Modeling Tidal Marsh Distribution with Sea-Level Rise: Evaluating the Role of Vegetation, Sediment, and Upland Habitat in Marsh Resiliency

Abstract

Tidal marshes maintain elevation relative to sea level through accumulation of mineral and organic matter, yet this dynamic accumulation feedback mechanism has not been modeled widely in the context of accelerated sea-level rise. Uncertainties exist about tidal marsh resiliency to accelerated sea-level rise, reduced sediment supply, reduced plant productivity under increased inundation, and limited upland habitat for marsh migration. We examined marsh resiliency under these uncertainties using the Marsh Equilibrium Model, a mechanistic, elevation-based soil cohort model, using a rich data set of plant productivity and physical properties from sites across the estuarine salinity gradient. Four tidal marshes were chosen along this gradient: two islands and two with adjacent uplands. Varying century sea-level rise (52, 100, 165, 180 cm) and suspended sediment concentrations (100%, 50%, and 25% of current concentrations), we simulated marsh accretion across vegetated elevations for 100 years, applying the results to high spatial resolution digital elevation models to quantify potential changes in marsh distributions. At low rates of sea-level rise and mid-high sediment concentrations, all marshes maintained vegetated elevations indicative of mid/high marsh habitat. With century sea-level rise at 100 and 165 cm, marshes shifted to low marsh elevations; mid/high marsh elevations were found only in former uplands. At the highest century sea-level rise and lowest sediment concentrations, the island marshes became dominated by mudflat elevations. Under the same sediment concentrations, low salinity brackish marshes containing highly productive vegetation had slower elevation loss compared to more saline sites with lower productivity. A similar trend was documented when comparing against a marsh accretion model that did not model vegetation feedbacks. Elevation predictions using the Marsh Equilibrium Model highlight the importance of including vegetation responses to sea-level rise. These results also emphasize the importance of adjacent uplands for long-term marsh survival and incorporating such areas in conservation planning efforts.

The Impact of Lidar Elevation Uncertainty on Mapping Intertidal Habitats on Barrier Islands

“…Our results confirm findings of others, which suggest that lidar DEMs can have a substantial level of vertical uncertainty in intertidal areas [17][18][19], and this uncertainty should be accounted for if data are directly used in classification algorithms for habitat mapping or for use in sea-level rise modeling efforts [42,43]. Our findings highlighted that optimal results with regards to the maximum identification of actual intertidal areas (i.e., highest producer's accuracy) are likely produced when site-specific RTK GPS data are used.…”

Factors controlling sediment trapping in two freshwater tidal wetlands in the Biesbosch area, The Netherlands

“…However, we conclude that sediment fluxes for longer periods may be underestimated, since events with high discharge and suspended sediment concentrations with return periods considerably greater than the monitoring period are missing in the observed time series. Furthermore, the role of vegetation in increased sedimentation of suspended material and accretion due to production of organic material as found by Darke and Megonigal (2003), Day et al (2011), Schile et al (2014 and (DeLaune et al 2016) is negligible in both the Kleine Noordwaard and Zuiderklip areas.…”

“…Both sedimentation and organic soil formation by vegetation contribute to elevation gain and delta aggradation (Reddy and DeLaune 2008;Calvo-Cubero et al 2013;Kirwan and Megonigal 2013;Schile et al 2014). However, many deltas are threatened by drowning due to sea-level rise, human-induced accelerated soil subsidence, sediment starvation due to upstream land use and river management, or increased river discharge (Ibáñez et al 1997;Syvitski and Saito 2007;Syvitski 2008;Syvitski et al 2009;Giosan et al 2014;Ibáñez et al 2014;Day et al 2016).…”

“…Previous studies have indicated that sediment deposition in wetlands is controlled by various factors including the flooding frequency, depth, and duration (French and Spencer 1993;Middelkoop and van der Perk 1998;Reed et al 1999;Temmerman et al 2003;Thonon et al 2007;Schuerch et al 2013), the surface area of the wetland, the suspended sediment load (French and Spencer 1993;Asselman and Middelkoop 1998;Morse et al 2004;Noe et al 2016), and the ability of sediment to settle, which in turn, depends on sediment flow paths (French and Spencer 1993;Siobhan Fennessy et al 1994;Reed et al 1999;Davidson-Arnott et al 2002;Temmerman et al 2003;Anderson and Mitsch 2007;Mitsch et al 2014), wind (Orson et al 1990;Delgado et al 2013), and vegetation (Darke and Megonigal 2003;Temmerman et al 2005;Schile et al 2014;Mitsch et al 2014). These studies were mainly conducted in salt marshes or river flood plains; only few field-based studies were undertaken in freshwater tidal wetlands that represent the transition between these environments.…”

Global change effects on decomposition processes in tidal wetlands: implications from a global survey using standardized litter

“…However, aspects of S and k are key components of many tidal wetland resiliency models (Schile et al, 2014;Swanson et al, 2014) Our findings imply that particularly the vulnerability of organic systems might increase with global change because in these systems soil volume is almost exclusively generated by the 470 preservation of OM. At the same time, however, mineral dominated systems, such as temperate European salt marshes, experience large amounts of easily decomposable allochthonous-OM input that relies on substantial stabilization in order to become sequestered (Middelburg et al, 1997;Allen, 2000;Khan et al, 2015).…”