Tidal restoration: a valuable but fading tool for salt marsh restoration in New England
Salt marshes have been building in elevation and expanding across coastal New England for the past 4,000 years as sea levels rose 1-2 mm/yr. With population growth over the past 400 years, vast areas of tidal marsh were destroyed and degraded; some intentionally (e.g., filled) and some unintentionally (e.g., undersized culverts). As the biophysical feedbacks that sustain marshes have become better known over the past 40 years, many of our colleagues have devoted their careers to restore tidal hydrology and ecological functions to marshes. We organized a volume authored by scientists, engineers, and restoration practitioners to share our experiences from New England and Atlantic Canada and to synthesize the science and practice of restoring tidal flow to salt marshes. The book serves as a valuable reference and guide to tidal marsh restoration, but as sea level rates rise, there is uncertainty if tide-restored marshes, often having undergone decades of subsidence, can keep up. Tide-restricted marshes should be restored now. However, the balance between restored hydrology (water levels) and marsh elevation capital (relationship between tide elevation, marsh elevation, and plant growth range) should be calculated in future restoration projects to determine the marsh area that will survive for some specified time and SLR rate. Without restoration, it is likely that these marshes will become unvegetated when barriers ultimately fail. Removing or managing barriers to tidal flow, facilitating landward migration through removal of shoreline structures, establishment of buffer zones, and providing sediments to marshes are all essential for the long-term sustainability of tidal marshes and their associated ecosystem services.