Maine's Dynamic Salt Marshes: Are Re-Interpretations of North-Temperate Salt Marsh Startigraphic Records Warranted?
Wells National Estuarine Research Reserve
Salt marshes are vulnerable to rising sea level. Studies in the Gulf of Mexico and Mid-Atlantic regions suggest that one response of salt marshes to sea-level rise is expansion of pools in interior marsh sections, leading to the rapid conversion of once-vegetated surfaces to open water over decadal scales. In Maine’s meso-tidal marshes (tidal range 2-6 m), previous work shows that a dynamic exchange between pools and tidal creeks is one mechanism that reverses this process at the local scale through pool drainage and subsequent re-vegetation. Lead-210 and 137Cs dating of sediments in two paired cores collected through re-vegetated pools and adjacent high-marsh surfaces from Wells and Brunswick, ME, indicate that re-vegetated pools rapidly accumulate sediment at 2-4.5 times the rate of the neighboring marsh platform. Our results have important implications for the overall sediment budget of salt-marsh systems, especially in the northeast where pools are prominent features and for the capacity of these systems to sustain themselves in response to rising sea level. With accelerated sea-level rise, two predicted system-level responses are an increase in the tidal prism and channel deepening, both of which will increase the hydraulic potential between pools perched on the salt-marsh platform and deepened tidal creeks, in places like Maine. It follows that in a system with a limited or finite sediment supply, pools may capture a disproportionate amount of the sediment load available to the marsh surface, in turn starving the platform and creating a positive and unsustainable feedback over the long term. Our results suggest that a re-examination of north-temperate, salt marsh stratigraphic records may be warranted, as the sedimentary signature of pool dynamics could be misinterpreted as high-frequency, sea-level oscillation. Models of marsh response to rising sea level should incorporate pool dynamics as an important process that drives marsh dynamics in meso-tidal settings.
Kristin Wilson is an interdisciplinary geoscientist interested in the response of salt marshes and mangroves to climate and coastal land-use change. She is a graduate of Middlebury College and holds a Masters in Marine Biology, a Masters in Marine Policy, and a Ph.D. in Ecology and Environmental Science, all from the University of Maine. She taught for two years in the Environmental Science Department at Allegheny College,and one year in the undergraduate and graduate Marine Science programs at the University of the Virgin Islands. Currently, she is the Research Director at the Wells National Estuarine Research (Wells, ME), a network of 28 NOAA-supported reserves nation-wide that are dedicated to protecting and restoring coastal ecosystems through integrated research, stewardship, education, and community partnerships.