Destruction and reinstatement of coastal hypoxia in the South China Sea off the Pearl River Estuary

Abstract

Abstract. We examined the evolution of intermittent hypoxia off the Pearl River Estuary during three cruise legs conducted in July 2018: one during severe hypoxic conditions before the passage of a typhoon and two post-typhoon legs showing destruction of the hypoxia and its reinstatement. The lowest ever regional dissolved oxygen (DO) concentration of 3.5 μmol kg−1 (~ 0.1 mg L−1) was observed in bottom waters during Leg 1, with a ~ 660 km2 area experiencing hypoxic conditions (DO

Persistent eutrophication and hypoxia in the coastal ocean

“…Hypoxia is also increasingly documented in coastal waters globally at increased frequency, spatial extent, and severity that threats the ecosystem health and food security (e.g., Breitburg et al, 2018;Diaz and Rosenberg, 2008;Grégoire et al, 2021;Rabalais et al, 2014). However, the formation and dynamics of hypoxia are subject to a suite of complex and interactive physical, chemical, and biological processes (e.g., Fennel and Testa, 2019;Rabouille et al, 2008), leading to https://doi.org/10.1017/cft.2023.7 Published online by Cambridge University Press spatiotemporal heterogeneity of hypoxia and sometimes an apparent decoupling of eutrophication-hypoxia relationship (e.g., Hetland and DiMarco, 2008;Zhao et al, 2021).…”

Drivers of Phytoplankton Variability in and Near the Pearl River Estuary, South China Sea During Typhoon Hato (2017): A Numerical Study

“…The PRE is located in the central area of the Guangdong‐Hong Kong‐Marco Greater Bay Area of China. In recent years, with a rapidly growing population and socioeconomic development, input of nutrients and diverse contaminants increased rapidly, which led to a wide range of environmental problems, such as eutrophication, hypoxia, and ocean acidification (Guo et al., 2020; Hu et al., 2021; Ke et al., 2022; Y. Zhao et al., 2021). Furthermore, during the past decade, the activity of typhoons (also referred to as tropical cyclones [TCs] or hurricanes) has increased because of global warming (Balaguru et al., 2012, 2016; Da et al., 2021; Elsner et al., 2008; Goldenberg et al., 2001; Mei et al., 2015; Webster et al., 2005; Wu et al., 2005).…”

Long‐Term Patterns of Dissolved Oxygen Dynamics in the Pearl River Estuary

“…Notably, more deoxygenation was observed in the bottom water of Mirs Bay, while DO supersaturation was mostly absent in the surface layer, suggesting that biological activities were weak (Zhao, Uthaipan, et al., 2021). Therefore, autochthonous organics and subsequent remineralization may not strongly explain the great decrease in DO concentrations.…”

“…Given the long‐term deoxygenation trend and rapid urbanization and industrialization in the PRE, bottom DO concentrations under deoxygenation in 2025 are estimated to be ∼2.0 mg L −1 and ∼1.7 mg L −1 in Southern Hong Kong and Mirs Bay, respectively, corresponding to the hypoxic criterion (2.0 mg L −1 ), which reflects that both regions probably become seasonally hypoxic. In addition, seasonal DO depletion has been observed from intermittent detection before the 2000s to consistent hypoxia covering ∼1,000 km 2 , particularly in the western part of the lower estuary by recent cruises (Qian et al., 2018; Su et al., 2017; Ye et al., 2012; Yin et al., 2004; Zhao, Uthaipan, et al., 2021). Therefore, eastern areas off the PRE adjacent to Hong Kong, not considered in most previous studies, are also vulnerable to hypoxia.…”