CWPtionary: Marsh Loss

Marsh loss is the destruction of marsh, often divided by location into two broad categories: shore erosion and interior loss. Shore erosion is the breakdown of shorelines caused by the actions of marine forces such as winds, currents, tides and wakes. Their continued effect gradually wears down the soil and eventually blows or washes it away.

Interior loss is caused by a variety of factors. The leveeing of the Mississippi River over the last two centuries so that people could inhabit Louisiana has been a major contributor. Historically, freshwater flooding from the rivers each spring left massive amounts of nutrient-rich sediment in the outlying wetlands. This sediment nourished existing plants and created new soil that was a fertile medium for vegetation. The roots of plants that sprouted in these soils helped hold the soil in place. Now that the levees keep the river from carrying sediments and nutrients to the wetlands, interior loss has increased.

The numerous canals, large ones for navigation and smaller ones for oil and gas extraction, that criss-cross the coastal marshlands are another cause of marsh loss. The canals that connect to the Gulf allow salt water to intrude into fresher wetlands. This saltier water can kill freshwater marsh vegetation, and if no other plants replace it, the soil can be washed away, causing a pond to form where marsh once was. In some places, hurricanes or other storms push salty water inland, killing the marsh. In addition, canals and their adjacent spoil banks can trap water and "drown" marsh - that is, the waterlogged soil allows chemical reactions that kill the plants.

A third cause of interior loss is the overabundance of nutria. These large rodents can eat out acres of marsh. Unless populations are controlled by hunting or trapping, this destruction will continue.