Spatial Variability in Vertical Accretion and Carbon Sequestration in Salt Marsh Soils of an Urban Estuary

Salt marshes in New York City's Jamaica Bay have been disappearing and deteriorating since early 1900s, resulting in the loss of long-term accumulated carbon storage. However, the spatial variations and mechanisms in vertical accretion and soil organic carbon (SOC) sequestration across this highly urbanized estuary remains unclear. In this study, we collected soil cores to a depth of similar to 50 cm across Jamaica Bay to study the spatial variability in long-term (50-100 years) vertical accretion, the accumulation of mineral sediment and organic matter, and SOC sequestration. Results of gamma spectrometry analysis of Cs-137 and Pb-210 show that there was moderate spatial variability in long-term vertical accretion rates across Jamaica Bay study sites (mean: 0.48 +/- 0.13 cm yr(-1), range: 0.36-0.78 cm yr(-1)). This local scale spatial variability in vertical accretion is largely driven by spatial variations of sedimentation. The magnitude of the long-term vertical accretion in Jamaica Bay is significantly correlated with organic matter accumulation, but not with mineral sediment. However, the role of organic matter in contributing to vertical accretion has been declining. The declining role of organic matter to vertical accretion is reflected by the lower SOC sequestration rate (mean: 128 and range: 26-189 g C m(-2) yr(-1) using the Pb-210 dating technique) compared to the global mean salt marsh SOC sequestration rate (244 g C m(-2) yr(-1)). This is especially so on the marsh islands in the degrading western part of the bay where SOC sequestration was less than half the global average.

Automated summary

Salt marshes in New York City's Jamaica Bay have been experiencing disappearing and deteriorating since the early 1900s, resulting in the loss of long-term carbon storage. This study investigates the spatial variations and mechanisms behind vertical accretion and soil organic carbon sequestration in this highly urbanized estuary. The findings show moderate spatial variability in long-term vertical accretion rates, primarily driven by variations in sedimentation. While organic matter accumulation is significantly correlated with vertical accretion, its role has been declining, leading to lower SOC sequestration rates compared to the global average.