Terrestrial Si dynamics in the Arctic: a study on biotic and abiotic controls

• Main Author: Alfredsson, Hanna
• Format: Doctoral or Postdoctoral Thesis
• Language: English
• Published: Department of Geology, Lund University 2015
• Subjects: Earth and Related Environmental Sciences; Arctic; Climate change; permafrost; Tundra
• Online Access: https://lup.lub.lu.se/record/8163618; https://portal.research.lu.se/files/4185493/8163673.pdf

Silicon is the next most abundant element in the Earth’s crust and its biogeochemical cycle is linked with that of carbon. Further, silicon is a beneficial nutrient for plants in terrestrial ecosystems and a key nutrient for diatoms in aquatic ecosystems. During the last decade the important role of terrestrial vegetation in controlling Si fluxes downstream aquatic environments, via incorporation of Si into biomass (as amorphous Si) and subsequent storage in soil, has been realized. Due to the high prevalence of high Si-accumulating plants, cold temperatures and perenially frozen soil conditions, Arctic terrestrial ecosystems is hypothesized to store a significant fraction of the global soil ASi stock. The Arctic environment is highly sensitive to climate change, with unknown effects for terrestrial Si cycling. Hence, in this thesis we utilized archived soil samples collected from different geographical regions of the Arctic tundra and continuous permafrost region. By combining results obtained through soil chemical analysis with literature review this thesis provide a conceptual framework for how climate change may alter the biological component of terrestrial Si cycling in Arctic regions underlain by permafrost. Further, permafrost thaw can mobilize previously frozen soil material initiating biogeochemical processing of the newly thawed material, such as dissolution of plant derived amorphous silica stored in soil. Hence, an additional aspect of this thesis is to shed light on the potential biotic control (i.e. microbial influence) on plant derived ASi dissolution rates during litter degradation. This question was explored by utilization of microcosm laboratory experiments. Dependent on land cover type, we found total ASi storage to range between 1,030 - 94,300 kg SiO2 ha-1 in Arctic shrub/graminoid tundra and peatland ecosystems. Further, the first estimate of total ASi storage (0 - 1 m) in the northern circumpolar tundra regions is presented in this thesis. Our estimates, based on upscaling by vegetation and ...