Mangroves provide multiple ecosystem services and are essential for mitigating global warming owing to their capacity to store large carbon (C) stocks. Due to widespread mangrove degradation, actions have been implemented to restore them worldwide. An important representative case in Colombia is the Ciénaga Grande de Santa Marta’s restoration plan. This management intervention focused on restoring the natural hydrological functioning after massive mangrove mortality (~25,000 ha) due to soil hyper-salinization after river water input from the Magdalena River was eliminated. A partial recovery occurred during subsequent years, and hydrological management is still being implemented today. To understand how the degradation and subsequent management have affected mangrove C stocks, we compared C stocks in stands with different intervention levels reflected in their current forest structure. We found that the total C stock (398–1160 Mg C ha⁻¹) was within the range measured in other neotropical mangroves without vegetation deterioration. The aboveground C was significantly higher in the stands where hydraulic connectivity was restored. By contrast, the belowground C was higher in the stands with low hydraulic connectivity due to channel clogging and a lack of sufficient maintenance. Our results show that hydrological management measures influenced above- and belowground C stocks, even at a 2 m depth. In addition, a strong indirect relationship useful for estimating carbon content from organic matter content was found.

Geomorphological setting and sedimentary environment are key controls on mangrove soil development and organic matter dynamics. This study quantified and compared soil organic matter (SOM) across mangroves established in two contrasting sedimentary environments: an open-coast carbonate system with minimal riverine influence and a deltaic terrigenous system characterized by fluvial inputs. We tested the hypothesis that higher allochthonous inputs in terrigenous environments influence SOM accumulation. Two stations were established within each environment, and soil profiles were sampled to 1 m depth to determine SOM (%) and associated physicochemical properties. SOM varied markedly across environments, with higher values in the carbonate environment (55.2–78.6%) compared to the terrigenous environment (3.6–34.7%). In contrast, porewater temperature (28.4–30.0 °C) and pH (6.8–7.1) showed limited variation among sites. The main gradients were associated with bulk density (0.13–0.94 g cm⁻³), salinity (8.4–38.2), and soil depth (0.92–3.7 m). Principal component analysis indicated a tendency for the carbonate environment to be associated with higher salinity and SOM density; although there was considerable overlap with the terrigenous environment. The high SOM values in the carbonate environment, where allochthonous inputs were minimal, indicate a significant contribution of autochthonous production to soil formation. This finding suggests environmental controls on SOM dynamics in Neotropical mangroves that must be considered to improve assessments of carbon storage across coastal settings.