GEOLOGY

Detailed explanation-1: -In estuaries, salinity levels are generally highest near the mouth of a river where the ocean water enters, and lowest upstream where freshwater flows in.

Detailed explanation-2: -Estuaries-areas where fresh and saltwater mix-are made up of many different types of habitats. These habitats can include oyster reefs, coral reefs, rocky shores, submerged aquatic vegetation, marshes, and mangroves.

Detailed explanation-3: -The mixture of seawater and fresh water in estuaries is called brackish water and its salinity can range from 0.5 to 35 ppt. The salinity of estuarine water varies from estuary to estuary, and can change from one day to the next depending on the tides, weather, or other factors.

Detailed explanation-4: -Because of the depth, mixing of fresh and salt water only occurs near the surface, so in the upper layers salinity increases from the head to the mouth, but the deeper water is of standard ocean salinity.