From glacier to gorge: Peking University study maps the hidden life of river carbon along the upper Yangtze

It begins as a trickle high on the Tibetan Plateau—icy, remote, and pure. By the time it reaches the Three Gorges, the Yangtze River has grown into a force of nature, carrying not just water, but the chemical fingerprint of an entire continent. Now, a groundbreaking study from Peking University reveals the invisible story hidden in the river’s flow: the molecular evolution of dissolved organic matter (DOM) along a 3,500-kilometer stretch of the upper Yangtze—the world’s third-longest river. Published on August 11, 2025, in Carbon Research as an open-access original article, this research was led by Dr. Dongqiang Zhu from the College of Urban and Environmental Sciences and the Key Laboratory of the Ministry of Education for Earth Surface Processes at Peking University, Beijing. Using a powerful suite of analytical tools—including fluorescence spectroscopy, lignin phenol markers, and ultra-high-resolution Fourier-transform ion cyclotron resonance mass spectrometry (FT-ICR MS)—Dr. Zhu’s team traced how organic carbon changes as it travels from the river’s high-altitude headwaters to its densely populated downstream reaches. And what they found is a dynamic, ever-changing mosaic of carbon chemistry shaped by glaciers, grasslands, wildfires, forests, and sunlight.

The Journey Begins: Grasslands and Glacial Melt

At the very source—Tuotuo River, the official headwater—the DOM tells a story of ice and erosion. Here, the team found the highest levels of nitrogen- and sulfur-containing molecules, along with biolabile aliphatic and carbohydrate-like compounds—signs of intense glacial meltwater scouring the landscape and releasing fresh, microbially digestible organic matter. Even more surprising: the lignin (a key plant biomarker) in this remote region comes not from trees, but from non-woody flowering plants—grasses and herbs thriving in the high-altitude meadows of the Tibetan Plateau. “This challenges the old assumption that river DOM is mostly tree-derived,” says Dr. Zhu. “In the headwaters, it’s the grasslands that feed the river’s carbon load.”

Fire and Sun: The Midstream Transformation

As the river flows eastward, the chemistry shifts. At Sanduizi, a site in the upper reaches, researchers detected a spike in highly aromatic and polycyclic aromatic molecules—the molecular scars of wildfires. These compounds, formed when vegetation burns, are highly photolabile, meaning they break down easily under sunlight. Sure enough, further downstream, their abundance drops, showing that sunlight acts as a natural filter, degrading these compounds as the river flows toward the lowlands. Meanwhile, another type of molecule grows steadily in concentration: lignin-like compounds. These tough, recalcitrant molecules resist breakdown and accumulate as the river passes through forested and agricultural zones, where plants continuously shed organic matter into the water. By the time the river reaches the Three Gorges Dam, the DOM has undergone a complete transformation. Here, the organic carbon-normalized lignin content reaches its peak, reflecting decades of terrestrial input from forests and croplands.

Why This Matters for the Planet

The Yangtze doesn’t just feed China—it feeds the global carbon cycle. DOM carried by large rivers like the Yangtze influences ocean productivity, greenhouse gas emissions, and long-term carbon storage. But until now, the spatial complexity of how DOM changes along such vast river systems was poorly understood. “This isn’t just about one river,” explains Dr. Zhu. “The Yangtze is a model system. What we learn here helps us understand how carbon moves from land to sea in major rivers worldwide—from the Amazon to the Mississippi.” The study underscores that DOM is not a uniform substance, but a dynamic mixture shaped by geology, vegetation, climate, and human activity. It also highlights the importance of high-resolution molecular analysis in predicting how river carbon will respond to climate change, deforestation, and land use shifts.

A Landmark Achievement for Peking University

This research showcases the leadership of Peking University’s College of Urban and Environmental Sciences in cutting-edge biogeochemistry. The Key Laboratory of the Ministry of Education for Earth Surface Processes provides the advanced instrumentation and interdisciplinary environment needed to tackle complex questions about Earth’s carbon flows.

Dr. Dongqiang Zhu’s work exemplifies how field-based science, combined with state-of-the-art lab analysis, can reveal the hidden mechanisms driving global environmental change.

The Big Picture: Carbon on the Move

The Yangtze’s journey is more than a geographic path—it’s a chemical metamorphosis. From glacial melt to wildfire ash, from grassland leachate to forest runoff, every molecule tells a story of Earth’s surface in motion. As climate change alters snowmelt patterns, increases wildfire frequency, and reshapes vegetation zones, the composition of river DOM will change too—potentially altering carbon cycling on a planetary scale. With this study, Dr. Dongqiang Zhu and his team have drawn the first detailed map of that transformation. So the next time you see the Yangtze—on a map, in a photo, or in person—remember: beneath the surface, a vast, invisible river of carbon is flowing, one molecule at a time.

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• Title: Spatial distribution of composition and chemodiversity of surface water dissolved organic matter (DOM) over the upper reach of the Changjiang River
• Keywords: Changjiang River; Dissolved organic matter; Spatial distribution; Chemodiversity; FT-ICR MS; Lignin phenols
• Citation: Yin, S., Wei, C., Liu, Y. et al. Spatial distribution of composition and chemodiversity of surface water dissolved organic matter (DOM) over the upper reach of the Changjiang River. Carbon Res. 4, 58 (2025). https://doi.org/10.1007/s44246-025-00223-7 

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About Carbon Research

The journal Carbon Research is an international multidisciplinary platform for communicating advances in fundamental and applied research on natural and engineered carbonaceous materials that are associated with ecological and environmental functions, energy generation, and global change. It is a fully Open Access (OA) journal and the Article Publishing Charges (APC) are waived until Dec 31, 2025. It is dedicated to serving as an innovative, efficient and professional platform for researchers in the field of carbon functions around the world to deliver findings from this rapidly expanding field of science. The journal is currently indexed by Scopus and Ei Compendex, and as of June 2025, the dynamic CiteScore value is 15.4.

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