SEDIMENT SOURCING AND ACCUMULATION ON NEW ENGLAND SALT MARSHES

Coastal salt marshes buffer coastal settings from the threats of accelerated sea level rise and storms. Understanding which factors are most important for salt marshes to maintain lateral and vertical extents as sea level rises are needed for advising policy and future climate research. One of the major factors for ensuring salt marsh resilience to sea level rise is the supply of clastic sediment; however, there is limited data on the sourcing, timing, and mechanisms of sediment delivery. Here we present a regional assessment of sediment delivery to and accumulation on marsh platforms. We do this by analyzing instrumental data from turbidity sensors and water level loggers, as well as measuring accumulation of clastic sediments on the marsh surface through sediment traps and cores. The instrumentation and sediment traps were deployed synchronously in the spring, summer, and fall from 2018-2021. To cover the wide variety of oceanographic conditions, marsh morphologies, and coastal geologies in the region we chose sites that ranged from the microtidal marshes south of Cape Cod, MA to the mesotidal marshes in mid-coast Maine. Previous work in the North and South Rivers in Scituate, MA indicates that the marine sediment mobilized and delivered during coastal storms is the primary clastic sediment source to the marsh platform, rather than upland sediment delivered by rivers. Due to the differences in marsh morphology, geology, and oceanographic conditions throughout the region, however, there may be geographic variability in sourcing, mechanisms, and timing of sediment supply. This study seeks to assess what geologic, geomorphic, and oceanographic features control sediment sourcing, delivery, and accumulation of clastic sediment on salt marshes across a variety of timescales and geomorphic settings.