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Isotope Hydrology: Tracing Water’s Journey and Water–Rock Interactions in a Changing World

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A special issue of Water (ISSN 2073-4441). This special issue belongs to the section "Hydrology".

Deadline for manuscript submissions: 20 May 2026 | Viewed by 6830

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Special Issue Editors

Prof. Dr. Tianming Huang

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Institute of Geology and Geophysics, Chinese Academy of Sciences, Beijing, China
Interests: isotope hydrology; water–rock interactions; groundwater recharge; fate of nutrients (S-N-C); groundwater age dating
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Prof. Dr. Buli Cui

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School of Resources and Environmental Engineering, Ludong University, Yantai 264025, China
Interests: isotope hydrology; water–rock interactions; water cycle; moisture cycling; hydrochemistry; runoff process
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Prof. Dr. Xianjun Xie

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School of Environmental Studies, China University of Geosciences, Wuhan, China
Interests: isotope hydrology; groundwater contamination; arsenic hydro-biogeochemistry; aquifer remediation; machine learning in groundwater

Dr. Zhongyin Cai

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Institute of International Rivers and Eco-Security, Yunnan University, Kunming, China
Interests: isotope hydrology; monsoon; El Niño–Southern Oscillation; ice core; atmospheric water cycle

Prof. Dr. Jinlong Zhou

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Guest Editor

College of Hydraulic and Civil Engineering, Xinjiang Agriculture University, Urumqi 830052, China
Interests: isotope hydrology; groundwater recharge; groundwater age dating; water contamination tracing
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Prof. Dr. Zhonghe Pang

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Guest Editor

Institute of Geology & Geophysics, University of Chinese Academy of Sciences, Beijing, China
Interests: isotope hydrology; water–rock interaction; dynamics of the water cycle; water–rock–gas interaction; geothermal resources
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Special Issue Information

Dear Colleagues,

Isotope hydrology has emerged as a pivotal tool for understanding hydrological processes, tracing water movement, and addressing critical challenges in water resource management under changing climatic and anthropogenic pressures. By leveraging stable and radioactive isotopes, researchers gain unique insights into the origin, age, distribution, and interactions of water across the hydrological cycle. This Special Issue aims to highlight recent advancements, innovative methodologies, and interdisciplinary applications in isotope hydrology, fostering collaboration to tackle pressing global water security issues.

We invite contributions that explore the integration of isotopic techniques with hydrological, ecological, and climatological studies. Topics of interest include, but are not limited to, the following:

Isotopic tracing of groundwater recharge, flow pathways, and surface water–groundwater interactions;
Applications in climate change studies (e.g., paleohydrology, precipitation dynamics);
Water resource sustainability and contamination assessment using isotopic tracers;
Advances in analytical techniques (e.g., high-resolution spectrometry, compound-specific isotopes);
Ecohydrological processes and isotope-enabled modeling;
Isotopes in addressing transboundary water management and policy challenges.

This Special Issue seeks to showcase cutting-edge research, case studies, and reviews that bridge scientific discovery with practical solutions. By uniting diverse perspectives, we aim to advance the role of isotope hydrology in promoting resilient water systems and informed decision making.

We look forward to your submissions and to fostering a dynamic exchange of ideas within this critical field.

Prof. Dr. Tianming Huang
Prof. Dr. Buli Cui
Prof. Dr. Xianjun Xie
Dr. Zhongyin Cai
Prof. Dr. Jinlong Zhou
Prof. Dr. Zhonghe Pang
Guest Editors

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Keywords

isotope hydrology
water–rock–gas interaction
surface water–groundwater interaction
groundwater recharge
fate of nutrients (S-N-C-P)
groundwater age dating
water contamination tracing
water quality
atmospheric water cycle
paleoclimate
geothermal resources
CCUS (carbon capture, utilization, and storage)

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Published Papers (6 papers)

