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Sewage is a problem along the US coastal areas and therefore, also affects salt marshes.
There are two ways in which sewage influences salt marshes. The first is in the form of
fertilizer. A case study in Massachusetts revealed that fertilizing salt marshes in an
attempt to nourish them and help them to flourish does not prove to be sound. The
fertilizer used contained high concentrations of nitrogen and was made from sewage sludge.
As a result of the fertilization, one particular plant native to salt marshes, Spartina
Alterniflora, overpopulated the marsh while other native species died off. The end result
surprisingly increased the productivity of certain portions of the salt marsh and increased
the number of wading birds in the area, but destroyed part of the fragile ecosystem.
Overall, the addition of the fertilizer destroyed many of the natural features of the
salt marsh and created the exact opposite of the desired outcome. The other way that sewage can be introduced to salt marshes is directly from sewage plants themselves. It is thought that salt marshes serve as perfect natural cleansers of sewage. Salt marshes could theoretically take the place of the last step of sewage cleansing before it is drained out into the ocean because they absorb nitrogen and phosphorus. The damage that nitrogen and phosphorus alone cause the salt marsh ecosystem is significant, but not as drastic as the problems caused by the other toxins that are contained in the sewage. It is the absorbed lead, cadium, and zinc that actually poison the vegetation. Once the salt marsh plants have been contaminated with these toxins they may survive, but will not be able to reproduce effectively. If reproduction does occur, the plant offspring is also contaminated, weak, and has a low chance at ever becoming full-grown. (Graphic: http://www.dredgepro.com )
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