Enhanced nighttime gas emissions from a lake

7th International Symposium on Gas Transfer at Water Surfaces

Podgrajsek, E.^1 ; Sahlée, E.^1 ; Rutgersson, A.^1

Department of Earth Sciences, Air Water, and Landscape Sciences, Uppsala University, Uppsala, Sweden^1

关键词: Carbon dioxide flux;    Eddy covariance measurements;    Eddy covariance method;    High gas fluxes;    Large parts;    Methane fluxes;    Natural sources;    Transfer velocity;   

Others  :  https://iopscience.iop.org/article/10.1088/1755-1315/35/1/012014/pdf
DOI  :  10.1088/1755-1315/35/1/012014

来源: IOP

【 摘 要 】

Methane (CH4) and carbon dioxide (CO2) are two important greenhouse gases. Previous studies have shown that lakes can be important natural sources of atmospheric CH4and CO2. It is therefore important to monitor the fluxes of these gases between lakes and the atmosphere in order to understand the processes that govern the exchange. Most previous lake flux studies are based on chamber measurements, by using the eddy covariance method, the resolution in time and in space of the fluxes is increased, which gives more information on the governing processes. Eddy covariance measurements at a Swedish lake show that both methane fluxes (FCH4) and carbon dioxide fluxes (FCO2) experience high nighttime fluxes for a large part of the data set (largest median FCH4night≈ 13 nmol m2s-1and smallest median FCH4day≈ 4.0 nmol m-2s-1, largest median FCO2night≈ 0.2 μmol m2s-1and smallest median FCO2day≈ 0.02 μmol m-2s-1, with larger variability during night). For the diel cycle of the CH4fluxes it is suggested that water side convection could enhance the transfer velocity, transport CH4rich water to the surface, as well as trigger ebullition. The high nighttime CO2fluxes could to a large extent be explained with enhanced transfer velocities due to water side convection. If gas fluxes are not measured during nighttime, when water side convection normally is generated, periods of potential high gas flux might be missed and estimations of the total amount of gas released from lakes to the atmosphere will be biased.