AP BIOLOGY

Detailed explanation-1: -In fresh water the concentration of salts, or salinity, is nearly zero. The salinity of water in the ocean averages about 35 parts per thousand (ppt). The mixture of seawater and fresh water in estuaries is called brackish water and its salinity can range from 0.5 to 35 ppt.

Detailed explanation-2: -An estuary is an area where a freshwater river or stream meets the ocean. In estuaries, the salty ocean mixes with a freshwater river, resulting in brackish water. Brackish water is somewhat salty, but not as salty as the ocean. An estuary may also be called a bay, lagoon, sound, or slough.

Detailed explanation-3: -Strong tidal currents eliminate the vertical layering of freshwater floating above denser seawater, and salinity is determined by the daily tidal stage. An estuary’s salinity is highest nearest the ocean and decreases as it moves up the river.

Detailed explanation-4: -Estuaries are home to unique plant and animal communities that have adapted to brackish water-a mixture of fresh water draining from the land and salty seawater. However, there are also several types of entirely freshwater ecosystems that have many similar characteristics to the traditional brackish estuaries.

Detailed explanation-5: -Estuaries are partially enclosed bodies of water where the salt water is diluted by fresh water input from land, creating brackish water with a salinity somewhere between fresh water and normal seawater.