Asynchronous Methane and Carbon Dioxide Fluxes Drive Temporal Variability of Mangrove Blue Carbon Sequestration
Xudong Zhu, Jingke Chen, Lichun Li, Mingjie Li, Tingting Li, Zhangcai Qin, Fan Wang, Xiaosong Zhao
Abstract
Abstract The climate benefit of blue carbon sequestered by mangrove forests can be partially offset by CH 4 emission, but this offset is rarely assessed using multi‐year high‐frequency measurements. Here, four‐year eddy covariance measurements were used to examine temporal patterns of CH 4 flux and its blue carbon offset (i.e., reduced climate benefit) in a subtropical estuarine mangrove in China. We found both diel and seasonal CH 4 fluxes were mainly driven by soil temperature and tidal activities, showing greater nighttime emission. On average, one‐tenth of CO 2 uptake was offset by CH 4 emission using the sustained‐flux global warming potential metric at a 20‐year time horizon, while this offset could vary over an order of magnitude due to asynchronous fluxes of CH 4 and CO 2 across diel and seasonal cycles. These results highlight the significant contribution of nighttime emission to mangrove CH 4 budget and the importance of asynchronous flux variations in assessing mangrove's climate benefit.