A synthesis of research and practice on restoring tides to salt marshes

The structure and ecological function of salt marshes are defined by many interacting factors, including salinity, substrate, nutrient and oxygen availability, sediment supply, and climate, but hydrology (the frequency and duration of tidal flooding) is a dominating factor (e.g., Chapman 1960; Ranwell 1972; Daiber 1986). When tidal flow is restricted there can be dramatic changes to physical and biological processes that affect vegetation patterns, fish and avian communities, and biogeochemical cycling, among others. Throughout the developed coastal zone, roads and railroads that cross salt marshes often have inadequately sized bridges and culverts that restrict tides (fig. 1.1). Tide gates are also a common feature, eliminating or dramatically restricting flood tides from entering salt marshes but allowing for some drainage on the ebb tide. Other tide-restricting practices that have been ongoing for centuries include impoundments for wildlife management purposes (Montague et al. 1987) and diking and draining to facilitate grazing and agriculture (Daiber 1986; Doody 2008). Diking is particularly extensive in Atlantic Canada (Ganong 1903), Europe (Davy et al. 2009), and the United States (e.g., Delaware Bay, Sebold 1992; San Francisco Bay, Nichols et al. 1986)