Tracing the influence of earthquakes and storms on the erosion of particulate organic carbon based on ramped pyrolysis/oxidation

Earthquakes and storms can trigger extensive landslides, enhancing the erosion and transport of fluvial sediments and organic carbon, thereby affecting carbon cycle processes across multiple timescales. However, due to the stochastic nature of these extreme events and the scarcity of long-term observational data, coupled with the limitations of traditional methods for tracing particulate organic carbon (POC) sources, the mechanisms underlying the impacts of earthquakes and storms on POC sources and fluxes remain poorly understood. In particular, decadal-scale monitoring of earthquake impacts on riverine POC remains absent, limiting a systematic understanding of POC dynamics under extreme events. In this study, the ramped pyrolysis/oxidation (RPO) technique was applied to analyze the organic carbon composition of suspended sediment, vegetation, soil, and rock samples from the upper Min Jiang. RPO results demonstrate that organic carbon in vegetation and soils exhibits lower oxidation temperatures (<530 °C) and correspondingly lower activation energy (Ea<200 kJ mol⁻¹), whereas rock-derived petrogenic organic carbon (POC_petro) is characterized by higher activation energy (Ea>200 kJ mol⁻¹). Based on these significant differences in thermal stability, and the observed correlation between the ¹⁴C activity of organic carbon in suspended sediments and the proportion of the Ea<200 kJ mol⁻¹ fraction, RPO analysis is considered an effective approach for distinguishing biospheric POC (POC_bio) derived from vegetation and soils, and POC_petro in the Min Jiang basin. Using this approach, the study quantifies the variations in POC sources and fluxes before and after storms in the upper Min Jiang. Results show that storms mobilized more POC_bio into the river, with only two days of storms contributing approximately 30% of the annual suspended sediment and POC flux. Furthermore, RPO-based estimate of POC sources and fluxes in the upper Min Jiang during 2020–2021, compared with pre- and post-earthquake data, reveals that a decade after the earthquake, POC_bio concentrations have decreased at equivalent suspended sediment concentration levels compared to a decade ago as vegetation recovered, whereas the retention of landslide-derived rock debris and its continuous supply to the river led to a significant increase in the proportion of POC_petro. This study highlights the critical role of extreme events in basin-scale carbon cycle and emphasizes that the cumulative effects of earthquakes and storms can efficiently enhance riverine POC transport, thereby affecting regional carbon cycle processes.