The high organic carbon accumulation in estuarine wetlands necessarily does not represent a high CO2 sequestration capacity

Mengdi Xie; Liwei Qian; Haoyu Dong; Wenxuan Mei; Xiaohua Fu; Yu Hu; Jianfang Yan; Ying Sun; Pengfei Wu; Xiuzhi Chen; Lei Wang

doi:10.1016/j.envint.2023.107762

The high organic carbon accumulation in estuarine wetlands necessarily does not represent a high CO₂ sequestration capacity

Environ Int. 2023 Feb:172:107762. doi: 10.1016/j.envint.2023.107762. Epub 2023 Jan 18.

Authors

Mengdi Xie¹, Liwei Qian², Haoyu Dong¹, Wenxuan Mei¹, Xiaohua Fu³, Yu Hu¹, Jianfang Yan⁴, Ying Sun⁵, Pengfei Wu⁵, Xiuzhi Chen⁵, Lei Wang⁶

Affiliations

¹ Key Laboratory of Yangtze River Water Environment, Ministry of Education, College of Environmental Science and Engineering, Tongji University, Shanghai 200092, China.
² Key Laboratory of Yangtze River Water Environment, Ministry of Education, College of Environmental Science and Engineering, Tongji University, Shanghai 200092, China; Research Department of Energy and Eco-Environment, Zhejiang Development & Planning Institute, Hangzhou 310030, China.
³ Key Laboratory of Yangtze River Water Environment, Ministry of Education, College of Environmental Science and Engineering, Tongji University, Shanghai 200092, China; Shanghai Institute of Pollution Control and Ecological Security, Shanghai 200092, China.
⁴ Key Laboratory of Yangtze River Water Environment, Ministry of Education, College of Environmental Science and Engineering, Tongji University, Shanghai 200092, China; College of Geography and Environmental Sciences, Zhejiang Normal University, Jinhua, Zhejiang 321004, China.
⁵ Shanghai Jiuduansha Wetland Nature Reserve Management Center, Shanghai 200135, China.
⁶ Key Laboratory of Yangtze River Water Environment, Ministry of Education, College of Environmental Science and Engineering, Tongji University, Shanghai 200092, China; Shanghai Institute of Pollution Control and Ecological Security, Shanghai 200092, China. Electronic address: 20310222@tongji.edu.cn.

PMID: 36689865
DOI: 10.1016/j.envint.2023.107762

Abstract

Estuarine wetlands with high organic carbon (OC) accumulation rates due to their high plant biomass and interception of tide-derived OC are generally considered as large CO₂ sinks. However, our previous study found that tidal OC input seems to stimulate soil CO₂ emissions, potentially weakening CO₂ sequestration in estuarine wetlands. To further verify this phenomenon, we first established a structural equation model, which confirmed a positive correlation between tidal OC input and soil organic carbon (SOC) and soil respiration. We then performed trace analysis to determine the stability of SOC derived from different sources and its effect on soil CO₂ emissions by analyzing the input and retention of OC derived from tides and plants in the Yangtze Estuary wetlands. From upstream to downstream, as tidal OC input decreased, the relative retention ratio of the tidal OC in wetland soil increased from 1.259 to 2.148, whereas the relative retention ratio of plant OC in the soil decreased from 61.5% to 14.8%. Our findings indicated that the degradability of tidal OC was higher upstream than that downstream, but both inhibited plant OC degradation, thus providing an important reason for the higher CO₂ emissions upstream of wetlands (with higher tidal OC input). In addition, the primarily contributor to CO₂ (δ¹³) emissions' transforming from plant SOC (81.35%) to tidal SOC (91.18%) was an increase in organic matter input from the tide in a microcosm system. Consequently, a higher CO₂ output than CO₂ input (plant OC) due to the ready degradation of tidal OC consequently weakens the CO₂ sequestration capacity of the estuarine wetlands. This phenomenon is cause for concern regarding the CO₂ sink function of estuarine wetlands intercepting large amounts of organic matter.

Keywords: Plant derived carbon; Soil carbon sink; Soil respiration; Tidal input; Trace analysis; Yangtze River estuary wetlands.

Publication types

Research Support, Non-U.S. Gov't

MeSH terms

Biomass
Carbon Dioxide
Carbon Sequestration
Carbon* / analysis
China
Plants
Soil / chemistry
Wetlands*

Substances

Carbon
Carbon Dioxide
Soil