Wetland Sediment Dynamics at Crissy Field Marsh 2007 Annual Report

Callaway, John

One of the key issues for the management and restoration of intertidal wetland habitats is the long-term stability of the relative elevation of the wetland (Boesch et al. 1994). Previous work has shown that wetland vegetation is sensitive to small differences in elevation, due to shifts in the frequency of tidal inundation. Most natural coastal and estuarine salt marshes tend to be depositional environments, with the accumulation of both mineral and organic matter. Mudflats and creeks adjacent to marshes tend to have higher rates of accumulation with greater intra- and inter-annual variability due to the higher velocity currents in these areas. Marsh elevation remains relatively stable because this accumulation is balanced by eustatic sea-level rise, subsidence, decomposition of organic matter, and tectonic activity (Reed 1995). If these processes are not balanced, gradual changes in elevation will lead to shifts in vegetation communities over time (Warren and Niering 1993). In extreme cases, salt marshes can experience substantial shifts in elevation leading to the loss of habitat, as in areas with high rates of subsidence, such as Louisiana and the Chesapeake Bay (Baumann et al. 1984, Kearney and Stevenson 1991, Boesch et al. 1994). In addition, excessive sediment inputs can lead to substantial increases in elevation and shifts in plant distributions. In Tijuana Estuary, Cahoon et al. (1996), Weis et al. (2001), and Ward et al. (2003) have all documented high rates of sediment accumulation, and vegetation shifts have been noted throughout the estuary.