Effects of human activities on soil organic carbon redistribution at an agricultural watershed scale on the Chinese Loess Plateau

Abstract

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 (OCpetro) and young biospheric organic carbon (OCbio) from the watershed, which has a positive impact on the regulation of atmospheric CO2 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.