Urbanization and seasonality strengthens the CO2 capacity of the Red River Delta, Vietnam

Salgado, J. et al. (2022) Urbanization and seasonality strengthens the CO2 capacity of the Red River Delta, Vietnam. Environmental Research Letters, 17(10), 104052. (doi: 10.1088/1748-9326/ac9705)

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Tropical rivers are dynamic CO2 sources. Regional patterns in the partial pressure of CO2 (pCO2) and relationships with other a/biotic factors in densely populated and rapidly developing river delta regions of Southeast Asia are still poorly constrained. Over one year, at 21 sites across the river system in the Red River Delta (RRD), Vietnam, we calculated pCO2 levels from temperature, pH, and total alkalinity and inter-linkages between pCO2 and phytoplankton, water chemistry and seasonality were then assessed. The smaller, more urbanized, and polluted Day River had an annual median pCO2 of 5,000 ± 3,300 µatm and the larger Red River of 2,675 ± 2,271 µatm. pCO2 was 1.6 and 3.2 times higher during the dry season in the Day and Red rivers respectively than the rainy season. Elevated pCO2 levels in the Day River during the dry season were also 2.4-fold higher than the median value (2,811 ± 3,577 µatm) of calculated and direct pCO2 measurements in > 20 sub/tropical rivers. By further categorizing the river data into Hanoi City vs. other less urban-populated provinces, we found significantly higher nutrients, organic matter content, and riverine cyanobacteria during the dry season in the Day River across Hanoi City. Forward selection also identified riverine cyanobacteria and river discharge as the main predictors explaining pCO2 variation in the RRD. After accounting for the shared effects (14%), river discharge alone significantly explained 12% of the pCO2 variation, cyanobacteria uniquely a further 21%, while 53% of the pCO2 variance was unexplained by either. We show that the urbanization of rivers deltas could result in increased sources of riverine pCO2, water pollution, and harmful cyanobacterial blooms. Such risks could be mitigated through water management to increase water flows in problem areas during the dry season.

Item Type:Articles
Additional Information:This work was supported by funding from the UKRI-GCRF NE/S008926/1 Living Deltas Hub and the NERC-NAFOSTED Research Partnerships Grant NE/P014577/1 Assessing human impacts on the Red River system, Vietnam, to enable sustainable management. We also thank the lab members of the Analytical Chemistry Department, Institute of Chemistry Vietnam Academy of Science and Technology A18, Hanoi, Vietnam, for fieldwork and laboratory support.
Glasgow Author(s) Enlighten ID:Zheng, Dr Ying and Bass, Dr Adrian
Authors: Salgado, J., Duc, T. A., Nga, D. T., Pannizo, V. N., Bass, A. M., Zheng, Y., Taylor, S., Roberts, L. R., Lacey, J. H., Leng, M. J., and McGowan, S.
College/School:College of Science and Engineering > School of Geographical and Earth Sciences
Journal Name:Environmental Research Letters
Publisher:IOP Publishing
ISSN (Online):1748-9326
Published Online:03 October 2022
Copyright Holders:Copyright © 2022 The Author(s)
First Published:First published in Environmental Research Letters 17(10): 104052
Publisher Policy:Reproduced under a Creative Commons License

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