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Research

17 pages, 1824 KB

Open AccessArticle

Performance Evaluation and Application of TOC-CRDS for Various Stable Carbon Isotope Analyses in Groundwater

by Zhipeng Gao, Hao Zheng, Hai Lu, Di Zhang and Huaming Guo

Water 2026, 18(7), 783; https://doi.org/10.3390/w18070783 - 26 Mar 2026

Viewed by 443

Abstract

The comprehensive analysis of stable carbon isotopes in dissolved organic carbon (δ¹³C-DOC) and dissolved inorganic carbon (δ¹³C-DIC) is essential for understanding carbon cycling in groundwater systems. This study evaluated the performance, stability, and accuracy of a Total Organic Carbon analyzer coupled with Cavity Ring-Down Spectroscopy (TOC-CRDS) for the determination of δ¹³C-DOC and δ¹³C-DIC. Long-term stability tests using solid standards (acetanilide) demonstrated an average precision of 0.21‰ over five days, though initial instrument stabilization was found to be critical. Systematic sensitivity experiments revealed a strong dependence of isotopic accuracy on carbon mass. For liquid samples, a minimum carbon threshold of 50 μg C (equivalent to 6.25 mg/L DOC in an 8 mL injection) was established; above this threshold, analytical precision consistently remained better than 0.3‰. Validation using synthetic samples showed excellent agreement between measured and calculated values for both DOC and DIC. Furthermore, comparative analysis of natural groundwater samples revealed that TOC-CRDS results were highly consistent with those obtained by GasBench–Isotope Ratio Mass Spectrometry, with relative deviations within 5% for DOC and 6% for DIC. The study confirms that TOC-CRDS provides a robust, high-precision (<0.3‰), and cost-effective alternative to mass spectrometry for analyzing groundwater carbon isotopes, provided that sample carbon content exceeds the determined thresholds and appropriate calibration strategies are employed. Full article

(This article belongs to the Special Issue Isotope Hydrology: Tracing Water’s Journey and Water–Rock Interactions in a Changing World)

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26 pages, 3077 KB

Open AccessArticle

Hydrochemical and Isotopic Characterization of the Transboundary Ruo River Catchment (Malawi–Mozambique) and Its Impact on the Shire River Basin, Southern Africa

by Owen L. Phiri, Harold W. T. Mapoma, Bernard Thole, Limbikani C. Banda and Robert M. Kalin

Water 2026, 18(4), 458; https://doi.org/10.3390/w18040458 - 10 Feb 2026

Viewed by 989

Abstract

Integrating an end member catchment offers a mechanistic foundation for interpreting large basin hydrology. This critical aspect is rarely evident in Malawi’s river basin studies. This study characterizes the hydrochemistry of surface and groundwater and stable isotopes of water to gain a regional picture of how the Ruo River Transboundary Catchment (RRC) influences the Shire–Zambezi River Basin. Hydrochemistry (2013 to 2024) and stable isotope (2020 to 2022) data are used. Both Gibbs and Piper diagrams were used to interpret surface and groundwater facies and hydrogeochemical processes controlling mineralization of water. SI biplots were used to trace water sources, mixing signals, and evaporation trends. Low to moderate mineralization is noted in surface and groundwater sources, and electrical conductivity varied between 19 and 622 µS/cm and 31 and 1930 µS/cm for surface (12 sites) and groundwater (151 boreholes), respectively. Piper diagram analysis reveals a Ca-Mg-HCO₃ water type dominance. Gibbs plots suggested dissolution of silicate minerals and interaction of surface and groundwater. Stable oxygen (δ¹⁸O) and hydrogen (δ²H) isotope ratios in precipitation, surface, and groundwater exhibit a similar pattern, indicating a common meteoric input, variability in moisture source, and significant interaction of surface water and groundwater. SI plots indicate mixing of precipitation, surface, and groundwater of RRC. Finally, the Ruo River at flood stage reverses the flow of the Shire River sub catchments, impacting the water quality and quantity of the Zambezi, and, therefore, should be considered an important mixing end member in the Lower Shire Basin. Full article

(This article belongs to the Special Issue Isotope Hydrology: Tracing Water’s Journey and Water–Rock Interactions in a Changing World)

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26 pages, 4391 KB

Open AccessArticle

Origin and Hydrogeochemical Evolution of Jety-Oguz Mineral Waters (Issyk-Kul Basin, Tien Shan)

by Ekaterina I. Baranovskaya, Natalia A. Kharitonova, George A. Chelnokov, Farid S. Salikhov and Irina A. Tarasenko

