Salt marsh mosquito-control ditches: Sedimentation, landscape change, and restoration implications

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Mosquito ditches are a prolific physical feature of Atlantic coast salt marshes, dug most intensely since the 1930s to control the breeding of salt marsh mosquitoes. Removal of ditches by filling or other methods is under consideration as a restoration alternative at a Fire Island, New York, salt marsh. This study evaluated sediment dynamics and marsh landscape structure of the ditched marsh, thereby providing information to better support efforts to predict marsh responses to restoration alternatives. Field surveys, historic and recent aerial photography analysis, and radiometric dating techniques were used. The estimated average natural sedimentation rate within the ditches was 0.52 cm y-1, a rate greater than the accretion rate of the adjacent marsh surface. The average time for a Fire Island ditch to naturally fill would be 175 years from present, but spatially this is highly variable, with some ditches completely filled and others showing no evidence of natural filling. Active filling of ditches may be a feasible restoration alternative, pending the findings of pilot studies, but given concerns for marsh submergence with accelerated rates of sea level rise, restoration design should provide a hydrologic network to facilitate adequate marsh drainage. © 2012 Coastal Education & Research Foundation.

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Journal of Coastal Research