Sediment Accumulation, Elevation Change, and the Vulnerability of Tidal Marshes in the Delaware Estuary and Barnegat Bay to Accelerated Sea Level Rise

Abstract

Tidal marshes protect coastal communities from the effects of sea level rise and storms, yet they are vulnerable to prolonged inundation and submergence. Uncertainty regarding their vulnerability to sea level rise motivated the establishment of a monitoring network in the Delaware Estuary and Barnegat Bay. Using data collected through these efforts, we determined whether rates of tidal marsh sediment accumulation and elevation change exceeded local sea level rise and how these dynamics varied along geographic and environmental gradients. Marker horizons, surface elevation tables, elevation surveys, water level data, and water column suspended sediment concentrations were used to evaluate sea level rise vulnerability. Of 32 study sites, 75% had elevation change that did not keep pace with long-term rising sea levels and 94% did not keep pace with recent sea level rise (2000)(2001)(2002)(2003)(2004)(2005)(2006)(2007)(2008)(2009)(2010)(2011)(2012)(2013)(2014)(2015)(2016)(2017)(2018). Mean high water rose 2 most rapidly in the freshwater tidal portion of the Delaware Estuary with rates nearing 1 cm yr -1 from 2000-2018. We noted that greater sediment accumulation rates occurred in marshes with large tidal ranges, low elevations, and high water column suspended sediment concentrations.We found correlations between rates of shallow subsidence, increasing salinity, and decreasing tidal range. Marsh elevation and water level surveys revealed significant variability in elevation capital and summer flooding patterns (12-67% inundation). However, rapid increases in mean high water over the past 19 years suggests that all marsh platforms currently sit at or below mean high water. Overall, these data suggest that tidal marshes in the Delaware Estuary and Barnegat Bay are vulnerable to submergence by current rates of sea-level rise. While we observed variability in marsh elevation capital, the absence of strong correlations between elevation trends and environmental parameters makes it difficult to identify clear patterns of sea level rise vulnerability among wetlands.

Improved mapping of coastal salt marsh habitat change at Barnegat Bay (NJ, USA) using object-based image analysis of high-resolution aerial imagery

“…This study addresses the need for trends analyses of salt marsh habitat that adequately capture the complex marsh topography, including channels, ponds, and ditches, for Barnegat Bay, New Jersey. Located in a region where rapid SLR ( Haaf et al, 2021 ) and eutrophication co-occur ( Kennish and Fertig 2012 ), accurate high-resolution geospatial analysis is needed to inform coastal management efforts and to guide effective SLR planning ( Weis et al, 2021 ). To determine rates of marsh areal change in Barnegat Bay from 1995 to 2015, we conducted a trend analysis using land cover classifications of aerial imagery and digital elevation models produced via object-based image analysis.…”

Complexity, Variance, and Nonlinearity: A Multisite, Multiseasonal Study of Tidal Marsh Sedimentation Processes in the St. Lawrence Estuary, Canada

“…In the context of falling RSL, the surface area of the tidal marshes under study can be expected to remain stable or prograde seaward; however, RSL behavior is far from linear, and such generalization risks masking variability that can affect SDRs (Haaf et al ., 2022). An important periodic RSL variation was noted by Dionne (1986), but its origins were not investigated.…”

“…It is well documented that most sediment deposition occurs at high tide during flooding of the marsh surface, at which time there are complex interactions between several factors exhibiting high temporal and spatial variability (Allen, 1990, 1995, 1997, 2000; Bartholomä et al ., 2009; Drapeau, 1992; Fagherazzi et al ., 2012; French, 2019; Nolte et al ., 2013; Silinski et al ., 2016; Temmerman et al, 2003b). These interactions include flood duration and frequency ( e.g., Allen and Duffy, 1998; Cahoon and Reed, 2015; Leonard, 1997), distance to the sediment source (Butzeck et al ., 2015; Esselink et al ., 1998; Temmerman et al ., 2003b), suspended sediment concentrations (SSCs; Bartholomä et al ., 2009; Fettweis, Sas, and Monbaliu, 1998; Temmerman et al ., 2003b), marsh height (Butzeck et al ., 2015; French, 2006; Haaf et al ., 2022), type and abundance of vegetation (D'Alpaos et al ., 2007), salinity gradient ( e.g., Butzeck et al ., 2015), tidal characteristics and currents (Carniello et al ., 2005; Shi et al ., 1996), relative sea-level changes (Hill and Anisfeld, 2015; Kirwan and Temmerman, 2009), seasonal variations in water levels and wind regimes (Amos and Tee, 1989; Neumeier and Amos, 2006; Schuerch et al ., 2016; van Proosdij, Ollerhead, and Davidson-Arnott, 2006b), and anthropogenic activities (Hatvany, 2014, 2020). In the St. Lawrence Estuary, ice and herbivores ( e.g ., geese) must also be taken into account (Allard and Champagne, 1980; Allard, 2008; Dionne, 1969; Dionne, 2002; Kirwan et al ., 2011; Lefebvre et al ., 2017; Mattheus et al ., 2010).…”

Watershed sediment cannot offset sea level rise in most US tidal wetlands

“…Yet sediment delivery to estuaries from large watersheds (>10 3 km 2 ) and their coastal plain rivers during large floods may be lower than upstream measurements would suggest ( 26 , 27 ), in part because effects due to backwater slow and spread floodwater across broad coastal plains and enhance sediment deposition near the head of tide ( 28 , 29 ). Ultimately, the response of tidal wetlands to sea level rise over just the next decade will have considerable consequences on coastal habitats ( 30 ). Therefore, the exclusion of river floods with long recurrence intervals in our analysis may not necessarily affect our interpretation of the role of river sediment on tidal wetlands in the short term, particularly given the uncertainty in the magnitude of sediment actually delivered to estuaries during these events.…”