Contrasting Decadal-Scale Changes in Elevation and Vegetation in Two Long Island Sound Salt Marshes
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Northeastern US salt marshes face multiple co-stressors, including accelerating rates of relative sea level rise (RSLR), elevated nutrient inputs, and low sediment supplies. In order to evaluate how marsh surface elevations respond to such factors, we used surface elevation tables (SETs) and surface elevation pins to measure changes in marsh surface elevation in two eastern Long Island Sound salt marshes, Barn Island and Mamacoke marshes. We compare marsh elevation change at these two systems with recent rates of RSLR and find evidence of differences between the two sites; Barn Island is maintaining its historic rate of elevation gain (2.3 ± 0.24 mm year−1 from 2003 to 2013) and is no longer keeping pace with RSLR, while Mamacoke shows evidence of a recent increase in rates (4.2 ± 0.52 mm year−1 from 1994 to 2014) to maintain its elevation relative to sea level. In addition to data on short-term elevation responses at these marshes, both sites have unusually long and detailed data on historic vegetation species composition extending back more than half a century. Over this study period, vegetation patterns track elevation change relative to sea levels, with the Barn Island plant community shifting towards those plants that are found at lower elevations and the Mamacoke vegetation patterns showing little change in plant composition. We hypothesize that the apparent contrasting trend in marsh elevation at the sites is due to differences in sediment availability, salinity, and elevation capital. Together, these two systems provide critical insight into the relationships between marsh elevation, high marsh plant community, and changing hydroperiods. Our results highlight that not all marshes in Southern New England may be responding to accelerated rates of RSLR in the same manner.
KeywordsSalt marsh Surface elevation change Sea level rise Sediment supply Salinity
We thank the editors of Estuaries and Coasts for publishing this thematic issue related to the pressures faced by salt marsh ecosystems in Southern New England. JCC thanks J. Tang for allowing her time to work on this manuscript. The authors thank Elizabeth Watson for sample analysis, Nels Barrett and Ron Rozsa for significant contributions to establishment and measurement of the Barn Island SETs, and William R. Funk for help in the 2014 sampling at Mamacoke. SET and related work at Barn Island was supported by the State of Connecticut Department of Energy and Environmental Protection, Office of Long Island Sound Programs through Long Island Sound License Plate Program Contract: PSA 2002-20332. The Department’s Wildlife Unit manages the Barn Island Wildlife Management Area and provided access and significant technical assistance. The Connecticut College Arboretum gave access and logistical support for work on the Mamacoke Marsh.
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