Evasion of CO₂ from streams : quantifying a carbon component of the aquatic conduit in the boreal landscape

• Lateral export of carbon (C) from soils to running waters is a persistent pathway for C with terrestrial origin. This "aquatic conduit" might be especially important in boreal regions where a significant part of the global C stock is stored in the soil. Even though the awareness of the fate of terrestrially derived C is increasing in regional and global C budgets, the scarcity of data on the contribution of streams is widely acknowledged. In particular, the evasion (degassing) of gaseous C (i.e. CO₂ and CH₄) from the water surface of streams requires better characterization. This thesis aims to quantify the evasion of CO₂ from boreal streams within the 67 km2 Krycklan catchment, and explore the factors controlling this diffuse flux. All streams in the Krycklan catchment were consistently supersaturated in CO₂ and were hence a source for atmospheric CO₂ all year around. The source for this supersaturation of CO₂ was to a great extent explained by the export of respired C from the catchment soils. This was shown by exploring the export of dissolved inorganic carbon (DIC) across the soil/stream/atmosphere interfaces in a headwater catchment. The study also found that CO₂ evasion from the stream surface is a rapid process, and that much of the DIC leaving the soils is returned to the atmosphere as CO2 before leaving the headwaters. Evasion of CO₂ is dependent on the water-atmosphere concentration gradient, but also the gas exchange ability across the water-atmosphere interface (the gas transfer coefficient). The spatiotemporal variability of the gas transfer coefficient for carbon dioxide (KCO2) was found to be large, but the slope of the stream can be used to predict the spatial component of this variability. The positive relationship between KCO2 and stream section steepness was used to determine the spatial distribution of gas exchange ability for the entire stream network of forested Sweden. By combining concentration measurements and field-determined relationships with a high resolution digital elevation model (DEM) we were able to model the CO₂ evasion for each grid-cell of stream in the Krycklan catchment. Evasion of CO₂ from the entire stream network constituted a major component (<69 %) of the entire aquatic C flux. This study highlights the importance of including CO₂ evasion from streams in estimates of the aquatic conduit for carbon in boreal regions.

Subject headings

NATURVETENSKAP  -- Geovetenskap och miljövetenskap -- Oceanografi, hydrologi och vattenresurser (hsv//swe)

NATURAL SCIENCES  -- Earth and Related Environmental Sciences -- Oceanography, Hydrology and Water Resources (hsv//eng)

NATURVETENSKAP  -- Geovetenskap och miljövetenskap -- Miljövetenskap (hsv//swe)

NATURAL SCIENCES  -- Earth and Related Environmental Sciences -- Environmental Sciences (hsv//eng)

NATURVETENSKAP  -- Geovetenskap och miljövetenskap -- Annan geovetenskap och miljövetenskap (hsv//swe)

NATURAL SCIENCES  -- Earth and Related Environmental Sciences -- Other Earth and Related Environmental Sciences (hsv//eng)

Publication and Content Type

vet (subject category)

dok (subject category)