Tracing monsoon precipitation, surface–groundwater interaction and seawater intrusion using stable isotopes in a subtropical river system

TY - JOUR

T1 - Tracing monsoon precipitation, surface–groundwater interaction and seawater intrusion using stable isotopes in a subtropical river system

AU - Nguyen, Nho Lan

AU - Do, Thu Nga

AU - Stumpp, Christine

AU - Stockinger, Michael

AU - Leng, Melanie J.

AU - McGowan, Suzanne

AU - Large, Andrew

AU - Henderson, Andrew C.G.

AU - Trinh, Anh Duc

N1 - Publisher Copyright: © 2026 IAHS.

PY - 2026/6/4

Y1 - 2026/6/4

N2 - This study identifies dominant moisture sources, develops an isotope-based framework for characterizing precipitation across a transboundary basin, and evaluates hydrological and anthropogenic influences using long-term isotope records from the lower Red River, Vietnam. Bi-monthly to monthly δ¹⁸O and δ²H measurements of rainfall and river-water were collected from February 2018 to June 2024. Strong rainfall–isotope relationships were observed, with d-excess values of 8–12‰ indicating dominant moisture contributions from the western equatorial Pacific. Isotope-altitude–continental–amount relationships were used to generate isotope time series for unmonitored sub-basins. River-water isotope seasonality agreed with GNIR data at similar latitudes but differed from the Mekong River due to contrasting latitudinal extent and moisture sources. Three river-water sources groups were identified: delta-origin, upstream inflow, and seawater-mixed. Enhanced evaporation, seawater intrusion, and increasing groundwater discharge due to anthropogenic activities are evident. d-excess is a robust indicator of seasonal evaporation in regulated and wetland-rich basins.

AB - This study identifies dominant moisture sources, develops an isotope-based framework for characterizing precipitation across a transboundary basin, and evaluates hydrological and anthropogenic influences using long-term isotope records from the lower Red River, Vietnam. Bi-monthly to monthly δ¹⁸O and δ²H measurements of rainfall and river-water were collected from February 2018 to June 2024. Strong rainfall–isotope relationships were observed, with d-excess values of 8–12‰ indicating dominant moisture contributions from the western equatorial Pacific. Isotope-altitude–continental–amount relationships were used to generate isotope time series for unmonitored sub-basins. River-water isotope seasonality agreed with GNIR data at similar latitudes but differed from the Mekong River due to contrasting latitudinal extent and moisture sources. Three river-water sources groups were identified: delta-origin, upstream inflow, and seawater-mixed. Enhanced evaporation, seawater intrusion, and increasing groundwater discharge due to anthropogenic activities are evident. d-excess is a robust indicator of seasonal evaporation in regulated and wetland-rich basins.

KW - Amount effect

KW - evaporation

KW - groundwater discharge

KW - seawater intrusion

KW - Southeast Asia

U2 - 10.1080/02626667.2026.2669190

DO - 10.1080/02626667.2026.2669190

M3 - Article

AN - SCOPUS:105041122465

SN - 0262-6667

JO - Hydrological Sciences Journal

JF - Hydrological Sciences Journal

ER -