Farmers in the Marsh: Lessons from History and Case Studies for the Future by Susan C. Adamowicz and others

Abstract

Salt marshes across coastal New England are undergoing rapid change characterized by increased areas of saturation resulting in shifts in vegetation communities, large areas of vegetation dieback, and increases in shallow standing water. In the early 2000s, gently sloped leading edges of salt marshes (“low marsh” dominated by Spartina alterniflora and flooded daily) began to be lost from Maine to Connecticut. More marsh edges are now “cliff-faced” with steep, vertical edges often characterized by peat calving. In many places, the “high marsh” (the irregularly flooded marsh platform normally dominated by Spartina patens, Distichlis spicata, and Juncus gerardii, as well as forbs) has been overtaken by short- (<0.10 m) to intermediate- (>0.60m – 1.0 m) form S. alterniflora, bare patches, and large areas of shallow standing water. The marsh platform between the ubiquitous ditches has subsided. In extreme cases, the marsh has ‘collapsed’ and now holds shallow water in a mega-pool with the only vegetation occurring along the ditch margins, in a “waffle-maple syrup” pattern. Elsewhere, the mega-pool becomes large and amorphous or interlocking in a jig-saw puzzle fashion suggestive of northern patterned fens with strings and flarks. While a few researchers have documented traits and trajectories of “natural” pools, the relatively sudden appearance and geographic extent of these changes suggests large-scale drivers. At the same time, research into historical salt marsh alterations for farming purposes dating as far back as the 1600s with large corporate works in the 1800s, has led this team to realize that remnant infrastructure from past agriculture coupled with accelerated sea-level rise is driving wide-scale salt marsh degradation. Tidal marsh obligate birds, such as the saltmarsh sparrow, which nest in narrow portions of “high marsh”, are at increasing peril from the loss of marsh elevation due to subsidence trajectories exacerbated by a heretofore largely unrecognized historical agricultural infrastructure. With species extinction modelled at 2050 and a metonic cycle shifting toward increasing tide ranges in 2024, it is imperative to halt subsidence trajectories by re-balancing marsh hydrology to optimize vegetation, accretion, and elevation gain. Obligate wildlife species and their habitats can then be supported over the long-term through the development of strategic management plans for each salt marsh system. Following a review of the historical literature, which documents the breadth of standardized farming practices, we identify these features on several sites, then present a four-step process to restore hydrologic function using innovative restoration practices at two case studies located in Rhode Island and Massachusetts, USA.