Salt Marshes

Salt Marsh

Salt Marsh (.jpg - 43k)

Salt marshes are coastal wetlands that form in areas protected from erosion, typically behind a barrier beach or tidal flat, and extend from the mid-tide line to the highest spring tide line. Salt marshes are dominated by grasses, and characterized by dense peat layers beneath the lush surfaces.

Lower marsh vegetation is dominated by salt water cord-grass (Spartina alterniflora), and upper marsh by salt meadow-grass (Spartina patens). These form the base of very complex marine and estuarine food webs.

The vegetation is outstandingly productive. In fact salt marshes are among the most productive of all ecosystems on the planet. The grasses take up nutrients (sometimes from pollution), and the anaerobic bacteria that live in the ecosystem break down nitrates so efficiently that water quality is often improved by flowing through a marsh. The grasses also slow down the tidal currents and capture sediments, which gradually raises the level of the marsh until only high tides flood it.

The dense vegetation of a salt marsh acts to stabilize sediments, and provides protection from destructive wave energy. Salt marshes provide haven for many different organisms, with two thirds of all commercially important fish and shellfish spending at least part of their lives in a salt marsh.

Salt marshes are destroyed by draining, filling and the dumping of dredge spoils, which typically occurs with development. Heavy metals, pesticides and other contaminants may enter the marsh system, become concentrated in the sediments, and eventually work their way up the food web.