A wetland may be one of several different kinds of ecosystems, depending on the presence of water, the type of vegetation and soil, and its proximity to the water table. There are several types of wetlands, including barrier beaches and rocky shores, salt marshes and estuaries, ponds and lakes, bogs and swamps, and rivers and streams. Each has its own distinct ecological profile. This means that certain species of plants and animals may occupy a specific wetland, depending on several environmental conditions.
One of the most important wetland ecosystems is the salt marsh. There are extensive salt marshes along the east coast of North America, including Massachusetts, although most of them are located in the southeast. The Great Barnstable Marsh consists of about 4,000 acres, including the area behind the six mile Sandy Neck barrier beach. A salt marsh is periodically submerged and contains an incredibly diverse community of plants and animals. Not all marshes are exactly alike in shape and size, but they all share certain features which justify their protection.
A salt marsh is a significant nursery for large populations of commercially important fish and shellfish. The dominant plant species in a marsh is cordgrass (Spartina alterniflora). These plants are able to tolerate the presence of high salt concentrations. They provide a major food source to large numbers of animals, either through direct consumption, or after they have died and decayed. Such decayed organic matter, called detritus, may be transported throughout the marsh and even offshore by daily tidal action.
The organic material supports an abundant fauna including clams, mussels, blue crabs, shrimp, and several species of fish. They in turn are consumed by birds and mammals which spend a portion of their lives in and around a salt marsh. In terms of biodiversity, a salt marsh is one of the most productive ecosystems.
Salt marshes play an important physical role along the coast too. They act as buffer zones between the powerful energy of oceanic waves and the land. Upland regions may be protected by marshes, particularly during coastal storms and hurricanes. In some low lying sections of the country, a salt marsh may help prevent salt water intrusion into drinking water supplies. Recent evidence also shows that salt marshes are very effective sinks for carbon, thus helping reduce the effects of climate change.
Over the last few years the public has come to understand that salt marshes are not wastelands or merely breeding grounds for mosquitoes and greenhead flies. Too many acres have been cleared and filled, thus damaging the coastline by promoting erosion. Yet in spite of coastal regulations, salt marshes are not fully protected. Encroachment by development will continue to threaten these valuable ecosystems as long as population pressures continue to squeeze the last remaining acres of upland.
Care must be exercised particularly if an area surrounding a salt marsh is radically altered – for example, by major grading and filling, the clearing of vegetation, or the construction of a large scale development like a shopping center or a group of office buildings.
Certain measures can be taken to minimize the impact on a salt marsh. Vegetated buffer zones surrounding the marsh should be maintained throughout and after construction. The plants will trap any sediments and prevent them from running into the wetland. Grading should be reduced wherever possible. The construction of sediment basins, and in some cases retaining walls, can hold any sediment from entering the marsh.
But probably the most important way of preventing and controlling erosion is with vegetation. It is always disturbing to see a construction site that has been completely cleared when it is unnecessary. As many trees, bushes, and shrubs should be retained as possible in the upland area around a marsh. Clearing should be done in stages as needed, and not months before a building goes up. More careful planning on how a site is to be used should precede actual construction. Sometimes a small effort can prevent significant environmental damage.
However, the most effective way of protecting salt marshes is to acquire them and preserve them in their natural state. The greatest threat to salt marshes in Barnstable is their incremental loss due to human activities in upland areas. Salt marsh systems are the most important along the coast and will need our constant care and protection.