Multiscale studies of the peatland-atmosphere interactions in northern Eurasia

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Title: Multiscale studies of the peatland-atmosphere interactions in northern Eurasia
Author: Alekseychik, Pavel
Other contributor: Helsingin yliopisto, matemaattis-luonnontieteellinen tiedekunta, fysiikan laitos
Helsingfors universitet, matematisk-naturvetenskapliga fakulteten, institutionen för fysik
University of Helsinki, Faculty of Science, Department of Physics, Division of Atmospheric Sciences
Publisher: Helsingin yliopisto
Date: 2017-12-01
Language: en
Thesis level: Doctoral dissertation (article-based)
Abstract: North Eurasia (NE) is recognized as a region of high importance for the global climate change. Large and systematic shifts in temperature and precipitation, predicted for NE, are expected to cause irreversible disturbances in the ecosystem-atmosphere interactions. The region is dominated by natural boreal and arctic ecosystems, which are experiencing increasing levels of anthropogenic influence through environmental pollution (mainly agriculture- and mining-related) and land use change. However, despite the general consensus on the importance of environmental changes in NE, many aspects of the problem remain poorly understood. Due to the great extent of NE, many crucial areas remain inaccessible or lack the required infrastructure, thereby relevant surface-atmosphere exchange measurement data remains scarce. This thesis examines the surface budgets of carbon dioxide and energy of subarctic peatlands, which count among the most important ecosystems in NE owing to their large carbon storage and areal coverage, and their high sensitivity to climate and land use changes. Peatlands are also heterogeneous ecosystems, with large diversity found both internally and between the ecosystem subtypes. Peatland heterogeneity is notable on several characteristic scales, including the single plant, microsite, microtopography element and ecosystem type. Different scales of variation are covered with specific measurement techniques, i.e. plant-scale gas exchange, chamber and eddy-covariance (EC) technique. The latter is in the focus of this work. Aerodynamic roughness length (z0) and photosynthesis rate measured by EC were compared with the plant- and microsite-scale measurements of leaf area index (LAI) and photosynthesis rate. High correspondence between the estimates on different scales was found, indicating that the transition between the upscaled plant and ecosystem-scale estimates is possible, and thus adding credibility to both. In the fen Siikaneva-1, LAI showed a strong linear relationship with z0, while the EC-derived photosynthesis rate closely followed the upscaled plant chamber estimate. Ecosystem-scale EC measurements made in 2015 at a typical raised bog in West Siberian middle taiga (Mukhrino Field Station) revealed a high cumulative May-August net ecosystem exchange (NEE) of 202 gC m-2 and a mean Bowen ratio (ratio of sensible to latent heat flux) of 0.28, which was lower than expected. Inter-site differences in terms of energy balance were investigated for a selection of eight Fennoscandian peatland sites with different mire types and management histories. The site mean Bowen ratio ranged from 0.28 to 1.35, evapotranspiration (ET) from 1.2 to 2.8 mm/day, and the decoupling parameter (Ω, indicating the relative strength of radiation and surface conductance controls on evapotranspiration) from 0.11 to 0.48. Generally, the energy balance and ecosystem features were found to be tightly linked, corroborating the predictability of peatland energy balances across a wide spectrum of ecosystems. Finally, on a yet larger scale, the current measurement station network of the entire NE is discussed. Measurement gaps are identified based on ecosystem type and climate representation by the existing field stations, with the focus on peatlands. Tentative developments for the NE measurement network are proposed.It is established that Siberia is a region very sparsely covered by ecosystem and climate change monitoring sites, especially when state of the art techniques are concerned (e.g. EC).N/A
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