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

Qian, Wei; Zhang, Shi; Tong, Chuan; Sardans, Jordi; Peñuelas, Josep; Li, Xiaofei

doi:10.1029/2022jg006967

Cited by 12 publications

(7 citation statements)

References 75 publications

(130 reference statements)

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“…The low oxygen conditions have also remarkably deteriorated in the bottom waters of the lower estuary (Qian et al, 2018;Su et al, 2017;Zhao et al, 2020), even though its shallow topography (averaged depth of ~10 m) and relatively strong mixing (induced by tides and wind) physically make the estuary less prone to develop large-scale hypoxic events (Harrison et al, 2008). A significant decline in bottom-water oxygenation, at a rate of ~2 ± 0.9 µmol kg -1 yr -1 , has been observed in the lower estuary over the past three decades (Qian et al, 2018;Qian et al, 2022), with an expansion of the hypoxic area over the last two decades (Figure S5d). Two prominent hypoxic centers have been found with a total area of ~ 700 km 2 in the coastal transition zone off the estuary (Hu et al, 2021;Su et al, 2017;Yin et al, 2004;Zhao et al, 2020;Zhao et al, 2021).…”

Section: Pearl River Estuarymentioning

confidence: 99%

Persistent eutrophication and hypoxia in the coastal ocean

Dai

Chai

Chen

et al. 2023

Camb. prisms Coast. futures

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Nutrient loading (notably nitrogen and phosphorus) to coastal oceans from food production, fossil fuel burning, aquaculture operations, and wastewater from humans, livestock, and industry has accelerated during the past decades, causing over-enrichment of nutrients, or eutrophication. Eutrophication degrades coastal water quality with two most common symptoms, hypoxia and harmful algal blooms, creating profound ecological and societal consequences such as biodiversity decline, seagrass loss, coral bleaching, fish kills and marine mammal mortalities, and human health threats. Such marine pollution symptoms have persisted although billions of dollars have been invested in both research and management as well as efforts of restorations in many developed countries. Consequently, we are still witnessing trends in the expansion of coastal eutrophication and hypoxia from developed regions into developing regions. Though the limited efficacy of mitigation witnessed so far suggests the complexity of the issue, we contend that closing the knowledge gaps in the causality between eutrophication and hypoxia is essential and crucial towards making science-and evidence-based policies. We recognize that the non-linear cause-effect relationship in coastal marine ecosystem degradation caused by multi-stressors is complex.The strength and synergistic effect of multiple driving forces of coastal eutrophication is dependent on regional geographic feature, economic development, and societal management, while the long-term trends of eutrophication and hypoxia are subject to the control of the trends in nutrient loadings and physical dynamics under a changing climate. This review also examines lessons from past eutrophication management practices, and advocates for a better, more efficient indexing system of coastal eutrophication and an advanced regional earth system modeling framework to facilitate the development and evaluation of effective policy and restoration actions.

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Section: Pearl River Estuarymentioning

confidence: 99%

Persistent eutrophication and hypoxia in the coastal ocean

Dai

Chai

Chen

et al. 2023

Camb. prisms Coast. futures

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“…In some cold periods, the DO concentrations were recorded up to ~15.0 mg/L at a salinity of 31.6 and 7.8 • C of water temperature (30 March 2015; 158% supersaturation of DO). This hyperoxic condition is commonly observed in areas with high nutrient supply [38], as well as in the semi-enclosed bays, which are typical along the Korean coast [12,13,39].…”

Section: Surface Do Distributionmentioning

confidence: 91%

Assessment of Water Quality in a Coastal Region of Sea Dike Construction in Korea and the Impact of Low Dissolved Oxygen Concentrations on pH Changes

Lee

et al. 2023

JMSE

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To investigate the factors affecting water quality in coastal regions with sea dike constructions, surface water outside a sea dike was monitored for six years from 2015 to 2020 in the Saemangeum region of Korea. Statistical analyses of the six years of high-frequency measurements revealed that the water quality in this system was predominantly governed by natural processes followed by pollutant inputs as the secondary influencing factor. Severe dissolved oxygen (DO) depletion was observed in the surface waters during warm periods, probably owing to the advection of DO-depleted water from elsewhere to the surface layer. Based on the apparent oxygen utilization (AOU)–pH relationship (r = 0.52, n = 1837), the maximum AOU (180 µM) led to a pH decrease from 8.04 to 7.50, which was considerably lower than the estimated value of 7.72. This extra pH drop was probably due to a reduction in the buffering capacity associated with increased CO2 in the water column originating from the atmosphere and in situ production, as well as local water column redox reactions associated with benthic inputs of reduced chemical species. Overall, persistent DO depletion with ongoing eutrophication/hypoxia could accelerate ocean acidification in Korean coastal waters, which could be more acute in coastal regions with artificial coastal constructions.

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“…Nevertheless, there are currently not many studies on the spectral signature of DO in water due to several factors that influence oxygen availability, such as temperature, salinity, pH, and organic matter. DO concentrations were summarized and analyzed as the crucial drivers of hypoxia in Northwestern and Southern Hong Kong and Mirs Bay over the past three decades [20].…”

Section: Related Workmentioning

confidence: 99%

UV Absorption Spectrum for Dissolved Oxygen Monitoring: A Low-Cost Proposal for Water Quality Monitoring

Miura,

Parra,

Lloret

et al. 2023

Photonics

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One of the key indicators of water quality is dissolved oxygen. Even though oxygen is important in environmental monitoring, the sensors for dissolved oxygen are expensive and require periodic maintenance due to the use of membranes. In this paper, we propose using ultraviolet light absorption to estimate dissolved oxygen saturation in water samples. The absorption spectrum of dissolved oxygen in the ultraviolet range is investigated over a water matrix with different levels of complexity. First, the difference between different water matrixes is studied. The results indicate similar variations between river water and tap water matrices for comparative purposes. Both samples present much higher absorbance signals than distilled water. Thus, the rest of the tests were performed with only three water matrixes (ultrapure, distilled, and river water). By aerating, water samples were completely saturated. Then, nitrogen gas was used to remove dissolved oxygen from samples to obtain saturations of 75, 50, 25, and 3%. The absorption was measured from 190 to 380 nm, using LLG-uniSPEC 2. The obtained data were used to generate regression models for selected wavelengths (190, 210, 240, and 250 nm). The differences beyond 260 nm for the studied dissolved oxygen saturations were null. The generated models had correlation coefficients from 0.99 to 0.97 for ultrapure water, 0.98 to 0.95 for distilled water, and 0.90 to 0.83 for river water. The maximum differences were found between samples with 75 and 100% of saturation.

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

Cited by 12 publications

References 75 publications

Persistent eutrophication and hypoxia in the coastal ocean

Persistent eutrophication and hypoxia in the coastal ocean

Assessment of Water Quality in a Coastal Region of Sea Dike Construction in Korea and the Impact of Low Dissolved Oxygen Concentrations on pH Changes

UV Absorption Spectrum for Dissolved Oxygen Monitoring: A Low-Cost Proposal for Water Quality Monitoring

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