Soil organic carbon stocks along depth profiles in mangrove and sago wetland forests of Southwest Papua, Indonesia

Wetland ecosystems are important natural carbon sinks, yet data on soil organic carbon (SOC) in eastern Indonesian wetlands are limited. This study quantified SOC stocks and their vertical distribution in mangrove and sago wetland forests in Southwest Papua, Indonesia. Using a nested sampling design, soil cores were collected from 11 mangrove sites to a depth of 300 cm and from 11 sago forest sites to a depth of 50 cm. SOC content was determined by using the loss-on-ignition method and combined with bulk density to estimate SOC stocks by depth. Across the full soil profile, mangrove stored more SOC (mean 702.38 Mg C ha⁻¹) than sago forests (average 338.74 Mg C ha⁻¹), mainly because of their deeper organic soil layers. In both ecosystems, SOC declined with depth, but deeper soil layers still contributed substantially to total carbon stock in mangroves. Regression analysis showed that SOC stock decreased with depth, while higher canopy cover corresponded to greater SOC stocks. These findings show that sampling depth strongly affects cross-ecosystem comparisons and confirm that Southwest Papua’s wetland forests are significant carbon stores. The study provides baseline data for an understudied region, supporting the conservation of mangrove and sago wetlands for climate regulation and carbon sequestration.