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https://doi.org/10.5194/bg-2018-380
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Research article 13 Sep 2018

Research article | 13 Sep 2018

Review status
This discussion paper is a preprint. It is a manuscript under review for the journal Biogeosciences (BG).

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

Wenqing Shi1,2, Qiuwen Chen1,2, Jianyun Zhang1,3, Cheng Chen2, Yuchen Chen2, Yuyu Ji2,4, Juhua Yu1,2, and Bryce R. Van Dam5 Wenqing Shi et al.
  • 1State Key Laboratory of Hydrology-Water Resources & Hydraulic Engineering, Nanjing Hydraulic Research Institute, China
  • 2Center for Eco-Environment Research, Nanjing Hydraulic Research Institute, China
  • 3Research Center for Climate Change, Ministry of Water Resources, China
  • 4College of Water Conservancy and Hydropower Engineering, Hohai University, China
  • 5Institute of Marine Sciences, University of North Carolina at Chapel Hill, USA

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 10.4mgh−1m−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 −0.2–1.6mgh−1m−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 4.80mgL−1 at the island bank edge to 0.43mgL−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.

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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.
As the second most important greenhouse gas, the production of methane undermines the green...
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