Relevance of carbon burial and storage in two contrasting blue carbon ecosystems of a north-east Pacific coastal lagoon

Abstract

Coastal vegetated ecosystems constitute very productive habitats, characterized by efficient C_org sequestration and long-term preservation in sediments, so they play an important role in climate change mitigation. The temporal evolution of C_org content, stocks and burial rates were evaluated in seagrass and salt marsh habitats in San Quintin Bay (northeast Pacific, Mexico) by using ²¹⁰Pb-dated sediment cores. Salt marsh cores were characterized by fine-grained sediments, higher salinities, lower terrigenous input and lower mass accumulation rates (MAR: 0.01-0.03 g cm^-2 yr^-1) than seagrass cores (MAR: 0.02-3.21 g cm^-2 yr^-1). Accumulation rates in both habitats steadily increased throughout the past century most likely because of soil erosion promoted by land use changes in the surroundings. The C_org stocks were highest in salt marsh cores (12.2-53.6 Mg ha^-1 at 10 cm depth; 259-320 Mg ha^-1 at 1 m depth) than in seagrass cores (5.7-14.4 Mg ha^-1, and 80-98, Mg ha^-1, respectively), whereas C_org burial rates were considerably lower in salt marsh (13-60 g m^-2 yr^-1) than in seagrass (9-144 g m^-2 yr^-1) habitats, and the temporal variations observed in C_org burial rates were mostly driven by changes in the accumulation rates. The overall C_org stock (485 ± 51 Gg C) for both habitats together was comparable to the carbon emissions of a major city nearby. Our results highlight the need to protect these environments as relevant carbon reservoirs.

Keywords: (210)Pb chronology; Blue carbon ecosystems; California Current Large Marine Ecosystem; Coastal sediments; Spartina foliosa salt marsh; Zostera marina seagrass.