Using stable isotopes to estimate young water fractions in a heavily regulated, tropical lowland river basin

Trinh, Anh Duc; Do, Thu Nga; Panizzo, Virginia N.; McGowan, Suzanne; Leng, Melanie J.

Abstract

© 2020 John Wiley & Sons Ltd The young water fraction of streamflow (Fyw), an important hydrological variable, has been calculated for the first time, for a monsoon-fed coastal catchment in northern Vietnam. Oxygen stable isotopes (δ18O) from six river sites in the Day River Basin (DRB) were analysed monthly, between January 2015 and December 2018. River δ18O signatures showed sine wave variability, reflecting the amount effect and tropical (dry-rainy) seasonality of the region. The δ18O composition of precipitation ranged from −12.67 to +1.68‰, with a mean value of −5.14‰, and in-streamflow signatures ranged from −11.63 to −1.37‰ with a mean of −5.02‰. Fractions of young water (Fyw) were calculated from the unweighted and flow-weighted δ18O composition of samples. Unweighted Fyw ranged between 29 ± 8% and 82 ± 21% with a mean value of 51 ± 19%, and was not significantly different from flow-weighted Fyw (range between 33 ± 25% and 92 ± 73%, mean 52 ± 36%). Both unweighted and flow-weighted Fyw were highest in the middle of stream and lowest in downstream sites, capturing the impacts of landuse changes, hydrology and human activities in the catchment. Our calculations imply that more than a half of rainwater reaches the DRB river mainstream within the first 3 months. The Fyw is much higher than the global average (of one-third) and insensitive to discharge due to the combination of a humid catchment with high rainfall, low storage capacity, flat landscape and an intensive drainage system in the DRB. Also the low discharge sensitivity of Fyw in the DRB implies that the regional hydrology is severely altered by humans.

Citation

Trinh, A. D., Do, T. N., Panizzo, V. N., McGowan, S., & Leng, M. J. (2020). Using stable isotopes to estimate young water fractions in a heavily regulated, tropical lowland river basin. Hydrological Processes, 34(22), 4239-4250. https://doi.org/10.1002/hyp.13878

• Journal Article Type: Article
• Acceptance Date: Jul 23, 2020
• Online Publication Date: Aug 27, 2020
• Publication Date: Oct 30, 2020
• Deposit Date: Sep 8, 2020
• Publicly Available Date: Aug 28, 2021
• Journal: Hydrological Processes
• Print ISSN: 0885-6087
• Electronic ISSN: 1099-1085
• Publisher: Wiley
• Peer Reviewed: Peer Reviewed
• Volume: 34
• Issue: 22
• Pages: 4239-4250
• DOI: https://doi.org/10.1002/hyp.13878
• Keywords: Day River, discharge sensitivity, sine wave fitting, Vietnam, water isotopes
• Public URL: https://nottingham-repository.worktribe.com/output/4882223
• Publisher URL: https://www.onlinelibrary.wiley.com/doi/abs/10.1002/hyp.13878
• Additional Information: This is the peer reviewed version of the following article: Trinh, A. D., Do, T. N., Panizzo, V. N., McGowan, S., & Leng, M. J. (2020). Using stable isotopes to estimate young water fractions in a heavily regulated, tropical lowland river basin. Hydrological Processes, https://doi.org/10.1002/hyp.13878, which has been published in final form at https://onlinelibrary.wiley.com/doi/abs/10.1002/hyp.13878. This article may be used for non-commercial purposes in accordance with Wiley Terms and Conditions for Use of Self-Archived Versions.