Blue carbon in mangrove sediments from Mazatlán, Mexican Pacific; a century of urbanization and neglect

Abstract

Despite ranking among the most productive and most efficient blue carbon sink ecosystems, mangrove forests still face worldwide loss due to deforestation and land-use change. Uncertainties remain about the impact of anthropogenic disturbances on belowground mangrove carbon stock and the potential contribution of their destruction to global warming through CO₂ emissions. In this study, geochemical data (element composition, grain size distribution, and magnetic susceptibility) obtained from two ²¹⁰Pb-dated sediment cores, were used to evaluate temporal changes in sediment and C_org accumulation over the past century in the urbanized mangrove area of Estero El Infiernillo, a northern channel of the coastal lagoon Estero de Urías, in Mazatlán (southern Gulf of California). Sediment accumulation rates (0.06–2.4 g cm⁻² yr⁻¹) and C_org burial rates (22–1100 g m⁻² yr⁻¹) increased over time in tandem with population growth in Mazatlán. Multivariate analysis of geochemical data revealed a progressive transition from a predominantly marine environment (before the 1900s) to a more terrigenous one over the past 100 years. The time-dependent C_org stock (1.9–6.5 Mg ha⁻¹) decreased owing to reductions in sea water exchange and marine-C_org inputs as a result of anthropogenic coastline modifications and ecosystem disturbances. The destruction of the present carbon stock would release 26,000 ± 13 to 44,000 ± 14 t CO_2eq, thereby contributing to global warming and causing a mean economic loss of ∼1.2 million USD for Mazatlán. These findings demonstrate the effects of anthropic activities on the climate regulation services afforded by mangroves. The methods employed here can be replicated worldwide to underscore the importance of integrated coastal management in preserving blue carbon ecosystems as a nature-based solution for mitigation of climate change.