Salt marshes are one type of estuarine habitat that acts like an enormous filter, removing pollutants such as herbicides, pesticides, and heavy metals out of the water flowing through it (USEPA, 1993). In addition to pollutants, the same water often brings with it all of the nutrients from the surrounding watershed. A watershed, or drainage basin, is the entire land area that drains into a particular body of water, like a lake, river or estuary. The nutrients flowing into an estuarine habitat often provide for lush plant growth. For this reason, estuaries are some of the most fertile ecosystems on Earth. Yet, due to the pollutants they extract from waters running through them, they may also be some of the most polluted as well.
In the animation below, as groundwaters flow into the salt marsh from the surrounding drainage area, marsh grasses and the surrounding peat extract excess pollutants and nutrients from it.