Subsurface low dissolved oxygen occurred at fresh- and saline-water intersection of the Pearl River estuary during the summer period

Li, Gang; Liu, Jiaxing; Diao, Zeng-Hui; Jiang, Xin; Li, Jiajun; Ke, Zhixin; Shen, Pingping; Ren, Lijuan; Huang, Liangmin; Tan, Yehui

doi:10.1016/j.marpolbul.2017.09.061

Cited by 27 publications

(25 citation statements)

References 25 publications

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“…The data used for analysis comprise multiyear cruise observations in the PRE and its adjacent coastal waters compiled from five datasets (see Li et al (2020), in which the methods of sampling and chemical analysis were described in their Sect. 2.1.…”

Section: Data Sources Sample Collections and Measurementsmentioning

confidence: 99%

“…This emerging exacerbation of low-oxygen conditions in the surface water was primarily attributed to the influence of low-oxygen inflows from the upstream reaches (Zhai et al, 2005;He et al, 2014) and increasing sewage discharge brought by rapid economic development and urbanization in the Pearl River Delta over the past 30 years (X. Li et al, 2020). At the bottom, apparent low-oxygen conditions prevailed in all the summer months except August 1976 (a period prior to the implementation of China's reform and openingup policy), and their locations and spatial extent varied substantially between different periods (Fig.…”

Section: Seasonal Variations In Do-related Variables In the Prementioning

confidence: 99%

“…1) is the central area of the Guangdong-Hong Kong-Macao Greater Bay Area, surrounded by several megacities (including Guangzhou, Shenzhen, and Hong Kong). With a rapidly growing population and socioeconomic development, the PRE receives large inputs of nutrients and diverse contaminants, which has led to a wide range of severe problems in the estuary, such as eutrophication, red tides, hypoxia, and a decline in fishery resources (Dai et al, 2008;Harrison et al, 2008;X. Li et al, 2020).…”

Section: Introductionmentioning

confidence: 99%

“…Results showed that hypoxia mainly appeared in the bottom waters during summer, and freshwater-induced stratification and sediment oxygen consumption are the dominant factors leading to its generation (Zhang and Li, 2010;Wang et al, 2017;Yin et al, 2004); however, due to the combined effects of relatively shallow depth, high water turbidity, strong physical processes, and the short duration of vertical stratification (eroded by periodic tidal forcing and strong wind events; Luo et al, 2009;Lu et al, 2018), hypoxia was generally confined to a very small scale and occurred in an episodic and intermittent manner (X. Li et al, 2020;Rabouille et al, 2008). Nevertheless, notable low-oxygen (DO < 4 mg L −1 ) events, with their spatial extent much larger than that of previous ones, have been reported in recent works (Shi et al, 2019;Lu et al, 2018;Su et al, 2017;Li et al, 2018).…”

Section: Introductionmentioning

confidence: 99%

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Long-term spatiotemporal variations in and expansion of low-oxygen conditions in the Pearl River estuary: a study synthesizing observations during 1976–2017

Zhang

Wang

et al. 2021

Biogeosciences

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Abstract. The Pearl River estuary (PRE) frequently experiences low-oxygen conditions in summer, with large-extent low-oxygen events and a long-term deoxygenation trend being reported recently. In this study, we provide a synthesis of the spatiotemporal patterns and incidence of different low-oxygen levels in the PRE based on the in situ observations collected from 1976 to 2017 and aim to elucidate the underlying mechanisms of low-oxygen conditions and their changes over the past 4 decades. The long-term observations show that the dissolved oxygen (DO) content in the PRE has had significant temporal variability and spatial heterogeneity. Low-oxygen conditions (DO < 4 mg L−1) have occurred mostly in the bottom waters of 5–30 m during summer and early autumn, with locations and severity varying substantially between years. Coastal waters from the southwest of Lantau Island to the northeast of the Wanshan Archipelago were identified as a hotspot area prone to subsurface low-oxygen conditions due to the combined effects of comparatively deep topography, a certain residence time and stability of the water column, and enhanced oxygen depletion related to high phytoplankton biomass. In addition, the low-oxygen waters, either directly imported from the upstream reaches or generated locally and further transported with the estuarine circulation, also had considerable impacts on the oxygen levels in the estuary. As for early autumn, marked low-oxygen conditions were present in both the surface and the bottom waters. A large area affected by low oxygen (∼ 4450 km2) was found in September 2006, where the low-oxygen conditions were comparable to the most severe ones observed in summer. The area was formed by the inflows of low-oxygen waters from the upstream reaches and enhanced oxygen depletion driven by an intricate coupling of physical and biogeochemical processes. Our analysis also reveals there has been an apparent expansion of the summertime low-oxygen conditions at the bottom of the PRE since the years around 2000, coincident with major environment changes in the Pearl River region. Overall, the PRE seems to be undergoing a transition from a system characterized by episodic, small-scale hypoxic events (DO < 2 mg L−1) to a system with seasonal, estuary-wide hypoxic conditions in summer. Although exacerbated eutrophication associated with anthropogenic nutrient inputs has generally been considered the primary cause for the deterioration of low-oxygen conditions in the PRE, the sharp decline in sediment load may play an important role as well via increasing water transparency and thereby supporting higher and broader phytoplankton biomass in the estuary.

