A 17-yr record of sediment accretion in the salt marshes of Maine (USA)

Marker horizons of brick dust were established in 1986 in 26 salt marshes along the coast of Maine (USA). In 2003 we measured the sediment accumulation rates for the 17 year period in 11 relocated sites and obtained results varying from 1.4 to 4.2 mm/yr. The mean accretion rate for all marshes was 2.8 mm/yr. Accretion rates measured from 1986 to 2003 were comparable to those measured at the sites in 1987 and 1990, indicating that marsh accretion rates are similar on annual and decadal time scales. Inorganic material was found to be the primary constituent of Maine salt-marsh sediments. Several marshes show clear evidence of transgression since 1986 in the form of landward moving plant zones or encroachment of mudflat onto salt marsh. Indications for regressive changes were not observed. Marsh sediment accumulation rates are generally higher than mean rates of relative sea-level rise, indicating that most salt marshes are currently keeping pace with sea-level rise. However, if relative sea-level rise were to exceed rates of ∼ 4 mm/yr, many salt marshes in Maine may not survive.