CO2 Emissions from Northern Lakes : Insights on regulation and spatiotemporal variability across contrasting lakes in Sweden

Lakes cover only ~2 % of the global land area, but their connections to the surrounding catchment make them important for the global carbon cycle. A considerable amount of the carbon input to lakes is emitted to the atmosphere as carbon dioxide (CO2) through diffusive flux. This CO2 flux varies with surface water CO2 concentrations (CwCO2) and the transfer velocity of CO2 across the thin boundary layer between surface water and atmosphere (k), which both in turn depend on physical, biological, and chemical factors that interplay with lake and catchment characteristics over various time scales. Comprehensive studies of these interlinkages across lake types are rare, and current assessments of lake CO2 emissions are therefore uncertain. In this thesis, the variability and regulation of lake CO2 fluxes across a latitudinal gradient in Sweden is investigated. The thesis explores how CwCO2 and k regulate lake CO2 fluxes and how spatiotemporal patterns of CO2 fluxes vary within and across lakes. Regulation of CO2 flux at shorter temporal scales (