Water 2026, 18(1), 75; https://doi.org/10.3390/w18010075 - 26 Dec 2025

Viewed by 827

Abstract

This article presents a comprehensive study of the nitrogen-radon thermal mineral waters of the Jety-Oguz area, located in the southeastern part of the Issyk-Kul intermountain artesian basin (Northern Tien Shan). Based on new data from chemical and isotopic (δ¹⁸O, δD) analyses of natural waters (lake, river, and mineral) and the chemical composition of the water-bearing rocks, we identify the formation mechanisms of mineral waters with diverse composition, total dissolved solids (TDS), and temperature. Three main genetic types have been identified: (1) saline, high-TDS (up to 12.8 g/L) chloride sodium-calcium thermal waters (up to 32 °C). These waters are of meteoric origin and circulate within Middle Carboniferous carbonate rocks, acquiring their unique composition at depths of up to 3.0 km, where reservoir temperatures reach ~105 °C; (2) chloride-sulfate sodium-calcium waters (0.5 g/L, fresh, 22 °C), formed in alluvial deposits within the zone of active water exchange; and (3) low-TDS (1.8 g/L, brackish) waters of mixed composition, resulting from the mixing of a deep fluid with infiltrating meteoric waters. Isotopic data confirm a meteoric origin for all studied waters, including the high-TDS thermal types. The chemical composition diversity is attributed to several processes: mixing between the deep, high-TDS fluid and low-TDS infiltration waters, intense dissolution of evaporite rocks, and water–rock interaction. These findings are crucial for understanding the genesis of mineral waters in the Tien Shan intermountain basins and provide a scientific basis for their sustainable balneological exploitation. Full article

(This article belongs to the Special Issue Isotope Hydrology: Tracing Water’s Journey and Water–Rock Interactions in a Changing World)

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17 pages, 3818 KB

Open AccessArticle

Water and Soil Salinization Mechanism in the Arid Barkol Inland Basin in NW China

by Ziyue Wang, Chaoyao Zan, Yajing Zhao, Bo Xu, Rui Long, Xiaoyong Wang, Jun Zhang and Tianming Huang

Water 2025, 17(24), 3462; https://doi.org/10.3390/w17243462 - 5 Dec 2025

Viewed by 1220

Abstract

Identifying the dominant mechanisms of water and soil salinization in arid and semi-arid endorheic basins is fundamental for our understanding of basin-scale water–salt balance and supports water resources management. In many inland basins, mineral dissolution, evaporation, and transpiration govern salinization, but disentangling these processes remains difficult. Using the Barkol Basin in northwestern China as a representative endorheic system, we sampled waters and soils along a transect from the mountain front through alluvial fan springs and rivers to the terminal lake. We integrated δ¹⁸O–δ²H with hydrochemical analyses, employing deuterium excess (d-excess) to partition salinity sources and quantify contributions. The results showed that mineral dissolution predominated, contributing 65.8–81.8% of groundwater salinity in alluvial fan settings and ~99.7% in the terminal lake, whereas direct evapoconcentration was minor (springs and rivers ≤ 4%; lake ≤ 0.2%). Water chemistry types evolved from Ca-HCO₃ in mountainous runoff, to Ca·Na-HCO₃·SO₄ in groundwater and groundwater-fed rivers, and finally to Na-SO₄·Cl in the terminal lake. The soil profiles showed that groundwater flow and vadose-zone water–salt transport control spatial patterns: surface salinity rises from basin margins (<1 mg/g) to the lakeshore and is extremely high near the lake (23.85–244.77 mg/g). In spring discharge belts and downstream wetlands, the sustained evapotranspiration of groundwater-supported soil moisture drives surface salt accumulation, making lakeshores and wetlands into terminal sinks. The d-excess-based method can robustly separate the salinization processes despite its initial isotopic variability. Full article

(This article belongs to the Special Issue Isotope Hydrology: Tracing Water’s Journey and Water–Rock Interactions in a Changing World)

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23 pages, 5337 KB

Open AccessArticle

Hydrogeochemical Characteristics of Hot Springs and Mud Volcanoes and Their Short-Term Seismic Precursor Anomalies Around the Muji Fault Zone, Northeastern Pamir Plateau

by Shihan Cui, Fenna Zhang, Xiaocheng Zhou, Jingchao Li, Jiao Tian, Zhaojun Zeng, Yuwen Wang, Bingyu Yao, Gaoyuan Xing, Jinyuan Dong, Miao He, Han Yan, Ruibin Li, Wan Zheng, Kayimu Saimaiernaji, Chengguo Wang, Wei Yan and Rong Ma

