Temporal effects of soil organic carbon mineralization during the formation of a siltation body produced by erosion

The construction of check dams on the Loess Plateau has altered the landscape through the creation of a large erosive siltation volume. Understanding the mechanisms that drive biogeochemical cycling within this unique, high-volume carbon pool is crucial for accurate assessments of global organic carbon dynamics. Understanding the time-scale effects of soil organic carbon (SOC) mineralization during the formation of siltation bodies is critical for a mechanistic understanding of these dynamics and for estimating the carbon storage potential of check dams. Through nuclear tracer elements (137Cs, 210Pb) analyze combining with the precipitation data during the operation of the check dam, we analyzed the siltation profiles formed by these dams to determine the year of formation and to classify the silt stages. We also observed SOC mineralization in different siltation stages with an average of 2.83 mg·kg−1·d-1, using field sampling and indoor incubation experiments, while the maximum value appeared in ST-4 (4.64 mg·kg−1·d-1). We found that the SOC mineralization in the initial (ST-1) and mid-term (ST-2) stages decreased, while mineralization in the late (ST-3) and terminal (ST-4) stages first increased before decreasing. In ST-3, mineralization lagged significantly and increased more slowly compared to ST-4 (ST-4: 26.78 % > ST-3: 9.60 %). There were significant differences in the type of carbon source utilized by soil microorganisms, and the degree of utilization gradually increased with siltation stage. The factors limiting SOC mineralization also varied across stages, and we quantified the direct and interactive contributions of each factor to mineralization. The direct effect of factors on SOC mineralization was significantly higher than the interaction between factors at all stages of siltation (ST-4:0.82>0.17; ST-3:0.94>0.05; ST-2:0.93>0.06; ST-1:0.96>0.04). We also calculated the amount of SOC fixed and released at each stage. During the 58 years the check dam has been operating, 41.56 kg of SOC has been mineralized and 1644.77 kg has been deposited to net 1603.16 kg of net SOC storage. Ultimately, we conclude that siltation bodies formed by check dams can significantly reduce SOC mineralization and play a positive role in the net storage of SOC. Thus, these mechanisms ought to contribute to the creation of a cohesive theory about the SOC pool evolution in check dams.