A 5000 year record of carbon sequestration from a coastal lagoon and wetland complex, Southern California, USA

Coastal wetlands have the potential to accumulate C at high rates over long time periods because they continuously accrete and bury organic-rich sediments, giving soils in coastal wetlands a distinct advantage over many other environments in the sequestration of organic C. Given that coastal wetlands are being lost worldwide, it is important to understand their C sequestration potential. Sediments in a southern California, USA coastal lagoon–wetland complex were cored, and depositional environments were interpreted. Suitable materials were radiocarbon dated. Bulk density and organic C were grouped by depositional environments, and average mass of C per unit volume and C accumulation rates in each depositional environment were calculated. The total organic C sequestered and rates of sequestration in each depositional environment were in the following order from most (fastest) to least (slowest): lagoon, intertidal, salt marsh, freshwater marsh, aeolian. This study demonstrated that high levels of organic C are sequestered per unit volume of sediment (35.9±3.2 kg m−3), and the mean rate of C accumulation was high (0.033±0.0029 kg C m−2 year−1) over a long time period (5000 years). Results of this study strongly demonstrate the importance and necessary high priority for preserving and restoring coastal wetlands both in the USA and internationally. However, despite their excellent potential to sequester C, significant losses of coastal wetlands are occurring in the United States and elsewhere in the world.