title: Different Apparent Gas Exchange Coefficients for CO2 and CH4: Comparing a Brown-Water and a Clear-Water Lake in the Boreal Zone during the Whole Growing Season.
abstract: The air-water exchange of carbon dioxide (CO2) and methane (CH4) is a central process during attempts to establish carbon budgets for lakes and landscapes containing lakes. Lake-atmosphere diffusive gas exchange is dependent on the concentration gradient between air and surface water and also on the gas transfer velocity, often described with the gas transfer coefficient k. We used the floating-chamber method in connection with surface water gas concentration measurements to estimate the gas transfer velocity of CO2 (kCO2) and CH4 (kCH4) weekly throughout the entire growing season in two contrasting boreal lakes, a humic oligotrophic lake and a clear-water productive lake, in order to investigate the earlier observed differences between kCO2 and kCH4. We found that the seasonally averaged gas transfer velocity of CH4 was the same for both lakes. When the lakes were sources of CO2, the gas transfer velocity of CO2 was also similar between the two study lakes. The gas transfer velocity of CH4 was constantly higher than that of CO2 in both lakes, a result also found in other studies but for reasons not yet fully understood. We found no differences between the lakes, demonstrating that the difference between kCO2 and kCH4 is not dependent on season or the characteristics of the lake.
authors.affiliation: Department of Physics, University of Helsinki , P.O. Box 48, 00014 University of Helsinki, Finland.|Department of Environmental Sciences, University of Helsinki , P.O. Box 65, 00014, Finland.
authors.forename: Miitta
authors.initials: M
authors.lastname: Rantakari
authors.affiliation: Department of Physics, University of Helsinki , P.O. Box 48, 00014 University of Helsinki, Finland.
authors.forename: Jouni
authors.initials: J
authors.lastname: Heiskanen
authors.affiliation: Department of Physics, University of Helsinki , P.O. Box 48, 00014 University of Helsinki, Finland.
authors.forename: Ivan
authors.initials: I
authors.lastname: Mammarella
authors.affiliation: Lammi Biological Station, University of Helsinki , 16900 Lammi, Finland.
authors.forename: Tiina
authors.initials: T
authors.lastname: Tulonen
authors.affiliation: Department of Environmental Sciences, University of Helsinki , Niemenkatu 73, 15140 Lahti, Finland.
authors.forename: Jessica
authors.initials: J
authors.lastname: Linnaluoma
authors.affiliation: Department of Biology, University of Eastern Finland , Joensuu Campus, Tulliportinkatu 1, 80130 Joensuu, Finland.
authors.forename: Paula
authors.initials: P
authors.lastname: Kankaala
authors.affiliation: Department of Environmental Sciences, University of Helsinki , Niemenkatu 73, 15140 Lahti, Finland.|Department of Forest Sciences, University of Helsinki , P.O. Box 27, 00014 University of Helsinki, Finland.
authors.forename: Anne
authors.initials: A
authors.lastname: Ojala
mesh_terms: D001272:Atmosphere; D002244:Carbon; D002245:Carbon Dioxide / Q000032:analysis*; D017753:Ecosystem; D005387:Finland; D060106:Lakes / Q000737:chemistry; D008697:Methane / Q000032:analysis*; D012621:Seasons
chemical_list: D002245:Carbon Dioxide; D002244:Carbon; D008697:Methane