I was looking up salt marsh because the Chattahoochee Nature Center has several near its location on the Chattahoochee River. This park is great for younger children. They have several beavers, bald eagles, owls and hawks.
The salt marsh is important to the river. Pictured here in these rich green photographs are the marsh in June of 2009 and also a close up of the tall grasses of the marsh. In these images the water is high. The plants that live in the marsh are able to grow in salty conditions. Tidal surges bring in nutrients including salt. Grasses first establish in the mud of the flat. Once they flourish, their root system carries oxygen, which allows other plants to take hold. The marsh collects unwanted nutrients from the river and sends "clean" water back out to the river. If you drive by a pond on a regular basis, notice how its changes with the contents of the water. I'll add a photo another day when the water is low, so you can see the difference.