Spatial distribution of soil organic carbon and nutrients in the southern Sundarbans of Bangladesh

• Surface soils in the southern Sundarbans region range from neutral to saline. • Significant spatial variations in surface soil nutrients were observed, mainly influenced by salinity and pH gradients. • A strong correlation was found between surface soil organic carbon (%OC), nitrogen (%N), salinity, and soil pH. • The topsoil organic carbon content is lower than previously reported estimates, with significant variations influenced by changes in surface soil pH and salinity. • Salinity, Mg, and pH were the main factors influencing surface soil OC distribution, emphasizing the importance of managing these parameters for soil health and carbon retention. The Sundarbans, the world’s largest mangrove forest plays a crucial role in carbon sequestration and coastal ecosystem stability. This study investigated the spatial distribution of surface soil nutrients, organic carbon (%OC), salinity, and pH, along with their interrelationships, at a regional scale in the southern part of the Sundarbans. In this study, a total of 21 soil samples were taken from 10 cm depth at 21 locations in the southern part of the Sundarbans areas. The surface soil samples were analyzed in the laboratory to determine essential soil properties, including organic carbon (%OC), nitrogen (%N), phosphorous (P), potassium (K), magnesium (Mg), calcium (Ca), sulfur (S), pH, electric conductivity (EC), and salinity. The results showed spatial variations of nutrient concentrations, with higher surface soil organic carbon (%OC) and nutrient levels observed in areas with lower salinity and pH. Pearson’s correlation matrix (PCM) analysis revealed a significant negative correlation between surface OC and both salinity and pH (p < 0.05). Moreover, the soils were predominantly silt-textured, with nutrient levels ranging from normal to brackish-saline, largely influenced by salinity intrusion. Cluster analysis (CA) and principal component analysis (PCA) revealed distinct patterns in surface soil physicochemical properties, suggesting that salinity, pH, and organic carbon are main factors influencing nutrient distribution in the study area. The study emphasizes the need to conserve the Sundarbans by reducing anthropogenic activities, regulating freshwater inflows to control salinity, and promoting mangrove regeneration to maintain soil health and ecological balance.