Daily pCO2 and CO2 flux variations in a subtropical mesotrophic shallow lake

Carbon dioxide (CO2) emissions from lakes have been proven to be an important component of the continental carbon balance, but most CO2 evasion estimates ignore daily variability of partial pressure of CO2 (pCO(2)). To discern the variability of pCO(2) and its effect on CO2 outgassing estimations, we conducted in-situ biweekly pCO(2) 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(2) varied largely from 154 to 1698 mu atm with an average of 736 atm, while daytime CO2 flux ranged from -43 to 284 mmol m(2) h(-1) averaging at 44 mmol m(2) h(-1). Significant decreases in pCO(2) and CO2 fluxes from mornings to late afternoons were observed throughout the study period. Specifically, in morning hours average pCO(2) and CO2 fluxes were 940 atm and 83 mmol m(2) h(-1), respectively, while in afternoon hours average pCO(2) and CO2 fluxes were only 410 mu atm and 6 mmol m(2) h(-1), respectively. Relationships between pCO(2) and ambient factors reveal that solar radiation, lake trophic status and water temperature play a major role in pCO(2) and CO2 dynamics in lake water. We argue that uncertainties may exist in the current regional and global CO2 evasion estimates due to this high daily pCO(2) variability. (C) 2019 Elsevier Ltd. All rights reserved.