By George Humphrey

Among the most beautiful and environmentally important features of the South Shore coastline are the salt marshes that form in the estuaries where the region’s rivers meet the sea. These sensitive yet surprisingly resilient habitats mark the transition from sea to land, nurturing microorganisms, fish, birds and invertebrates; sequestering carbon; stabilizing sedimentation; and moderating the impact of coastal storms. While quietly going about their daily chores, the marshes also provide a uniquely peaceful setting for kayakers, bird watchers and nature photographers.

We have not always been kind to our marshes. During the Colonial period, trenches were dug so that cattle could graze on the marsh grass, which was also harvested for animal feed and thatched roofs. In the 19th century, approximately 80% of Boston’s salt marshes were drained and filled to accommodate urban expansion. And during the Great Depression, additional ditches were created in a misguided attempt to control mosquito infestation. Ecologists have estimated that Massachusetts lost 41% of its tidal marsh between 1777 and 2005.

With the passage of the Wetlands Protection Act, such adverse practices have largely ceased and today’s salt marshes are much healthier than they once were. There are still some serious stressors, however: wastewater and fertilizer runoff, burrowing green crabs, and boat wake all contribute to marsh grass loss by weakening the underlying peat. But by far the most serious challenge is the increase in sea level, which has risen at an annual rate of 2.80mm since 1921 or almost 11 inches!

NSRWA’s Watershed Ecologist and MassBays Regional Coordinator, Dr. Sara Grady, has been studying the region’s salt marshes since 2001, when she led a major study of the marshes in the estuary formed by the confluence of the North, South, and Herring rivers. In 2014, she worked with Alex Mansfield of the Jones River Watershed Association to replicate and expand the study to include the Jones River in Kingston. The results show that, while the marshes along the North and South rivers are in reasonably good health, they experienced a significant loss of high marsh grass during the 13-year period between the two surveys due to increased salinity caused by more frequent tidal inundation.

As part of the Association’s continuing effort to monitor the salt marshes within the watershed area, Sara has formed a team of “Salt Marsh Sentinels” who use their docks, located along the North and South rivers, as giant rulers to measure vegetation bands at regular intervals. Data gathered by the Sentinels are used to document changes to the marshes over time and to promote scientifically informed policies and management decisions. Additional Sentinels are always welcomed and are particularly needed in the Humarock area. If you own a dock on one of the rivers and are interested in this important project, please contact Sara Grady at

Looking to the future, Sara is working on a study of the green crab population in order to assess its effect on the marshes and to use aerial photography to monitor changes over time. The more we know about these unique environments, the better able we are to protect and nourish them.