Reclamation substantially increases soil organic and inorganic carbon stock in riparian floodplains

Purpose In recent decades, riparian floodplains have undergone intensive reclamation worldwide, which has potential to influence soil carbon (C) accumulation. Such influence generally varies based on reclamation duration. Therefore, a study on changes in soil C stock along the reclamation chronosequence can help reveal the impact of reclamation on terrestrial C cycling. Materials and methods We chose natural floodplains (as the control) and croplands reclaimed for 13, 24, and 33 years in the lower reaches of the Yellow River and determined soil organic C (SOC) and soil inorganic C (SIC) contents at different depths and the stocks in 0-100 cm profiles. Results and discussion The SOC and SIC stocks generally increased at average rates of 2.73 and 5.54 Mg C ha(-1) yr(-1), respectively, and the SIC stock was closely related with the SOC stock across the reclamation chronosequence. The SOC content increased more at 0-20 cm depth in the profile along the reclamation chronosequence, but the SIC content often had a higher rate of increase in the deep soil layers. Significantly, the contents of SOC and SIC were both positively correlated with the proportion of silt fractions. Conclusions Our findings suggest that reclaimed croplands from riparian floodplain play an important role in C accumulation, highlighting the importance of soil inorganic C in C budget. Moreover, soil C accumulation relates closely to soil texture, which changes continuously along the reclamation chronosequence and often varies due to spatial heterogeneity.