Daily Variations in pCO2 and fCO2 in a Subtropical Urbanizing Lake
Rongjie Yang, Yingying Chen, Jie Du, Xiangjun Pei, Jinghua Li, Zan Zou, Huixing Song
Abstract
The transfer of CO 2 from lakes to the atmosphere is a component of the global carbon equilibrium, while the quantification of the CO 2 partial pressure ( p CO 2 ) is critical for exploring the contribution of freshwater CO 2 emissions in the regional/global carbon budget. To investigate the daily variability of p CO 2 and CO 2 fluxes ( f CO 2 ), we conducted in situ biweekly p CO 2 detection at 7:00, 10:00, 14:00, and 17:00 China Standard Time (CST) from Jan. to Sept. 2020 in the subtropical urbanizing Qinglonghu Lake in Chengdu, Sichuan, China. The p CO 2 during the daytime varied greatly from 8.3 to 1,061.3 μatm, with an average of 137.7 μatm, while the average p CO 2 ( n = 11) clearly gradually decreased from 7:00 CST (204.9 ± 295.7 μatm) to 17:00 CST (93.5 ± 105.5 μatm). Similarly, the average f CO 2 values were −19.3 (±27.5), −24.8 (±20.7), −29.2 (±9.1) and −30.4 (±10.7) mmol m 2 h −1 at 7:00–17:00 CST, respectively. Further, we observed a negative correlation between p CO 2 and water temperature and dissolved oxygen, but a positive correlation between p CO 2 and total organic carbon and chlorophyll a . By a systematic overview of previously published data, we also discussed the differences and uncertainties in p CO 2 and f CO 2 estimates at regional and global scales. We therefore speculate that uncertainties may exist in the contributions of CO 2 balance on lake surface in regional/global carbon budgets due to this daily p CO 2 variation.