Jan Åberg

Buoyancy flux, turbulence, and the gas transfer coefficient in a stratified lake.

Gas fluxes from lakes and other stratified water bodies, computed using conservative values of the gas transfer coefficient k600, have been shown to be a significant component of the carbon cycle. We present a mechanistic analysis of the dominant physical processes modifying k600 in a stratified lake and resulting new models of k600 whose use will enable improved computation of carbon fluxes. Using eddy covariance results, we demonstrate that i) higher values of k600 occur during low to moderate winds with surface cooling than with surface heating; ii) under overnight low wind conditions k600 depends on buoyancy flux β rather than wind speed; iii) the meteorological conditions at the time of measurement and the inertia within the lake determine k600; and iv) eddy covariance estimates of k600 compare well with predictions of k600 using a surface renewal model based on wind speed and β.

Gas transfer rate and CO2 flux between an unproductive lake and the atmosphere in northern Sweden

Measurements of the gas transfer rate of CO2 between lake water and the atmosphere present a critical problem for the understanding of lake ecosystem carbon balances and landscape carbon budgets. W ...

Importance of water temperature and thermal stratification dynamics for temporal variation of surface water CO2 in a boreal lake

Variation of the surface water CO2 concentration is likely to be the result of biological activity and physical processes as water mixing and gas exchange with the atmosphere. Here we have studied ...

Variations in pCO2 during summer in the surface water of an unproductive lake in northern Sweden

Unproductive lakes are generally supersaturated with carbon dioxide (CO2) and emit CO2 to the atmosphere continuously during ice-free periods. However, temporal variation of the partial pressure of CO2 (pCO2) and thus of CO2 evasion to atmosphere is poorly documented.We therefore carried out temporally high-resolution (every 6 h) measurements of the pCO2 using an automated logger system in the surface water of a subarctic, unproductive, lake in the birch forest belt. The study period was June–September 2004. We found that the pCO2 showed large seasonal variation, but low daily variation. The seasonal variation was likely mainly caused by variations in input and mineralization of allochthonous organic matter. Stratification depth probably also influenced pCO2 of the surface water by controlling the volume in which mineralization of dissolved organic carbon (DOC) occurred. In lakes, with large variations in pCO2, as in our study lake a high (weekly) sampling intensity is recommended for obtaining accurate estimates of the evasion of CO2.

Contributions of internal and external sources to the CO2 emission from a subarctic lake

Emission of COz from lakes takes place during stages of COz-supersaturation in the surface water, and most lakes can be considered as sources o f COz to the atmosphere (COLE et al. !994 ). The sources of emitted COz have been suggested to be externally loaded dissolved inorganic carbon (DIC) (KLING et al. !992, RI ERA e t al. !999, JONES e t al 200 l), o r mineralization of allochthonous organic carbon within the lake (HESSEN !992, JONSSON et al. 200 l). However, the relative importance of these different C02 sources have seldom been quantified. Here, we presenta DIC budget including emission ofCOz in a subarctic lake. Our hypothesis was that interna! supply ofDIC from mineralization o f externally supplied organic matter was the main source o f emitted COz.