Terrigenous organic carbon drives methane dynamics in cascade reservoirs in the upper Yangtze China. (1st July 2022)

• Record Type: Journal Article
• Authors: Zhang, Yuanyuan; Su, Youheng; Li, Zhe; Guo, Shuhui; Lu, Lunhui; Zhang, Bin; Qin, Yu
• Is Part Of: Water research. Volume 219(2022)
• Publication Date: 2022-07-01
• Subjects: Methane dynamics -- Terrigenous POC -- Carbon footprint -- Cascade reservoirs -- Hydropower production; Water -- Pollution -- Research -- Periodicals; 363.7394
• DOI: 10.1016/j.watres.2022.118546
• Languages: English
• ISSNs: 0043-1354

Abstract

Highlights: Operation of cascade reservoirs shapes POC transport and CH4 dynamics. 55% of POC was terrigenous, and was regulated by water level and flow. Cumulative effect in cascade reservoirs was limited due to reduced retention time. Sedimentation of terrigenous POC displayed a major role in CH4 accumulation. Low level of CH4 was caused by reduced sedimentation of POC and CH4 oxidation. Abstract: Methane (CH4 ) emissions from freshwaters to the atmosphere have a profound impact on global atmospheric greenhouse gas (GHG) concentrations. Anthropogenic footprints such as dam construction and reservoir operation significantly changed the fate and transport of CH4 in freshwaters. The source of particulate organic carbon (POC) in reservoirs is a critical factor controlling CH4 production and emissions. However, little is known of how reservoir operation mediates the transport of POC and regulates CH4 accumulation in cascade hydroelectric reservoirs. Here, spatial and temporal variations in POC and CH4 were explored in the Xiluodu (XLD) and Xiangjiaba (XJB) reservoirs which are deep valley cascade reservoirs located in the main channel of the upper Yangtze River. Based on the δ 13 C-POC and N/C mole ratio of particulate organic matter, the results of multi-endmember stable isotope mixing models by a Bayesian model showed that terrigenous POC and autochthonous POC accounted for approximately 55% ± 18% and 43% ± 19% (SD, n = 179) of POC, respectively. Together with other hydrological and environmental parameters, we found that the input of terrigenous POC was dominantly influenced by water level variations and flow regulation due to reservoir operation. The cumulative effect of POC caused by cascade dams was not apparent. Terrigenous POC were more likely to drive CH4 accumulation in our study. Evident low level of CH4 in both reservoirs were likely affected by low sedimentation of POC and microbial CH4 oxidation. We hope our study could provide a conceptual framework for further modeling of CH4 dynamics in cascade reservoirs. Graphical abstract: Image, graphical abstract