Daily pCO and CO flux variations in a subtropical mesotrophic shallow lake.

Carbon dioxide (CO) emissions from lakes have been proven to be an important component of the continental carbon balance, but most CO evasion estimates ignore daily variability of partial pressure of CO (pCO). To discern the variability of pCO and its effect on CO outgassing estimations, we conducted in-situ biweekly pCO measurements during daylight from November 2017 to June 2018 at 7:00, 10:00, 14:00, and 17:00 Central Standard Time of the United States (CST) in a subtropical shallow lake in Louisiana, USA. Daytime pCO varied largely from 154 to 1698 μatm with an average of 736 μatm, while daytime CO flux ranged from -43 to 284 mmol m h averaging at 44 mmol m h. Significant decreases in pCO and CO fluxes from mornings to late afternoons were observed throughout the study period. Specifically, in morning hours average pCO and CO fluxes were 940 μatm and 83 mmol m h, respectively, while in afternoon hours average pCO and CO fluxes were only 410 μatm and 6 mmol m h, respectively. Relationships between pCO and ambient factors reveal that solar radiation, lake trophic status and water temperature play a major role in pCO and CO dynamics in lake water. We argue that uncertainties may exist in the current regional and global CO evasion estimates due to this high daily pCO variability.