Increasing salinization and organic carbon burial rates in seagrass meadows from an anthropogenically-modified coastal lagoon in southern Gulf of Mexico

Abstract

Intertidal ecosystems, such as marshes, mangroves, and seagrasses, contribute to the global carbon storage, helping to regulate atmospheric CO2 concentrations. Organic carbon (Corg) data from seagrass meadows in the Mexican coastline are still scarce, preventing appropriate evaluations of its contribution to mitigate global climate change. Recent temporal changes (≤100 years) of Corg concentrations and burial rates were assessed in 210Pb dated cores from seagrass meadows at Terminos Lagoon, the largest coastal lagoon in the southern Gulf of Mexico. Irrespective of the predominant seagrass species, the cores showed comparable Corg concentrations (0.04–3.9%) and burial rates (2.5 – 66.7 g m−2 yr−1). Increasing salinization, likely caused by sea level rise, favoured Corg concentrations and burial rates in sediments with Halodule wrightii, while in sediments with Thalassia testudinum only Corg burial rates increased, owing to increasing mass accumulation rates, likely promoted by erosion induced by land use changes, and sea level rise. The mean Corg stock (1 m depth; 130 ± 29 Mg ha−1) was comparable with the global average Corg stock for seagrasses in other tropical areas around the world. Our results suggested that, under the current scenario of land use change and marine transgression, the seagrass meadows in Terminos Lagoon preserve the capacity for Corg accumulation and long-term preservation. However, both factors are also known to reduce seagrass resilience caused by water quality deterioration, thus these ecosystems must be monitored and protected from global change impacts, as part of climate change mitigation efforts.