Impacts of Fertilization and Tidal Inundation on Elevation Change in Microtidal, Low Relief Salt Marshes

We evaluated the importance of both tidal inundation and nutrient fertilization as drivers of elevation change in coastal salt marshes. The three sites investigated occurred along a 9-km stretch of the Atlantic Intracoastal Water Way in Central North Carolina. Despite their close geographic proximity, the sites varied in tidal range, elevation within the tidal frame, and stem height and stem density of Spartina alterniflora. Total standing aboveground biomass and marsh surface elevation change (measured by surface elevation tables; SETs) were documented during a 3-year period of nutrient fertilization and for two additional years after fertilization ceased. Measured elevation change rates in control plots varied from 0.2 to 1.2 cm year(-1) and were negatively correlated with starting elevation (r(2) = 0.82, p < 0.05). Fertilization resulted in increases in both standing aboveground biomass and marsh surface elevation change. Fertilized sites gained 0.69 to 2.1 cm year(-1) during the 3-year application period and 0.02 to 0.97 cm year(-1) during the post application period. The magnitude of the fertilization-induced elevation response was mediated by position in the tidal frame with sites that were lower gaining less elevation relative to controls than sites that were higher. The data presented here suggest that nutrient fertilization may be an effective adaptive management strategy for helping minerogenic marshes keep pace with sea level, but that the impact of fertilization may depend on tidal inundation.