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Salt Marshes

A view of Long Marsh from Long Reach Lane.

By Ed Robinson

Wetlands that occur along the seashore, where salt water regularly flows in and out with the tides, are known as salt marshes. These marshes are some of the most productive natural habitats on earth, and they play a vital role in protecting the water quality of the surrounding ocean. They can be found in a wide variety of locations from small pockets along secluded bays to vast stretches along major river deltas. A salt marsh serves as a transition zone, where fresh water from rain, small creeks and rivers meets the ocean. The interaction of fresh and salt water, and the resulting salinity, determines the mix of plants and wildlife that exist in and around the marsh.

While salt marshes in the past were often seen as waste areas, subject to all kinds of man-made pollution and destruction, today they are more often recognized as essential habitats. Not only do they serve as buffers to protect sensitive shorelines from erosion, they provide vital breeding and nursery grounds for valuable plants, microbes, fish, invertebrates, mollusks, mammals, insects and birds. Salt marshes can buffer wave action and flooding, while trapping sediments and filtering runoff and excess nutrients. Heavy metals and other contaminants may be sequestered by plants within the marsh to avoid ocean pollution. Over time, as sediments settle the bottom and are broken down, a thick layer of mud will form and a layer of peat below that.

Because of daily tidal flooding, and the resulting brackish water, relatively few plants are adapted to thrive in salt marshes. If you look closely, you will notice distinct zones within the marsh, with different plants living in the center of the marsh, compared to the plants living at the edges where only the highest tidal waters can penetrate a few days each month. Not surprisingly, the wildlife that exists will also vary within the different marsh zones. The center or low marsh will be populated by smooth cordgrass, microalgae or glassworts, while the higher marsh will feature salt hay grass, spike grass, salt marsh asters, sedges, rushes and sea lavender.

At the outer edges of a salt marsh, where tidal waters rarely flow and the salinity is quite low, a diverse collection of plants will be found in the transition to upland conditions. Here you might find marsh elder, sweet gale, seaside goldenrod, switchgrass, herbs, shrubs and even small trees. These border areas are popular nesting areas for certain bird species, secure bedding areas for deer, and productive hunting areas for raptors, fox, skunks and raccoons.

Thanks to ongoing scientific study of these wetlands, and increased public awareness of the need to protect these sensitive environments, the days of draining or filling in marshes are behind us, at least in most developed countries. There is still a need to monitor and protect these wetlands from development and any impacts from adjacent agriculture or highways. The fresh water sources flowing into salt marshes must be kept free of pollution from sewage, excess nitrogen from fertilizers, herbicides, pesticides or industrial wastes.

September 2017