Author(s)

Wu Ruibin ¹

Affiliation(s)

¹ Key Laboratory of Yangtze River Water Environment, Ministry of Education, Tongji University, Shanghai, 200092, China

Corresponding Author

Wu Ruibin

ABSTRACT

This study takes the Nangang River in southern China as a case example to explore the causes of low dissolved oxygen (DO) levels in urban rivers located within tidal river networks. Through field sampling, real-time monitoring, and data analysis, this study systematically examines the impacts of factors such as water quality patterns in main and tributary rivers, sediment oxygen demand (SOD), water temperature, and tides on DO. The results show that the DO concentration in the Nangang River decreases along the river's length, with concentrations at sections 10#, 12#, and 14# falling below 6.0 mg/L during certain periods, indicating that the downstream areas are at long-term risk of oxygen depletion. The Siqing North tributary (DO < 3.0 mg/L, BOD₅ > 6.0 mg/L, NH₃-N > 2.0 mg/L) and the Tangwei tributary (pH > 9, ORP < 50 mV) create high-intensity pollution pulses in the main river, representing significant external sources of pollution. The sediment oxygen demand (SOD) at points 7# and 9# reached 0.53 and 0.42 g·m⁻²·d⁻¹, respectively, far exceeding the hypoxia threshold of 0.3 g·m⁻²·d⁻¹, and constituting an important endogenous factor contributing to the continuous decline of DO. A significant negative correlation was found between water temperature and DO (r = -0.70, p < 0.01), with water temperature having a stronger influence than COD and NH₃-N. Tidal analysis showed that during the water diversion period, DO concentrations rapidly decreased, with the non-compliance rate reaching 99.6% in August 2022, indicating that tidal input under high-temperature conditions has a negative effect on reoxygenation. This study identifies the synergistic regulatory effects of multi-source coupling mechanisms, including tributary pollution, sediment oxygen demand, water temperature, and tidal interference, on the evolution of DO. It suggests prioritizing source control of highly polluted tributaries, sediment restoration in areas with high SOD values, and optimization of gate scheduling during summer to achieve the dual objectives of managing DO risks and restoring urban river ecosystems.

KEYWORDS

Dissolved Oxygen; Sediment Oxygen Demand; Pollution Input from Tributaries; Tidal River Networks; Urban Rivers

CITE THIS PAPER

Wu Ruibin, Study on the Spatiotemporal Distribution Characteristics of Dissolved Oxygen and Its Multi-source Driving Mechanisms in Typical Urban River Sections. Environment, Resource and Ecology Journal (2025) Vol. 9: 7-19. DOI: http://dx.doi.org/10.23977/erej.2025.090202.

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