Estuarine Salinity Zones in US East Coast, Gulf of Mexico, and US West Coast from 1999-01-01 to 1999-12-31 (NCEI Accession 0127396)

Each estuary is subdivided into three zones between the head(s) of tide, and the seaward boundaries based on annual-averaged and depth-averaged salinities. The salinities used to define the three zones are: (1) Tidal Fresh Zone (0 to 0.5 parts per thousand); (2) Mixing Zone (0.5 to 25 parts per thousand); (3) Seawater Zone (25 parts per thousand or greater).

This 3-zone scheme is considered static rather than dynamic, because it does not take into account the seasonal variations in salinity patterns and stratification that occur in most estuaries. Nonetheless, it provides a simple and readily understandable way to depict the long-term salinity characteristics of U.S. estuarine waters. Note that not all estuaries contain all three zones - for example, Baffin Bay, Texas, receives relatively little annual freshwater inflow, and is considered to be entirely Seawater Zone.