Diel cycle of lake-air CO2 flux from a shallow lake and the impact of waterside convection on the transfer velocity
2015 (English)In: Journal of Geophysical Research - Biogeosciences, ISSN 2169-8953, E-ISSN 2169-8961, Vol. 120, no 1, 29-38 p.Article in journal (Refereed) Published
Two years of eddy covariance measurements of lake carbon dioxide (CO2) fluxes reveal a dielcycle with higher fluxes during night. Measurements of partial pressure in the air (pCO2a) and in the water(pCO2w), during 4 months, show that the high nighttime fluxes are not explained by changes in the differencebetween pCO2a and pCO2w. Analyzing the transfer velocity (k600,meas), which is a measure of the efficiencyof the gas transfer, with respect to wind speed, shows that variations in wind speed do not explain thediel cycle. During nighttime, when the fluxes are high, the wind is normally low. Thus, a solely wind-basedparameterization of the transfer velocity (ku,CC) results in large errors compared to k600,meas, especially forwind speeds lower than 6ms1. The mean absolute percentage error between ku,CC and k600,meas is 79%. By subtracting ku,CC from k600,meas, we investigate how waterside convection influence k600,meas. Our resultsshow that the difference (k600,measku,CC) increases with increasing waterside convection. Separating thetransfer velocity parameterization in two parts, one depending on the wind speed and one depending onwaterside convection, the mean absolute percentage error compared to the measurements reduces to 22%. The results in this paper show that the high nighttime CO2 fluxes can, to a large extent, be explained bywaterside convection and that a transfer velocity parameterization based on both wind speed and watersideconvection better fits the measurements compared to a parameterization based solely on wind speed.
Place, publisher, year, edition, pages
2015. Vol. 120, no 1, 29-38 p.
Earth and Related Environmental Sciences
IdentifiersURN: urn:nbn:se:uu:diva-241576DOI: 10.1002/2014JG002781ISI: 000349899200003OAI: oai:DiVA.org:uu-241576DiVA: diva2:779888