Human activities control the source of eroded organic carbon in lake sediments over the last 100 years: Evidence from stable isotope fingerprinting.

Understanding the redistribution of soil organic carbon (OC) driven by erosion contributes to the global carbon budget and watershed management. Quantifying the sources of eroded OC in sediments provides new insights to addressing this issue. However, limited quantitative information on the factors influencing OC sources has constrained the behavior of regulating the OC exported from the watershed. Here, we explored the sources of OC in lake sediments over the last 100 years and quantified the effects of climate change and human activities on OC sources. Results from the stable isotope fingerprinting and MixSIAR model indicated that phragmites (30.34%) and croplands (21.48%) were consistently the main OC sources. Therefore, efforts should be concentrated on controlling soil erosion from cropland and managing the endogenous environment. In addition, the partial least squares pathways (PLS-PM) and random forests revealed that human activities (Path coefficients (r): 0.45 to 0.61) have controlled the OC sources over the last hundred years. Agricultural activities, urbanization, and land use change altered the quality of OC sources by affecting the vegetation productivity in source areas. The quantity of OC sources was also influenced by underlying surface and surface connectivity changes. The effects of climate change (temperature (r): -0.41 to 0.1; precipitation (r): 0.1 to 0.29) on OC sources have not been significant, but their long-term effects cannot be ignored. These findings provide a better insight into the origin and behavior of OC in lake sediments under global change, which is crucial for basin management and lake governance.