ANNUAL TO DECADAL SEDIMENT ACCUMULATION RATES AND RELATIVE SEA-LEVEL RISE EFFECTS ON MAINE'S DIVERSE SALT MARSH SYSTEMS

Forecasts of increased rates of sea-level rise associated with climate change have sparked interest on the controls of vertical salt-marsh growth and whether marshes can keep pace with predicted rates of sea-level rise. Marker horizons of brick dust were established on 26 salt marshes along the coast of Maine in 1986. Sediment accumulation rates were measured in 1987, 1988, 1990 and 2003. In 2003, eleven sites were relocated. Sediment accumulation rates over the 17 year period ranged from 1.4 to 4.2 mm/yr with a mean accretion rate of 2.8 mm/yr. Accretion rates measured at sites over shorter timeframes were comparable to those measured in 2003, indicating that marsh accretion rates are similar on annual to decadal time scales. Sampling from both 1986 and 2003 found inorganic material to be the primary constituent of the sediment. Marsh sediment accumulation rates on most of the marsh sites are higher than mean rates of relative sea-level rise. Therefore, most salt marshes are currently keeping pace with sea-level rise. If relative sea-level rise were to exceed rates of approximately 4 mm/yr, many Maine salt marshes may not survive.