Marsh macrophyte responses to inundation anticipate impacts of sea-level rise and indicate ongoing drowning of North Carolina marshes

Christine M Voss,Robert R Christian,James T Morris

doi:10.1007/s00227-012-2076-5

Abstract

In situ persistence of coastal marsh habitat as sea level rises depends on whether macrophytes induce compensatory accretion of the marsh surface. Experimental planters in two North Carolina marshes served to expose two dominant macrophyte species to six different elevations spanning 0.75 m (inundation durations 0.4–99 %). Spartina alterniflora and Juncus roemerianus exhibited similar responses—with production in planters suggesting initial increases and then demonstrating subsequent steep declines with increasing inundation, conforming to a segment of the ecophysiological parabola. Projecting inundation levels experienced by macrophytes in the planters onto adjacent marsh platforms revealed that neither species occupied elevations associated with increasing production. Declining macrophyte production with rising seas reduces both bioaccumulation of roots below-ground and baffle-induced sedimentation above-ground. By occupying only descending portions of the parabola, macrophytes in central North Carolina marshes are responding to rising water levels by progressive declines in production, ultimately leading to marsh drowning.Electronic supplementary materialThe online version of this article (doi:10.1007/s00227-012-2076-5) contains supplementary material, which is available to authorized users.

Highlights

Coastal marshes have been identified as habitats at high risk of loss and functional degradation (Scavia et al 2002; Peterson et al 2008) from accelerating sea-level rise (IPCC 2007; Kemp et al 2011)
Coastal wetlands have a record of maintaining elevation relative to sea level for millennia (Redfield 1965, 1972) through both vertical accretion of the marsh surface and horizontal expansion across the landscape through transgression and progradation (Redfield 1972; Orson et al 1987; Reed 2002)
Spartina alterniflora Increasing duration of inundation produced similar patterns in the response to seasonal change in total and live above-ground biomass of Spartina (Table 2), the only statistically significant response detected in the ANOVAs was in total above-ground biomass in 2007 (Table 2)

Summary

Introduction

Coastal marshes have been identified as habitats at high risk of loss and functional degradation (Scavia et al 2002; Peterson et al 2008) from accelerating sea-level rise (IPCC 2007; Kemp et al 2011). Coastal wetlands have a record of maintaining elevation relative to sea level for millennia (Redfield 1965, 1972) through both vertical accretion of the marsh surface and horizontal expansion across the landscape through transgression and progradation (Redfield 1972; Orson et al 1987; Reed 2002). How effectively macrophytes facilitate vertical accretion of the marsh surface depends on the plants’ ecophysiological response to inundation (Turner et al 2000). Interacting relationships among marsh surface elevation relative to sea level, marsh hydrology, and macrophyte responses determine the ecophysiological performance of marsh macrophytes and in situ persistence of the marsh ecosystem (Morris et al 2002; Kirwan et al 2010)

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Conclusion