Brackish

Brackish water is water whose salinity lies between freshwater and seawater, typically about 0.5 to 30 practical salinity units (PSU). It often results from the mixing of riverine freshwater with seawater and is common in coastal areas such as estuaries, mangrove swamps, lagoons, and tidal channels. Salinity in brackish environments can vary widely over time and space due to tides, rainfall, evaporation, and freshwater inflow, and is commonly measured by conductivity and reported as PSU or parts per thousand (ppt).

Ecology and biology: Brackish habitats host species adapted to variable salinity, known as euryhaline organisms. Examples include certain fish such as striped bass and tilapia, crustaceans like some shrimps, and various mollusks. Many plants in brackish zones are halophytes, able to tolerate higher salt concentrations than typical freshwater flora. The fluctuating conditions create unique communities and dynamic food webs.

Geography and systems: Brackish conditions occur in many estuaries, deltas, coastal lagoons, and tidal rivers around the world. The Baltic Sea is a well-known large brackish water body, and numerous smaller estuaries exhibit brackish characteristics that shift with seasons and weather.

Human use and management: Brackish groundwater can be a source for municipal and agricultural use after treatment. Brackish water is also important for certain forms of aquaculture, including shrimp farming, and for industrial processes. Management often focuses on controlling salinity intrusion, protecting habitats, and maintaining water quality.

Environmental concerns: Sea-level rise, groundwater extraction, and land-use changes can increase inland salinity, extending brackish conditions and impacting freshwater ecosystems and infrastructure. Pollution and nutrient loading can further alter brackish environments.

See also: Estuary, Salinity, Osmoregulation.