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• Land use change significantly reduces the lateral transport of sediment and SOC. • About 21.6–42.9 % of the mobilized SOC is effectively buried behind the check dams. • Soil conservation measures generated significant carbon sequestration effect. • The composition and age of SOC were quantified by radiocarbon isotopes. Human activity is thought to perturb the dynamic change of organic carbon (OC), but its impact on the transportation and redistribution of erosion-induced OC is still poorly understood. Here, we use multi-source field sampling data and long-term hydrological observation data to clarify the transportation and redistribution of OC in an agricultural watershed on the Loess Plateau. The endmember mixing model based on the radiocarbon isotopes (14C) and a budget equation were used to assess the composition and budget of erosion-induced OC in a 187 km2 watershed. The results showed that compared with the period of agricultural activities (1960−1969), soil conservation activities in 1970−1999 and 2000−2019 reduced soil erosion by 31.5 % and 75.4 %, respectively. Additionally, land use changes significantly reduced the mobilized OC, from 14,370 ± 1966 (1960−1969) to 3311 ± 431 Mg C yr−1 (2000−2019). Check dam construction led to the mobilized OC was effectively buried at a rate of 2125 ± 478 and 1420 ± 282 Mg C yr-1 in periods of 1970−1999 and 2000−2019, respectively. Further radiocarbon isotopes analysis shows that the land use changes and check dam construction effectively reduced the output of ancient petrogenic organic carbon (OC petro) and young biospheric organic carbon (OC bio) from the watershed, which has a positive impact on the regulation of atmospheric CO 2 level. Our results emphasize the positive effects of soil conservation activities on terrestrial carbon sequestration, which are of great significance to clarify the effects of soil erosion on the carbon cycle. [ABSTRACT FROM AUTHOR]

Soil erosion affects the redistribution of soil and associated soil organic carbon (SOC) from different landforms, and it has significant implications regarding the fate of eroded SOC and terrestrial carbon sequestration. Despite the importance of soil erosion, few studies have evaluated the sources and budget of eroded SOC in the Loess Plateau region, which suffers from severe soil erosion. Based on an 11.3 m check dam sediment profile, we used the 137 Cs activity and extreme rainfall events as dating methods to date sediment sequences. In addition, the natural abundance levels of the stable carbon isotope (δ 13 C) of bulk organic matter and a two-end-member mixing model were used to discriminate the sources of eroded SOC from different siltation stages retained by the check dam in an intensive agricultural catchment of the Loess Plateau, China. The eroded SOC captured by the check dam was compared to potential source materials from different landscape units, which included sloping cropland and gully surface soils (0–5 cm). The results showed that the check dam intercepted 98.5 Gg of eroded soil and 172.6 Mg of SOC. The eroded SOC was primarily sourced from sloping cropland, which contributed to 81.3% of the total SOC retained by the check dam, whereas the gully soils contributed to 18.7% during the entire siltation stage. Additionally, the contribution of sloping cropland to eroded SOC increased from 1960 to 1990 as a result of rainfall and anthropogenic activities. A total of 89.7 Mg SOC was lost during soil erosion processes at a rate of 0.17 Mg ha −1 yr −1 and accounted for approximately 30% of the total eroded SOC exported from the eroding areas. Our results indicate that the soil erosion process has been an important net source of SOC in the study catchment. The check dam served as a carbon storage and sequestration structure for the hilly loess region due to its beneficial conditions for carbon sequestration over broad temporal and spatial distributions. [ABSTRACT FROM AUTHOR]