Diel Variability of CO<sub>2</sub> Emissions From Northern Lakes
David Rudberg, N. T. Duc, Jonathan Schenk, Anna Sieczko, Gustav Pajala, Henrique O. Sawakuchi, H. A. Verheijen, John M. Mélack, Sally MacIntyre, Jan Karlsson, David Bastviken
Abstract
Abstract Lakes are generally supersaturated in carbon dioxide (CO 2 ) and emitters of CO 2 to the atmosphere. However, estimates of CO 2 flux ( ) from lakes are seldom based on direct flux measurements and usually do not account for nighttime emissions, yielding risk of biased assessments. Here, we present direct measurements from automated floating chambers collected every 2–3 hr and spanning 115 24 hr periods in three boreal lakes during summer stratification and before and after autumn mixing in the most eutrophic lake of these. We observed 40%–67% higher mean in daytime during periods of surface water CO 2 supersaturation in all lakes. Day‐night differences in wind speed were correlated with the day‐night differences in the two larger lakes, but in the smallest and most wind‐sheltered lake peaks of coincided with low‐winds at night. During stratification in the eutrophic lake, CO 2 was near equilibrium and diel variability of insignificant, but after autumn mixing was high with distinct diel variability making this lake a net CO 2 source on an annual basis. We found that extrapolating daytime measurements to 24 hr periods overestimated by up to 30%, whereas extrapolating measurements from the stratified period to annual rates in the eutrophic lake underestimated by 86%. This shows the importance of accounting for diel and seasonal variability in lake CO 2 emission estimates.