Deposition- and transport-dominated erosion regime effects on the loss of dissolved and sediment-bound organic carbon: Evaluation in a cultivated soil with laboratory rainfall simulations.

Abstract Erosion-induced soil carbon loss has been identified as a critical process in the global carbon (C) cycle. Surface coverage substantially alters the soil erosion process and the effects of net loss or deposition on soil organic C (SOC). However, information on SOC loss induced by soil erosion at the process level is limited. The aim of this study was to investigate how runoff and erosion regimes affect dissolved and sediment-bound organic C (DOC and SBOC) loss. Thus, six simulated rainfall events were conducted on two laboratory plots (9.75 m × 1.83 m) with different surface coverages (17–83%) and coverage distributions (upslope vs. downslope) using polypropylene geotextiles. The results showed that the variability in the process of runoff and sediment yield existed as a result of altered surface coverage over the erosion zone (SSerosion zone) and covered zone (SScovered zone) on the slope. Thus, the erosion regimes can be identified as deposition- and transport-dominated processes, which were the main soil erosion subprocesses. The surface coverage located downslope (SCtop-bottom slope) can more efficiently reduce runoff (21.9–85.7%) and sediment (67.6–98.3%) than the SCbottom-top slope (runoff: 20.1–83.0%; sediment: 35.0–93.3%), which has the surface coverage located upslope. DOC (8.0–11.3 mg L−1) and SBOC (0.3–0.5 mg g−1) in the deposition-dominated process on the SCtop-bottom slope were higher than in the transport-dominated process on the SCbottom-top slope (DOC: 6.8–10.2 mg L−1; SBOC: 0.2–0.3 mg g−1). The loading of DOC and SBOC was largely dependent on runoff and sediment yield, and DOC load contributed 83.9–89.7% of the SOC loss. Overall, laboratory results highlighted the soil C loss at different hydrological and erosion regimes (deposition- vs. transport-dominated process). This study provides important information that can be used to facilitate further implementations such as watershed modeling of soil C dynamics and the corresponding decision-making processes.