Sediment organic carbon (SOC) is a precious archive that synthesizes anthropogenic processes that remove geochemical fluxes from watersheds. However, the scarcity of inspection about the dynamic mechanisms of anthropogenic activities on SOC limits understanding into how key human factors drive carbon dynamics. Here, four typical basins with similar natural but significantly diverse human contexts (high-moderate-low disturbance: XJ-ZS and YJ-LS) were selected to reconstruct sedimentation rates (SR) and SOC dynamics nearly a century based on 200-cm corers. A partial least squares path model (PLS-PM) was used to establish successive (70 years) and multiple anthropogenic data (population, agriculture, land use, etc.) quantification methods for SOC. Intensified anthropogenic disturbances shifted all SR from pre-stable to post-1960s fluctuating increases (total coefficient: high: 0.63 < low: 0.47 < medium: 0.45). Although land use change was co-critical driver of SOC variations, their trend and extent differed under the dams and other disturbances (SOC mutated in high-moderate but stable in low). For high basin, land use changes increased (0.12) but dams reduced (-0.10) the downstream SOC. Furthermore, SOC mutation corresponded to soil erosion due to urbanization in both periods A and B. For moderate, SOC was reversed with the increase in afforestation and cropland (-0.19) due to the forest excitation effect and deep ploughing, which corresponded to the drought in phase B and the anthropogenic ecological project in A. For low, the increase in SOC corresponded to the Great Leap Forward deforestation in period B and the reed sweep in A, which suggested the minor land change substantially affected (0.16) SOC in fragile environments. Overall, SOC dynamics revealed that anthropogenic activities affected terrestrial and aquatic ecosystems for near the centenary, especially land use. This is constructive for agroforestry management and reservoir construction, consistent with expectations like upstream carbon sequestration and downstream carbon stabilization.

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.