Their high productivity results from their unique juxtaposition at the edge of the continent. The most important nutrient is nitrogen-a component of all protein. Phosphorus, silica, and other compounds in lesser amounts also serve as nutrients to living things in the estuary. The estuary functions as an efficient nutrient trap that is partly physical and partly biological. These plants are the foundation of complex food webs and provide structural habitats which create nursery habitat for most coastal shellfish and finfish.
Physical processes contribute to the acquisition and transformation of nutrients by living things.
For example, the importation of nutrients and exportation of waste products to and from the estuary are subsidized by gravitational energy in the form of streamflow and tidal exchange. As a result, the estuary becomes a productive seafood factory. Some watershed processes are vital. But the rivers do not discriminate. Water quality in the estuary is a key attribute affected by watershed events.