Recovery of a New England salt marsh six years after a natural sediment deposition event.

Abstract

In January 2018, Winter Storm Grayson deposited a spatially heterogeneous layer of sediment across the Great Marsh on the North Shore of Massachusetts in Essex Bay, Ipswich Bay, and Plum Island. A published study of short-term responses following one growing season showed percent cover of vegetation was significantly lower in plots receiving sediment than controls, while porewater chemistry (salinity, redox potential, and sulfide concentrations) shifted slightly as biogeochemical processes developed in the new sediment. Six growing seasons post-deposition, these sites were re-evaluated to determine whether storm-delivered sediment (i) increases vegetation percent cover and species richness without suppressing plant height, (ii) influences porewater conditions, and (iii) promotes belowground live root density. Results show that vegetation cover and height were not significantly impacted by sediment thickness or year, and no interaction was found between year and sediment thickness. Salinity significantly decreased from 2018 to 2024, while interactive effects appeared for both redox potential and sulfides, largely driven by changes in plots that received 0-2 cm of sediment. Interactive effects of depth and sediment thickness on live root density appear driven by biomass in the control and 4-6 cm plots. Live root density in the top 4 cm was approximately equivalent for all core types with biomass increasing with depth until 10 cm for the plots receiving greater than 2 cm of sediment. Our results suggest that natural sediment inputs can supplement elevation and stimulate belowground biomass, particularly at thicknesses between 2-6 cm, without negatively impacting vegetation cover, species richness, or porewater chemistry at the landscape scale.