Unraveling the factors influencing CO2 emissions from hydroelectric reservoirs in karst and non-karst regions: A comparative analysis

Wanfa Wang; Si-Liang Li; Jun Zhong; Yuanbi Yi; Fujun Yue; Zenglei Han; Qixin Wu; Ding He; Cong-Qiang Liu

doi:10.1016/j.watres.2023.120893

Unraveling the factors influencing CO₂ emissions from hydroelectric reservoirs in karst and non-karst regions: A comparative analysis

Water Res. 2024 Jan 1:248:120893. doi: 10.1016/j.watres.2023.120893. Epub 2023 Nov 19.

Authors

Wanfa Wang¹, Si-Liang Li², Jun Zhong³, Yuanbi Yi⁴, Fujun Yue³, Zenglei Han⁵, Qixin Wu¹, Ding He⁴, Cong-Qiang Liu³

Affiliations

¹ Key Laboratory of Karst Georesources and Environment, Ministry of Education, Guizhou University, Guiyang 550025, China; College of Resources and Environmental Engineering, Guizhou Karst Environmental Ecosystems Observation and Research Station, Ministry of Education, Guiyang 550025, China.
² Institute of Surface-Earth System Science, School of Earth System Science, Tianjin University, Tianjin 300072, China. Electronic address: siliang.li@tju.edu.cn.
³ Institute of Surface-Earth System Science, School of Earth System Science, Tianjin University, Tianjin 300072, China.
⁴ Department of Ocean Science, Center for Ocean Research in Hong Kong and Macau, The Hong Kong University of Science and Technology, Hong Kong, China.
⁵ Tianjin Key Laboratory of Water Resources and Environment, Tianjin Normal University, Tianjin 300387, China.

PMID: 38000226
DOI: 10.1016/j.watres.2023.120893

Abstract

Carbon migration, transformation, and emissions as CO₂ in reservoir and lake systems have been extensively studied. However, uncertainties persist regarding carbon cycling variations in both karst and non-karst regions within large thermal stratified river-reservoir systems. To address this knowledge gap, we combined measurements of water chemistry, isotopic compositions (δ¹³C), partial pressure of CO₂ (pCO₂), and CO₂ fluxes (F_CO2) to elucidate the differences, control mechanisms, and environmental effects of various carbon biogeochemical processes in the Hongjiadu reservoir (HJD, karst reservoir) and Shangyoujiang reservoir (SYJ, non-karst reservoir), Yangtze River basin, China. Our results demonstrate that key biogeochemical processes are associated with CO₂ production and emissions. The stronger biological carbon pump (BCP) effect in the lentic area of the HJD reservoir limited CO₂ emission (0.9 ± 5.0 mmol m^-2 d^-1) compared to the SYJ reservoir (50.9 ± 33.4 mmol m^-2 d^-1), leading to low dissolved inorganic carbon (DIC) and high saturation state of carbonate minerals in the lentic epilimnion. Although the released water from both reservoirs acted as hotspots for CO₂ emissions, the results of higher Revelle factor (RF) in the HJD reservoir than SYJ reservoir suggest the greater buffer capacity and lower sensitivity of OC degradation changes in DIC. Despite the shorter hydraulic retention time (HRT) of SYJ reservoir (120 d) compared to HJD reservoir (368 d), F_CO2 was 3.5 times higher than that of the HJD reservoir (652.9 mmol m^-2 d^-1). Moreover, upon analyzing selected reservoirs worldwide, it becomes apparent that karst reservoirs demonstrate a reduced potential for CO₂ emissions. Our results indicate that the impact of varying geologic settings should be considered to minimize errors in regional and global CO₂ emission estimates.

Keywords: Carbon cycling; Carbon isotope; Reservoirs, Biological carbon pump, Geologic setting.

MeSH terms

Carbon / analysis
Carbon Dioxide*
Carbonates / analysis
China
Environmental Monitoring*
Water / analysis

Substances

Carbon Dioxide
Water
Carbonates
Carbon