Sources, Mechanisms, and Timescales of Sediment Delivery to a New England Salt Marsh

Abstract

Tidal salt marshes are critical protectors of the coast; they buffer against erosion and flooding (Möller et al., 2014), sequester carbon (Chmura et al., 2003), provide habitat to juvenile species and migratory birds (Boesch & Turner, 1984;Hughes, 2004), and filter pollutants and excess nutrients (Sousa et al., 2010). Coastal wetland maintenance involves complex biophysical feedbacks between clastic (i.e., inorganic) sediment supply, nutrients, plant growth, and flooding (Deegan et al., 2012;Kirwan & Megonigal, 2013). Deposition of clastic sediment in the form of clays, silts, and sands allows marshes to accrete faster than would be possible via in-situ organic production alone; thus, the availability and delivery of clastic sediment is a key factor in determining salt marsh resilience to erosion and future sea level rise (e.g.,

Salt Marsh Response to Inlet Switch‐Induced Increases in Tidal Inundation

“…Panels (b) and (e) show Lead profiles from X‐ray fluorescence scans in units of ppm based on an empirical regression presented in Baranes et al. (2022). Panels (c) and (f) show loss on ignition profiles versus depth.…”

“…Proximal to the new inlet, average sediment accumulation rates based on a ∼1900 onset for bulk lead contamination have been even greater than that observed at N3, averaging 10 and 8 mm/yr respectively for N1 and N2. The high deposition rate at N1 is likely due to rapid subsidence providing accommodation space and abundant marine‐derived sediment (Baranes et al., 2022). We hypothesize that the high subsidence rate at N1 was caused by rapid peat oxidation due to the dense channel network at N1 that allows for efficient drainage of the marsh peat.…”

“…The North‐South Rivers comprise a bar‐built estuary, whose channels connect to the mesotidal Massachusetts Bay via a shared inlet (Figure 1). At its inlet, the North‐South Rivers Estuary's tidal range is about 3.5 m (Buynevich & Donnelly, 2006), with that range decreasing up‐estuary (Baranes et al., 2022). Channel widths of the North and South Rivers are approximately 100 m within their seaward reaches, and narrow landward.…”

“…At 65-66 cm, below the organic horizon, there was a switch in assemblage Figure 3. Bulk lead profiles from representative sediment cores from the North River (top row) and South River (bottom row) from ITRAX X-ray fluorescence corescanner data converted to parts per million according to a site-specific empirical regression reported in Baranes et al (2022) where PPM Pb = 1.14 * Counts xrf − 0.48. River distance from the shared NSRE inlet is shown at the bottom of each panel.…”

“…The x axis scale changes between plots to allow for visual resolution of the lead increase. Baranes et al (2022) explained the up-estuary increase in sediment lead abundance along the North River as evidence of dilution of contaminated watershed sediment by abundant, uncontaminated marine sediment.…”