Abstract
Carbon dioxide (CO2) emissions from aquatic surface to the atmosphere has been recognized as a significant factor contributing to the global carbon budget and environmental change. The influence of river damming on the CO2 emissions from reservoirs remains poorly constrained. This is hypothetically due to the change of hydraulic retention time (HRT) and thermal stratification intensity of reservoirs (related to the normal water level, NWL). To test this hypothesis, we quantified CO2 fluxes and related parameters in eight karst reservoirs on the Wujiang River, Southwest China. Our results showed that there was a significant difference in the values of pCO2 (mean = 3205.7 μatm, SD = 2183.4 μatm) and δ 13CCO2 (mean = −18.9‰, SD = 1.6‰) in the cascade reservoirs, suggesting that multiple processes regulate CO2 production. Moreover, the calculated CO2 fluxes showed obvious spatiotemporal variations, ranging from −9.0 to 2269.3 mmol m−2 d−1, with an average of 260.1 mmol m−2 d−1. Interestingly, the CO2 flux and δ 13CCO2 from reservoirs of this study and other reservoirs around the world had an exponential function with the reservoir effect index (Ri , HRT/NWL), suggesting the viability of our hypothesis on reservoir CO2 emission. This empirical function will help to estimate CO2 emissions from global reservoirs and provide theoretical support for reservoir regulation to mitigate carbon emission.
Highlights
Carbon dioxide (CO2) is one of the dominant greenhouse gases (GHGs), contributing 65% to global warming effects that has led to many environmental problems (Smith et al 2013), such as glacier melting, sea-level rise (Deemer et al 2016)
Our results showed that there was a significant difference in the values of pressure of CO2 (pCO2) and δ13CCO2 in the cascade reservoirs, suggesting that multiple processes regulate CO2 production
Characteristics of meteorological and water chemical components The average TA were 16.6 ◦C and 19.6 ◦C in the upstream and downstream of the Wujiang River while the average precipitation was close in the two reaches (1068.3 mm and 1062.8 mm) (Gzpwrd 2017)
Summary
Carbon dioxide (CO2) is one of the dominant greenhouse gases (GHGs), contributing 65% to global warming effects that has led to many environmental problems (Smith et al 2013), such as glacier melting, sea-level rise (Deemer et al 2016). It is critical to fully understand the global carbon cycle, especially regarding CO2 emissions from inland waters that was regarded as an important game player (Tranvik et al 2009, Raymond et al 2013, Räsänen et al 2018, Li et al 2018b, Maavara et al 2020). More than 67% of the world’s rivers have been dammed, especially in densely populated and energy-deficient areas (Grill et al 2019)
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