The Yangtze River, known as the third-longest river on the planet, embarks on a monumental journey beginning from the lofty heights of the Tibetan Plateau, then coursing nearly 3,500 kilometers to the east, carrying with it an intricate chemical signature that narrates the interplay between geological, biological, and climatic forces. A pioneering study conducted by researchers from Peking University, recently published on August 11, 2025, in the journal Carbon Research, unravels the molecular evolution of dissolved organic matter (DOM) along this vast waterway. Led by Dr. Dongqiang Zhu from the College of Urban and Environmental Sciences and the Ministry of Education’s Key Laboratory for Earth Surface Processes, this investigation utilized cutting-edge analytical technologies, including Fourier-transform ion cyclotron resonance mass spectrometry (FT-ICR MS), to expose the dynamic and diverse carbon chemistry hidden beneath the river’s surface.
From its inception, the Yangtze River’s DOM composition reveals a landscape shaped by extremes. At the official headwater, the Tuotuo River, high in the Tibetan Plateau, the DOM is dominated by nitrogen- and sulfur-bearing molecules indicating strong influences from glacial meltwater erosion. This initial stage is characterized by abundant biolabile aliphatic and carbohydrate-like compounds, chemical markers of freshly produced organic matter that microbes readily process. Surprisingly, lignin phenol analyses debunk the traditional view that riverine DOM primarily originates from forested trees; instead, non-woody flowering plants dominate, reflecting the unique high-altitude grassland and herbaceous vegetation of this remote environment. This insight revises long-held assumptions, suggesting that grassland ecosystems substantially contribute to the foundational organic carbon input in major river systems.
Progressing downstream, the chemistry of the river undergoes significant transformations. In the midstream region exemplified by the Sanduizi site, molecular signatures mark the impact of wildfires, revealing elevated levels of highly aromatic and polycyclic aromatic hydrocarbons formed during biomass burning. These fire-derived compounds are notably photolabile, breaking down rapidly when exposed to sunlight. This photodegradation results in a remarkable decline in these molecules further downstream, effectively demonstrating how solar radiation functions as a natural cleansing agent, transforming the river’s molecular makeup and influencing the fate of carbon compounds along its path.
Concurrently, another class of organic molecules demonstrates a contrasting behavior through the river’s continuum. Lignin-like compounds, recognized for their molecular resilience, accumulate progressively as the Yangtze traverses forested and agricultural regions. These recalcitrant carbon structures resist microbial and photochemical degradation, thereby persisting in aquatic environments and contributing to the peak organic carbon-normalized lignin content observed near the Three Gorges Dam. This accumulation reflects the extensive terrestrial inputs from mature forests and croplands, underscoring the profound influence of land use and vegetation cover on the river’s carbon composition.
Understanding the spatial heterogeneity of DOM in a river system of this scale is critical, not merely for regional environmental management but also for broader planetary carbon cycling. Large rivers like the Yangtze act as conduits, transporting vast quantities of organic carbon from land to ocean, thereby directly modulating coastal productivity, greenhouse gas exchange, and global carbon storage. Yet, prior to this comprehensive molecular-level assessment, the changes in DOM composition across large river stretches remained poorly understood. Dr. Zhu highlights that insights gleaned from the Yangtze serve as models applicable to global river systems, from the Amazon to the Mississippi, offering predictive frameworks for how carbon fluxes respond to environmental stressors.
The multidisciplinary approach embraced by Dr. Zhu’s team combined field-based sampling with sophisticated laboratory analyses, allowing for an unparalleled resolution in characterizing the molecular diversity and evolution of DOM. Techniques such as fluorescence spectroscopy and lignin phenol marker quantification complement the ultra-high-resolution FT-ICR MS to dissect the complex mixture of molecules constituting the river’s organic matter. This integrated analytical suite enables researchers to track subtle chemical changes and contextualize them within ecological and geochemical processes, providing a nuanced understanding of carbon transformations in dynamic freshwater systems.
Given the accelerating pace of climate change and human intrusion on natural landscapes, the findings raise speculation on how future environmental shifts may reshape the chemical trajectory of riverine organic matter. Warming temperatures are altering snowmelt timing and volume, potentially reshaping the quantity and quality of glacial inputs. Increased wildfire incidences instigate episodic pulses of aromatic compounds, while changing vegetation patterns due to land use and climate pressures redefine the terrestrial carbon landscape feeding the river. These cumulative effects could profoundly impact the river-to-ocean carbon transfer, with ramifications for global biogeochemical cycles.
Beyond its scientific contributions, this research signifies a significant milestone for Peking University, illustrating the institution’s leadership in environmental sciences and molecular-level earth system research. The collaboration fostered within the Key Laboratory of Earth Surface Processes provides a fertile ground for interdisciplinary initiatives that tackle complex carbon cycling questions. Leveraging such advanced infrastructure and intellectual capital, the team has not only answered longstanding questions but also paved avenues for future exploration of carbon dynamics within large river basins.
The Yangtze’s chemical story underscores the complexity embedded within so-called dissolved organic matter, far from a homogenous mixture, it represents a labyrinthine array of molecules—from labile to recalcitrant—each with distinct origins and environmental fates. This molecular mosaic encapsulates the intimate interactions between physical forces, biological communities, and anthropogenic influences, dynamically shaping carbon pathways in flowing waters. As Dr. Zhu puts it, the molecular fingerprints uncovered reflect “Earth’s surface in motion,” providing a powerful metaphor for how we perceive river systems not only as conveyors of water but as biologically active, chemically transforming networks.
For environmental scientists and policymakers alike, the implications of this work are profound. Effective management of carbon budgets and mitigation of climate change hinge on accurate predictions of organic carbon fluxes through freshwater systems. Molecular-level data such as that provided by this study furnish indispensable parameters for biogeochemical models, enhancing their ability to simulate future scenarios under varied anthropogenic and climatic pressures. Moreover, recognizing the variable lability of DOM components can inform water quality management, fisheries productivity, and conservation strategies within the river basin.
Looking forward, continuous monitoring and expanded molecular assessments across other large-river systems worldwide will be essential. Integrating the insights from the Yangtze with global datasets will improve our capacity to understand how terrestrial and aquatic ecosystems respond collectively to the accelerating environmental transformations. This study not only offers a detailed snapshot of current dynamics but establishes a benchmark against which future changes can be measured, serving the scientific community and the planet well.
Ultimately, the Yangtze River emerges as a living, breathing chemical entity, undergoing constant transformation driven by a confluence of natural and human forces. Dr. Dongqiang Zhu and his research team have illuminated this hidden dimension with unprecedented molecular clarity, showcasing the power of advanced analytical science to deepen our understanding of global carbon cycling. Beneath the river’s surface lies an invisible flow of carbon molecules—one that tells a rich and evolving story of Earth’s changing environment.
Article Title: Spatial distribution of composition and chemodiversity of surface water dissolved organic matter (DOM) over the upper reach of the Changjiang River
News Publication Date: 11-Aug-2025
References:
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). DOI: 10.1007/s44246-025-00223-7
Image Credits: Shujun Yin, Chenhui Wei, Yafang Liu & Dongqiang Zhu
Keywords: Changjiang River; Dissolved organic matter; Spatial distribution; Chemodiversity; FT-ICR MS; Lignin phenols
