Dissolved organic matter composition and characteristics during extreme flood events in the Yangtze River Estuary

Zhao Liang Chen; Haibo Zhang; Yuanbi Yi; Yuhe He; Penghui Li; Yuntao Wang; Kai Wang; Zhenwei Yan; Chen He; Quan Shi; Ding He

doi:10.1016/j.scitotenv.2023.169827

Dissolved organic matter composition and characteristics during extreme flood events in the Yangtze River Estuary

Sci Total Environ. 2024 Mar 1:914:169827. doi: 10.1016/j.scitotenv.2023.169827. Epub 2024 Jan 6.

Authors

Zhao Liang Chen¹, Haibo Zhang², Yuanbi Yi¹, Yuhe He³, Penghui Li⁴, Yuntao Wang⁵, Kai Wang⁶, Zhenwei Yan¹, Chen He⁷, Quan Shi⁷, Ding He⁸

Affiliations

¹ Department of Ocean Science and Center for Ocean Research in Hong Kong and Macau, The Hong Kong University of Science and Technology, Clear Water Bay, New Territories, 999077, Hong Kong.
² National Marine Environmental Monitoring Center, Dalian, Liaoning 116023, China. Electronic address: hbzhang@nmemc.org.cn.
³ State Key Laboratory of Marine Pollution, City University of Hong Kong, Tat Chee Avenue, Kowloon, 999077, Hong Kong.
⁴ School of Marine Sciences, Sun Yat-Sen University, Zhuhai, Guangdong 519082, China; Southern Marine Science and Engineering Guangdong Laboratory (Zhuhai), Zhuhai, Guangdong 519080, China.
⁵ State Key Laboratory of Satellite Ocean Environment Dynamics, Second Institute of Oceanography, Ministry of Natural Resources, Hangzhou, Zhejiang 310012, China.
⁶ Department of Ocean Science and Engineering, Southern University of Science and Technology, Shenzhen, Guangdong 518055, China.
⁷ State Key Laboratory of Heavy Oil Processing, China University of Petroleum, Changping, Beijing 102249, China.
⁸ Department of Ocean Science and Center for Ocean Research in Hong Kong and Macau, The Hong Kong University of Science and Technology, Clear Water Bay, New Territories, 999077, Hong Kong; State Key Laboratory of Marine Pollution, City University of Hong Kong, Tat Chee Avenue, Kowloon, 999077, Hong Kong; State Key Laboratory of Satellite Ocean Environment Dynamics, Second Institute of Oceanography, Ministry of Natural Resources, Hangzhou, Zhejiang 310012, China. Electronic address: dinghe@ust.hk.

PMID: 38190911
DOI: 10.1016/j.scitotenv.2023.169827

Abstract

Understanding the molecular composition and fate of dissolved organic matter (DOM) during transport in estuaries is essential for gaining a comprehensive understanding of its role within the global biogeochemical cycle. In 2020, a catastrophic flood occurred in the Yangtze River basin. It is currently unknown whether differences in hydrologic conditions due to extreme flooding will significantly impact the estuarine to oceanic DOM cycle. We determined the DOM composition in the Yangtze River estuary (YRE) to the East China Sea by using Fourier transform ion cyclotron resonance mass spectrometry (FT-ICR MS) during the high discharge and the flood period (monthly average discharge was 1.2 times higher) on the same trajectory. Our study found that the composition of DOM is more diverse, and more DOM molecules were introduced to the YRE during the flood, especially in the freshwater end member. The result revealed that the DOM was significantly labile and unstable during the flood period. A total of 1840 unique molecular formulas were identified during the flood period, most of which were CHON, CHONS, and CHOS compounds, most likely resulting from anthropogenic inputs from upstream. Only 194 of these molecules were detected in the seawater end member after transporting to the sea, suggesting that the YRE served as a 'filter' of DOM. However, the flood enhances the transport of a group of terrigenous DOM, that is resistant to photodegradation and biodegradation. As a result, YRE experienced ~1.6 times higher terrigenous DOC flux than high discharge period. Considering the increased frequency of future floods, our study provides a preliminary basis for further research on how floods affect the composition and characteristics of estuarine DOM. With the help of the FT-ICR MS technique, we can now better understand the dynamic of DOM composition and characteristics in large river estuaries.

Keywords: Dissolved organic matter; East China Sea; FT-ICR MS; Flood; Molecular dynamics; Yangtze River Estuary.