# Fate of Soil Carbon Transported by Erosional Processes
## 2 Selectivity of the Soil Erosion Process  
Global soil erosion by water and wind, exacerbated by agricultural expansion and intensification and other anthropogenic activities, transports, and redistributes large amounts of soil organic C (SOC) and soil inorganic carbon (SIC) with significant impacts on global C budget, atmospheric chemistry, and water quality. However, hydride erosion may have a more significant impact on transport of SOC and emission of GHGs. Indeed, soil erosion by water is a multistage process encompassing a range of pedological processes. Some of these processes are described below:  
1. **Breakdown of aggregates** and leading to the exposure of the hitherto protected SOC against microbial processes and environmental conditions, is the first process. Macroaggregates, containing labile fractions, are broken apart by the kinetic energy and momentum of the impacting raindrops and velocity of the runoff flow. The SOC thus exposed is accessible to microbial processes. 2. **Removal of the colloidal and light fractions** (clay, fine silt, SOC, SIC, sesquioxides) is aggravated by the breakdown of aggregates. Thus, the sediments have a high C-enrichment ratio (CER). The latter is defined as the ratio of C in sediment to that in the original soil from which the sediment are derived [13]. A high CER is observed in both hydric and aeolian sediments. 3. **Redistribution of the sediment and associated soil C** is a major pedological process on actively eroding landscapes. Furthermore, redistribution is accompanied by possible mineralization of biomass-C (into CO\({}_{2}\), CH\({}_{4}\), and N\({}_{2}\)O), depending on the hydrothermal regimes, Whereas CO\({}_{2}\) is the primary GHG evolved and emitted under aerobic conditions, CH\({}_{4}\) and N\({}_{2}\)O may be evolved under anaerobic environments. 4. **Deposition of sediments** SOC-laden sediments are deposited at depressional and other sites following Stokes Law. Accordingly, heavier fractions (e.g., gravels, sand and coarse silts are deposited in vicinity of the eroding sites and SOC and clay fractions are deposited either latter or carried farther away. Windblown sediments originating from the Sahara have been observed in the Caribbean and northern Europe. This process is the principal cause of eutrophication of water, pollution of air and responsible for the off-site adverse effects of the erosional process. 5. **Burial of SOC:** and SIC deposition following Stokes Law leads to burial and stratification, with coarser heavier sediments deposited first and the lighter fractions (SOC, SIC, clay particles) later. With multiple events over time, the layering can be observed in active depositional sites which are not disturbed by farm operations or natural perturbations. 6. **Reaggregation** Some of the dispersed clay, released by the breakdown of aggregates (step 1) and other pedological processes aggravating the slaking of structural units, may interact with SOC and cations and the reformation of aggregates. Therefore, some of the buried SOC may be stabilized through encapsulation within reformatted aggregates. 7. **Gaseous Emission from Eroding and Depositional Sites**: Erosional processes may aggravate emissions of GHGs from both eroding and depositional sites because of the drastic perturbations of soil structure. The magnitude and type of gaseous emission (CO\({}_{2}\), CH\({}_{4}\), and N\({}_{2}\)O), depend on site-specific conditions and their spatial and temporal variations because of natural and anthropogenic processes. However, pedological processes involved in the above listed erosional stages vary widely, depending on the stage of the erosion/deposition process and prevalence of the specific hydrothermal regime of the specific landscape position. The third stage, involving redistribution of soil C, is not uniform but affected by preferential transport and deposition.