Effects of Small-Scale Armoring and Residential Development on the Salt Marsh-Upland Ecotone

Abstract

Small-scale armoring placed near the marsh-upland interface to protect single-family homes is widespread but understudied. Using a nested, spatially blocked sampling design on the coast of Georgia, USA, we compared the biota and environmental characteristics of 60 marshes adjacent to either a bulkhead, a residential backyard with no armoring, or an intact forest. We found that marshes adjacent to bulkheads were at lower tidal elevations and had features typical of lower elevation marsh habitats: high coverage of the marsh grass Spartina alterniflora, high density of crab burrows, and muddy sediments. Marshes adjacent to unarmored residential sites had higher soil water content and lower porewater salinities than the armored or forested sites, suggesting that there may be increased freshwater input to the marsh at these sites. Deposition of Spartina wrack on the marsh-upland ecotone was negatively related to elevation at armored sites and positively related at unarmored residential and forested sites. Armored and unarmored residential sites had reduced densities of the high marsh crab Armases cinereum, a species that moves readily across the ecotone at forested sites, using both upland and high marsh habitats. Distance from the upland to the nearest creek was longest at forested sites. The effects observed here were subtle, perhaps because of the small-scale, scattered nature of development. Continued installation of bulkheads in the southeast could lead to greater impacts such as those reported in more densely armored areas like the northeastern USA. Moreover, bulkheads provide a barrier to inland marsh migration in the face of sea level rise. Retaining some forest vegetation at the marsh-upland interface and discouraging armoring except in cases of demonstrated need could minimize these impacts.

Impacts of Coastal Land Use and Shoreline Armoring on Estuarine Ecosystems: an Introduction to a Special Issue

“…For example, subestuary comparisons have been applied to studies of SAV (Li et al 2007;Patrick et al 2014), blue crab and bivalve abundance (King et al 2005), polychlorinated biphenyl (PCB) contamination of fish (King et al 2004), bird community diversity (DeLuca et al 2004), and the invasion of wetlands by a non-native form of Phragmites (King et al 2007). The two papers that were not part of the interdisciplinary project (Dugan et al 2017;Gehman et al 2017) were chosen to complement the other papers.…”

Linking Historical Changes in Salt‐Marsh Coverage to Lost Production of a Nektonic Bioindicator

“…The rising sea level and shoreline armoring efforts, which are directed at ensuring the persistence of valuable coastal development, are likely to drive the restriction and reduction of salt-marsh habitat area (Reed and Cahoon 1992;Feagin et al 2010), and this will affect the ecosystem services that are provided by tidal marsh (Craft et al 2009). Shoreline armoring is of particular concern along the southeastern U.S. coastline, where the practice is most common (Gehman et al 2018). In addition to anthropogenic loss of salt marsh, there are also naturally induced changes in salt-marsh areal coverage.…”

Influences of land use and ecological variables on trematode prevalence and intensity at the salt marsh‐upland ecotone

“…Marshes adjacent to these small bulkheads in Georgia have lower tidal elevations and thus have marsh characteristics typical of a lower elevation marsh; for example, high coverage of Spartina alterniflora in place of the traditional high marsh plant community (Bozek andBurdick 2005, Gehman et al 2017b). Even unarmored development, such as a lawn and house, can increase soil water content and decrease salinity in the adjacent marsh, which suggests increased freshwater input (Gehman et al 2017b). However, for habitat-crossing species, both armored and unarmored development can alter their distribution; for example, the high marsh crab Armases cinerum utilized the upland terrestrial system less in marshes adjacent to development (Gehman et al 2017b).…”

“…Even unarmored development, such as a lawn and house, can increase soil water content and decrease salinity in the adjacent marsh, which suggests increased freshwater input (Gehman et al 2017b). However, for habitat-crossing species, both armored and unarmored development can alter their distribution; for example, the high marsh crab Armases cinerum utilized the upland terrestrial system less in marshes adjacent to development (Gehman et al 2017b). Thus, even small-scale armoring can alter the marsh abiotic and biotic factors, and we might expect these changes to alter marsh use by hosts and subsequently the distribution and prevalence of their parasites too.…”