ABSTRACT
Burdick, S.A.; Puckett, B.J.; Currin, C.; Davis, J.; Exar, L., and Murray, A.B., 2025. Bulkheads reduce salt marsh extent: A multidecadal assessment using remote sensing.
Coastal development and shoreline armoring have contributed to rapid declines of salt marsh ecosystems. This study investigates multidecadal effects of bulkheads, a common shoreline armoring technique, on marsh extent in microtidal salt marshes. Aerial imagery of Bogue and Back sounds and Newport and North rivers (North Carolina, U.S.A) from 1981, 1992, 2006, and 2013 was used to measure changes in marsh extent at 45 sites with bulkheads landward of marsh and 45 control sites without bulkheads. At each site, change in marsh shoreline position (i.e. erosion or accretion) as well as landward marsh migration were measured. Rates of shoreline change and net change, the sum of shoreline change and landward migration, were compared among bulkhead and control sites. Over a 32-year period, salt marshes with landward bulkheads experienced higher mean rates of shoreline erosion than marshes without bulkheads (−0.14 ± 0.01 m/y vs. −0.09 ± 0.01 m/y). Sites without bulkheads as a barrier were able to offset some shoreline erosion through landward migration (mean migration rate = 0.05 ± 0.01 m/y). All bulkhead sites experienced net marsh loss, whereas 36% of control sites experienced net marsh gain. Net marsh loss was nearly three times higher at sites with bulkheads over the study period (−0.14 ± 0.01 m/y vs. −0.05 ± 0.01 m/y). Our results suggest that bulkheads can have a significant negative effect on marsh extent through increased erosion of the waterward edge and prevention of landward migration with sea-level rise (i.e. coastal squeeze). Land-use planning and conservation efforts protecting marsh migration corridors, combined with living shoreline strategies to reduce shoreline erosion, will be critical in protecting productive salt marsh ecosystems and the vital ecosystem services they provide.
