Abstract
The transfer of CO2 from lakes to the atmosphere is a component of the global carbon equilibrium, while the quantification of the CO2 partial pressure (pCO2) is critical for exploring the contribution of freshwater CO2 emissions in the regional/global carbon budget. To investigate the daily variability of pCO2 and CO2 fluxes (fCO2), we conducted in situ biweekly pCO2 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 pCO2 during the daytime varied greatly from 8.3 to 1,061.3 μatm, with an average of 137.7 μatm, while the average pCO2 (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 fCO2 values were −19.3 (±27.5), −24.8 (±20.7), −29.2 (±9.1) and −30.4 (±10.7) mmol m2 h−1 at 7:00–17:00 CST, respectively. Further, we observed a negative correlation between pCO2 and water temperature and dissolved oxygen, but a positive correlation between pCO2 and total organic carbon and chlorophyll a. By a systematic overview of previously published data, we also discussed the differences and uncertainties in pCO2 and fCO2 estimates at regional and global scales. We therefore speculate that uncertainties may exist in the contributions of CO2 balance on lake surface in regional/global carbon budgets due to this daily pCO2 variation.
Highlights
Since the Industrial Revolution, human activities, such as the consumption of fossil fuels and the exacerbation of land development, have increased atmospheric carbon (C) by approximately 40% (Xu et al, 2019; Li Q. et al, 2020; Wang et al, 2021)
As urbanization has accelerated in recent years, anthropogenic waste emissions have increased sharply, which has inevitably caused the deterioration of water quality in urbanizing lakes, the changes in hydrological processes, and the destruction of the water-nutrient-carbon cycle (Li S. et al, 2020)
We systematically investigated the daily fluctuations in pCO2 and related parameters at 3 h intervals from morning to afternoon from Jan. to Sept., 2020 in a subtropical urbanizing lake
Summary
Since the Industrial Revolution, human activities, such as the consumption of fossil fuels and the exacerbation of land development (e.g., uncontrolled deforestation and rapid urbanization), have increased atmospheric carbon (C) by approximately 40% (Xu et al, 2019; Li Q. et al, 2020; Wang et al, 2021). From 2007 to 2016, approximately 10.7 ± 1.2 Gg C yr−1 of anthropogenic carbon was released into the atmosphere globally, of which 4.7 ± 0.1 Gg C yr−1 remains in the atmosphere (Le Quéré et al, 2018; Chen and Hu, 2019; León-Palmero et al, 2020). CO2 emitted into the atmosphere from aquatic ecosystems, including inland freshwater ecosystems, such as urban lakes, can greatly contribute to climate change, as verified by previous works (IPCC, 2014; Wen et al, 2017). The global carbon balance and hydrological processes are rapidly becoming urgent issues in studies of anthropogenic impacts.
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