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Section: Data Sources Sample Collections and Measurementsmentioning

confidence: 99%

Section: Seasonal Variations In Do-related Variables In the Prementioning

confidence: 99%

Section: Introductionmentioning

confidence: 99%

Section: Introductionmentioning

confidence: 99%

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Long-term spatiotemporal variations in and expansion of low-oxygen conditions in the Pearl River estuary: a study synthesizing observations during 1976–2017

Zhang

Wang

et al. 2021

Biogeosciences

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show abstract

“…The data used for analysis comprise multiyear cruise observations in the PRE and its adjacent coastal waters compiled from five datasets (see were also used for analysis by X. Li et al (2020), in which the methods of sampling and chemical analysis were described in their Sect. 2.1.…”

Section: Data Sources Sample Collections and Measurementsmentioning

confidence: 99%

Long-term spatiotemporal variations and expansion of low-oxygen conditions in the Pearl River estuary: A study synthesizing observations during 1976–2017

Hu¹,

Zhang²,

Wang³

et al. 2021

Preprint

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Abstract. The Pearl River estuary (PRE) frequently experiences low-oxygen conditions in summer, with large extents of low-oxygen events and a long-term deoxygenation trend being reported recently. In this study, we provide a synthesis of the spatiotemporal patterns and incidence of different low-oxygen levels in the PRE based on the in-situ observations collected from 1976 to 2017, and aim to elucidate the underlying mechanisms of low-oxygen conditions and their changes over the past 4 decades. The long-term observations show that the oxygen content in the PRE had significant temporal variability and spatial heterogeneity. Low-oxygen conditions occurred mostly in the bottom waters of 5–30 meters during summer and early autumn, with locations and severity varying substantially among years. Coastal waters from the southwest of Lantau Island to the northeast of Wanshan Islands were identified as the hotspot area prone to subsurface low-oxygen conditions due to the combined effects of comparatively deep topography, proper residence time and stability of the water column, and enhanced oxygen depletion related to high phytoplankton biomass. In addition, the low-oxygen waters, either directly imported from the upstream reaches or generated locally and further transported with the estuarine circulation, also had considerable impacts on the oxygen levels in the estuary. As for early autumn, marked low-oxygen conditions were present both in the surface and bottom waters. A large area affected by low oxygen (~ 4,450 km2) was found in September 2006, where the low-oxygen conditions were comparable to the most severe ones observed in summer and formed by distinct mechanisms. Our analysis also reveals an apparent expansion of the summertime low-oxygen conditions at the bottom of the PRE since the years around 2000, coincident with the major environment changes in the Pearl River region. Overall, the PRE seems to be undergoing a transition from a system characterized by episodic, small-scale hypoxic events to a system with seasonal, estuary-wide hypoxic conditions. Although exacerbated eutrophication associated with anthropogenic nutrient inputs was generally considered the primary cause for the deterioration of low-oxygen conditions in the PRE, the sharp decline in sediment load may play an important role as well via increasing water transparency and thereby supporting higher and broader phytoplankton biomass in the estuary.

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Phytoplankton species composition as bioindicator in the largest fragmented channel of the Pearl River, China

Xie,

Hu,

Yang

et al. 2024

Environ Monit Assess

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Subsurface low dissolved oxygen occurred at fresh- and saline-water intersection of the Pearl River estuary during the summer period

Cited by 27 publications

References 25 publications

Long-term spatiotemporal variations in and expansion of low-oxygen conditions in the Pearl River estuary: a study synthesizing observations during 1976–2017

Long-term spatiotemporal variations in and expansion of low-oxygen conditions in the Pearl River estuary: a study synthesizing observations during 1976–2017

Long-term spatiotemporal variations and expansion of low-oxygen conditions in the Pearl River estuary: A study synthesizing observations during 1976–2017

Phytoplankton species composition as bioindicator in the largest fragmented channel of the Pearl River, China

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