming climate. A warming climate additionally alter the nature of these environments through expansion of shrub and forest stands, which entails an increase of carbon stored within the phytomass compared to present levels. These concerns are especially valid for subarctic environments, which are vulnerable to climate warming. However, potential alterations in carbon storage in subarctic areas are difficult to project due to limited knowledge regarding their size. Hence, it is of interest to conduct more field sampling in these environments to obtain proper estimates.
The main objectives with this thesis were to determine the carbon storages within the phytomass and the soil in two subarctic study areas, Abisko in northern Sweden and Utsjoki in northern Finland. The objectives were achieved through a stepwise process. First, field sampling was conducted at sites representing different land cover classes. The tree carbon was determined through allometric equations, i.e. relating physical properties of trees to biomass. The sampled field layer phytomass was dried and weighted. The carbon corresponds to half of the dry phytomass weight. The carbon in the soil samples was determined through dry bulk density, loss on ignition and elemental analyses, relating the weight loss of the soil samples after combustion to the organic carbon content. Site results corresponding to the same land cover were averaged, and the calculated mean used for upscaling against land cover classifications developed for of the two study areas. The obtained results regarding study area means for ecosystem total organic carbon storages were 7.01±1.67kgC m-2 for the Abisko area and 11.3±2.66kgC m-2 for the Utsjoki area. The difference between the areas are related to differences in extent of peatlands, which are the land cover classes with the highest carbon storages and constituted about 5.6% of the analysed part of the Abisko study area and 14.3% in Utsjoki. The partitioning of carbon storages reveals that most is stored within the soil, especially within the top organic layer. However, in Abisko more carbon is stored in the phytomass, especially within trees compared to Utsjoki, regulated by the greater areal extent and higher phytomass carbon content of forests in Abisko. Permafrost was only encountered at five sampling sites in Abisko and at one site in Utsjoki, all located in peatlands. Thus permafrost soil organic carbon constitutes only a minor share (<4%) of the total storages. The obtained results further reveal uncertainties and limitations, related to both natural variability, field and laboratory analysis and upscaling procedures, indicating more research should be conducted. Nevertheless, the results of this thesis contribute to further understanding of the ecosystem carbon storages in subarctic environments.
Place, publisher, year, edition, pages
2016. , 83 p.
SOC, Soil organic carbon, phytomass carbon, subarctic, Abisko, Utsjoki
IdentifiersURN: urn:nbn:se:su:diva-130713OAI: oai:DiVA.org:su-130713DiVA: diva2:932184
Kuhry, PeterSiewert, Matthias