Water 2025, 17(22), 3241; https://doi.org/10.3390/w17223241 - 13 Nov 2025

Viewed by 1349

Abstract

The Muji Fault Zone (MJF) in the northeastern Pamir Plateau hosts a well-developed non-volcanic geothermal system, characterized by widespread hot springs and mud volcanoes—where core processes of geothermal fluids, including atmospheric precipitation recharge, shallow crustal circulation, carbonate-driven water–rock interactions, and CO₂-rich fluid discharge, are tightly coupled with regional intense crustal deformation and frequent seismic activity. We collected and analyzed 22 geothermal water samples and 8 bubbling gas samples from the MJF periphery, finding that the geothermal waters are predominantly of the HCO₃-Ca·Mg hydrochemical type, with hydrogen (δD: −103.82‰ to −70.21‰) and oxygen (δ¹⁸O: −14.89‰ to −10.10‰) isotopes indicating atmospheric precipitation as the main recharge source. The Na-K-Mg ternary diagram classified the waters as immature, reflecting low-temperature water–rock interactions in the shallow crust (<3 km), while noble gas isotopes (³He/⁴He: 0.03–0.09 Ra, Ra = 1.43 × 10⁻⁶) and carbon isotopes (δ¹³C-CO₂) confirmed fluid origin from crustal carbonate dissolution; SiO₂ geothermometry estimated thermal reservoir temperatures at 67–155 °C. Long-term monitoring (May 2019–April 2024) of Tahman (THM) and Bulake (BLK) springs revealed significant pre-seismic anomalies: before the 2023 Tajikistan Ms7.2 and 2024 Wushi Ms7.1 earthquakes, Na⁺, Cl⁻, and SO₄²⁻ concentrations showed notable negative anomalies (exceeding 2σ of background values) with synchronous trends between the two springs. Integrating these findings, a “Fault-Spring-Mud Volcano-Earthquake” fluid response model was established, providing direct evidence of deep-shallow fluid coupling in mud volcano–geothermal fluid interactions. This study enhances understanding of the dynamic evolution of non-volcanic geothermal systems under tectonic stress and clarifies the mechanisms of hydrogeochemical variations in fault-controlled geothermal systems, offering a robust scientific basis for advancing research on tectonic–fluid interactions in active fault zones of the northeastern Pamir Plateau. Full article

(This article belongs to the Special Issue Isotope Hydrology: Tracing Water’s Journey and Water–Rock Interactions in a Changing World)

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17 pages, 1787 KB

Open AccessArticle

In Situ Monitoring of Water Isotopic Composition for Vapor and Precipitation Near-Surface Ground in East Asia Subtropical Monsoon Region

by Xingxian Li, Wenmin Qiu, Ziwei Lin, Changyuan Tang and Yingjie Cao

Water 2025, 17(20), 3011; https://doi.org/10.3390/w17203011 - 20 Oct 2025

Viewed by 884

Abstract

Hydrogen and oxygen isotopes in atmospheric water vapor (δ_v) and precipitation (δ_p or δ_r) were continuously measured using a laser-based water isotope spectrometer in Guangzhou, southeastern China, from March 2016 to February 2018. The measurements were conducted to investigate the variations in water isotopes in the hydrological cycle under the subtropical monsoon climate. The isotopic composition ranged from −24.4‰ to −11.1‰ for δ¹⁸O in water vapor (δ¹⁸O_v) and from −11.5‰ to 2.3‰ for δ¹⁸O in precipitation (δ¹⁸O_r). The values of δ_v and δ_r were enriched during the dry season and depleted during the wet season, exhibiting systematic seasonal variation. A negative correlation was observed between monthly δ_v and precipitation amount, indicating that the values of δ_v exhibits an ‘amount effect’. However, a corresponding amount effect was not observed in the values of δ_r. The mean difference between δ_v and δ_r was −9.7‰ for δ¹⁸O and −76‰ for δD, suggesting that equilibrium fractionation is the dominant process during precipitation. The local meteoric vapor line (LMVL) for Guangzhou (δD = 6.6δ¹⁸O − 6.4) exhibited a slope similar to that of the equilibrium local meteoric vapor line (ELMVL) but with an intercept difference of 8.6. This difference in intercepts can be attributed to the vertical profile of δ_v. The δD-q (q refers to water vapor concentration) relationship is useful for identifying water vapor sources and tracking isotopic changes during atmospheric transport and precipitation. The local water vapor was found to originate primarily from the mixing of oceanic air masses. Data points falling between the oceanic source mixing line and the Rayleigh curve likely reflect post-condensation processes, such as raindrop re-evaporation or mixing with surrounding ambient vapor. Short periods of heavy precipitation were observed to cause severe depletion in δ_v, resulting in values falling below the Rayleigh curve. Full article

(This article belongs to the Special Issue Isotope Hydrology: Tracing Water’s Journey and Water–Rock Interactions in a Changing World)

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