The sequestration of organic carbon in mangrove ecosystems is an environmental service that can be affected by changes in forest structure and in hydrological and sedimentary behavior. The foregoing can be promoted by natural causes or human interventions. This situation has been registered for 45 years in the mangroves of the Sistema de Marisma Nacionales (Nayarit, Mexico), which has been recognized as one of the most important wetland complexes in the Mexican Pacific. In the present investigation, the change in the sequestration of organic carbon under different scenarios of environmental conditions, development of anthropogenic activities and occurrence of hydrometeorological events was evaluated and validated in 12 mangrove forests bordering the San Pedro Mezquital riverbed. This, through the determination of organic carbon by means of an elemental analyzer, in sedimentary nuclei dated with the 210Pb method.
As a result, three Environmental Units were defined based on the sequestration of organic carbon, which presented significant differences between them (F = 9.2, p = 0.007). The highest values of sequestered organic carbon were registered in the middle basin (Environmental Unit II) of the San Pedro Mezquital River, where a lagoon geomorphology prevails that limits the export of sediments, unlike the deltaic regions (Environmental Unit I) or of the upper basin (Environmental Unit III). The variations in the rates of mass and sediment accumulation validated that the anthropogenic and natural pressure exerted in the period from 1970 to 2015 have impacted on the sequestration of organic carbon in the area under study.