Preprints
https://doi.org/10.5194/bg-2018-380
https://doi.org/10.5194/bg-2018-380
13 Sep 2018
 | 13 Sep 2018
Status: this preprint has been withdrawn by the authors.

Methane emissions from a sediment-deposited island in a Lancang-Mekong reservoir

Wenqing Shi, Qiuwen Chen, Jianyun Zhang, Cheng Chen, Yuchen Chen, Yuyu Ji, Juhua Yu, and Bryce R. Van Dam

Abstract. In dammed rivers, sediment accumulation creates potential methane emission hotspots, which have been extensively studied in forebays. However, methane emissions from sidebays remain poorly understood. We investigated methane emissions from a sediment-deposited island situated in the sidebay of the Manwan Reservoir, Lancang-Mekong River. High methane emissions (maximum 10.4 mg h−1 m−2) were observed at the island center, while a ring-like zone of low-to-negative methane emission was discovered around the island edge, whose flux varied between −0.2–1.6 mg h−1 m−2. The ring-like zone accounted for 89.1 % of the island area, of which 9.1 % was a methane sink zone. Microbial processes in the hyporheic zone, regulated by hydrological variations, were responsible for the low methane flux in this area. Under reservoir operation, frequent water level fluctuations enhanced hyporheic exchange and created redox gradients along the hyporheic flow path. Dissolved oxygen in hyporheic water decreased from 4.80 mg L−1 at the island bank edge to 0.43 mg L−1 at the center, which in turn decreased methanogen abundance for methane production and increased methanotroph abundance for methane oxidation at the ring-like zone. This study adds to our understanding of methane emissions from dammed rivers and helps to screen efficient strategies for future mitigation of the global warming effects of hydropower systems.

This preprint has been withdrawn.

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Wenqing Shi, Qiuwen Chen, Jianyun Zhang, Cheng Chen, Yuchen Chen, Yuyu Ji, Juhua Yu, and Bryce R. Van Dam

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Interactive discussion

Status: closed
Status: closed
AC: Author comment | RC: Referee comment | SC: Short comment | EC: Editor comment
Printer-friendly Version - Printer-friendly version Supplement - Supplement
Wenqing Shi, Qiuwen Chen, Jianyun Zhang, Cheng Chen, Yuchen Chen, Yuyu Ji, Juhua Yu, and Bryce R. Van Dam
Wenqing Shi, Qiuwen Chen, Jianyun Zhang, Cheng Chen, Yuchen Chen, Yuyu Ji, Juhua Yu, and Bryce R. Van Dam

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Short summary
As the second most important greenhouse gas, the production of methane undermines the green credentials of hydropower. We investigated methane emissions from a reservoir island and discovered self-mitigation of methane emissions in a ring-like zone around the island edge. Understanding the self-mitigation of methane emissions in dammed rivers will help to screen effective strategies for lessening the global warming effects of hydropower systems.
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