Background Water erosion is an important process which causes shifts in the soil organic carbon storage and the global carbon cycle process. The physicochemical and biological stabilities of soil organic carbon are strongly affected by water erosion. Recently, growing studies show that the replacement of soil carbon on an eroding area is a crucial mechanism, the transport of organic carbon is re-aggregated in a depositional area then buried in the deep layer, and episodic erosion can bury a lot of erosion materials in low-lying depositional sites. Therefore, more and more investigators suggest water erosion leads to an increase of soil organic carbon storage.

Methods We collected all relevant literature for this review. Based on these reference, we reviewed mechanisms of water erosion, current status and types of water erosion, divergence of carbon source or sink for CO₂ under water erosion, factors impacting water erosion, effects of water erosion on soil organic carbon stock, effects of water erosion on soil carbon stability, and to further strengthen the study areas.

Results Many investigators studied the relationship between water erosion and biogeochemical cycling at eroding and depositional zone, and obtained a series of beneficial results. 1) There are effects of water erosion on soil carbon storage. Soil scientists and agronomists understood that soil erosion by water released carbon, thus recognized as carbon source process. While geologist in sedimentation studied that water erosion resulted in soil carbon sink. 2) The mechanisms of soil organic carbon stability are classified as selective stabilization, physical protection, and orgao-mineral binding chemical stabilization. Selective stabilization refers to that the recycling period of some carbon is very long in over 100 years, thus they are not decomposed in this period. The physical protection refers to that soil particles, aggregates, layered silicate, molecular hydrophobicity and molecular nesting block the organic carbon and decomposer, so that it cannot be fully contacted and exist stably in the soil for a long time. Orgao-mineral binding chemical stabilization refers to that the organic carbon and soil mineral binding through coordination body exchange, polyvalent cationic bridge, hydrogen binding and molecular electrostatic attraction, so as to prolong the time of organic carbon turnover. 3) The research trends in this field include 4 aspects:Transport loss and composition change of dissolved organic carbon under erosion, migration and loss of organic carbon components by different erosion dynamics, renewal and stability of organic carbon in eroded in situ region, and stability of organic carbon in sedimentary area and its mechanism.

Conclusions Current researches about soil carbon stability under water erosion demonstrate that the mechanisms of soil organic carbon stability are affected by water erosion.