Greenhouse gas emission and storage in a small shallow lake

Small lakes are likely to show considerable temporal variability in greenhouse gas emissions given their transient stratification and short residence time. To determine the extent that CO2 and CH4 emission and storage depends on surface meteorology, we studied a shallow lake during 2 years with contrasting rainfall and thermal stratification. Gas fluxes were estimated with wind-based and surface renewal models and compared to direct measurements obtained with floating chambers. The assessment of greenhouse gases storage revealed that the lake gained CO2 in association with rainfall in both the rainier (2011) and drier summer (2012). In 2011, stratification was less extensive and disrupted frequently. The lake was a source of CO2 and CH4, and ebullition exceeded diffusive fluxes of CH4. In 2012, stratification was more persistent, the lake was a sink for CO2 during dry periods, CO2 and CH4 accumulated in the hypolimnion later in the summer when rainfall increased, diffusive fluxes of CH4 were similar to those in 2011 mid-summer and over four times higher during overturn. Ebullition was lower in the drier summer. Fluxes measured with chambers were closer to estimations from the surface renewal model and about two times values estimated with wind-based models.