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Contrasting Decadal-Scale Changes in Elevation and Vegetation in Two Long Island Sound Salt Marshes
Citation:
Carey, J., K. Raposa, C. Wigand, AND R. Warren. Contrasting Decadal-Scale Changes in Elevation and Vegetation in Two Long Island Sound Salt Marshes. Estuaries and Coasts. Estuarine Research Federation, Port Republic, MD, 40(3):651-661, (2017).
Impact/Purpose:
The research project, SHC 3.3.11, Wetlands and Nitrogen in Narragansett Bay Watershed, focuses on understanding components of sustainability, nutrient and other co-stressor effects, and decision-making beneficial to communities. The manuscript directly examines impacts of accelerated sea level rise on southern New England salt marshes. Recent studies suggest that some salt marshes are disappearing rapidly in the Northeast, leading to reductions in habitat quality, plant diversity, carbon sequestration, erosion resistance and coastal protection. Our results suggest that Barn Island marsh (CT) is maintaining its historic rate of elevation gain (2.3 ± 0.24 mm year−1 from 2003 to 2013), but is no longer keeping pace with relative sea level rise. While, nearby Mamacoke marsh (CT) shows evidence of a recent increase in rate (4.2 ± 0.52 mm year−1 from 1994 to 2014) to maintain its elevation relative to sea level rise. The results highlight that not all marshes in Southern New England may be responding to accelerated rates of sea level rise in the same manner and that other parameters such as deposition of sediments following storms may be important for understanding marsh responses to climate change.
Description:
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.
