Time dependence of sediment accretion rates: Short- and long-term variability in an urban tidal marsh

Understanding the temporal variability of sediment accretion is crucial
for assessing the resilience of tidal marshes to accelerated sea-level
rise, particularly in urban settings where sediment delivery and hydrology
are frequently altered. This study investigates sediment accretion across
multiple timescales in Tinicum Marsh, an urban tidal wetland in
Philadelphia. Using event-scale sediment traps, annual SET-MH
measurements, and decadal radioisotope dating, the research reveals that
sediment accretion rates vary significantly with timescale, aligning with
the Sadler Effect. Event-based rates were much higher than annual and
decadal rates, especially during storms, which delivered more mineral-rich
sediments. Accretion was influenced by elevation and distance from tidal
channels, and substantial shallow subsidence was observed. Although
current accretion exceeds long-term sea-level rise, it only marginally
keeps up with recent rates, highlighting the need for multi-scale analysis
to assess marsh resilience.