Research paperEffects of erosion on the microaggregate organic carbon dynamics in a small catchment of the Loess Plateau, China

- Sediments with fine microaggregate fractions had the high SOC amount.
- Sediments with coarse microaggregate fractions had the high SOC concentration.
- The microaggregate SOC dynamics are related to two main erosion processes.
- Rill and gully erosion are the dominant erosion processes in this small catchment.
- The <50 μm microaggregate fraction plays a key role in carbon sequestration.

Soil erosion significantly affects the dynamics of the terrestrial carbon (C) cycle. Erosion removes C-rich topsoil and deposits it in lower-elevation areas and exposes deeper C-poor horizons at the surface. However, the mechanisms responsible for the mobilization and deposition of microaggregate soil organic carbon (SOC) due to soil erosion at the catchment scale remain unclear. The main objective of this study is to illustrate the effects of different erosion processes on the distribution and deposition of microaggregate SOC. The activity of 137Cs and extreme rainfall events were used as dating methods Based on the microaggregate size distribution and the K-means clustering approach, 75 flood couplets were identified in an 11.3-m sediment deposit profile of the check dam in the Nianyangou catchment and classified into three couplet types. In each flood couplet, the SOC concentrations and amounts in three microaggregate fractions (250-50, 50-20 and <20 μm) were quantified. The following results were obtained. (1) 137Cs activity and a record of extreme rainfall events can be used to characterize the sediment deposition process. (2) Sediments with fine microaggregate fractions (Couplet Type I) contained abundant SOC and were mainly associated with low-intensity rainfall conditions, whereas sediments with coarse microaggregate fractions (Couplet Type III) had higher SOC concentrations and were mainly associated with high-intensity rainfall conditions. (3) Couplet Type I sediments were most likely related to sheet and interrill erosion, whereas Couplet Type III sediments were likely associated with rill and gully erosion. Our study contributes to the understanding of the effects of soil erosion on microaggregate SOC dynamics at the catchment scale and further illustrates the carbon sequestration mechanism active in check dams of the Loess Plateau.