CARBONDIOXIDE FLUXES FROM A CONTROLLED BOREAL RIVER

River, lakes and streams account for more carbon dioxide emissions than all other freshwater reservoirs together. However, there is still lack of knowledge of the physical processes that control the efficiency of the air-water exchange of CO2 in these aquatic systems. In the more turbulent water sections of a river, the gas transfer is thought to be governed by the river’s morphology such as bottom topography, slope and stream flow. Whiles for wider sections of the river, the gas transfer could potentially be influenced by atmospheric forcing (e.g. Wind speed). The main purpose of this project is to study the fluxes of carbon dioxide and how (wind speed and stream discharge) influence the CO2 fluxes in the river. In this study, direct and continuous measurements of CO2 emission was conducted for the first time in a controlled boreal river in Kattstrupeforsen (Sweden) from 18th April to 10th May 2018. A unique measurement setup which combines eddy covariance techniques, general meteorology and in situ water variables (for high accuracy emission measurements) was used. The results show that in the late winter, an upward directed CO2 fluxes measured in the river was approximately 2.2 μmol m−2 s−1. This value agrees with many other small and large rivers where CO2 fluxes has been studied. The river can be said to serve as source of CO2 to the atmosphere in the day due to the dominant upward fluxes recorded during the daytime. The results also show that carbon dioxide fluxes increase with increasing wind speed notably at wind speed above 2 m s-1. There was no relation between CO2 fluxes and stream discharge. This indicates that wind speed could be one principal factor for air- river gas exchange. The findings in this work on river gas exchange will provide a basis for a regional estimate and be applicable for many river systems on a global scale. 2018-07-09