Expansion of Tidal Marsh in Response to Sea-Level Rise: Gulf Coast of Florida, USA

Abstract

Understanding the influence of future sea-level rise (SLR) on coastal ecosystems is improved by examining response of coastlines during historic periods of SLR. We evaluated stability and movement of the estuarine intertidal zone along eastern Gulf of Mexico, known as the BBig Bend^of Florida. This relatively undeveloped, low-energy coast is dominated by broad expanses of tidal marsh, providing an opportunity to observe unobstructed response of a coastal ecosystem to SLR. Features from nineteenth century topographic surveys and late twentieth century satellite imagery were compared. Relative change was calculated for intertidal area and lateral migration over 120 years, a period when tidal amplitude increased in addition to SLR. Loss of tidal marsh at the shoreline was −43 km 2 , representing a 9 % loss to open water. At the same time, 82 km 2 of forest converted to marsh and 66 km 2 of forest converted to forest-to-marsh transitional habitat. The result was a net regional gain of 105 km 2 of intertidal area, an increase of 23 %, constituting a marine transgression of coastal lowlands. Forest retreat was lower at zones of high freshwater input, attributable to salinity moderation and was further complicated by coastal morphology and land-use practices. Shoreline migration may not represent full extent of habitat change resulting from SLR in regions with low coastal gradients. Forest retreat was consistent with what would be predicted by an inundation model; however, shoreline loss was considerably less, resulting in a net increase in intertidal area in this sediment-limited coast.

Sea level driven marsh expansion in a coupled model of marsh erosion and migration

“…In this initial effort, we assume for simplicity that marsh migration occurs continuously as uplands become progressively inundated by tides [ Brinson et al ., ], so that the position of the landward marsh boundary, B l , can be approximated as where m is the slope of the adjacent upland and R is the RSLR rate. Although more complicated ecological processes related to facilitation or competition between marsh and upland species may play a role in defining the upland‐marsh boundary [ Kirwan et al ., ; Poulter et al ., ; Smith , ], analysis of historical imagery indicates that our approach accurately characterizes migration over century timescales [ Raabe and Stumpf , ].…”

“…Salt marsh migration into adjacent uplands represents a fundamental process by which marshes respond to sea level rise [ Brinson et al ., ; Feagin et al ., ; Raabe and Stumpf , ] but has yet to be incorporated into dynamic, process‐oriented models of coastal evolution. In this initial effort, we assume for simplicity that marsh migration occurs continuously as uplands become progressively inundated by tides [ Brinson et al ., ], so that the position of the landward marsh boundary, B l , can be approximated as where m is the slope of the adjacent upland and R is the RSLR rate.…”

“…However, marshes also respond to RSLR by migrating into adjacent uplands where they are not restricted by topographic and anthropogenic barriers such as dykes, seawalls, and revetments [ Brinson et al ., ; Hussein , ; Feagin et al ., ; Smith , ; Raabe and Stumpf , ]. The processes by which marshes replace upland vegetation are poorly understood, but simple topographic analyses suggest that 1 m of RSLR could inundate an area of land similar in magnitude to the present‐day extent of coastal marshes in the continental U.S. [ Morris et al ., ].…”

Upslope development of a tidal marsh as a function of upland land use

“…Few studies have directly examined marsh migration, and these have generally looked at migration into natural landscapes dominated by woody vegetation (Williams et al, 1999;Denslow & Battaglia, 2002;Desantis et al, 2007;Saha et al, 2011;Smith, 2013;Wasson et al, 2013;Raabe & Stumpf, 2015). These studies have documented significant inland marsh migration over the last several decades, although in several cases, migration has been slowed by the resistance of coastal forests to salt stress (Williams et al, 1999;Denslow & Battaglia, 2002;Desantis et al, 2007), as predicted by Brinson et al (1995) in their conceptual model of marsh migration.…”

Sea‐level rise, habitat loss, and potential extirpation of a salt marsh specialist bird in urbanized landscapes

“…Salt marsh habitats lie within the intertidal zone and rely on a balance between accretion and erosion, as well as uplift and subsidence to maintain elevations with SLR. Salt marshes can trap mineral sediment and accumulate organic matter to maintain their position with rising seas (Kirwan et al, 2016), and they might migrate inland as upland habitats recede (Raabe & Stumpf, 2016). However, coastal development in the SCB acts as a backstop to transgression and likely reduces sediment available for accretion (Callaway & Zedler, 2004;Thorne et al, 2018).…”