CARBONDIOXIDE FLUXES FROM A CONTROLLED BOREAL RIVER

Sammanfattning: 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.