How salty are estuaries?

Estuaries are where rivers meet the sea, and the salinity of estuaries varies depending on the amount of freshwater input from the river and the tidal influence from the sea. Salinities can range from nearly freshwater to nearly full seawater. In general, estuaries are brackish, meaning that they have a salinity between 0.5 and 30 parts per thousand (ppt).

The salinity of an estuary is influenced by several factors, including:

* River discharge: The amount of freshwater input from the river dilutes the seawater and reduces the salinity of the estuary.

* Tidal influence: The tides bring in saltwater from the ocean, which increases the salinity of the estuary.

* Evaporation: Evaporation can increase the salinity of an estuary by removing water from the surface and leaving behind the dissolved salts.

* Precipitation: Precipitation can reduce the salinity of an estuary by adding freshwater to the system.

The salinity of an estuary can also vary over time. For example, during periods of heavy rainfall, the salinity of an estuary may decrease due to increased freshwater input from the river. During dry periods, the salinity of an estuary may increase due to reduced freshwater input and increased evaporation.

Estuaries are important habitats for a variety of plants and animals, and the salinity of the water is a critical factor in determining which species can survive in these systems. Some plants and animals are tolerant of a wide range of salinities, while others are more sensitive and can only survive in a narrow range of salinities.