A new study demonstrates that ramped pyrolysis/oxidation can distinguish the sources of carbon transported by rivers after extreme events.
When an earthquake or a rainstorm triggers widespread landslides, the landscape changes dramatically. At the same time, large amounts of organic carbon are eroded from the hillsides and transported downstream by rivers. Understanding the sources of this carbon is crucial because different types of organic carbon behave differently during erosion, transport, and burial, leading to distinct impacts on the global carbon cycle. Organic carbon derived from vegetation and soils, known as biospheric organic carbon, is relatively reactive and readily decomposes. However, when it is transported into lakes or oceans and buried in sediments, it can be stored for thousands of years, forming an important natural long-term geological carbon sink. In contrast, petrogenic organic carbon originates from sedimentary rocks that formed millions of years ago. Once this ancient carbon is exposed by erosion, transported into rivers, and oxidized, it releases carbon dioxide back to the atmosphere, acting as a geological carbon source.
A study by the researchers from the Institute of Earth Environment, Chinese Academy of Sciences applies a new way to answer this question. By establishing an emerging ramped pyrolysis/oxidation (RPO) equipment and analyzing suspended sediment samples collected before and after the 2008 Wenchuan earthquake, the team traced how earthquakes and extreme rainstorms mobilize different sources of particulate organic carbon (POC). Their findings provide new insight into the links between extreme events and the global carbon cycle, while revealing that earthquake-triggered landslides can continue to influence carbon transport in river systems for more than a decade after the initial event.
"Earthquakes and storms can transport vast amounts of sediment, but until now it has been difficult to determine how different sources of organic carbon are mobilized and evolve during river transport," said Dr. Jin Wang, the study's corresponding author. "The RPO equipment we recently installed at the Institute of Earth Environment allows us to distinguish carbon derived from vegetation, soils, and rocks within a single river sample, providing an entirely new way to investigate carbon cycling in mountain rivers."
Looking beyond traditional tracing methods
Mountain rivers transport organic carbon from forests, soils, and ancient sedimentary rocks to downstream lakes and oceans. These carbon sources play different roles in Earth's climate system. Conventional approaches often rely on stable isotopes, radiocarbon, or molecular biomarkers, but these tracers can overlap among different materials, making source identification difficult.
This study adopted RPO, a thermal analysis technique that separates organic matter according to its thermal stability. The technique progressively heats sediment samples and continuously measures the amount of carbon dioxide released at different temperatures. Because organic matter from plants, soils, and rocks possesses distinct chemical structures and thermal reactivity, each source produces a unique thermogram. These thermal fingerprints provide an additional and independent means of distinguishing organic carbon sources, particularly when sediments contain complex mixtures of material from multiple origins.
Earthquakes and storms mobilize different carbon pools
The team applied the technique to suspended sediments collected from the upper Min Jiang in southwest China, where the 2008 Wenchuan earthquake fundamentally altered the landscape by triggering tens of thousands of landslides. They also analyzed suspended sediment samples collected during a rainstorm event more than a decade after the earthquake.
The results revealed that earthquakes and storms affect carbon export in different ways. More than ten years after the earthquake, as vegetation gradually recovered across the catchment, the proportion of biospheric organic carbon transported by rivers decreased at equivalent suspended sediment concentrations. Nevertheless, loose rock debris generated by earthquake-triggered landslides resided on hillslopes, continuing to supply rivers with thermally stable, rock-derived organic carbon. In contrast, the extreme rainstorm primarily mobilized organic carbon from surface soils and vegetation, materials that are generally more reactive and more closely connected to the modern carbon cycle.
The study demonstrates that RPO can directly distinguish these contrasting carbon sources, allowing researchers to identify how different extreme events reshape carbon transport across mountain landscapes.
A new tool for studying Earth's carbon cycle in a changing world
Climate change is expected to increase the frequency and intensity of extreme rainfall in many mountain regions, while tectonically active landscapes will continue to experience large-scale earthquakes. These events can dramatically accelerate erosion, redistributing massive amounts of carbon from hillslopes into river systems.
Accurately simulating these processes is becoming increasingly important for improving global carbon cycle models and predicting future climate feedback. By demonstrating how RPO reveals pathways for carbon mobilization, the new study provides an innovative method for exploring one of the most dynamic and elusive components of the carbon cycle.
See the article:
Qu Y, Wang J, Zhu C, Cui X, Jin Z. 2026. Tracing the influence of earthquakes and storms on the erosion of particulate organic carbon based on ramped pyrolysis/oxidation. Science China Earth Sciences, 69(7): 2575–2585, https://doi.org/10.1007/s11430-025-1966-3
