Modeling the distribution of soil organic carbon in salt marshes dominated by various plant species along Egypt’s Delta coast

Abstract Background Understanding the vertical distribution and storage of soil organic carbon (SOC) in arid coastal salt marshes is essential for assessing their role in blue-carbon sequestration. This study examines SOC patterns in marshes dominated by Arthrocnemum macrostachyum , Halocnemum strobilaceum , and Salicornia fruticosa , as well as unvegetated areas. Using 200 soil cores (2,000 samples), we applied allometric, exponential, and sigmoid models to predict volumetric SOC density (SOC v ; kg C/m³) and cumulative SOC stocks (SOC c ; kg C/m²) across depth profiles. Results SOC content showed an inverse exponential relationship with soil bulk density across vegetation types, consistent with patterns documented in other salt-marsh and coastal wetland systems. The allometric model provided the best SOC v predictions for A. macrostachyum , whereas the sigmoid model performed best for H. strobilaceum , S. fruticosa , and unvegetated sites, based on mean normalized average error (MNAE), mean normalized bias (MNB), and residual mean squares (RMS). All three models accurately reproduced SOC c for within-core depth extrapolation, with no significant differences between measured and predicted values within the validation dataset. Conclusions This study provides an improved understanding of SOC dynamics in arid coastal salt marshes and demonstrates the utility of depth-based mathematical models for predicting SOC storage. These findings support local-scale efforts to evaluate carbon-sequestration potential, though broader spatial validation across heterogeneous landscapes remains necessary.