Research Background
Rivers and streams constitute a critical source of atmospheric methane (CH₄). Previous studies have documented that headwater streams generally exhibit high CH₄ emission intensities and act as key hotspots for riverine CH₄ emissions.
Nevertheless, it remains unclear whether this pattern holds true for high‑altitude cryospheric regions. Constrained by low temperature and scarce organic‑carbon substrates, methane‑related biogeochemical processes in such regions may be greatly limited. Meanwhile, continuous input of glacial meltwater may further modify the CH₄ emission patterns of rivers.
How exactly does glacial meltwater regulate riverine CH₄ emissions, and what are the underlying mechanisms?
To address this scientific question, the research team led by Dr. Tanguang Gao from Lanzhou University selected the upper Heihe River basin on the northern Tibetan Plateau as the study site. Based on continuous observations spanning 2020‑2023, the team systematically compared CH₄ emission characteristics between glacier‑fed rivers and non‑glacier‑fed rivers, and further explored the regulatory mechanisms of glacial meltwater over riverine CH₄ emissions.
Figure 1. (a) Overview of the study area. (b) On-site photographs of gas sampling conducted using the floating gas chamber method during three separate field campaigns.
Research Methods
Experimental design: This study targeted the upper Heihe River basin on the northern margin of the Tibetan Plateau. From 2020 to 2023, 25 sampling sites were set up across the study catchment, among which 9 sites belonged to glacier‑fed rivers and 16 to non‑glacier‑fed rivers. A total of 12 field sampling campaigns were carried out. Two representative monitoring sites (H17 and H18) were selected for 24‑hour continuous diel observations in June 2020 and July 2021, with CH₄ flux measured every two hours.
Measured parameters: CH₄ flux, water temperature (WT), pH, dissolved oxygen (DO), electrical conductivity (EC), wind speed, air temperature, total nitrogen (TN), dissolved organic carbon (DOC), dissolved inorganic carbon (DIC), and other variables.
Notably, the PS‑3010 Ultra-portable CH₄/CO₂ Soil Flux system（LICA United, China） was deployed in combination with floating chambers to measure CH₄ flux across the water‑air interface. During field measurement, the floating chamber was lowered onto the water surface to form a closed headspace. CH₄ concentrations within the chamber were recorded every 10 s, and CH₄ flux was calculated from the linear slope of temporal concentration change.
Data analysis: The Mann‑Whitney U test was used for inter‑group difference analysis. Spearman rank correlation analysis was adopted to quantify associations between environmental variables and CH₄ flux. Monte‑Carlo simulation was applied to assess the uncertainty of regional emission estimates.
Key Research Results
1.The median CH₄ flux of glacier‑fed rivers was 3.15 (−0.64 – 8.63) μmol m⁻² d⁻¹, significantly lower than 5.45 (2.05 – 14.40) μmol m⁻² d⁻¹ for non‑glacier‑fed rivers. Glacier‑fed rivers had markedly lower DOC, water temperature and pH relative to non‑glacier‑fed counterparts. No statistically significant differences in DIC, TN, DO and EC were detected between the two river groups.
Figure 2. Comparison of CH₄ fluxes and physicochemical characteristics between glacially-fed rivers and non-glacially-fed rivers: (a) CH₄ flux, (b) DOC, (c) DIC, (d) TN, (e) DO, (f) EC, (g) pH, and (h) WT
2.For both glacier‑fed and non‑glacier‑fed rivers, CH₄ flux showed no significant variation across stream orders. This finding breaks the conventional paradigm that low‑order headwater streams are methane‑emission hotspots.
Figure 3. (a) Relationship between CH₄ flux and (b) DOC with river order
3.For glacier‑fed rivers, median CH₄ fluxes in spring, summer and autumn were 2.10 (0.07 – 8.29), 3.22 (0.30 – 6.75), and 8.63 (−1.17 – 12.08) μmol m⁻² d⁻¹ respectively, without significant seasonal difference. In contrast, non‑glacier‑fed rivers exhibited substantially higher autumn CH₄ flux [11.45 (3.38 – 16.11) μmol m⁻² d⁻¹] than spring and summer values. Dissolved CH₄ concentration in glacier‑fed rivers was significantly lower in summer than in spring, while no obvious seasonal shift was observed for non‑glacier‑fed rivers.
Figure 4. Seasonal variations in (a) CH₄ flux and (b) CH₄ degree in rivers
4. No statistically‑significant diel difference in CH₄ flux was observed for the glacier‑fed river site (H17). By contrast, the non‑glacier‑fed river site (H18) presented prominent diel variability: nighttime CH₄ flux was distinctly higher than daytime flux, showing an inverse diel pattern (low by day, high at night).
Figure 5. Daily variation in CH₄ flux. (a, b) Glacially-fed rivers; dates: July 17,2021, and July 18–19,2021, respectively. (c, d) Non-glacially-fed rivers; dates: June 1–2, 2020, and July 18,2021, respectively.
5. Modelling results indicate that glacial‑meltwater input suppresses total riverine methane emissions of the catchment by approximately 13 % ± 7 %.
Figure 6. Seasonal variation in CH₄ emissions in the upper and lower reaches of the Heihe River
6. Mechanism interpretation of suppression effects
Thermal constraint: Low water temperature brought by glacial meltwater inhibits methanogenic microbial metabolism.
Biogeochemical dilution effect: Oligotrophic glacial meltwater dilutes the concentration of substrates required for methanogenesis and reduces substrate supply.
Figure 7. Seasonal variations in (a) DOC, (b) DIC, (c) TN, (d) DO, (e) EC, (f) pH, (g) WT, and (h) the proportion of runoff
Conclusion and Outlook
This study demonstrates that glacial meltwater serves not only as a fundamental component of river hydrology, but also exerts vital regulatory control over riverine CH₄ emissions. Against the backdrop of climate warming and ongoing glacier shrinkage, the impacts of glacial meltwater on cryospheric river carbon cycling deserve sustained attention. Future research shall integrate long‑term field monitoring and mechanistic investigations to deepen our understanding of greenhouse‑gas emission responses of rivers under cryosphere change.
Published journal: Journal of Hydrology (Impact factor = 7.3)
Institutions: Lanzhou University, Northwest Institute of Eco‑Environment and Resources, Chinese Academy of Sciences, and other collaborating organizations
Study area: Upper Heihe River basin, northern Tibetan Plateau
Instrument: PS‑3010 Ultra-portable CH₄/CO₂ Soil Flux system
DOI: https://doi.org/10.1016/j.jhydrol.2026.136372