Select Nitrogen Pollution Impacts & Solutions

Massachusetts: New study reveals role of nitrogen pollution in decline of salt marshes


Plum Island Sound, Mass Salt Marsh
photo credit: Amanda Vieillard

Every gardener knows too much nitrogen fertilizer spurs the growth of a plant's stalks and leaves. It turns out this principle applies to salt marsh grasses as well, perhaps with dire consequences, thanks to the results of a long-term study recently published in Nature by Linda Deegan at the Marine Biological Laboratory Ecosystems Center.

For the last twenty years, salt marshes along the US Eastern Seaboard have been dying and disintegrating, but no one fully understood why. Deegan's team learned that not only does excess nitrate increase above-ground growth, but it also reduces below-ground growth, thereby making the plants top-heavy. Importantly, they found that the excess nitrogen fundamentally altered the marsh structure, leading it to crack, and causing the grassy banks of the nitrogen treated tidal marsh to collapse. The fertilized creek also experienced more erosion.

The Boston Globe reported that the study demonstrated "the profound damage fertilizers and sewage can wreak on marshes," and that it was the "first to show that marshes may be crumbling from the inside out from a massive overload of nutrients."

Loss of marsh habitat is of major environmental concern, as these are critical areas of migratory bird and commercially important fish habitat. They also help sequester carbon and filter nutrients, and can mitigate storm surges - especially important as sea levels rise.

The study points to the need for an integrated approach to managing and reducing pollution from several sources - cities, agriculture, and industry - that upstream waterways carry into the sea.

-- R.W. Fulweiler