Net CO2 and CH4 emissions from restored mangrove wetland: New insights based on a case study in estuary of the Pearl River, China

Xiaosong Zhao; Chunlin Wang; Tingting Li; Chengyi Zhang; Xingwang Fan; Qing Zhang; Qiang Zhang; Xianyan Chen; Xukai Zou; Chong Shen; Yuqi Tang; Zhangcai Qin

doi:10.1016/j.scitotenv.2021.151619

Net CO₂ and CH₄ emissions from restored mangrove wetland: New insights based on a case study in estuary of the Pearl River, China

Sci Total Environ. 2022 Mar 10:811:151619. doi: 10.1016/j.scitotenv.2021.151619. Epub 2021 Nov 12.

Authors

Xiaosong Zhao¹, Chunlin Wang², Tingting Li³, Chengyi Zhang⁴, Xingwang Fan⁵, Qing Zhang⁶, Qiang Zhang⁷, Xianyan Chen⁷, Xukai Zou⁷, Chong Shen⁸, Yuqi Tang⁹, Zhangcai Qin¹⁰

Affiliations

¹ Key Laboratory of Watershed Geographic Sciences, Nanjing Institute of Geography and Limnology, Chinese Academy of Sciences, Nanjing 210008, China; Southern Marine Science and Engineering Guangdong Laboratory (Zhuhai), Zhuhai 519000, China.
² Southern Marine Science and Engineering Guangdong Laboratory (Zhuhai), Zhuhai 519000, China; Guangzhou Climate and Agrometeorology Center, Guangzhou 510080, China.
³ Southern Marine Science and Engineering Guangdong Laboratory (Zhuhai), Zhuhai 519000, China; State Key Laboratory of Atmospheric Boundary Layer Physics and Atmospheric Chemistry, Institute of Atmospheric Physics, Chinese Academy of Sciences, Beijing 100029, China. Electronic address: litingting@mail.iap.ac.cn.
⁴ National Climate Center, China Meteorological Administration, Beijing 100081, China. Electronic address: zhangchy@cma.cn.
⁵ Key Laboratory of Watershed Geographic Sciences, Nanjing Institute of Geography and Limnology, Chinese Academy of Sciences, Nanjing 210008, China.
⁶ State Key Laboratory of Atmospheric Boundary Layer Physics and Atmospheric Chemistry, Institute of Atmospheric Physics, Chinese Academy of Sciences, Beijing 100029, China.
⁷ National Climate Center, China Meteorological Administration, Beijing 100081, China.
⁸ Guangzhou Climate and Agrometeorology Center, Guangzhou 510080, China.
⁹ School of Atmospheric Sciences, Nanjing University, Nanjing 210023, China.
¹⁰ Southern Marine Science and Engineering Guangdong Laboratory (Zhuhai), Zhuhai 519000, China; School of Atmospheric Sciences, Guangdong Province Key Laboratory for Climate Change and Natural Disaster Studies, Sun Yat-sen University, Zhuhai 519000, China.

PMID: 34780816
DOI: 10.1016/j.scitotenv.2021.151619

Abstract

Mangroves have the potential to affect climate via C sequestration and methane (CH₄) emissions. With half of the world's mangroves lost during the 20th century, mangrove restoration in mitigating greenhouse gases has been increasingly recognized. However, the carbon exchanges during restored processes still remain large uncertain. In this study, we analyzed the temporal variations of CO₂ and CH₄ fluxes and their environmental controls during 2019 and 2020 based on a closed-path eddy covariance (EC) system in a 12-year restored subtropical mangrove wetland, in estuary of the Pearl River, southeastern China. We also estimated the CO₂ and CH₄ fluxes and their climate effect from the beginning of restoration by Random Forest algorithm (RF). The EC observations showed that annually the 12-year restored mangrove acted as CO₂ and CH₄ sources, with net CO₂ ecosystem exchange (NEE) of 82-175 gC·m^{- 2}·a^-1 and CH₄ fluxes of 24.7-26.3 gC·m^-2·a^-1. Low vegetation gross primary productivity (GPP) and high ecosystem respiration (Re) caused net CO₂ emissions in the mangroves. The estimation by RF indicated that the mangroves were always a CO₂ source after the beginning of restoration, but the annual NEE was linearly decreased from 233 to 131 gC·m^-2·a^-1 from 2008 to 2020. The annual CH₄ emissions continually increased from 19.0 to 25.8 gC·m^-2·a^-1 after restoration. As a result, the restored mangrove had a positive effect on climate warming, with increased GWP from 1276 to 1386 g CO₂-eq ·m^-2·a^-1 from 2008 to 2020. This is mainly due to lower GPP and higher Re by young restored mangroves, large water area as well as low salinity induced strong CH₄ emissions. Our results indicate new sights that young restored mangrove with large area of water surface may act as carbon sources. However, the long-term climate and ecosystem benefits due to mangrove restoration should not be ignored in future.

Keywords: Carbon exchange; Eddy covariance; Mangrove restoration; Random forest algorithm; Southeast China.

MeSH terms

Carbon Dioxide* / analysis
China
Ecosystem
Estuaries
Methane / analysis
Rivers
Wetlands*

Substances

Carbon Dioxide
Methane