Terrain indices control the quality of soil total carbon stock within water erosion-prone environments

This study aimed the potential of terrain indices to control the relative proportion of soil organic and inorganic carbon contained in soil total carbon stock (STCs) within water erosion-prone environments. Three elevation groups (1,000-1,300 masl, 1,300-1,500 masl, and 1,500-2,000 masl) within a watershed were selected. Terrain indices, which included slope, stream power index (SPI), and topographic wetness index (TWI), were extracted. Furthermore, STCs, soil organic and inorganic C, microbial biomass carbon and nitrogen, and alkaline cations were measured. Despite both organic and inorganic carbon demonstrated a significant increase in the elevation ranges of 1,000-1,300 and 1,300-1,500 masl compared with the range of 1,500-2,000 masl, the SICs/SOCs ratio exhibited the higher rate only at the range of 1000-1300 m. The higher SICs values at 1,000-1,300 masl showed a significant positive relationship with TWI and a negative relationship with SPI and slope. The SICs was significantly positively correlated with alkaline cations in 1,000-1,300 masl, whereas this relationship was significant and negative with SOCs. These findings showed that decreased SPI values and, consequently, decreasing the erosive power of surface runoff stimulated the higher concentration of the fine particle on 1,000-1,300 masl. The fine particles accumulated on these positions together with the carbon dioxide generated by microbial respiration bond with alkaline cations to create carbonate production. These findings show the importance of terrain attributes not only in variation of the soil organic C but also in the creation of mineral forms of carbon, causing variation in the quality of STCs within different watershed positions.