Marine-Sourced Sediment Supply Supports Salt Marsh Resilience to Sea Level Rise in the Northeastern US

Abstract

Salt marshes rely on sediment to maintain elevation and resist sea level rise (SLR). While riverine sediment is well studied, marine-sourced sediment remains understudied, particularly in regions with limited river input. We examined the influence of marine-sourced sediment on salt marsh stability across 103 sites in the Northeastern US, using a new satellite-derived suspended sediment concentration (SSC) product. Marsh vulnerability was assessed using the Unvegetated-to-Vegetated Ratio (UVVR) and relative marsh elevation (Z*). We identified two thresholds: SSC >20 mg/L and RSLR <5.2 mm/year. Marshes meeting either threshold tended to remain intact, while those with both low SSC and high RSLR were more vulnerable to degradation. A north–south gradient was observed, with most unstable marshes in the southern region, where SSC declined by 0.9% per decade on average, compared to 0.072% in the north. These findings highlight the need to include coastal sediment dynamics in restoration and adaptation planning.